Luminous Landscape Forum

Raw & Post Processing, Printing => Colour Management => Topic started by: RogerEle on July 21, 2013, 10:28:56 pm

Title: Camera Calibration for Copy Work
Post by: RogerEle on July 21, 2013, 10:28:56 pm
Hello everyone, I am hoping for some advice as to what steps I might take to improve my current camera profile, or any other workflow suggestions ... I just don't want to waste money or time on anything that won't make much difference - and looking at all of the different products our there for camera color management that all promise improvement and so on ... ;) ... just  hoping for some guidance to help sort this out.

I have a portrait studio, we do lots of copy work of old photos.  Most of the photos we get are faded / old / dirty, so we are fooling with the colors and tones no matter what.  20% of what we get we are hoping to match the original.  We can currently do that pretty close with a few tweaks - current profile skin tone is a little more red and a little less yellow and the blues / greens are not as strong as they should be, I can live with this and adjust the images but since these are important colors in a lot of images, I am hoping for improvement.  

We copy everything using a Nikon D3 with a nikon 60mm macro, 80A filter, polarizing filter on camera and polarizing sheets in front of tungsten lights (halogen i think). We have the X-Rite ColorChecker and the Datacolor Studio Kit that includes the SpyderCheckr and the print calibration spectro meter.  A number of years age I created profiles using the adobe dng profile editor with the color checker target and also profiles with SpyderCheckr target and software.  I ended up liking the Spyder better for color, just had to dial the saturation way down after I opened it up in Photoshop.  A week ago I started testing again to see if I could improve things and made some interesting discoveries ... I read in another thread here that the Datacolor system is 'bogus' - I am not trying to defend Datacolor here, just giving a history of what I have and what I have done so far :)

For the camera white balance I set the kelvin in the camera, fine tuned and re-shot until I got it as close as possible to neutral.  These are the steps I have done (omitting random testing to figure out what I am doing) :) ...

1) Made a profile with the ColorChecker and the X-rite passport software per instructions.  
2) Made 3 profiles with the SpyderCheckr per instructions using 3 different camera profiles, first using Adobe Standard, then neutral and finally mode 1 (since we use that in our studio for our portraits).  Datacolor documentation says it doesn't matter which camera profile you use, just use the same one you created the profile with - not what I found, there is some variation between each profile created.
3) I then read the ColorChecker patches with my spectro and recorded each of the lab values (they were pretty close to the published values on the X-rite site).  Used Photoshop in Adobe (1998) space to determine RGB values for each of those readings.
4) Opened ColorChecker image in each profile in ACR in the Adobe (1998) space (which adjustes the HSL slides in ACR, set the camera profile to the same one used to create the 'profile', used Tone Curve / Point Curve to create a curve to match the actual readings from the spectra readings for the grey values across the bottom of the chart (#19 to #24) - saved each as a preset.  The greater the contrast of the camera profile the bigger the curve ended up being to reverse it.

All 4 presets are slightly different visually when clicking back and forth in a few of the color patches - no difference perceived in the grey patches.  When physically looking at the ColorChecker none of the profiles match #2 and the blue green in the upper right corner - the #2 skin tone patch looks more red and the blue green patch looks different (writing this from home - don't remember what direction it is off).  All of the new profiles do give me more separation in the shadows so that is a good thing! :)

My budget is up to around $400 for improvements if appropriate, I am looking for suggestions on whether I should purchase a different target and/or on using/purchasing different profiling software.

Thanks in advance!
~Roger
Title: Re: Camera Calibration for Copy Work
Post by: Vladimirovich on July 22, 2013, 11:12:17 am
topic popcorned...

rawdigger (-> CGATS), (CGATS -> argyll), rpp
Title: Re: Camera Calibration for Copy Work
Post by: Tim Lookingbill on July 22, 2013, 11:51:36 am
Quote
All 4 presets are slightly different visually when clicking back and forth in a few of the color patches - no difference perceived in the grey patches.  When physically looking at the ColorChecker none of the profiles match #2 and the blue green in the upper right corner - the #2 skin tone patch looks more red and the blue green patch looks different (writing this from home - don't remember what direction it is off).  All of the new profiles do give me more separation in the shadows so that is a good thing!

My budget is up to around $400 for improvements if appropriate, I am looking for suggestions on whether I should purchase a different target and/or on using/purchasing different profiling software.

You mention two color patches that are off and you now want to solve this by throwing more money at it because you think correcting these two patches is going to reduce the added time of color correcting? Save your money.

Outside of what the CCchart looks like how off are your actual Raw captures using the profiles as is from what you see under those halogens which have a dominant reddish spectra compared to daylight flash. Because of this it is to be expected you would see red in #2 patch and blue green patch off due to the halogens diminished blue spectra.

How about switching to flash or use a Solux 4700K setup? Did you set your illuminant for 2800K in the PE CCchart Wizard? Or did you create a dual illuminant camera profile?

I can tell you this from experience shooting a lot of stuff in my studio in and around next to my display with my 6 year old Pentax K100D DSLR with available light from window light to GE Soft White 2800K and daylight balanced flash and flotubes, I rarely have a problem getting an exact match to what I see to what's on my display. It does take some post processing, but then I'm not setting up my camera as a copy stand. If I did, then I'ld have FAR LESS post processing to do between shots. Fix one frame, save settings and apply to the rest.

The most trouble I have is shooting materials whose color gamut is beyond my camera's AND display's ability to reproduce namely deep, rich and vibrant cyans (turn to a dark baby blue). Skin tone can come out slightly green or red but can easily be tweaked with HSL. Sometimes I just use ACR's default "ACR 4.4" profile and get more accurate results.

You're shooting photos that may have chemical residue that can reflect back spectra you're eyes don't see but the camera records. A profile is not going to fix this. Profiles expect uniform spectra from both subject and light. The CCchart's patches are created with uniform spectra.

A DSLR is not a precision scientific instrument so you can't expect perfection and consistency shooting all types of reflected materials.

Title: Re: Camera Calibration for Copy Work
Post by: Vladimirovich on July 22, 2013, 11:56:49 am

How about switching to flash or use a Solux 4700K setup?


he can just gel halogen lights
Title: Re: Camera Calibration for Copy Work
Post by: Vladimirovich on July 22, 2013, 12:14:50 pm
We copy everything using a Nikon D3 with a nikon 60mm macro, 80A filter, polarizing filter on camera and polarizing sheets in front of tungsten lights (halogen i think).

about the filter 80A on lens to correct halogen - here is your brother in arms = www.luminous-landscape.com/forum/index.php?topic=80130

PS: just skip the feud between Iliah and his best friends  ;D
Title: Re: Camera Calibration for Copy Work
Post by: 32BT on July 22, 2013, 12:15:40 pm
The contrast curve in LR seems to produce oversaturation of reds, yellow, and cyan for D800 files. Could this be a factor in your observations for the D3 as well? Does reducing the contrast in the RAW converter change the colors significantly (while not necessarily producing a pleasing result)?
Title: Re: Camera Calibration for Copy Work
Post by: RogerEle on July 22, 2013, 01:03:34 pm
topic popcorned...

rawdigger (-> CGATS), (CGATS -> argyll), rpp

Thanks Vladimirovich,
I see on the rawdigger web site a mention of CGATS, if rpp is output parameters for Argyll, it seems I will be able to work it :)  ... if not rpp?
~Roger
Title: Re: Camera Calibration for Copy Work
Post by: RogerEle on July 22, 2013, 01:21:16 pm
How about switching to flash or use a Solux 4700K setup? Did you set your illuminant for 2800K in the PE CCchart Wizard? Or did you create a dual illuminant camera profile?

Haven't researched Solux, but am open to it ... I am not copying paintings or watercolors, but if it is a better light source for photos I am all ears :)
Didn't use the Adobe Profile Editor on this round of testing, used the Xrite Passport profile builder, no illuminant setting that I could see, and no with the one color of light source I wouldn't know how to make a dual illuminate camera profile (not trying to solve calibrating to a range of color temp light sources)

Quote
You're shooting photos that may have chemical residue that can reflect back spectra you're eyes don't see but the camera records. A profile is not going to fix this. Profiles expect uniform spectra from both subject and light. The CCchart's patches are created with uniform spectra.

Don't expect that to be fixed, but when I see it on both the CC Chart and on original it becomes a light source / camera sensor / profile issue though, not one of chemical residue.

Thanks Tim,
~Roger
Title: Re: Camera Calibration for Copy Work
Post by: Tim Lookingbill on July 22, 2013, 01:22:55 pm
You want a visual match using lights (halogens) that don't deliver a match to D50 and that your eyes see totally different to D50 reference numbers? And you want all that to be precise? Precise to what? D50 numbers or what you see with your eyes? So how do you know you have a match?

I just rattled off a shot of one of my self promo 4x6 one hour minilab color print on glossy Kodak Royal Digital silver halide paper. It's a perfect match shot under daylight flotubes which have a spikey green spectra which WB correction indicates with a huge shift to ACR magenta tint slider).

I used incamera AWB and adjusted in ACR 4.6 using default ACR4.4 profile. I get pinky skin also clicking for R=G=B but the differences between the warmer eyeball WB adjust and the precision version only affects the amount yellow in my own skin but not much in the skin tone restoration shot.

And your expecting precision color using halogen lights?
Title: Re: Camera Calibration for Copy Work
Post by: RogerEle on July 22, 2013, 01:28:15 pm
about the filter 80A on lens to correct halogen - here is your brother in arms = www.luminous-landscape.com/forum/index.php?topic=80130

PS: just skip the feud between Iliah and his best friends  ;D

Thanks Vladimirovich,

Took a quick look, with my untrained eyes it was hard to tell where said feud starts and stops, but I will give it a read.  My in camera white balance is 4260K with the 80A filter ... I read through the first page of 9 pages, will get to the rest tonight ...
Title: Re: Camera Calibration for Copy Work
Post by: Tim Lookingbill on July 22, 2013, 01:39:40 pm
You're making this harder than it has to be.
Title: Re: Camera Calibration for Copy Work
Post by: Vladimirovich on July 22, 2013, 01:43:53 pm
Thanks Vladimirovich,
I see on the rawdigger web site a mention of CGATS, if rpp is output parameters for Argyll, it seems I will be able to work it :)  ... if not rpp?
~Roger

rawdigger output CGATS /read instructions how to/, then either argyll (command line) or Iliah made a GUI frontend for that purpose = http://sail2ithaki.livejournal.com/188062.html, then feed custom icc profile to RPP... you can always ask technical questions to authors (if that is a good /= technically challenging/ question then you will get a good answer)

Title: Re: Camera Calibration for Copy Work
Post by: RogerEle on July 22, 2013, 01:47:30 pm
The contrast curve in LR seems to produce oversaturation of reds, yellow, and cyan for D800 files. Could this be a factor in your observations for the D3 as well? Does reducing the contrast in the RAW converter change the colors significantly (while not necessarily producing a pleasing result)?

I don't have the spectro readings with me, I will look tonight so that I can compare the effect on saturation of reducing the contrast using the tone curve ... my memory is that it reduces the saturation to close to matching the color checker spectro numbers.  There will be a slight varience because the tone curve is built by hand from only the 6 grey patches allowing for a little human error.

Not sure which way to take 'pleasing results', if I was photographing real world scenes the profile/settings for copy work would look flat and very unpleasing - shooting copy though of a perfect original I will be more 'pleased' the closer they match the original.  :)

Note that the polarizing filters used increase the contrast, so some of the reason for the lowering of the contrast is the polarizing.  (from memory) the darkest grey square number 24 comes up from around 30 to 54 rgb, patch 23 is close to the same, a dip in the lighter tone with little change in the lightest tone at patch number 19

Thanks!
Title: Re: Camera Calibration for Copy Work
Post by: RogerEle on July 22, 2013, 02:01:48 pm
rawdigger output CGATS /read instructions how to/, then either argyll (command line) or Iliah made a GUI frontend for that purpose = http://sail2ithaki.livejournal.com/188062.html, then feed custom icc profile to RPP... you can always ask technical questions to authors (if that is a good /= technically challenging/ question then you will get a good answer)



Thaks, it looks like rpp = RAW PHOTO PROCESSOR and is mac only ... I am on pc, is there a second choice? :)
Title: Re: Camera Calibration for Copy Work
Post by: Vladimirovich on July 22, 2013, 02:06:37 pm
Thaks, it looks like rpp = RAW PHOTO PROCESSOR and is mac only ... I am on pc, is there a second choice? :)
well...  I run RPP on PC/Win using VmWare... in your case then try to find the right method for repro work with ACR/LR (people do that - so there is a way) - we have a number of experienced people here (see nicknames in that feud between Iliah and others in the thread above) who master that art or rerpoduction work using just colorchecker + Adobe PE and proper target illumination.
Title: Re: Camera Calibration for Copy Work
Post by: RogerEle on July 22, 2013, 02:34:02 pm
You want a visual match using lights (halogens) that don't deliver a match to D50 and that your eyes see totally different to D50 reference numbers? And you want all that to be precise? Precise to what? D50 numbers or what you see with your eyes? So how do you know you have a match?

You must be implying that halogens with and 80A filter doesn't get me there? ... ;)
I first look with my eyes and then check the numbers to make sure it is not a viewing issue ... my poor brain needs to translate the rgb color to hsl to really make sense of it so that can be a slower process ;) ...

It may be that the polarizing filter adds some of the contrast that you are not seeing in your test.  So many of the originals I see are improved with polarizing that I sure do not want to lose the polarizing from my normal workflow ...

I appreciate your test but am confused ... are you saying in both methods you used you get a match to the original that is better that using tungsten with an 80a filter?  And they are better because your test image matches close except for your skin tone?  It is not conclusive without comparing the same test with tungsten lighting and an 80a filter ... I am not suggesting you need to do this testing for me, just that it doesn't really prove a point.

It does suggest that I would be smart to create a profile using flash with the polarizing filters (I have flash, would need to purchase the solux), if there is a difference in the profiles created then that will prove your proof of concept if I am understanding you correctly.

Thanks!
Roger
Title: Re: Camera Calibration for Copy Work
Post by: 32BT on July 22, 2013, 02:40:50 pm
Do you happen to have a test-shot available for us to try? Something including the CC from which you made the profiles?
Title: Re: Camera Calibration for Copy Work
Post by: RogerEle on July 22, 2013, 02:55:37 pm
Do you happen to have a test-shot available for us to try? Something including the CC from which you made the profiles?

Sure this is the .nef, I use Google drive personally so I made the file public with this link ...

https://docs.google.com/file/d/0B-YoFPgh003pUzZwV1RIRWlPNVk/edit?usp=sharing

If there is any consensus that I should first shoot the CC with flash with polarizing rather than the tungsten I am happy to before anyone goes to any work on my behalf.  I do really appreciate the effort!

~Roger
Title: Re: Camera Calibration for Copy Work
Post by: 32BT on July 22, 2013, 04:15:51 pm
Okay, this is what I get from a calibrator using default plain-vanilla ICC conversion in linear space.

The Gray1 image shows the result of the gray patches. It does show a contrast increase. Normally I would associate this with an unevenly lit chart. If you know this is a result of the polarizer, then that must be accepted as is, otherwise I would double check whether the chart is evenly lit.

I wonder though what is the advantage of using the polarizer? I get a distinct impression that the benefits may not outweigh the lower consistency of calibration.

Title: Re: Camera Calibration for Copy Work
Post by: RogerEle on July 22, 2013, 04:49:33 pm
Okay, this is what I get from a calibrator using default plain-vanilla ICC conversion in linear space.

The Gray1 image shows the result of the gray patches. It does show a contrast increase. Normally I would associate this with an unevenly lit chart. If you know this is a result of the polarizer, then that must be accepted as is, otherwise I would double check whether the chart is evenly lit.

I wonder though what is the advantage of using the polarizer? I get a distinct impression that the benefits may not outweigh the lower consistency of calibration.



Very interesting, I have never used calibrator software so this is all new to me ... :)  Thank you!

Regarding the polarized lights and filter - I started running a b&w custom lab in the early 70's, 14 years of that and then copy and restoration work from when we opened our studio in '86 ... so many tests and so many times polarizing has saved my butt!  Polarizing fixes photos with a texture to the surface of the paper (the top of each bump in the texture reflects the light source and that becomes part of the image without polarizing) or silvering (dark areas of the print take on a metallic silver glow).  Even photos with wrinkles and tears handle better with polarization. Sometimes this is subtle, sometimes a huge difference but it is always appreciated!  So no, just got to figure the best with polarizing.

I did photograph the target with the polarizing filter on the camera turned to let in all light (effectively off).  I have the .nef file if it is some use, I tested it so I could see if there was a difference ... my memory is that the colors were very similar once the point curve reversed the increase in contrast.  As I always use polarization I thought it would make more sense to concentrate on getting that right :)

Thanks again,
Roger 
Title: Re: Camera Calibration for Copy Work
Post by: louoates on July 22, 2013, 06:19:26 pm
I appreciate you trying to get 100 perfect color every time and applaud your perseverance. Your particular market may demand exceedingly accurate reproductions. Thank goodness my copy work flow for artists were never that stringent. I promised 95% color accuracy for most colors and only best-possible approximations for florescent and rare-earth type paints. Maybe it was because I wasn't charging as much as others in the area. In the four years I was printing for 45-some artists (mostly for art show sales) I never had to re-shoot a painting because of artist dissatisfaction. In my case the strategy of under-promise and over-deliver worked well.
   I was also surprised at how many artists had trouble evaluating color values in their own work.
Title: Re: Camera Calibration for Copy Work
Post by: Tim Lookingbill on July 22, 2013, 06:27:11 pm
Quote
I am not suggesting you need to do this testing for me, just that it doesn't really prove a point.

It proves that I get a better and quicker match with my setup with very little effort over yours which you seem to be having trouble with by the fact you're having to split hairs over two CCchart color patches that are off by the numbers instead of just getting the work done.

The real problem that you don't address is how you expect to get a visual match under the warm glow of halogen lighting while expecting the Lab numbers to be perfect which are derived and measured from a D50 light source.

Of course it would make sense you shouldn't get an exact CCchart match by the numbers which I have to admit I certainly don't get using the ACR 4.4 profile (in fact the numbers are far more off than yours using that profile), however, I do get a visual match with that particular photo which is the purpose of this whole process. For all intents and purposes I shouldn't get a visual match but I do.

What's going to happen when you go through all this trouble to get all the numbers perfect, but the appearance of the final copy doesn't match what you see due to the fact your eyes have adapted to that warm halogen glow which isn't a D50 light source? And filters add another level of complexity because you, the camera and PP software don't know the exact spectra formulation and its effect on your "variety" of halogen which there can be quite a few hues to contend with.

Not all what's called D50 looks the same between manufacturers of various color matching processes.
Title: Re: Camera Calibration for Copy Work
Post by: Iliah on July 22, 2013, 07:02:07 pm
> is there a second choice?
PhaseOne CaptureOne (60-day trial), RawTherapy (free), and pretty much any other raw converter from a third party. You can with some effort make Nikon View (free) or Nikon Capture (30-day trial) work with a custom profile as well. ColorChecker SG is a better target for profiling compared to DataColor's - more consistent and wider gamut. If you rotate the pola filter the profile can be off.
Title: Re: Camera Calibration for Copy Work
Post by: Iliah on July 22, 2013, 07:04:41 pm
Some brief how-to http://sail2ithaki.livejournal.com/187421.html
Title: Re: Camera Calibration for Copy Work
Post by: Iliah on July 22, 2013, 07:07:49 pm
> https://docs.google.com/file/d/0B-YoFPgh003pUzZwV1RIRWlPNVk/edit?usp=sharing

The shot is close to 1 stop underexposed.
Title: Re: Camera Calibration for Copy Work
Post by: RogerEle on July 22, 2013, 11:20:55 pm
> https://docs.google.com/file/d/0B-YoFPgh003pUzZwV1RIRWlPNVk/edit?usp=sharing

The shot is close to 1 stop underexposed.

Iliah, thanks for the input and the links

Regarding the linked image being underexposed - I just downloaded it (I am at home :) ), the lightest patch reads rgb 253, 253, 252 in Adobe(1998) - there is room for more exposure ....  :o ?  Darker tones are darker because of polarizing - would you expose for the midtone and the bring the light tones down with adjustments?

Thanks,
Roger
Title: Re: Camera Calibration for Copy Work
Post by: RogerEle on July 22, 2013, 11:28:54 pm
I appreciate you trying to get 100 perfect color every time and applaud your perseverance. Your particular market may demand exceedingly accurate reproductions. Thank goodness my copy work flow for artists were never that stringent. I promised 95% color accuracy for most colors and only best-possible approximations for florescent and rare-earth type paints. Maybe it was because I wasn't charging as much as others in the area. In the four years I was printing for 45-some artists (mostly for art show sales) I never had to re-shoot a painting because of artist dissatisfaction. In my case the strategy of under-promise and over-deliver worked well.
   I was also surprised at how many artists had trouble evaluating color values in their own work.

Hi louoates,

I too under promise and over deliver, as a conscious way of doing business!  We get happier clients and more referrals! :) I have a personality that always has to be tweaking something ... this is the focus of the moment ... hoping to bump what I do a little closer to perfection :)

Thanks
Title: Re: Camera Calibration for Copy Work
Post by: RogerEle on July 22, 2013, 11:49:18 pm
It proves that I get a better and quicker match with my setup with very little effort over yours which you seem to be having trouble with by the fact you're having to split hairs over two CCchart color patches that are off by the numbers instead of just getting the work done.

You are right, but from time to time I just need to prove to myself that I have it nailed as well as I can.  I live by the motto's ...
- It is what it is
- I do the best I can
- I don't know what I don't know

Quote
The real problem that you don't address is how you expect to get a visual match under the warm glow of halogen lighting while expecting the Lab numbers to be perfect which are derived and measured from a D50 light source.

Because I didn't know that was a problem (third motto), but now that I do I will test it with flash :)

Quote
Of course it would make sense you shouldn't get an exact CCchart match by the numbers which I have to admit I certainly don't get using the ACR 4.4 profile (in fact the numbers are far more off than yours using that profile), however, I do get a visual match with that particular photo which is the purpose of this whole process. For all intents and purposes I shouldn't get a visual match but I do.

I get a visual match on many of the images that I am copying - just seeing if I can up my percentages - every time that I have poked at this stuff in the past I have learned something that reinforces the third motto

Quote
What's going to happen when you go through all this trouble to get all the numbers perfect, but the appearance of the final copy doesn't match what you see due to the fact your eyes have adapted to that warm halogen glow which isn't a D50 light source? And filters add another level of complexity because you, the camera and PP software don't know the exact spectra formulation and its effect on your "variety" of halogen which there can be quite a few hues to contend with.

Not all what's called D50 looks the same between manufacturers of various color matching processes.

I don't understand the 'eyes have adapted to that warm halogen glow' part - I am not looking at the copy stand and lights while working on the computer - but regardless, if it is all messed up - that teaches something too - I will test the calibration with the flash instead of the halogen / 80a mix so that I 'for sure' know the difference!

Thanks!
Roger
Title: Re: Camera Calibration for Copy Work
Post by: Vladimirovich on July 23, 2013, 12:11:25 am
Regarding the linked image being underexposed - I just downloaded it (I am at home :) ), the lightest patch reads rgb 253, 253, 252 in Adobe(1998) - there is room for more exposure ....  :o ?
I think Iliah is talking about the raw data (check the patch with rawdigger) for the purpose of icc profile creation... you posted a target shot.

PS: for example Eric Chan for Adobe PE (and .dcp camera profiles) suggested to bracket exposure and use the most exposed raw (converted to DNG) that Adobe PE still accepts.
Title: Re: Camera Calibration for Copy Work
Post by: MarkM on July 23, 2013, 04:32:54 am
Roger,

I think you should hang on to that $400 until you've spent more time with what you have. If you are willing to get in and tweak the profiles, you can get a colorchecker arbitrarily close to published values with nothing more than free software. Whether this will actually be useful in practice with real-world images and workflow is debatable. But if you're like me you'll find it an interesting and educational process.

I spend a few minutes with you RAW file in the Adobe DNG profile Editor and was able to get all the patches within less than Delta-E 2 of published RGB numbers for the color checker. The profile alone can do this without touching a single slider in ACR (other than making sure your white balance is right, which, based on the 4th grey patch of your raw, I set to Temp: 4250, Tint: +26).

The most important part of the profile if you are going for numerical accuracy in my experience is getting the tone curve right. The default is almost always too contrasty and a linear leaves the shadows too dark. Once you get the tone curve right, many of the other colors fall in line. Depending on the character of your camera and light, you may need to push a few of the patches around a bit.

Personally, I don't think there's anything wrong with using hot lights and a cooling filter. The spectrum from that combination is going to be pretty decent especially when you have tools like ACR and DNG profiles at you disposal.

I've attached the processed raw, a diagonal cut comparison with published numbers—not perfect, but pretty good for a minimal effort, and the DNG profile I made/used.

Good luck.
Title: Re: Camera Calibration for Copy Work
Post by: 32BT on July 23, 2013, 07:01:01 am
To me colormanagement and profiling is about consistency of results. Exact reproduction of a colorchecker is a side effect of that, it is not a goal in itself.

What currently happens is that a non-linear response is introduced at the start of a colormanagement chain which is entirely based on a linear response assumption. Using the DNG profiler to adjust the profile with all kinds of contorted hue shifts then is equivalent to "introducing errors" for the sake of reproducing a colorchecker correctly. It doesn't guarantee consistency of color at all, and, in fact, may simply enlarge the actual error of colorreproduction.

What needs to be done in my opinion is create the profile with the polarizer in "off mode" and specifically NOT try to adjust for individual colorchecker colors. i.e. get as close to a clean matrix profile as possible. With this profile, try to take a polarized shot and only adjust the contrast curve in LR and see if that gets the colors in place.

The unfortunate issue is that the colormanagement chain in LR is simply not transparent enough to know how to implement the "technically" correct steps, so that you can actually conclude that it does or does not work for your purposes. The technically correct steps for your workflow imo like are:

1. take a polarized shot of artwork
(introduces non-linearities in the form of contrast increase)

2. compensate for the contrast increase

3. apply a clean linear matrix profile
(based on a non-polarized shot of the colorchecker).

Title: Re: Camera Calibration for Copy Work
Post by: Vladimirovich on July 23, 2013, 09:20:16 am
What needs to be done in my opinion is create the profile with the polarizer in "off mode" and specifically NOT try to adjust for individual colorchecker colors. i.e. get as close to a clean matrix profile as possible.

you can strip LUTs from .dcp using SandyMc' dcptool... however if you are using Adobe PE - you are always using some base profile (so unless you create some genuinely new one /matrix wise/ with for example OEM Xrite software or if QPCard will release a plugin for XRite passport or by changing matrices manually) you are using Adobe's supplied matrices and then if you do not need LUT you do not need to shoot colochecker at all at that stage - just strip the details from Adobe's profile (Standard or one of OEM emulations) and get a clean base profile that is matrix only (with proper curve and BaselineExposureOffset as well)
Title: Re: Camera Calibration for Copy Work
Post by: Iliah on July 23, 2013, 09:21:35 am
> Regarding the linked image being underexposed

It is a shot in 12 bit mode with 2660 max in it in green channel; while technically it should be around 4000 (2^12-1). You can open the shot with RawDigger and see for yourself. You can shoot a scene with a specular highlight in it (like from some metal ball) to determine the maximum for your camera.

Second, you filled the frame with the target, so you are making lighting task more difficult, and also get into any lens and sensor irregularities. Better to have the target in 1/3 of the frame.

Target is shot in sharp focus, it does not help too.

Target is not clean, readings will be off.

To equalize the light put some uniform white or grey sheet in the first shot, then use flat field feature of RawDigger to export CGATS corrected against light non-uniformity.

I would be glad to help you further if needed.
Title: Re: Camera Calibration for Copy Work
Post by: RogerEle on July 23, 2013, 01:22:24 pm
I spend a few minutes with you RAW file in the Adobe DNG profile Editor and was able to get all the patches within less than Delta-E 2 of published RGB numbers for the color checker. The profile alone can do this without touching a single slider in ACR (other than making sure your white balance is right, which, based on the 4th grey patch of your raw, I set to Temp: 4250, Tint: +26).

Thanks!

Quote
The most important part of the profile if you are going for numerical accuracy in my experience is getting the tone curve right. The default is almost always too contrasty and a linear leaves the shadows too dark. Once you get the tone curve right, many of the other colors fall in line.

Not so much numerical accuracy, but no surprises when copying - the numbers seemed a good place to to start - I won't be sweating the tiny differences that don't show up in actual use.
Thanks you for describing this so clearly! - it lets me know I wasn't off in what I was finding

Quote
Personally, I don't think there's anything wrong with using hot lights and a cooling filter. The spectrum from that combination is going to be pretty decent especially when you have tools like ACR and DNG profiles at you disposal.

Good to hear :)

Thanks! Mark,
Title: Re: Camera Calibration for Copy Work
Post by: RogerEle on July 23, 2013, 01:28:04 pm
To me colormanagement and profiling is about consistency of results. Exact reproduction of a colorchecker is a side effect of that, it is not a goal in itself.

What currently happens is that a non-linear response is introduced at the start of a colormanagement chain which is entirely based on a linear response assumption. Using the DNG profiler to adjust the profile with all kinds of contorted hue shifts then is equivalent to "introducing errors" for the sake of reproducing a colorchecker correctly. It doesn't guarantee consistency of color at all, and, in fact, may simply enlarge the actual error of colorreproduction.

What needs to be done in my opinion is create the profile with the polarizer in "off mode" and specifically NOT try to adjust for individual colorchecker colors. i.e. get as close to a clean matrix profile as possible. With this profile, try to take a polarized shot and only adjust the contrast curve in LR and see if that gets the colors in place.

The unfortunate issue is that the colormanagement chain in LR is simply not transparent enough to know how to implement the "technically" correct steps, so that you can actually conclude that it does or does not work for your purposes. The technically correct steps for your workflow imo like are:

1. take a polarized shot of artwork
(introduces non-linearities in the form of contrast increase)

2. compensate for the contrast increase

3. apply a clean linear matrix profile
(based on a non-polarized shot of the colorchecker).



Thanks Oscar!

I did photograph the CC target with the polarizer turned to the off position - I stopped test with it in off when I discovered the colors were close and I realized that I would never be actually using it in the off position - I will definitely give what you suggest a try!

Roger
Title: Re: Camera Calibration for Copy Work
Post by: RogerEle on July 23, 2013, 01:31:24 pm
you can strip LUTs from .dcp using SandyMc' dcptool... however if you are using Adobe PE - you are always using some base profile (so unless you create some genuinely new one /matrix wise/ with for example OEM Xrite software or if QPCard will release a plugin for XRite passport or by changing matrices manually) you are using Adobe's supplied matrices and then if you do not need LUT you do not need to shoot colochecker at all at that stage - just strip the details from Adobe's profile (Standard or one of OEM emulations) and get a clean base profile that is matrix only (with proper curve and BaselineExposureOffset as well)

Wow, I will have to come back to this after fooling with the recommended raw software - gives me a peek though, thanks!
Title: Re: Camera Calibration for Copy Work
Post by: RogerEle on July 23, 2013, 01:51:46 pm
> Regarding the linked image being underexposed

It is a shot in 12 bit mode with 2660 max in it in green channel; while technically it should be around 4000 (2^12-1). You can open the shot with RawDigger and see for yourself. You can shoot a scene with a specular highlight in it (like from some metal ball) to determine the maximum for your camera.

Second, you filled the frame with the target, so you are making lighting task more difficult, and also get into any lens and sensor irregularities. Better to have the target in 1/3 of the frame.

Target is shot in sharp focus, it does not help too.

Target is not clean, readings will be off.

To equalize the light put some uniform white or grey sheet in the first shot, then use flat field feature of RawDigger to export CGATS corrected against light non-uniformity.

I would be glad to help you further if needed.

Thanks Iliah! - I will be on vacation for a week and will load the software's to my laptop while relaxing - will see if I can photo new targets before I leave ...
Title: Re: Camera Calibration for Copy Work
Post by: RogerEle on July 23, 2013, 02:03:53 pm
Notes ... :)

I did shoot new targets yesterday before the latest replies.  Not knowing any better I have been exposing to place the exposure in the middle of the histogram. 

Here is the flash .nef

https://docs.google.com/a/eleakis.com/file/d/0B-YoFPgh003pS1hHQkhTc1BpZkU/edit?usp=sharing

It is definitely different from either of the tungsten/80a images (with polarizer on and off), will have to see how the profiles pan out but adds initial credence to the idea that tungsten with 80a is not equivalent to a clean D50 light source - will have to see :)

Here is the .nef with polarizer turned off, way under exposed by my current understanding

https://docs.google.com/a/eleakis.com/file/d/0B-YoFPgh003pdHZFUEpIbTN5Yjg/edit?usp=sharing

Thanks!
Roger
Title: Re: Camera Calibration for Copy Work
Post by: MarkM on July 23, 2013, 02:11:42 pm
Roger, it looks like those files are not publicly accessible.
Title: Re: Camera Calibration for Copy Work
Post by: Iliah on July 23, 2013, 02:16:42 pm
The idea is to profile for light. My setup includes Rosco #1991 or #1995, CTB, pola filter, and a 50% magenta filter on the halogen lights. This way I have full spectrum and equal exposure for all raw channels.

I seriously suggest looking at ColorChecker SG target for profiling, setting the exposure from SpyderCUBE or similar self-made, and having a flat grey surface for both profiling and repro work.
Title: Re: Camera Calibration for Copy Work
Post by: RogerEle on July 23, 2013, 02:46:18 pm
Roger, it looks like those files are not publicly accessible.

Works now, Thanks!
Title: Re: Camera Calibration for Copy Work
Post by: Iliah on July 23, 2013, 03:11:52 pm
The shot at your http://www.luminous-landscape.com/forum/index.php?topic=80491.msg649791#msg649791 is more suitable for profiling as the neutrality curve on it is the least bumpy. However it is really necessary to keep target sterile clean.
Title: Re: Camera Calibration for Copy Work
Post by: Ellis Vener on August 01, 2013, 11:18:30 am
Are you using Lightroom or Adobe Camera Raw? try the attached ColorPassport generated  profile: even if you do not use DNG as your archiving format for raw files the profile should work in Lightroom 4 and 5 and ACR.
Title: Re: Camera Calibration for Copy Work
Post by: bjanes on August 01, 2013, 12:45:23 pm
The idea is to profile for light. My setup includes Rosco #1991 or #1995, CTB, pola filter, and a 50% magenta filter on the halogen lights. This way I have full spectrum and equal exposure for all raw channels.

I seriously suggest looking at ColorChecker SG target for profiling, setting the exposure from SpyderCUBE or similar self-made, and having a flat grey surface for both profiling and repro work.

Iliah has made some excellent suggestions. Placing the CTB (and magenta filter, if used) over the light source rather than the lens makes sense since one does not need optical grade filters, and composing and focusing would be easier since the light loss from the filters does not occur in the camera optical pathway. Using ICC profiles made with the ColorChecker SG would obviate the use of LR/ACR for rendering, but one could use Capture One or Rawtherapee.

Bill
Title: Re: Camera Calibration for Copy Work
Post by: Iliah on August 03, 2013, 11:13:42 am
Dear Bill,

SG contains a set of patches that are very close to CC24 ("24 patches from original ColorChecker", "the corresponding patches are laid out on the SG chart in the same configuration as in the standard ColorChecker"). If one wants to be very accurate he can replace the Passport spectral measurements contained in X-Rite profiler for ACR/LR with the respective values from SG.

Now, if "classic" part of SG is used in X-Rite profiler, and the error is computed using all other SG patches one can evaluate the accuracy of profile in a more reasonable way.
Title: Re: Camera Calibration for Copy Work
Post by: Bart_van_der_Wolf on August 03, 2013, 11:44:05 am
SG contains a set of patches that are very close to CC24 ("24 patches from original ColorChecker", "the corresponding patches are laid out on the SG chart in the same configuration as in the standard ColorChecker").

Hi Iliah,

Yes, but they are different enough to not mix the different chart patches in an evaluation.

Cheers,
Bart
Title: Re: Camera Calibration for Copy Work
Post by: Iliah on August 03, 2013, 12:39:14 pm
Hi Iliah,

Yes, but they are different enough to not mix the different chart patches in an evaluation.

Cheers,
Bart

Dear Bart,

Can you please explain?
Title: Re: Camera Calibration for Copy Work
Post by: Bart_van_der_Wolf on August 03, 2013, 02:16:48 pm
Dear Bart,

Can you please explain?

Hi Iliah,

See ColorChecker charts formats (http://www.babelcolor.com/main_level/ColorChecker.htm#ColorChecker_charts_formats) where it is explained.

ColorChecker Digital SG (NOT COMPATIBLE)
Quote
24 of the chart patches have colors similar to the original ColorChecker and are laid out in the same configuration.
Quote
However, because of its Semi-Gloss finish, the SG in the chart name, the chart colors are not the same as in the other ColorCheckers (see more info below (http://www.babelcolor.com/main_level/ColorChecker.htm#The_problem_with)); thus, you should NOT USE the data in this page for the ColorChecker patches of this chart

Hope that helps to explain.

Cheers,
Bart
Title: Re: Camera Calibration for Copy Work
Post by: Iliah on August 03, 2013, 02:45:23 pm
Dear Bart,

But I specifically mentioned "If one wants to be very accurate he can replace the Passport spectral measurements contained in X-Rite profiler for ACR/LR with the respective values from SG."
Title: Re: Camera Calibration for Copy Work
Post by: Bart_van_der_Wolf on August 03, 2013, 03:42:23 pm
Dear Bart,

But I specifically mentioned "If one wants to be very accurate he can replace the Passport spectral measurements contained in X-Rite profiler for ACR/LR with the respective values from SG."

Hi Iliah,

Then I misunderstood. Good to have it clarified, they have to be replaced. The CC24/Passport and CCSG patches have different specific values, not simply to be used at will.

Cheers,
Bart