Luminous Landscape Forum

Raw & Post Processing, Printing => Colour Management => Topic started by: jc1 on August 14, 2011, 05:43:44 am

Title: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 14, 2011, 05:43:44 am
Installation Procedure
1. Download and unzip file. 2 icc files were enclosed in the zip file.
    Download here (http://www.luminous-landscape.com/forum/index.php?topic=56978.msg470454#msg470454) <ver 1.0>
    a) 0_jc1RGB (beta1).icc    
    b) 0_sRGB_D50_jc1 (beta1).icm
2. Drag or copy the files into the system icc file folder or
    in PC, left click on the icc file and select install.
3. Start Photoshop CS and confirm that the 2 icc files are available for selection.

Perceptual Rendering Intent -- conversion from ProPhoto to sRGB color space
Load your ProPhoto (wide gamut rgb, best rgb or beta rgb ) image file into Photoshop CS.
1. In CS, convert with 0_jc1RGB (beta1).icc
    Rendering intent is always absolute regardless of intent selected.
    You may observe insignificant changes on your display screen if color gamut for your image is well within the color gamut for 0_jc1RGB. Make sure you click OK to complete the conversion.

    Both the downloaded icc files use standard D50 illuminant and Gamma 2.2 and they are of V2 icc specification.
      
2. Next, convert with 0_sRGB_D50_jc1 (beta1).icm
    This icc profile resemblances closely the standard sRGB, but has added saturation and perceptual rendering intents.
    Choose Perceptual rendering for best image reproduction.
    Toggle PREVIEW to detect the differences before and after conversion.
    Depending on the image color gamut, the other rendering intents may work for you as well.

Now, your image has been converted to sRGB color space from ProPhoto color space, perceptually (provided it works!). You can do a profile assign to sRGB or convert to sRGB. The file size for 0_sRGB_D50_jc1 (beta1).icm is about 1.4 Mbytes and hence may increase the storage file size significantly if you choose not to re-assign or convert to standard sRGB.

Examine your converted image and compare it with the original image.

Problem encountered so far:
1) Blue channel for Wide Gamut rgb has knee effect (higher red), but only limited to range  240< B <255. Unsure if this phenomenon is due to highly saturated color being displayed on a standard sRGB monitor.  < Solved >
2) My testings are limited to using simulated color patches. I am unsure how well it works for actual high gamut images.
3) I am using a standard sRGB monitor and hence cannot see the true reproduction color for highly saturated colors. I can only peek and poke the color values ( rgb and Lab).  8)

Feedback your observation and post your converted image here. You can help me in fine tuning these icc profiles for better color reproduction.

You may send your image file to jcrgb@yahoo.com, tiff file preferred and limited to total 10 files for now.

Thanks.

jc


... Update download link (http://www.luminous-landscape.com/forum/index.php?topic=56978.msg470454#msg470454) (pm me if you can't download)
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 14, 2011, 09:12:50 am
Example 1
Converting a ProPhoto GrangerRainbow to sRGB color space with Perceptual Rendering Intent
 
The analog version can be generated with ArgyllCMS. I sampled it with 50x100 pixels and output it to RGB color patches.
 
You can download my digital GrangerRainbo Here (https://www.yousendit.com/download/ZUd2aXRFdVVQb0kwTVE9PQ). The file was tagged with ProPhoto profile and it can be easily re-assigned to other color spaces with Photoshop.
 
Following images were captured in sRGB. Before capturing, my custom monitor profile was disabled and switched to sRGB color space. So the RGB values for the captured images were truly sRGB.
 
1) Converting using the 2-step workflow

(http://2.bp.blogspot.com/-7PrWmCHLJp4/TkfC1C9WXhI/AAAAAAAAAKg/qeSjltnUudw/s1600/01++Digital+GrangerRainbow.png)
 
(http://1.bp.blogspot.com/--_P6dJgP3sg/TkfC9mPj20I/AAAAAAAAAKk/WD3TRdyxnzo/s1600/02+convert+with+0_jc1RGB+profile.png)
 
(http://4.bp.blogspot.com/-ZDA9XpnMbes/TkfDIY8erFI/AAAAAAAAAKo/gIEfdeLhkCY/s1600/03+0_sRGB_D50_jc1.icm.png)
 
(http://2.bp.blogspot.com/-dWox3mVhNtE/TkfDQ9EVDbI/AAAAAAAAAKs/3cbltD8ViLs/s1600/04+Assigned+or+Converted+to+sRGB.png)
 
 
2) Converting without step1
 
(http://1.bp.blogspot.com/-pHE-vuhf930/TkfE7kWJd7I/AAAAAAAAAKw/-HqIw_bciZo/s1600/05+Converting+without+step+1.png)

Cheers

jc

... / update download link + file attachment
.../  Disable the tif and change it to .rar, as pc always auto download the tif when I login to LL. (unsure why?)
.../  Problem might be coming from attachment of one of the thread by a forum-er, kindly archive it.
.../  Do not attach jpg or tif file attachment directly. Thanks
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 15, 2011, 02:48:35 am

 
Upate: jcRGB_beta2 (attachment)
 
a) Revised:  0_jc1RGB (beta2)                 
b) Renamed: 0_sRGB_D50_jc1 (beta2)       
 
Change: Re-locate slightly Blue Primary in 0_jc1RGB
. This greatly improves the Blue rendering when B>240  (R=G=0) when converting from Wide Gamut RGB to sRGB.
. Effect on ProPhoto mapping to sRGB is insignificant.

Wide Gamut RGB to sRGB perceptual rendering
(http://4.bp.blogspot.com/-JE7WLfTYeCs/Tki-a6fLl9I/AAAAAAAAALA/XCZ1ZRA6m7o/s1600/07+beta2.png)

jc
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 15, 2011, 10:09:22 pm

(http://1.bp.blogspot.com/-wBZpMbfJcYY/TknNFqh2bvI/AAAAAAAAALI/6b_lXQ6xES8/s1600/08+jcRGB+spec.png)

Color Matching Test: sRGB_D50_jc1 (AbsCol) vs standard sRGB (RelCol)
Total of 4096 RGB test points with pitch of 15 were created. The corresponding Lab values for the RGB data were generated for the 2 profiles, sRGB and sRGB_D50_jc1, respectively. Theirs color differences in ΔE2000 under D50 illuminant (relative intent for sRGB) were then determined. Results are illustrated as follows.
 
(http://3.bp.blogspot.com/-fK0LFcI4Qyc/TkigHEo682I/AAAAAAAAAK0/nWMNKh-Ld1Q/s1600/06a++4096+test+patches.png)

(http://2.bp.blogspot.com/-m9OWDv1lbaI/TkigMmb-lTI/AAAAAAAAAK4/qfJ5itgAOb0/s1600/06b+Color+reproduction+comparison+between+sRGB+and+sRGB_D50_jc1.png)

(http://4.bp.blogspot.com/-Se4mEWlMDiw/TkigghjmLFI/AAAAAAAAAK8/Ojpjg8WGgeY/s1600/06c+graph.png)

jc
 
.../ RGB-4096_test_patches is attached, in CGATS txt file. Please help to verify/confirm above result.
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 16, 2011, 04:17:32 am
Example 2
Converting a ProPhoto Ramp Pattern to sRGB


(http://2.bp.blogspot.com/-yX3HP6PPh6A/Tkoa4oT_J8I/AAAAAAAAALM/R8BmfiGGwy8/s1600/01+126+digital+ramp.png)

Procedure
1. Read and assign ProPhoto profile to the digital Ramp pattern.  <  DL (https://www.yousendit.com/download/ZUdzdFdRT00xUUJjR0E9PQ) >
2. Convert with 2-Step approach. Convert again to sRGB and save in Tiff file.
3. Repeat above but with sRGB RelCol.
4. Import Tiff into CTP3.
5. Enjoy.

(http://1.bp.blogspot.com/-_k23O1dUXms/Tkoi8iX0IYI/AAAAAAAAALk/zXG0t5Kmbjk/s1600/04+Converted+images+in+sRGB+color+space.png)

Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: Alan Goldhammer on August 16, 2011, 08:36:28 am
Maybe I'm a little dense, but could you briefly explain what you are trying to do with these posts.  Thank you.
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 16, 2011, 06:33:57 pm
Hi,

I am inspired and wish I can provide solution after reading http://www.luminous-landscape.com/forum/index.php?PHPSESSID=24205b19480ced199ad3e9e3a10ee9ce&topic=50249.0 (http://www.luminous-landscape.com/forum/index.php?PHPSESSID=24205b19480ced199ad3e9e3a10ee9ce&topic=50249.0) and other similar threads.
 
Above illustrations are hypothetical examples which may represent worst case scenario (?) for the converting color space. I believe most photographers who are in need for such a solution may not have the appropriate software tool to visualize and analyze them.
 
Whether the approach is workable, again I am unsure, only some real life examples can prove it.
 
If there is similar solution, kindly enlighten.
 
Thanks.
 
With best regards
jc
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: PeterAit on August 16, 2011, 07:37:02 pm
Maybe I'm a little dense, but could you briefly explain what you are trying to do with these posts.  Thank you.

I am wondering, too. But, the fact is that some people are interested in the technology and gadgets of photography, the art and beauty of it do not matter to them. Pixel peepers! Graphs, technical specs, sharpness, these are the things that matter. Faced with a Weston pepper they would immediately put their nose against the glass and whine about the lack of sharpness.
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: louoates on August 16, 2011, 08:20:17 pm
I'm not sure I can wrap my brain around these conversion procedures. That means I don't know if I can apply those downloaded files correctly. I do know that when I convert from ProPhoto to srgb in "save for web" in CS5, I rarely like the result. But even when I post a regular ProPhoto jpeg shot, unconverted to srgb, onto facebook it looks bad. I suspect they do the srgb conversion there. I probably should go back to the top of this string and study harder.
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: digitaldog on August 16, 2011, 08:50:48 pm
I do know that when I convert from ProPhoto to srgb in "save for web" in CS5, I rarely like the result.

Why? Can you post examples (in some color managed means) of what results you donít like?
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: louoates on August 16, 2011, 11:12:18 pm
I should have said that while the conversion from ProPhoto to sRGB in "save for web" looked okay in Bridge but awful when viewing in Firefox or in facebook. I've had the same problem with going from ProPhoto to max quality jpgs and then to some of my microstock sites. I believe they convert to sRGB also. Sorry, I don't think I can duplicate them and have them show up the same way here.
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: JeffKohn on August 17, 2011, 12:57:13 am
I should have said that while the conversion from ProPhoto to sRGB in "save for web" looked okay in Bridge but awful when viewing in Firefox or in facebook. I've had the same problem with going from ProPhoto to max quality jpgs and then to some of my microstock sites. I believe they convert to sRGB also. Sorry, I don't think I can duplicate them and have them show up the same way here.
If they looked OK in Bridge after conversion, the problem wasn't with the conversion to sRGB. More likely, your web browser is not using your monitor profile to display the image, but Bridge is.

FireFox does support ICC profiles, but there are some limitations depending on which version you're running, how it's configured, and what version the ICC profile is.
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: digitaldog on August 17, 2011, 10:00:02 am
I should have said that while the conversion from ProPhoto to sRGB in "save for web" looked okay in Bridge but awful when viewing in Firefox or in facebook.

As Jeff pointed out, that isnít due to the conversions from ProPhoto to sRGB. If it looked fine in SFW, it will look that way in other ICC aware applications. The issue is Firefox (probably some older version) and facebook. When you convert using either SFW or Convert to Profile from ProPhoto or for that matter all RGB working spaces, the conversions should look very similar if not identical after the conversion.
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: Peter_DL on August 18, 2011, 03:26:38 am

Load your ProPhoto (wide gamut rgb, best rgb or beta rgb ) image file into Photoshop CS.
1. In CS, convert with 0_jc1RGB (beta1).icc
    Rendering intent is always absolute regardless of intent selected.
    You may observe insignificant changes on your display screen if color gamut for your image is well within the color gamut for 0_jc1RGB. Make sure you click OK to complete the conversion.

    Both the downloaded icc files use standard D50 illuminant and Gamma 2.2 and they are of V2 icc specification.
      
2. Next, convert with 0_sRGB_D50_jc1 (beta1).icm
    This icc profile resemblances closely the standard sRGB, but has added saturation and perceptual rendering intents.
    Choose Perceptual rendering for best image reproduction.
    Toggle PREVIEW to detect the differences before and after conversion.
    Depending on the image color gamut, the other rendering intents may work for you as well.

Now, your image has been converted to sRGB color space from ProPhoto color space, perceptually (provided it works!). You can do a profile assign to sRGB or convert to sRGB. The file size for 0_sRGB_D50_jc1 (beta1).icm is about 1.4 Mbytes and hence may increase the storage file size significantly if you choose not to re-assign or convert to standard sRGB.

Please kindly explain the components of these profiles (matrix primaries, white point, TRC / gamma, ...)
and the idea behind the double conversion starting with AbsCol.

Thanks.
& Best regards, Peter

--
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 18, 2011, 08:45:31 am
Update: Beta2.1  [ DL (https://www.yousendit.com/download/ZUd0OGNkNEhwcFd4dnc9PQ)  ]
Changes: minor adjust made to RGB primaries.

Hi Peter,

Please kindly explain the components of these profiles (matrix primaries, white point, TRC / gamma, ...)
and the idea behind the double conversion starting with AbsCol.

Thank you for your response. It may be easier if I answer briefly with some graphs which are self explanatory.

1) jc1RGB.icc (Intermediate space for color conversion, Step 1)

(http://2.bp.blogspot.com/-Kri5ZerjspY/Tkz98KjhI_I/AAAAAAAAALo/mt-Dkmo3fpE/s1600/05++jc1RGB+color+space.png)

2) sRGB_D50_jc1.icm (Perceptual mapping, Step2)
Supports rendering intents (AbsCol / RelCol, Saturation and Perceptual).
Following graph is a repeat of a previous post and more details can be found there.

(http://1.bp.blogspot.com/-wBZpMbfJcYY/TknNFqh2bvI/AAAAAAAAALI/6b_lXQ6xES8/s1600/08+jcRGB+spec.png)

3) Why AbsCol?
All with D50 illuminant, RelCol is thus irrelevant.

4) Why double step conversion? Why not direct Space-to-Space gamut mapping? Why not use BetaRGB, RonRGB, Wide_Gamut_RGB or other standard and available wide spaces as intermediate conversion space?

Before an answer can be given, let me first shoot some photos with real objects (colorful and saturated objects  8)) to confirm if above conversion can be applied practically and satisfactory  ;). I shall organize my observation before back to here. (Sorry if more graphs and photos be posted)

Thanks

jc

.../spelling correction
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 19, 2011, 01:49:37 am
Test Image 1   Image ref: Dsc_2933.nef

Setup: Nikon 300s with 60mm macro lens, 
          Indoor, available light from window, custom WB with ColorRight Pro.
          Use in-camera matrix metering -0.7 stop, manual mode.
          Set camera picture mode to Neutral and shoot with 12-bit RAW.
Import: Read with Capture NX2 and assigned color profile to ProPhoto.
Export: Image was exported with 16-bit Tiff.
 
Duplicated 3 Tiff. Set Monitor profile to sRGB. Start CS.
Read all 3 files into CS.
1) No change
2) Conversion with 2-Step work flow, then to sRGB.
3) Conversion with RelCol sRGB.
 
The screen images were captured, re-arranged, & saved in png.
 
Converted sRGB files (2 files) can be downloaded here: 2933_converted_jpeg_sRGB_RelCol & Perceptual.rar (https://www.yousendit.com/download/ZUdzK3BDOC9UWUN4dnc9PQ)

Below is the highlight.
(http://4.bp.blogspot.com/-RJJ26EEyINE/Tk3UR-hOykI/AAAAAAAAALs/-7Cob-4LsHI/s1600/06+2933+test+image.png)
 
To be convincing, I need more images to test . If you have for instance, flower shot with highly saturated color and lot of fine details, please give it a go. If possible, post and share your picture here.

jc
 
 
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 19, 2011, 09:44:36 pm
 
Comparison between various options for ProPhoto to sRGB conversion
 
For the following illustration, the colors for the sRGB image were intentionally saturated by assigning it to ProPhoto profile before subjecting it to the conversion.
 
A) Color Reproduction
 
(http://1.bp.blogspot.com/-n6vUGEptef8/Tk8H6QHzQ2I/AAAAAAAAALw/fAKmpvdZ9Qc/s1600/01+4-+version-options.png)
 
B) Brief Summary

1) RelCol sRGB
    .Work fine for image without excessive saturated color.
    .Unpleasant color and loss of details for highly saturated image after conversion.
 
2) Pro2sRGB
    .Dedicated source-to-destination pairwise mapping from ProPhoto to sRGB.
    .Smooth perceptual rendering, always.
    .Can result in excessive color shift and dull color.
    .Perceptual rendering only works for L*a*b* where a* and b* are within the range (-127 to +128).
 
3) 1-Step sRGB perceptual with (0_sRGB_D50_jc1)
    .Works satisfactorily if color gamut for the image is not bigger than that for BetaRGB, for instance.
 
4) 2-Step sRGB perceptual with (0_jc1RGB + 0_sRGB_D50_jc1)
    .Need 2 steps (unsure if collink (http://www.argyllcms.com/doc/collink.html) is applicable for combining them to a single profile)
    .Works satisfactorily for all cases,  including a* and b* values that are out of range of (-127 to +128)
    .Good color saturation can still be realised.
    .Perceptual and pleasant color rendering at the expense of colorimetric accuracy*
 
* This applies to perceptual rendering intent in general.   
     
jc
 
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: Peter_DL on August 20, 2011, 11:48:56 am
For the following illustration, the colors for the sRGB image were intentionally saturated by assigning it to ProPhoto profile before subjecting it to the conversion.

By means of such pRGB assignment it can easily happen that "imaginary colors" are created which do not exist in reality. Then, it could be a kind of creating a problem first, before solving it. But I donít want to sound negative at all.

If I get you right, suggested approach is as follows:

regular ProPhoto RGB w/ D50 white, 1.8 gamma, pRGB gamut
-- Abs/RelCol -> jc1RGB (beta2.1) w/ D50 white, 2.2 gamma, gamut: somewhat smaller but still large
-- Perceptual -> sRGB_D50_jc1 (beta 2.1) w/ D50 white, 2.2 gamma, sRGB gamut (?)
-- Abs/RelCol -> sRGB IEC61966-2.1

Right ?

The file offered for download of the profiles seems to be a .rar, not a .zip
I for one am not familiar with this format, although Google points me to some freeware for decoding.

JC, - while I have a true respect for people who can "mangle" profiles the way you do,
my impression is that you donít make it easy for us / people to follow your thoughts.

Best regards, Peter

--
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 20, 2011, 09:00:54 pm
Hi,

By means of such pRGB assignment it can easily happen that "imaginary colors" are created which do not exist in reality. Then, it could be a kind of creating a problem first, before solving it. But I donít want to sound negative at all.

If I get you right, suggested approach is as follows:

regular ProPhoto RGB w/ D50 white, 1.8 gamma, pRGB gamut
-- Abs/RelCol -> jc1RGB (beta2.1) w/ D50 white, 2.2 gamma, gamut: somewhat smaller but still large
-- Perceptual -> sRGB_D50_jc1 (beta 2.1) w/ D50 white, 2.2 gamma, sRGB gamut (?)
-- Abs/RelCol -> sRGB IEC61966-2.1

Sorry if I did not make myself clear to you.

Imaginary values may be produced via mathematical transformation.
Adobe color model is based on CIELAB 50 hence imaginary color cannot  be created in that way.

You are correct and thank for the clarification.
In practice, rendering intent can be set to Perceptual as follows.
-- Perceptual -> jc1RGB 
-- Perceptual -> sRGB_D50_jc1 
-- Perceptual -> sRGB IEC61966-2.1

By the way, the intermediate color space was chosen after tedious trial and error as I can't find a easy way out.
 
With best regards
jc
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: Nigel Johnson on August 21, 2011, 09:52:25 am
jc

AFIK, when you assign a profile in Photoshop (versus Convert to a profile) CIE LAB conversion is not used, rather the RGB values in the file are left unchanged and only the associated profile information (colour primaries and tone curve) is changed. Hence, as Peter stated, it is possible to produce imaginary colours in the image.

Here is a test I have done to confirm this (all files are 8-bit TIFF).
This confirms that Assigning can create imaginary colours.

Regards
Nigel
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: bjanes on August 21, 2011, 11:34:50 am
Please kindly explain the components of these profiles (matrix primaries, white point, TRC / gamma, ...)
and the idea behind the double conversion starting with AbsCol.

Thanks.
& Best regards, Peter
--

In his response JC showed some custom RGB matrix profiles. I can't follow the complexities of his workflow, but it should be noted that matrix profiles lack the lookup tables necessary for perceptual rendering. There are many problems with current perceptual rending algorithms since they apply arbitrary compression of the color gamut without actually looking at what color values are in the image. For a narrow range gamut, no compression at all may be needed. Ver 4 ICC profiles are supposed to handle perceptual rendering, but are not widely available. The purpose of this post is to invite further discussion.

Regards,

Bill
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: digitaldog on August 21, 2011, 01:02:50 pm
Imaginary values may be produced via mathematical transformation.
Adobe color model is based on CIELAB 50 hence imaginary color cannot  be created in that way.

And yet the chromaticity diagrams you yourself have provided here show two colors (primaries) that are imaginary.
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: digitaldog on August 21, 2011, 01:05:47 pm
Ver 4 ICC profiles are supposed to handle perceptual rendering, but are not widely available.

Right, and ideally, both profiles in the chain are V4 and implement the PRMG. I donít know if this is the case here.
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: Peter_DL on August 21, 2011, 03:57:30 pm
  
  
JC , - the Coding Efficiency of ProPhoto RGB is 87.3%, the Coding Efficiency of the Lab gamut is just 35.1%. The Coding Efficiency % indicates the relative portion of the encoding space that represents real colors. Some of the larger volume working spaces contain many RGB (or Lab) triplets for which there is no physical counterpart, and therefore could be considered wasteful.
Source:  www.brucelindbloom.com

How comes? The percentage with Lab is quite poor. The Lab Gamut is essentially the same as CIEXYZ. Going back to the original color matching experiment done with CIE RGB primaries it was found that a negative r matching function is needed to match colors outside the limited CIE RGB triangle. To avoid such negative matching  function, a mathematical construct was derived, CIE XYZ which bears all positive matching functions, at the cost of primaries XYZ which are not real colors.
Reference: http://www.fho-emden.de/~hoffmann/ciexyz29082000.pdf

The ProPhoto RGB gamut which is a subset of CIEXYZ  is likewise bearing "imaginary" primary colors. These are needed to hold other saturated colors, particularly yellow hues which actually DO exist in reality.

Not sure if this is a most accurate or comprehensive way of description,
however, it may meet your question.
 

Ver 4 ICC profiles are supposed to handle perceptual rendering, but are not widely available.

Never got these profiles to work for me.

The purpose of this post is to invite further discussion.

+1, same with me.

Bill, actually Iím quite happy with the PhotoGamut RGB pathway (+ local contrast enhancement on the most saturated colors) as outlined in this earlier discussion (http://www.luminous-landscape.com/forum/index.php?topic=50249.msg416147#msg416147) also referenced above. Depending on image. Others are better served with straight RelCol, pRGB to sRGB.

Regards,

Peter

--
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: TylerB on August 21, 2011, 07:08:33 pm
I have found utilizing PhotoGamut at some point in a workflow to be helpful in certain circumstances, primarily in working down to a space smaller than itself, sRGB for an on demand book for example. Unfortunately some colors currently available in the gamut of the newest inkjets available are not within PhotoGamut, and therefore some available colors from the printer/paper/inkset my never be utilized. An update of PhotoGamut considering contemporary printer gamut might be welcome.
The discussion and experimentation is useful though. One of th ongoing problems, under discussed, is getting from large working spaces down to output or web spaces in a viable manner. There is still no really good way to do it, and often massaging colors into eventual gamut before conversion is a frustrating task given the usual tools- Hue/Sat, Selective Color, Replace Color, etc- often seem to create as many problems as they solve. Tools for putting as cow's heads on a pig continue to improve, but color editing seems a bit in a rut.  V4 and smart cmms seem promising but still a pipe dream, and potentially have new unforseen problems as well....
So, seems like a good thread.
Tyler
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 21, 2011, 08:05:19 pm
Hi,

AFIK, when you assign a profile in Photoshop (versus Convert to a profile) CIE LAB conversion is not used, rather the RGB values in the file are left unchanged and only the associated profile information (colour primaries and tone curve) is changed. Hence, as Peter stated, it is possible to produce imaginary colours in the image.

Here is a test I have done to confirm this (all files are 8-bit TIFF).
  • Firstly I created an sRGB file and filled it with 0-R 255-G 0-B a real colour in sRGB (file: sRGB.tif).
  • I then assigned the ProPhoto RGB profile to the file (file: ProPhoto_assigned.tif). When the colour is checked it is still 0-R 255-G 0-B which in ProPhoto RGB is entirely imaginary.
  • Finally I took the original sRGB file and converted it to ProPhoto RGB (file: Converted_to_ProPhoto.tif). As expected this did not change the appearance of the colour on-screen but it did change the colour values to 138-R 237-G 78-B which in ProPhoto RGB is the same colour as 0-R 255-G 0-B in sRGB.
This confirms that Assigning can create imaginary colours.

Regards
Nigel

When an image is assigned or tagged with a profile, the corresponding lab value will have to be re-determined. Logically speaking, it must be done with an internal color model. I hope someone more knowledgeable in PS can verify that.

It is true that ProPhoto RGB=(0, 255 0) in xyz is imaginary.
But, you may be wrong by simply stating that the Lab values for RGB=(0 255 0) in PS is imaginary.


Where is ProPhoto RGB=(0, 255 0)?

(http://2.bp.blogspot.com/-gFOnA06McdI/TlGaAb2DgeI/AAAAAAAAAL0/jS9kWN2tZsE/s1600/10a++Green1%25261a%25261b.png)

a) Green_1:   XYZ=(13.519161 71.187450 0.000005) --> Lab=(87.58 -186.69 150.99)
b) Green_1a:  Lab=(87.58 -186.69 150.99) --> Lab=(87.58 -128 127)  (simply clipped it)
c) Green_1b:  Lab=(88 -79 81)

Green_1:   An imaginary color
Green-1a: To show direct clipping is different from colorimetric transformation.
Green_1b: The Lab value in PS is (88 -79 81) and it is a realizable color.


sRGB --> ProPhoto (smaller gamut --> Bigger gamut)
When converting sRGB to ProPhoto, Lab value remains unchanged. Since this point has the same Lab value, it must be of the same color.


jc

.../clarification 1 (http://www.luminous-landscape.com/forum/index.php?topic=56978.msg462646#msg462646)
.../clarification 2 (http://www.luminous-landscape.com/forum/index.php?topic=56978.msg466225#msg466225)
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 21, 2011, 09:24:36 pm
In his response JC showed some custom RGB matrix profiles. I can't follow the complexities of his workflow, but it should be noted that matrix profiles lack the lookup tables necessary for perceptual rendering. There are many problems with current perceptual rending algorithms since they apply arbitrary compression of the color gamut without actually looking at what color values are in the image. For a narrow range gamut, no compression at all may be needed. Ver 4 ICC profiles are supposed to handle perceptual rendering, but are not widely available. The purpose of this post is to invite further discussion.

Regards,

Bill

Hi Bill,

"JC showed some custom RGB matrix profiles"
a)  jc1RGB is matrix profile
b) sRGB_D50_jc1 is output type profile
The technical aspects were already given.
 
"can't follow the complexities of his workflow"
Sorry if it sounds complex but it is not my intention.
 
" it should be noted that matrix profiles lack the lookup tables necessary for perceptual rendering"
sRGB_D50_jc1 is an output profile with Cluts. Its colorimetric accuracy AbsCol /RelCol is on par with standard sRGB. It has been clearly shown.
 
"There are many problems with current perceptual rending algorithms since they apply arbitrary compression of the color gamut without actually looking at what color values are in the image"
Over here the scope is well defined, ProPhoto to sRGB.
 
"For a narrow range gamut, no compression at all may be needed. Ver 4 ICC profiles are supposed to handle perceptual rendering, but are not widely available"
Can't agree more. Unsure in practice if anyone uses V4 for perceptual compression?
 
"The purpose of this post is to invite further discussion"
Yes and please try it. It is a working model unless someone can prove it otherwise.
 

Best regards
jc

.../typo err
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 21, 2011, 10:37:24 pm
And yet the chromaticity diagrams you yourself have provided here show two colors (primaries) that are imaginary.
If that chromaticity diagram was incorrectly presented, I shall try to clarify.


Right, and ideally, both profiles in the chain are V4 and implement the PRMG. I donít know if this is the case here.
PRMG model is a nice concept. But it may or may not work for matrix with imaginary primaries as in the case of ProPhoto.
I am using V2, it is simply based on practical applied engineering current available. It is nothing fanciful here.
 

Best regards
jc
 
 
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 22, 2011, 04:14:05 am
Hi,

 
JC , - the Coding Efficiency of ProPhoto RGB is 87.3%, the Coding Efficiency of the Lab gamut is just 35.1%. The Coding Efficiency % indicates the relative portion of the encoding space that represents real colors. Some of the larger volume working spaces contain many RGB (or Lab) triplets for which there is no physical counterpart, and therefore could be considered wasteful.
Source:  www.brucelindbloom.com
Brucelindbloom's hard work is much appreciated.
Practical implementation for Lab encoding causes the wastefulness. The waste if can be recovered at all, it may not carry any significant impact on real color reproduction, but it may render color conversion less painful.

 
"How comes? The percentage with Lab is quite poor. The Lab Gamut is essentially the same as CIEXYZ. Going back to the original color matching experiment done with CIE RGB primaries it was found that a negative r matching function is needed to match colors outside the limited CIE RGB triangle. To avoid such negative matching  function, a mathematical construct was derived, CIE XYZ which bears all positive matching functions, at the cost of primaries XYZ which are not real colors.
Reference: http://www.fho-emden.de/~hoffmann/ciexyz29082000.pdf".

There is distinctive difference between Lab and XYZ in that Lab is perceptually equal distance, XYZ is not. Lab is derived from XYZ, no?

The ProPhoto RGB gamut which is a subset of CIEXYZ  is likewise bearing "imaginary" primary colors. These are needed to hold other saturated colors, particularly yellow hues which actually DO exist in reality."
Unless there is direct transformation (XYZ) from RAW, I can't figure out where else can the imaginary color comes from. The practical implementation in the real world has put multiple barriers to restrict it from happening, from tiff (V6 spec) to PhotoShop CS, for instance.

Thanks

jc

Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: digitaldog on August 22, 2011, 09:41:43 am
If that chromaticity diagram was incorrectly presented, I shall try to clarify.

Its not wrong. It shows that two primaries of ProPhoto RGB are imaginary colors, they fall outside the chromaticity diagram. Technically they are not colors (humans canít see em).

Quote
PRMG model is a nice concept. But it may or may not work for matrix with imaginary primaries as in the case of ProPhoto.

The PRMG is what makes the V4 profiles kind of useful!
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: joofa on August 22, 2011, 12:00:52 pm
There is distinctive difference between Lab and XYZ in that Lab is perceptually equal distance, XYZ is not.

Unfortunately, an incorrect interpretation of the XYZ color space has also resulted in it being labeled as perceptually bad. There is a new realization now regarding what went wrong in the original interpretation.

Sincerely,

Joofa
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: Nigel Johnson on August 22, 2011, 05:36:56 pm
But, you may be wrong by simply stating that the Lab values for RGB=(0 255 0) in PS is imaginary.

Please do not misquote me. If you bother to read my post you will see that I stated that RGB=(0 255 0) is imaginary for ProPhoto RGB and is a real colour in sRGB and I do not state that an arbitrary RGB=(0 255 0) will be imaginary. The purpose of my test was to demonstrate that assigning a ProPhoto RGB profile to an sRGB image could create imaginary colours.

When a profile is assigned in Photoshop the RGB values in the file are not changed and NO internal colour model is used. Therefore if you create a ProPhoto RGB test image from an sRGB file by assigning the ProPhoto profile you may possibly create an image with imaginary colours (you could probably check if the image actually contains imaginary colours by using ColorThink or a similar utility). Hence, when you compare your complex process for converting from a large gamut (ProPhoto RGB) to a smaller gamut (sRGB) against a standard single profile conversion you may be showing differences that are purely a result of the imaginary colours in your test image.

sRGB --> ProPhoto (smaller gamut --> Bigger gamut)
When converting sRGB to ProPhoto, Lab value remains unchanged. Since this point has the same Lab value, it must be of the same color.

This only applies if you use convert to profile (my third bullet and example file) it does not apply if you use assign profile.

Nigel

(Edited so quotes show original source)
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: Peter_DL on August 22, 2011, 06:53:05 pm
... Therefore if you create a ProPhoto RGB test image from an sRGB file by assigning the ProPhoto profile you may possibly create an image with imaginary colours (you could probably check if the image actually contains imaginary colours by using ColorThink or a similar utility). Hence, when you compare your complex process for converting from a large gamut (ProPhoto RGB) to a smaller gamut (sRGB) against a standard single profile conversion you may be showing differences that are purely a result of the imaginary colours in your test image.

Nigel, - this is perfectly what I meant
(but did not reach to make clear). Many thanks.


JC, - if we can come over this,
Iíd be interested what exactly determines the gamut primaries of your initial host space jc1RGB. If you need a somewhat smaller, handier space than ProPhoto RGB to tailor the subsequent perceptual conversion, why not using something known like e.g. Bruce Lindbloomís Beta RGB. However, you mentioned that you canít find an easy way out Ö (?).

By the way, it is summer (at least in the northern hemisphere). Many colorful flowers out there, to shoot and testÖ

Regards, Peter

--
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 22, 2011, 07:49:57 pm
Unfortunately, an incorrect interpretation of the XYZ color space has also resulted in it being labeled as perceptually bad. There is a new realization now regarding what went wrong in the original interpretation.

Sincerely,

Joofa
Hi,

Thank you for sharing. More pointers please.

Regards,
jc


Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 22, 2011, 08:12:20 pm
Hi Nigel,

Thanks and welcome for sharing your thought with us.
Sorry if that was misunderstood. Let's move on.

I shall clarify if I did not make clear on thread:  http://www.luminous-landscape.com/forum/index.php?PHPSESSID=24205b19480ced199ad3e9e3a10ee9ce&topic=56978.msg462413#msg462413 (http://www.luminous-landscape.com/forum/index.php?PHPSESSID=24205b19480ced199ad3e9e3a10ee9ce&topic=56978.msg462413#msg462413)

Regards,
jc


.../Just found
 I regret a mistake was made on a sentence in that thread, the below added words in red were what I intended to include originally.

But, you may be wrong by simply stating that the Lab values for RGB=(0 255 0) for ProPhoto in PS is imaginary.
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 22, 2011, 09:24:20 pm

Iíd be interested what exactly determines the gamut primaries of your initial host space jc1RGB. If you need a somewhat smaller, handier space than ProPhoto RGB to tailor the subsequent perceptual conversion, why not using something known like e.g. Bruce Lindbloomís Beta RGB. However, you mentioned that you canít find an easy way out Ö (?).

By the way, it is summer (at least in the northern hemisphere). Many colorful flowers out there, to shoot and testÖ

Regards, Peter

BetaRGB was among my choices as an intermediate color space. I have had tested a few profilers too, including ArgyllCMS and i1Profiler with some simulated color test patches but result is unsatisfactory, and that certainly can be further improved. Each profiler has it strength and color rendering can be quite difference, where saturated colors are concerned. Most commercial profilers work great normally but the weakness is that there is no provision for fine tuning. Though i1Profiler has great performance, due to copyright, I cannot release the profiles to the general public.

If I will to post anything on that, I have to be better prepared on technical issue.

Great! The last time I had been to the west coast was 30 years ago on  an company assignment (non photography related and I didn't even has a camera with me). Beautiful and lovely place it was!

Now over here it is hot weather plus rainy season.

Regards,
jc
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 22, 2011, 10:43:55 pm
I have found utilizing PhotoGamut at some point in a workflow to be helpful in certain circumstances, primarily in working down to a space smaller than itself, sRGB for an on demand book for example. Unfortunately some colors currently available in the gamut of the newest inkjets available are not within PhotoGamut, and therefore some available colors from the printer/paper/inkset my never be utilized. An update of PhotoGamut considering contemporary printer gamut might be welcome.

With good printer profile, high color reproduction is still possible.
When image was converted from one color space to another color space with profiles and with perceptual intent, colors will be shifted due to cmm mapping process, that is inevitable.

If there are profiles to convert  perceptually to say sRGB (Beta2.1) or Adobe RGB, do we need another color space?

I am still trying hard to understand the audience here.

Thank you for feedback.

Regards,
jc

Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 23, 2011, 01:25:53 am
Hi all,

I was not presenting a new invention, but just trying to convince the audience that the conversion from ProPhoto to sRGB can be performed perceptually with the current cmm but with a different approach. The aim is to improve the color re-generation process.  Certainly, there may have other better way to do it that I am unaware of.

I do not have a real and good example to show. I had used the hypothetical model (see Example 2 (http://www.luminous-landscape.com/forum/index.php?topic=56978.msg461255#msg461255)) which covers all the most saturated colors (be it R, G or B) in ProPhoto to demonstrate its capability. My supplemented photo images may not represent the best examples, but I still think they do not mislead the reproduction capability of this conversion process.

Let's move on by looking at it from a different perspective.

PhotoGamutRGB's Perceptual vs. jc1's Perceptual

I am using just one example here. If you have example to show that PhotoG does perform better, you are encouraged to show your image and with histograms if possible.

(http://3.bp.blogspot.com/-nvBz5ewILUk/TlHehBtFafI/AAAAAAAAAL4/tiyZkWcyPsg/s1600/0+0+photoGamut+perceptual.png)

1. Original Tiff image
    Nikon raw --> Import into NX2 with ProPhoto profile --> Cropped and output to Tiff --> Import into CS

Following conversions were performed in PS.
2. a) Convert from Tiff to photoGamut
    b) Further convert to sRGB with RelCol sRGB

3) Convert with jc1's  2-step* suggestion.

Differences
For PhotoGamut, it was first converted perceptually to a much smaller space than that for ProPhoto, and then Relcol to sRGB.

As for my approach, the image was first AbsCol (or RelCol) to a intermediate color space which is smaller than ProPhoto but still significantly larger compared to sRGB. Then to sRGB with perceptual intent.


Notes:
a) * I shall keep using the same term to avoid further confusion.
b) Compare by observing the shadow detail as shown in the histograms.

Thank you.

jc
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: joofa on August 23, 2011, 12:49:51 pm
More pointers please.

Sign of the times - there was a time when my word would suffice.  :-\

Take your example of color = [0,255,0], convert it to xyz and compare and see if you spot a discrepancy there. This is a little off topic to your OP so if you want then we can take it offline.

Sincerely,

Joofa
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: Peter_DL on August 23, 2011, 01:36:53 pm
BetaRGB was among my choices as an intermediate color space. I have had tested a few profilers too... Though i1Profiler has great performance, due to copyright, I cannot release the profiles to the general public.

I don't understand this reply.
It sounds like your LUT for perceptual mapping were fixed, and you are adjusting the gamut primaries of the initial, intermediate host space.
 
 
Referring to Photogamut RGB
If there are profiles to convert  perceptually to say sRGB (Beta2.1) or Adobe RGB, do we need another color space?

You are needing two other color spaces, not just one.
 
 
b) Compare by observing the shadow detail as shown in the histograms.

Channel clipping / saturation clipping (in the histogram) resulting from gamut conversion is unfortunately completely meaningless.

Just think about a chessboard pattern of gray vs a highly saturated color. Straight RelCol conversion from a large source to a small target space will most likely beat any perceptual gamut compression algorithm. Saturation clipping - in this general context - does not disclose the degree of image degradation and loss of perceivable texture.

Visually I find it hard to see the differences with the above illustration,
however, this may also have to do with the details of preparing these screenshots for posting.

Regards, Peter

--
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 23, 2011, 07:50:58 pm

Take your example of color = [0,255,0], convert it to xyz and compare and see if you spot a discrepancy there. This is a little off topic to your OP so if you want then we can take it offline.

I make use of the latest version of PatchTool to compute those numbers.  I have gone through the same exercise repeatedly and no discrepancy was found. My knowledge is that much.
 
As for Lab=(88 -79 81)  for ProPhoto RGB=(0 255 0), the Lab values were read out directly from the CS info screen.

Regards,
jc
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: joofa on August 23, 2011, 08:00:12 pm
I make use of the latest version of PatchTool to compute those numbers.  I have gone through the same exercise repeatedly and no discrepancy was found. My knowledge is that much.
 
As for Lab=(88 -79 81)  for ProPhoto RGB=(0 255 0), the Lab values were read out directly from the CS info screen.

Regards,
jc


No, that is not the issue. Think about distances here, after all that is what the "perceptual equality" notion is about, which you mentioned.

Sincerely,

Joofa
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 23, 2011, 08:04:07 pm
It sounds like your LUT for perceptual mapping were fixed, and you are adjusting the gamut primaries of the initial, intermediate host space.
This is an old V2 engine with no PRMG intelligence. As for the intermediate host space, I shall compare it with BetaRGB in subsequent stage.
 

"Referring to Photogamut RGB
You are needing two other color spaces, not just one"
Got your point.
 
 
"Channel clipping / saturation clipping (in the histogram) resulting from gamut conversion is unfortunately completely meaningless."
View is respected.


"Just think about a chessboard pattern of gray vs a highly saturated color. Straight RelCol conversion from a large source to a small target space will most likely beat any perceptual gamut compression algorithm. Saturation clipping - in this general context - does not disclose the degree of image degradation and loss of perceivable texture."
As said, perceptual rendering is not always the best solution, so does RelCol or other rendering algorithm.


Regards,
jc
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 23, 2011, 09:44:52 pm
No, that is not the issue. Think about distances here, after all that is what the "perceptual equality" notion is about, which you mentioned.

Sincerely,

Joofa

Subject might be too academic and I shall leave it alone for now.

On a side note, I am more interested in determining optimal primaries as much time was spent with trial and error. For instance, if 2 primaries are fixed, how to determine 3rd primary optimally, or fixed 1 and find the other 2.

Regards,
jc
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 23, 2011, 09:58:46 pm
Why jc1RGB is chosen as Intermediate Color Space?

Intermediate Color Space Consideration: BetaRGB vs jc1RGB

I shall try to present it as brief as possible. Believe me, it is tedious and uninteresting exercise.

1) Compute the RGB-Lab Profile data for ProPhoto, call it the Source.
    Convert the Souce to Destination space for both BetaRGB and jc1RGB
    I shall not go into details on how they were created.

2) How to interpret my data
    Refer to below attached tables, Table1 and Table2.

    The data colored in green is the RGB-Lab data for ProPhoto (source space)
    The data colored in red in Table1 is the RGB-Lab data for  BetaRGB (destination space)
    The data colored in red in Table2 is the RGB-Lab data for  jc1RGB   (destination space)

    The data colored in red is the converted data with AbsCol from ProPhoto space.

     They are of the following format:

For example: Red 1

ID Name    R          G       B         L*       a*       b*                  R        G        B        L*       a*       b*
1   Red1 255.000 0.000 0.000 60.608 139.169 104.497  --->  255.000 0.000 21.000 61.947 107.273 100.699  (BetaRGB) Table 1
                                                                             
                                                                          --->  255.000 52.000 0.000 58.764 124.016 98.898    ( jc1RGB)  Table 2

Above example shows Photo RGB=(255 0 0) is mapped to BetaRGB RGB = (255 0 21) with AbsCol
                                                     and is mapped to  jc1RGB  RGB = (255 52 0) with AbsCol

3) Examining the data sets
    a) When converting from ProPhoto to BetaRGB
        Red1 to Red6      RGB = ( 255 0 21)  these colors are indistinguishable after conversion
        Red7 to Red21    RGB = ( 255 0 22)  these colors are indistinguishable after conversion

       note: Red21 in ProPhoto is RGB = (235 0 0)
       
    b) When converting from ProPhoto to j1RGB
        Red4 and Red5  =  (255 49 0)          these colors are indistinguishable after conversion

       note: Red4 in ProPhoto is RGB = (252 0 0)
       As I mentioned earlier, further optimazation is still possible by moving primaries G & B, for perfectness.

4) Above was done for RED channel only.
    As for the GREEN and BLUE, the results are comparable for both BetaRGB and jc1RGB and I shall not repeat here.

5) Examine the data in the tables to convince yourself.

(http://1.bp.blogspot.com/-dbGj9oXEkAM/TlPDKzpwQmI/AAAAAAAAAL8/OaQCvliC0bI/s1600/0+0+pro+to+beta+and+jc1RGB.png)


Regards,
jc

Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: joofa on August 23, 2011, 11:09:23 pm
Subject might be too academic and I shall leave it alone for now.

That is okay. We can leave it for now. I must also say that I like the graphs and the analysis you do. It is so refereshing than endless messages on ETTR, which camera has how much SNR, etc. Your messages are welcoming relief at least for me.

However, the subject is not all academic IMHO. Think about some of the gamut maps that many programs show, the gamut volume calculations, the presentation of chromacity diagrams in books, and very importantly, is there really a need to go to a nonlinear space (say Lab) to claim the supposed "perceptual uniformity", while not properly analyzing linear spaces (say xyz, rgb, etc.)?

Quote
On a side note, I am more interested in determining optimal primaries as much time was spent with trial and error. For instance, if 2 primaries are fixed, how to determine 3rd primary optimally, or fixed 1 and find the other 2.


That is an interesting proposition and one can try to devise a methodology for that.

Sincerely,

Joofa
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 24, 2011, 02:27:00 am
I must also say that I like the graphs and the analysis you do. It is so refereshing than endless messages on ETTR, which camera has how much SNR, etc. Your messages are welcoming relief at least for me.

Thank you for your words of encouragement.

Regards,
jc
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 24, 2011, 02:37:02 am
Why jc1RGB is chosen as Intermediate Color Space? Part 2

Intermediate Color Space Consideration: BestRGB vs jc1RGB vs BetaRGB
 
 
BestRGB is another candidate, its Gamut volume if viewed with CTP3 is marginal larger than that for jc1RGB.

(http://3.bp.blogspot.com/-F0lJilgEXNg/TlS92R8xrJI/AAAAAAAAAMI/MJKt_4ywmlY/s1600/00+betaRGB+%2526+bestRGB.png)
 
Performance Comparison
 
As there is no benchmark to follow, I use my method of comparison as outlined in previous post.
ProPhoto (Source) --> BestRGB (Destination)
                         --> jc1RGB   (Destination)
                         --> BetaRGB (Destination)
Rating
Rating 1 is better than Rating 2, and that Rating 2 is better than Rating 3.

The performance is summarized as follows.
 
      BestRGB   jc1RGB   BetaRGB        Remark
R       2              1           3            G=B=0
G       1              1           1            R=B=0
B       3              1           2            R=G=0
 

Regards,
jc

../ update graph
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: Peter_DL on August 24, 2011, 04:54:10 pm
On a side note, I am more interested in determining optimal primaries as much time was spent with trial and error.
Ö
ProPhoto (Source) --> BestRGB (Destination)
                         --> jc1RGB   (Destination)
                         --> BetaRGB (Destination)
Rating 1 is better than Rating 2, and that Rating 2 is better than Rating 3.

I think for me, and maybe for others as well, it is not so clear at which stage of progress with "trial and error" suggested procedure already is. Understandable though due to the complex nature of the subject.


As said, perceptual rendering is not always the best solution, so does RelCol or other rendering algorithm.

Another conclusion from my earlier pRGB-to-sRGB perceptual gamut compression exercises was that an relevant advantage with real-world images can only be produced by subsequent local contrast enhancement on the most saturated colors (versus straight RelCol + same post-processing). Isnít it the core of this subject, to keep perceivable, graduated differences with highly saturated colors, smooth transitions + texture.

Regards, Peter

--
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 24, 2011, 10:35:38 pm
it is not so clear at which stage of progress with "trial and error" suggested procedure already is. Understandable though due to the complex nature of the subject.

The current beta 2.1 are working profiles.  I have stopped further development work and concentrating on analyzing the profiles' quality . If there is no negative feedback for the next 2 to 3 months, I may remove the beta status, but not too sure though at this point in time.

Regards,
jc
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 25, 2011, 08:57:04 pm
Intermediate Color Space Consideration
 
Color Saturation Comparison: BetaRGB vs jc1RGB
 
The saturation performance was examined with Gamutvision at L=0.5 (default setting) when converting from ProPhoto (Input or Source profile) to BetaRGB and jc1RGB (Output or Destination profiles)
 
If you have Gamutvision, you can do the same with the following settings.
1 ProPhoto       3 ProPhoto
2 BetaRGB        4 0_jc1RGB (beta2.1)
Rendering: Absolute, for both
Select: xy Chromaticity (Saturation map)
 
The following diagrams show how the  gamut boundaries (in 2D) are mapped between the source profile and  the detination profiles at L=0.5, where BetaRGB is on the left and jc1RGB is on the right.
 
Hints:
1) The gamut boundary for ProPhoto is represented with dotted lines (at different saturation levels)
    and that for the destination profiles (BetaRGB and jc1RGB) by solid lines.
 
2) The saturation analysis tellies with my previous tabulated result and my observation.
 
3) This implies "larger is better."
    http://www.brucelindbloom.com/BetaRGB.html (http://www.brucelindbloom.com/BetaRGB.html)
 
For more detailed explanation, kindly refer to http://www.gamutvision.com/docs/gamutvision_displays.html#CIE_xy (http://www.gamutvision.com/docs/gamutvision_displays.html#CIE_xy)
 
(http://2.bp.blogspot.com/-SX0FYcKve4E/TlYU5Bl-3QI/AAAAAAAAAMM/LVBEZi8aMgU/s1600/0+0+chromaticity+beta+vs+jc1TGB.png)
 

OT:
CP800 user, you might be interested in some of my work done which can be found here (http://cp800.blogspot.com/).

Regards
jc
 
 
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: Bart_van_der_Wolf on August 26, 2011, 03:45:53 am
3) This implies "larger is better."
    http://www.brucelindbloom.com/BetaRGB.html (http://www.brucelindbloom.com/BetaRGB.html)

Hi JC,

You are mis-representing what Bruce Lindbloom says:

Quote from: Bruce Lindbloom's website
One important characteristic would be that the working space is suffiently large that it can properly encode (or contain) all colors that are important to an application. This implies "larger is better."

Another attribute, which conflicts with the above, is that the working space should be as small as possible, so that quantization errors may be minimized. This implies "smaller is better."

Bruce describes two conflicting attributes of an ideal workingspace, you pick one. By doing so, you allow larger quantization error for the 99% (?) most common colors, in order to accomodate a few outliers. What is your rationale for that choice? Do you encounter many real life (!)colors that are outside the BetaRGB gamut?

Cheers,
Bart
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 26, 2011, 09:37:55 am
Hi Bart,

You are mis-representing what Bruce Lindbloom says:
Bruce describes two conflicting attributes of an ideal working space, you pick one.

I stated conclusively that " larger is better" and that is implying jc1RGB is the better choice as an intermediate color space.
Gamut for jc1RGB is about 16.3% (using gamut calculation with PatchTool and with simple arithmetic) larger than that for BetaRGB, hence "larger is better". I have no intention in proposing another working space.

My definition of an ideal intermediate space would be one that color difference and clipping is minimized when converting from one color space to the other or vice versa. Gamut volume is not the deciding factor.

Quote
By doing so, you allow larger quantization error for the 99% (?) most common colors, in order to accommodate a few outliers.

(I may not fully understood your concern but for purpose of discussion...let me try... )
If you are implying that if a larger working space is chosen than that for BetaRGB, then (severe or may be not that severe) quantization error may be introduced.  I think that may not be the main concern. My reasons are as follows.

Choice of gamma may has a direct influence in quantization error as gamma affects distribution of RGB points within the gamut. As both spaces use gamma 2.2,  and that the difference in gamut volume is not that great, I can't feel the effect. Frankly, I do not know how to compute it.  ;)

Sometimes ago, I analyzed the error introduced  due to choice of 8-bit (per channel) against 16-bit (per channel), or vice verse, and with GRAXol2006_Coated_1 as Reference test data, I have the following result to share.

(http://4.bp.blogspot.com/-T7IwvnkEsMo/Tld7yDmXwBI/AAAAAAAAAMQ/fcw-yaQ2KVY/s1600/0+8+vs+16-bit.png)
(note: unit in dE2000)

a) For sRGB, it is not critical if either 8-bit or 16-bit is used. Hence there is no good reason to use 16-bit for sRGB image.
b) For 16-bit, dE for Adobe RGB and Prophoto is comparable.

So, if 16-bit is used, dE is about the same for work space that is larger than Adobe RGB, be it BetaRGB, jc1RGB,  BestRGB or ProPhoto. I am not hinting that 16-bit must be used for aRGB image, the choice is greatly depends upon the user. I am unsure if above illustration is appropriate. Please note that above results are merely based on my test condition.

Quote
What is your rationale for that choice?
Which is more appropriate as an intermediate color space, BetaRGB or jc1RGB?


Quote
Do you encounter many real life (!)colors that are outside the BetaRGB gamut?
No. But if you are converting from ProPhoto to BetaRGB, it is possible that highly saturated Red may be clipped. I have demonstrated that with  ProPhoto, red channel will be clipped if  R>235 (B=G=0) and if BetaRGB is chosen as the intermediate color space, and that is what I am trying to avoid.  If this is not the concern, then use direct RelCol sRGB.

Have a nice day.

jc

.../spelling check
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 27, 2011, 10:22:31 pm
Matrix vs Cluts (Part 1)
 
My recommended approach for perceptual color space conversion from ProPhoto to sRGB is known to be "complex" . In actual fact, it is not, just that additional steps are involved.
 
Using my method, the image with ProPhoto profile is converted to jc1RGB, subsequently to sRGB_jc1 and finally to standard sRGB. The initial step is similar to converting to sRGB with straight RelCol. The main difference is that by converting to an intermediate color space first, the " color distortion" that could have been introduced due to conversion is significantly smaller, compare with directly convert to sRGB. This loss is further reduced to its minimal with jc1RGB as the choice of intermediate color space.
 
The matrix conversion has its advantages, not only that its profile size is relatively smaller and portable, color transformation can be carried out within the known xyz color space. The shortfall is, either sRGB, Adobe RGB, ProPhoto or other proposed color spaces, which are known to be Absolute color space, are not associated with mapping functions.
 
In V2 (icc profile specification version 2), color rendering with perceptual rendering intent in CMM can be carried with output type profile such as printer profile. Output profile uses Cluts ( Color Look Up Tables). ProPhoto has 2 of its primaries extended outside the visible locus and hence problem could arise if the image with ProPhoto has colors that are not within the visible locus. Are these invisible colors exist? I do not know. The fact is, if they are non existence, why we care?
 
I am going to show the clipping effect of converting ProPhoto to sRGB  with straight RelCol or matrix transformation, based on the following illustration. Your may have to refer back to my earlier thread, for how my tabulated data is interpreted.
 
(http://2.bp.blogspot.com/-u0cHDR3bWPs/Tlifk3c-baI/AAAAAAAAAMU/ogh4fIx9JtQ/s1600/0+0+1+pro+relcol+srgb.png)

Note: * these are clipped if import into PS.
 
Again, above only shows the RED channel. In general, there are less clipping effect on the GREEN, but could have more clipping effect on the BLUE if the blue components are outside the visible locus (non conclusive!). For BLUE, I noticed that these clipped  components that are falling outside the horse-shoe-shape could have their L (L in L*a*b*) values virtually zero.
 
Regards,
jc
 
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 28, 2011, 11:11:39 pm
Matrix vs Cluts (Part 2)
 
Color Degradation Analysis: RelCol vs Perceptual
 
Test Sample: 4096 test point as before.  <Reference Link (http://www.luminous-landscape.com/forum/index.php?PHPSESSID=24205b19480ced199ad3e9e3a10ee9ce&topic=56978.msg461201#msg461201)>
 
Conversion Spaces
a) Source Space: jc1RGB
b) Destination Space: sRGB
 
Methodology
A)
1. Define reference
    Start with Source space, generate RGB's Lab values, our Reference data.
2. Convert from Source space to sRGB with straight Relcol. Compute Lab and compare it with Reference.
    Refer to first Diagram for result.
3. Convert from Source space to sRGB perceptually with sRGB_D50_jc1. Compute Lab and compare it with Reference.
    Refer to second Diagram for result.
 
B) Generate Tiff (RGB) Reference chart, import to PS. Assign profile with jc1RGB, that is our source image.
1. Convert from Source space to sRGB with straight Relcol. Import result to CTP3
2. Convert from Sources space to sRGB perceptually, use jc1 approach. Import result to CTP3.
    Results are shown with last Diagram.

(http://2.bp.blogspot.com/-BrUkRdfijpE/Tlrn2i7jOtI/AAAAAAAAAMc/um6GvnqZz1M/s1600/01+jc1RGB+to+sRGB+%2528relcol%2529.png)
 
(http://4.bp.blogspot.com/-95T1r72ugxE/Tlrn63okIHI/AAAAAAAAAMg/_RMVojPzA9M/s1600/01+jc1RGB+to+sRGB+%2528perceptual%2529.png)
 
(http://4.bp.blogspot.com/-ltLR0LHzHcg/Tlrn-m2G4tI/AAAAAAAAAMk/VM69i49g098/s1600/02+relcol+vs+perceptual.png)
 
 
Observations:
1) Refer to first 2 diagrams. No color degrading was observed.
2) Refer to last or third diagram.
    a) For conversion with RelCol, relative position of test points is well maintained. This is in comparison with test points in source space ( not shown).
    b) For conversion with Perceptual rendering, converted test points were re-distributed locally. More data points can be clearly seen with compare to that using convert with straight RelCol.
 
Comments
1) Above results show no color degrading with Perceptual rendering using output profile, sRGB_D50_jc1. Is conversion with perceptual rendering yields better color reproduction (with sRGB_D50_jc1) than with straight Relcol?
The observation is inconclusive, reason being that the sample size might be too small and that the RGB pitches of the test patches are too far apart. Further evaluation should be carried out with larger sample size or with real image. With real image, at your own time own target, anyone?
2) One thing for sure, more color details can be recovered with perceptual rendering, which has been clearly illustrated.
 

Regards,
jc
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 29, 2011, 02:52:26 am
Inviting Comments on
 
If "complexity" is not the deciding factor, can jc1's approach replace straight Relcol, when converting from ProPhoto to sRGB?


Thank you.

Sincerely,
jc
 

.../rephrase question
 
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: joofa on August 30, 2011, 11:17:18 pm
Inviting Comments on
 
If "complexity" is not the deciding factor, can jc1's approach replace straight Relcol, when converting from ProPhoto to sRGB?


Thank you.

Sincerely,
jc
 

.../rephrase question
 

Unfortunately, JC1, it seems like that complexity is the issue here. There are some capable people here that contribute to the color forum. Unfortunately, it seems Iliah Borg is no longer contributing, but Peter_DL, DigitalDog, Schewe, and others are still here. Complexity of operations is a thing that people dread. But, it seems like you might have to distill your approach a little to make it more presentable and understandable. I think you want to say something useful here but the message is not coming across the way you want it.

Sincerely,

Joofa
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 31, 2011, 12:01:37 am
Matrix vs Cluts (Part 3)
 
Space Conversion Analysis
 
Aim: To examine color reproduction capability with jc1RGB and sRGB_D50_jc1, by comparing with conversions to and from other popular color spaces such as sRGB, aRGB (Adobe RGB) and  PhotoGamut RGB.
 
Test sample: 5852 test points, covering from RGB=(0 0 0) to (255,255,255) with pitch of 15.
Color Matching: CIEΔE 2000, under D50 illuminant, 2į observer.
 
Results are summarized as follows.

(http://2.bp.blogspot.com/-ye5QIsIO8Fg/Tl83Bgw2svI/AAAAAAAAAA8/hbTm6_tftNc/s1600/10c++space+conversion+comparison.png)

 
Comment:
Data speak for itself.


.../re-grouping for clarify.
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 31, 2011, 12:05:28 am
Unfortunately, JC1, it seems like that complexity is the issue here. There are some capable people here that contribute to the color forum. Unfortunately, it seems Iliah Borg is no longer contributing, but Peter_DL, DigitalDog, Schewe, and others are still here. Complexity of operations is a thing that people dread. But, it seems like you might have to distill your approach a little to make it more presentable and understandable. I think you want to say something useful here but the message is not coming across the way you want it.

Got your point.

Thanks.
jc
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 31, 2011, 02:44:57 am
Photoshop action: Pro2sRGB_perceptual.atn
1-click action is available now.
Download the PS action from the below link.
 
Procedure
1. Load your ProPhoto image into CS.
2. Load PS action: Pro2sRGB_perceptual.atn
3. Shift F9 to execute the perceptual conversion from ProPhoto to sRGB
 
 
Download Link
1) Pro2sRGB_perceptual.atn (https://www.yousendit.com/download/M0RyS3dwY3lVVGswTVE9PQ)
2) jc1RGB beta 2.1 (https://www.yousendit.com/download/M0RyS3duTWNoMlh2Wmc9PQ)
 
All are in WinZip
Action was tested with CS4 under Windows xp3.
 
Do feel free to request if further details are needed.

Thank again Joofa for your valuable advice.
 
Regards,
jc
 

.../make sure the 2 profiles are installed correctly.
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: cybis on August 31, 2011, 05:05:07 pm
Photoshop action: Pro2sRGB_perceptual.atn
1-click action is available now.
Download the PS action from the below link.
 
Procedure
1. Load your ProPhoto image into CS.
2. Load PS action: Pro2sRGB_perceptual.atn
3. Shift F9 to execute the perceptual conversion from ProPhoto to sRGB

jc1, thanks for sharing! The last step of the action converts to the current RGB working space which might be set to something other than sRGB. Not sure if this was intentional. Shouldn't the last step be an assign sRGB?

I've only tried it on one image but was impressed by the extra details in deep blue shadows. Thanks!

.../Turns out BPC was turn off in my first convertion...
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 31, 2011, 08:22:05 pm

Hi,

The last step of the action converts to the current RGB working space which might be set to something other than sRGB. Not sure if this was intentional. Shouldn't the last step be an assign sRGB?

Yes, that was done intentionally.
As sRGB_D50_jc1 resembles sRGB (refer to Color Matching Test (http://www.luminous-landscape.com/forum/index.php?PHPSESSID=24205b19480ced199ad3e9e3a10ee9ce&topic=56978.msg461201#msg461201)),  choice of assign function or convert function for this case, in my opinion, should has no impact on the final color reproduction. 

In my earlier post (http://www.luminous-landscape.com/forum/index.php?PHPSESSID=24205b19480ced199ad3e9e3a10ee9ce&topic=56978.msg464252#msg464252), I mentioned about higher ΔE and that might be due to colorimetric adaptation, when converting from aRGB to sRGB_D50_jc1. I shall investigate to see if there is any difference at all if assign is used instead of convert.

Quote
.../Turns out BPC was turn off in my first conversion...
Understood. The convert function has options such as BPC.
BPC is activated in Pro2sRGB_perceptual.atn.

Thanks for your feedback.

Regards,
jc
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: cybis on August 31, 2011, 08:31:47 pm
Yes, that was done intentionally.

Just to be sure, my RGB working space is set to AdobeRGB. When I run your action the final result is an image in AdobeRGB colorspace, not sRGB. Is that the intended result?
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: cybis on August 31, 2011, 08:43:20 pm

Understood. The convert function has options such as BPC.
BPC is activated in Pro2sRGB_perceptual.atn.


In the first two steps BPC is OFF. In the third step BPC in ON.
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 31, 2011, 08:57:22 pm
Just to be sure, my RGB working space is set to AdobeRGB. When I run your action the final result is an image in AdobeRGB colorspace, not sRGB. Is that the intended result?
Ooops! I see your point now.
If the working space is set to AdobeRGB, the final color space is converted (by default ?) to AdobeRGB  instead of sRGB. Let me check if CS is doing it correctly or assign function is more appropriate.

Quote
In the first two steps BPC is OFF. In the third step BPC in ON.
Yes, unsure about its final effect.

Regards,
jc
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 31, 2011, 09:10:00 pm
My bad. The 3rd step I set it to convert to AdobeRGB.
I shall post the update.


jc
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: cybis on August 31, 2011, 09:25:45 pm
Also currently, the first two steps are perceptual intent. I thought the first step should have been relative color, no?
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on August 31, 2011, 10:33:25 pm
Also currently, the first two steps are perceptual intent. I thought the first step should have been relative color, no?
Actually no difference in final result, as both are Absolute color space with no mapping function.


Pro2sRGB_perceptual.atn (revised)
To avoid further confusion, they are updated in the revised action to reflect actual intents used for the conversion.
For Step 1, rendering intent is set to Absolute, as both source space and destination space are with D50 illuminant.
The steps are shown below.

(http://4.bp.blogspot.com/-Fumwg7ticVo/Tl71CbdPEnI/AAAAAAAAAMs/RNyoOtkh-Zs/s1600/00+Pro2sRGB_perceptual+revised.png)

 
New download link for Pro2sRGB_perceptual.atn  <  revised (https://www.yousendit.com/download/M0RweFVZeDNPSHl4dnc9PQ) >

As for jc1RGBR beta 2.1, no change was made, just a repost  < jc1RGB beta 2.1 (https://www.yousendit.com/download/M0RyS3duTWNoMlh2Wmc9PQ) >

Regards,
jc
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on September 01, 2011, 09:06:54 pm
Demo_ jc1RGB_Beta2.1 down load link:  < Demo_ jc1RGB_Beta2.1 (https://www.yousendit.com/download/M0RvK3BQcGtGR0d4dnc9PQ) >
 
It consists of following 6 files.
a. 0_jc1RGB (beta2.1).icc
b. 0_sRGB_D50_jc1 (beta2.1).icm
c. timage-50x100_prophoto.tif
d. jc1-saturated-color_prophoto.tif
e. Pro2sRGB_perceptual.atn
f. Pro2sRGB_perceptual_interactive.atn
 
 
Setup
1. Download and unzip Demo_ jc1RGB_Beta2.1.zip to a folder
2. Copy or Drag & Drop both 0_jc1RGB (beta2.1).icc and 0_sRGB_D50_jc1 (beta2.1).icm into system icc folder
3. Start CS and load both action files, Pro2sRGB_perceptual.atn and Pro2sRGB_perceptual_interactive.atn
 
note: PS action will remain in CS unless it is unloaded.
 
 
Interactive Mode
1. Start CS
2. Load one of above tiff files, or other image file with ProPhoto, BetaRGB or BestRGB profile.
    You may also like to conduct a torturing test with any file, be it sRGB or aRGB.
3. Press <shift>+<F10> to start interactive perceptual conversion.
    Follow the screen instruction or press Shift-C to continue.

            (http://2.bp.blogspot.com/-yVmLnNZmPQs/TmAexAOIsjI/AAAAAAAAAMw/bIMm42u1GK0/s1600/0+0+0+interactive+conversion.png)
 
4. Repeat by going to the drop down File menu, do a Revert.
 
 
Non-Interactive Mode
1. Start CS
2. Load tiff file
3. Press <shift>+<F9> for 1-step non-interactive conversion.
 
For further improvement, your feedback would be much appreciated.

Thank you.

Regards
jc
 
.../ Tips (http://www.photoshopessentials.com/basics/photoshop-actions/) on PS action
.../ jc1RGB's Preliminary specification (http://jc1rgb.blogspot.com/2011/08/about-jc1rgb-color-space.html)
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: cybis on September 02, 2011, 10:05:52 am
I applied the 3 steps convertion to Bill Atkinson's twenty-eight balls test image and noticed some strange artifacts in the blue ball. Looks like banding (the Red value goes up and down several times).
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on September 02, 2011, 04:47:56 pm
I applied the 3 steps convertion to Bill Atkinson's twenty-eight balls test image and noticed some strange artifacts in the blue ball. Looks like banding (the Red value goes up and down several times).
Sound interesting.

I don't seem to be able to download this test image.
Could you advice where this test image can be downloaded, or pm me a link of that.

TIA

jc

Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: cybis on September 02, 2011, 07:17:16 pm
Sound interesting.

I don't seem to be able to download this test image.
Could you advice where this test image can be downloaded, or pm me a link of that.


https://public.me.com/billatkinson (https://public.me.com/billatkinson) Look for Twenty-Eight Balls.tif.zip.
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on September 02, 2011, 09:40:38 pm
https://public.me.com/billatkinson (https://public.me.com/billatkinson) Look for Twenty-Eight Balls.tif.zip.
Thanks for the link.

Blue Ball Test

IMHO, examine color smoothness on screen is best by disabling the monitor profile, especially if monitor profile is created with cluts. As for monitor that is profiled with matrix, inaccuracy has direct influence on the color smoothness as well.

I agree with you that banding after conversion was observed, but unsure how severe it is, and whether or not it is within the norm. Other who has better experience may like to comment on that.

Here is my suggestion on how color smoothness should be examined on screen.
Set soft proof to monitor, zoom in 100% or higher, use the Navigator in CS to assist in viewing the problem area.

    (http://2.bp.blogspot.com/-In0Q3c308qo/TmF1aSVkqWI/AAAAAAAAAM0/-QLjG6HutBE/s1600/04+Blue_Ball-smoothness.png)


Following is not a direct apple-to-apple comparison, as one is converted from ProPhoto to photogamut profile and other from ProPhoto to sRGB, both did that perceptually.

    (http://4.bp.blogspot.com/-LQfIEHYaqnI/TmF5Dlb483I/AAAAAAAAAM4/WePNHUBagr4/s1600/04a+Blue_Ball-smoothness+photog+vs+perc-sRGB.png)

I may carry out more extensive study on this matter.

Regards
jc

Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on September 03, 2011, 12:44:37 am
Blue Ball Test 2
 
The Blue Ball was extrated from the original file, Twenty-Eight Balls.tif which can be downloaded from https://public.me.com/billatkinson.

The RGB data pre and post conversion along with the original data points, were illustrated as follow.
a)  The converted data in Lab space do not deviate much between rendering with RelCol and with Perceptual.
b)  In xyz space (not shown), more shadow details were recovered with perceptual conversion, these additional details are likely from data of the original image outside the visible locus.
 
(http://2.bp.blogspot.com/-LnTCy3M3-x0/TmGtsqvuMiI/AAAAAAAAAM8/GzQdraP71e8/s1600/05+Blue+ball+test+-+rgb+points+in+Lab+space.png)
 
jc
 
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on September 03, 2011, 10:35:27 pm
The Mysteries of the 28 Balls

Photoshop CS5 vs Nikon Capture NX2

Following is one of them.

Observation
Differences in color space conversion between Photoshop CS5 (x32 dot4) and Capture NX2 (2.2.7).

Test point: Background color of the 28 balls, refer to below diagram for clarify.

Discrepancy
Refer to diagram, arrow 1
a) CS5 histogram, Pink line
b) NX2 histogram, Grey line  
 
    (http://4.bp.blogspot.com/-EO2quR98ox8/TmLV1f0p0fI/AAAAAAAAANA/kRcora9mCeg/s1600/00+28_balls+mysteries+CS5+vs+NX2.png)


                                        RGB             HSB            Lab
A) Direct RelCol

1 ProPhoto (CS5)            192,192,192     0,0,75         82,0,0
   ProPhoto (NX2)            192,192,192     0,0,75          ---

2 RelCol to sRGB    
    CS5 (ACE)                  203,203,203     0,0,80        82,0,0    
    CS5 (ICM)                  203,203,203     90,0,80       82,0,0
    NX2                          203,203,203      0,0,80           ---   

B) Perceptual workflow

1 ProPhoto (CS5)            192,192,192     0,0,75         82,0,0
   ProPhoto (NX2)            192,192,192     0,0,75         ---
-
2. AbsCol to jc1RGB
    CS5 (ACE)                  202,202,202     60,0,79       82,0,0            ACE throughout
    CS5 (ICM)                  202,202,202     30,0,79       82,0,0            ICM throughout
    NX2                           202,202,202      0,0,79          ---

3. Perceptual to sRGB_D50_jc1
    CS5 (ACE)                  203,204,203     144,0,80     82,0,0             Pink line?
    CS5 (ICM)                  204,205,206     193,1,81     82,-1,0
    NX2                           203,203,203      0,0,80          ---              Grey line?    

Notes:
All data were read directly from info screen.
Always on BPC
 
Comment
NX2 is consistence, but inconclusive.


Regards
jc

.../Further Observation
In CS, it seemed that the color space conversion was not affected by the problematic HSB values. With a color picker, I re-confirmed that the image was displayed correctly. Only the HSB info and possibly the histogram, are bad.

.../Clarification
Such phenomenon on histogram is probably due to very slight displacement on converted RGB values (R, G and B not exactly equal for grey) and it was further "amplified" on a compact info screen. So do not be alarmed by that. Similar effect was observed in NX2.

.../Logical reason I can think of now is smart PS modified the color of this line as it has the same color as the histogram background.
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on September 05, 2011, 02:27:56 am
 
Effect of BPC
 
The effect on color space conversion due to BPC (Black Point Compensation) was studied with below 22-level grey scale.
 
  (http://1.bp.blogspot.com/-7O50C1fI1HE/TmRBsf757AI/AAAAAAAAANE/MEPWab2ZYPY/s1600/00+22-level+grey+scale.png)
 
Results (with Histograms)

                  (http://4.bp.blogspot.com/-98RuNVGi3vw/TmRqsbOqlFI/AAAAAAAAANc/RTTVM91Dyao/s1600/00+effect+of+BPC.png)

 
Comments
1. BPC has no effect on conversion with RelCol in absolute color space.
    In general, conversions in PS are carried out under condition D50 illuminant in that all absolute color spaces
    have the same black point ( Lab=0,0,0) and White point (Lab=100,0,0).
    Inviting comment.
2. For perceptual rendering, the effect due to BPC can be realized on shadow area.
3. There is no loss in  neutrality (not shown) and luminosity with perceptual conversion, in comparison to conversion with RelCol.
 
jc
 
 
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on September 06, 2011, 07:01:35 pm
Example: ProPhoto to sRGB Conversion without clipping on Highlight

  (http://1.bp.blogspot.com/-iHi9FazePzU/TmlQ-bRTf1I/AAAAAAAAANo/Z_l-yBQGUvk/s1600/01+flower1a.png)

Download link for the example's tiff image < Example1a (https://www.yousendit.com/download/M0RwZ28yRStkMnQzZUE9PQ) >
 
Note: All my links are limited to 500 downloads.  Keep me informed if you are unable to download.
 
Thank you.
 
jc

.../update pic+link

Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: Peter_DL on September 07, 2011, 03:49:57 pm
 
Here is a practical test.
Screenshots copy&pasted into a new file in PS, monitor profile assigned, Converted to sRGB.
Monitor comprises more saturated Reds than sRGB, so sRGB destination space is really the limiting factor.
Bpc enabled will all conversions:

Screenshot # 1:
Image a) at the left:  Straight conversion from Prohoto RGB -RelCol-> sRGB.
Image b)  ProPhoto RGB -Perc.-> PhotoGamut RGB -RelCol-> sRGB.
Image c)  same as the first one: straight conversion from Prohoto RGB -RelCol-> sRGB.
Image d)  at the right:  ProPhoto RGB -RelCol->  0_jc1RGB (beta 2.1) -Perc.-> 0_sRGB_D50_jc1 (beta 2.1) -RelCol-> sRGB

All quite close together so far, however, letís do some post-processing on images b) to d) i.e. local-contrast-enhancement on the most saturated colors, as given with Screenshot # 2. Iíll desist from a final conclusion. Visually it seems that all other options are better than plain RelCol for this image.

Cheers!
Peter

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Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on September 08, 2011, 02:42:26 am
Thank you, Peter.

Below are what I have observed.

Color de-saturation due to conversion with PhotoGamut RGB's is more obvious than with jc1's perceptual conversion. 
As for RGB clipping due to conversion, it would be nice if that can be shown with histogram.


Regards,
jc
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: crames on September 08, 2011, 10:31:21 am
Example: ProPhoto to sRGB Conversion without clipping on Highlight

Download link for the example's tiff image < Example1 (https://www.yousendit.com/download/M0RvN3RVdkdFd2Z2Wmc9PQ) >


Although it has the ProphotoRGB profile embedded, the linked image does not seem to contain anything that exceeds the sRGB gamut. Is that the image you intended to show?
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: Peter_DL on September 08, 2011, 11:49:45 am
Below are what I have observed.

Sorry, can't see any images / attachments below of your post.
Maybe it did not upload.


Color de-saturation due to conversion with PhotoGamut RGB's is more obvious than with jc1's perceptual conversion.

My visual impression was that some of the "Perceptual nature" of jc1's conversion got lost with the very final conversion, RelCol to sRGB.  Could this be ? I did not futher follow up on this.


As for RGB clipping due to conversion, it would be nice if that can be shown with histogram.

Believe me, the histogram is unfortunately totally useless as for a (desired) correlation of saturation/gamut-clipping and a best-possible rendition.

When we squeeze something large into something small, sometimes compression is the best option, sometimes it is clipping. And often enough we might wish that it is something in-between. Depends on the content.

Peter

--

Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on September 08, 2011, 07:45:13 pm
Although it has the ProphotoRGB profile embedded, the linked image does not seem to contain anything that exceeds the sRGB gamut. Is that the image you intended to show?

Have updated the link or Here (https://www.yousendit.com/download/M0RwZ28yRStkMnQzZUE9PQ)

Thank you

jc
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on September 08, 2011, 10:17:02 pm
Hi,

Sorry, can't see any images / attachments below of your post.
Maybe it did not upload.
No attachment, I was referring to your image Untitled-11b (photogamut) and Untitled-11d (jc1 perceptual).

Quote
My visual impression was that some of the "Perceptual nature" of jc1's conversion got lost with the very final conversion, RelCol to sRGB.  Could this be ? I did not futher follow up on this.
The main difference between sRGB and sRGB_D50_jc1 is the file size. The file size for sRGB_D50_jc1 is much larger than that for sRGB and therefore no advantage to tag the converted image with a large icc profile.

I have proved that they have similar (so close) color matching (http://www.luminous-landscape.com/forum/index.php?PHPSESSID=24205b19480ced199ad3e9e3a10ee9ce&topic=56978.msg461201#msg461201) characteristic and that difference is negligible if they are interchanged (by assign function in PS). Hence, imho, no loss for this step of the conversion.

Quote
the histogram is unfortunately totally useless as for a (desired) correlation of saturation/gamut-clipping and a best-possible rendition.

When we squeeze something large into something small, sometimes compression is the best option, sometimes it is clipping. And often enough we might wish that it is something in-between. Depends on the content.
I have proved theoretically that there is no color degradation with my approach, compared with conversion with striaght Relcol. Refer to Color Degradation Analysis: RelCol vs Perceptual (http://www.luminous-landscape.com/forum/index.php?PHPSESSID=24205b19480ced199ad3e9e3a10ee9ce&topic=56978.msg463856#msg463856)

It will be much appreciated if someone could prove it untrue with just one real image (non descriptive type!).

Thank you.

Sincerely,
jc



Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: crames on September 09, 2011, 09:42:27 am
Have updated the link or Here (https://www.yousendit.com/download/M0RwZ28yRStkMnQzZUE9PQ)

Thanks. That one also seems within sRGB gamut, except for the very lightest whites.

While trying to catch up with this thread, I have a few questions:

Where does the Green_1b come from in your post #25 (http://www.luminous-landscape.com/forum/index.php?topic=56978.msg462413#msg462413) ?

How do your results compare to using the ICC v.4 sRGB profile?

What is your gamut mapping strategy? It seems you are allowing hue to change - usually undesirable.
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: Peter_DL on September 09, 2011, 01:36:52 pm
I have proved that they have similar (so close) color matching (http://www.luminous-landscape.com/forum/index.php?PHPSESSID=24205b19480ced199ad3e9e3a10ee9ce&topic=56978.msg461201#msg461201) characteristic and that difference is negligible if they are interchanged (by assign function in PS). Hence, imho, no loss for this step of the conversion.

Ok, got it.


I have proved theoretically that there is no color degradation with my approach...
It will be much appreciated if someone could prove it untrue with just one real image (non descriptive type!).

"Prove to me that Iím wrong" is probably not an ideal way to promote your idea.
Sounds a bit like "the defense" of a thesis as rooted in the European academic tradition.
Anyway.

For me, the question is more why to leave the PhotoGamut RGB pathway (?).
Hey, they have a nice website (http://www.photogamut.org/E_ICC_profile.html). A kind of public source.
Also, as we find / as shown above, post-processing is as important as the way of gamut mapping,
i.e. Local contrast enhancement applied through an inverted Saturation Mask in order to defeat the loss of "compressed" image details.

Peter

--
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on September 09, 2011, 07:12:37 pm
That one also seems within sRGB gamut, except for the very lightest whites.
True

Quote
Where does the Green_1b come from in your post #25 (http://www.luminous-landscape.com/forum/index.php?topic=56978.msg462413#msg462413) ?
Thank for pointing it out. It is a mistake. Green_1b is for sRGB, RGB=(0 255 0).
In CS, Lab vaule is (88 -128 128) for Prophoto RGB=(0 255 0), same as Green_1a except the value b.
I am wondering what should be the correct limits for a and b, 127 or 128? 

Quote
How do your results compare to using the ICC v.4 sRGB profile?
That v4 profile does not seem to work the way it should be.

Quote
What is your gamut mapping strategy? It seems you are allowing hue to change - usually undesirable.
Minimum channel clipping, preserving color details after conversion, reversible conversion (sRGB to jc1RGB or Adobe RGB, for example) with minimum loss,  and most importantly, to produce perceptually pleasing result.
Change in hue or color shift is unavoidable in perceptual rendering, may be that is one good reason why perceptual rendering is not always the only choice.

Thanks

jc


Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on September 09, 2011, 09:09:03 pm
"Prove to me that Iím wrong" is probably not an ideal way to promote your idea.
Sounds a bit like "the defense" of a thesis as rooted in the European academic tradition.
Sorry for my words. I did it without that intention at all. Thanks for pointing it out.

Quote
the question is more why to leave the PhotoGamut RGB pathway (?).
If it works better, I intend to make it publicly available. That was my original intention and it still remains the same.

Quote
as we find / as shown above, post-processing is as important as the way of gamut mapping,
i.e. Local contrast enhancement applied through an inverted Saturation Mask in order to defeat the loss of "compressed" image details.
Fully agreed. In most cases, the perceptually compressed details have negligible differences compared with conversion with straight RelCol.

Regards,
jc







Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: Peter_DL on September 10, 2011, 04:58:13 am
... I intend to make it publicly available.
That was my original intention and it still remains the same.

Good idea.
I believe you have a "story" to tell and something to offer to the community.


If of interest, here is the Action I used.

Kind regards, Peter

--
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on September 12, 2011, 03:39:18 am
here is the Action I used.
Thanks for sharing it with us.


It seems you are allowing hue to change - usually undesirable.
If you have specific concern or example showing the severe color shift with jc1's conversion, share with us and I am willing to do a study on that.

Regards,
jc


Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: crames on September 12, 2011, 11:38:55 pm
If you have specific concern or example showing the severe color shift with jc1's conversion, share with us and I am willing to do a study on that.

I took a Color Checker image and boosted the Chroma by 78% in ProphotoRGB, making 10 of the patches out of gamut for sRGB. After converting the super-colorful image to sRGB with your method, the hues for most patches changed very little - a few degrees or less (CIECAM02 hue). The largest hue change of 11 degrees was in the cyan patch (sixth in the third row). Lightness of the patches are also well preserved, again the worst is cyan which has been lightened by 7 J (CIECAM02 lightness).

No severe color shifts - actually I would say that your method does a very good job!

 
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: Peter_DL on September 13, 2011, 12:24:09 pm
No severe color shifts - actually I would say that your method does a very good job!

Once ago in another discussion, a serious (printer) profiling expert claimed
that all serious profiling software is based on any somewhat distorted Lab-color models (today we may call it a color appearance model)
to write the Lut while suppressing the know hue shifts when walking along iso-Lch lines.

Peter

--
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on September 13, 2011, 10:21:56 pm
No severe color shifts - actually I would say that your method does a very good job!
That's encouraging.

Once ago in another discussion, a serious (printer) profiling expert claimed that all serious profiling software is based on any somewhat distorted Lab-color models (today we may call it a color appearance model) to write the Lut while suppressing the know hue shifts when walking along iso-Lch lines.
Wonder if he has alternative or other suggestion.


Update: jc1RGB and sRGB_jc1 0.9 (RC)

Changes:
a) jc1RGB:
    G and B primaries are further optimized.
    Profile size is compacted to below 1K bytes.
    Created with another profiler.
    Color rendering in blue may be improved slightly.
b) sRGB_jc1:
    Optimizing profile size.
    Based on test sample, no difference at all in color reproduction with compared to Beta 2.1     
 
Downloads
jc1RGB and sRGB_jc1 0.9 (RC)  (https://www.yousendit.com/download/bHlDZEV6Rnc1R04zZUE9PQ)
PS actions (https://www.yousendit.com/download/bHlEV296Y1NlM1RIRGc9PQ)

jc


Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: Peter_DL on September 14, 2011, 12:48:06 pm
Once ago in another discussion, a serious (printer) profiling expert claimed
that all serious profiling software is based on any somewhat distorted Lab-color models (today we may call it a color appearance model)
to write the Lut while suppressing the know hue shifts when walking along iso-Lch lines.

Wonder if he has alternative or other suggestion.

The person to ask is Ethan Hansen.
I think, he is sometimes around here as well, although I was referring (from my memory) to a discussion a couple of years ago in the Rob Galbraith forum.

Peter

--
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on September 17, 2011, 09:30:13 pm
Color Space Comparison: PhotoGamut vs sRGB_jc1

        (http://2.bp.blogspot.com/-DargdYCPjkk/TnVDXUsw27I/AAAAAAAAACY/KuvmQdODsKs/s1600/0+photogamut+vs+sRGB_jc1.png)

Basic Property         PhotoGamut     sRGB_jc1
White                     D50                   D50
Color space             RGB                   RGB
Implementation        Cluts                  Cluts
Profile size(bytes)    148,480              589,928
icc format version    2.0                     2.1
Gamut Volume*       902,827              770,429
Profile Device type   OutputClass         OutputClass
Rendering Intent      All**                  All**
Last Update            2004, avg6c        2011, ver 1.0***
Availability              FOC                   Publicly available        

*     Under D50 condition
**   Colorimetric, Saturation and Perceptual
*** < Link (http://www.luminous-landscape.com/forum/index.php?topic=56978.msg470454#msg470454) >

Proposed Usage
PhotoGamut: was proposed as a RGB working space.
sRGB_jc1: as a conversion bridge between wide gamut RGB (ProPhoto or scanner space) and sRGB.
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on September 20, 2011, 08:59:37 pm
Converting aRGB (Adobe RGB) to sRGB

Converting aRGB to sRGB with Relative Colorimetric Intent (RelCol)
Refer to below illustration, data for destination1 was computed with straight Relcol to sRGB, whereas data for destination2 was computed with perceptual conversion to sRGB with icc profile sRGB_jc1.

          (http://2.bp.blogspot.com/-lWd4LT7pBCg/TnhnlIwqjsI/AAAAAAAAACo/wwqtsOr4L88/s1600/1+argb+t0+srgb+%2528revised%2529.png)

  (http://1.bp.blogspot.com/-meG_rHD3tTM/TniMsYjDnWI/AAAAAAAAACw/uu3Fu2ULzww/s1600/1+argb+to+srgb+LAB+space.png)

Above result shows that for color space conversion from aRGB to sRGB with Relcol, the RED channel (G=B=0) begins to clip at R=219 (source space) onwards. These clipped colors are  indistinguishable in sRGB color space.

jc

Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on September 30, 2011, 10:06:42 pm
jc1RGB Release v1.0
It can be downloaded from this link < click (http://jcrgb.blogspot.com/) >


My next project: Perfect Color Space

What is Perfect Color Space (http://perfectcolorspace.blogspot.com/2011/09/what-is-pefect-color-space.html)
                                        (http://2.bp.blogspot.com/-1r_5KwdSXls/ToZviJ_xxUI/AAAAAAAAAF4/5Q_wJG-4NYw/s1600/0+0+0+PCS+certified.png)

Thanks

jc
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: Tim Lookingbill on October 01, 2011, 12:20:52 pm
Could you show us what the advantage of using jc1RGB as a working/editing space over the established ones already in use today?

To be more specific how will it improve editing images in that space? Will it make it easier? Faster? With less posterization? Less noise? Less artifacts?

Why should we use it?
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on October 01, 2011, 08:02:52 pm
Hi,

Could you show us what the advantage of using jc1RGB as a working/editing space over the established ones already in use today?
My original idea was to use jc1RGB as an intermediate space for converting image with ProPhoto to sRGB, perceptually.

Refer to my previous thread for jcSPACE color space which resemblances jc1RGB. jcSPACE is created with the profile quality on par with ProPhoto,  Adobe RGB and sRGB, just to name a few. It will be made publicly available as well.

Unlike ProPhoto, all colors in jcSPACE are visible.  IMHO, it is the largest possible absolute color space with visible color and that possesses the scalable color characteristic when converting  with colorimetric intent between the same family ( ProPhoto, jcSPACE, Adobe RGB and sRGB and a few others). The main advantage with visible color space is that it connects to the output device more readily with the current CMM environment. The trade off is, similar to ProPhoto, 16-bit workflow is needed.


Quote
To be more specific how will it improve editing images in that space? Will it make it easier? Faster? With less posterization? Less noise? Less artifacts?
No. jcSPACE is similar to other icc profile and it has color gamut in between ProPhoto RGB and Adobe RGB. In order to take full advantage of the output device color reproduction capability, the working space should ideally encompass the printer color space.


Quote
Why should we use it?
That should be decided by the color reproduction requirement.
 

Regards,
jc




Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: Tim Lookingbill on October 02, 2011, 05:03:08 am
Quote
The main advantage with visible color space is that it connects to the output device more readily with the current CMM environment.

Can you show visual samples of this happening between the display (soft proofing on or off) and the final print? Is your term "connect to the output device more readily" something physically happening or theoretically happening?

What does this intermediary color space of yours fix or prevent that shows up in a print other than printing from ProPhotoRGB?

How does printing out of jc1RGB improve the appearance of the print over just printing out of ProPhotoRGB?
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: jc1 on October 02, 2011, 07:59:41 pm
My analysis was done mostly with test patches, for instance,  ProPhoto GrangerRainbow to sRGB wiith Perceptual intent (http://www.luminous-landscape.com/forum/index.php?PHPSESSID=24205b19480ced199ad3e9e3a10ee9ce&topic=56978.msg460822#msg460822) and Blue Ball test (http://www.luminous-landscape.com/forum/index.php?PHPSESSID=24205b19480ced199ad3e9e3a10ee9ce&topic=56978.msg464983#msg464983).
 
Perceptual rendering intent is based on Lab and Cluts,  imaginary colors  in source space may not be rendered correctly as illustrated by the above examples. But that may change, as I see improvement in handling such issue for newer released profiler.
 
Download the profile and test chart to experience it yourself. I have read about perceptual intent may not always be the best option for better color reproduction compared with RelCol, but I am unsure if that was due to colors outside the visible spectral locus. Do you print directly for image with ProPhoto?
 
The download links for Digital graner rainbow and jc1RGB profile are reloaded below.
 
Digital graner rainbow (https://www.yousendit.com/download/ZUd2aXRFdVVQb0kwTVE9PQ)
jc1RGB (https://www.yousendit.com/download/T2djUGhaY3lGOFExZXNUQw)
 
jc
 
 
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: Tim Lookingbill on October 03, 2011, 03:13:05 pm
I see what you're doing.

Try these test swatches and gradients I came up with that noticeably shift when converting directly from ProPhotoRGB to sRGB.

Create a new document in ProPhotoRGB in Photoshop and make these RGB color swatches:

Yellow: R240,G230,B30
Cyan:   R10,G100,B245
Navy Blue: R35,G10,B120
Cobalt Blue: R30,G20,B235...

From these create a white to color gradient for each and afterward convert normally to sRGB the entire document and see if you get a shift. If you do see a shift, try it using your JcSPACE or jc1RGB method described in this thread in order to reduce shifting of these colors.
Title: Re: Perceptual Rendering Intent -- ProPhoto to sRGB
Post by: Steve Rolls on December 04, 2014, 12:54:02 pm
Sorry for necro.

http://rghost.net/59423022 - this is the file which I am converting.
http://rghost.net/59423929 - this is the result of two step conversion.

http://www.color.org/profiles/srgb_appearance.xalter - beta v4 sRGB profile.

http://rghost.net/59424083 - perceptual conversion to "appearance" profile.
http://rghost.net/59424089 - relative conversion to "apperance" profile.

As you may see none of conversions results in smooth image, every one of those three has artifacts.

Is there really no way to convert saturated rainbow to sRGB without artifacts?