Luminous Landscape Forum
Raw & Post Processing, Printing => Digital Image Processing => Topic started by: Guillermo Luijk on March 03, 2009, 02:18:10 pm
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I wanted to see the sequence of histogram changes when subsequently converting from Adobe RGB to Lab and back to Adobe RGB in Photoshop (CS2, Adobe ACE engine).
It seems the more times we convert and come back to the original profile levels aggregate in peaks which rise in relative amplitude after every conversion process. Looking at that aggregation of levels it seems this could end in posterization in the long term.
(http://img11.imageshack.us/img11/8124/chicak.jpg) (http://img11.imageshack.us/my.php?image=chicak.jpg)
This is the entire original histogram, representing the animation sequence only the highlighted portion:
(http://img11.imageshack.us/img11/439/entire.gif) (http://img11.imageshack.us/my.php?image=entire.gif)
This is how the histogram changed after each conversion:
(http://img11.imageshack.us/img11/680/lab.gif) (http://img11.imageshack.us/my.php?image=lab.gif)
BTW I remember to have read something about errors in the implementation of the conversion in PS's internal routines, so the strong differences could not be only due to the 16-bit rounding errors? Maybe the experts could explain more about this issue.
The image was of course 16-bit and after the 14 conversions showed slight but clear differences with the original, specially in the shadows where posterization occurred (100% crops):
(http://img11.imageshack.us/img11/1457/postere.jpg) (http://img11.imageshack.us/my.php?image=postere.jpg)
BR
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For fun, try ProPhoto RGB. I suspect its even "worse".
Of course, there's at least one industry "pundit" who tells everyone to ignore Histograms and convert to and from Lab as often as you wish, there's no visible damage (in 8-bit no less).
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Andrew what's your recommended way to adjust luminance levels (i.e. adjust contrast) using a curve?
- RGB colour profile in Normal blending mode (this slightly alters H and strongly alters S, in the HSB model)
- RGB colour profile in Luminance blending mode (this preserves H and alters S but less than Normal blending mode, in the HSB model)
- Use Lab but reducing profile conversions to a minimum (this totally preserves colour information (a and b channels), roughly preserves both H and S in the HSB model)
- Other
In ProPhoto RGB is the same story. I only did 2 conversions:
(http://img401.imageshack.us/img401/3374/pro.gif) (http://img401.imageshack.us/my.php?image=pro.gif)
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Andrew what's your recommended way to adjust luminance levels (i.e. adjust contrast) using a curve?
Using whatever produces the appearance I desire <g>. Curves in Photoshop or Lightroom/ACR?
In Photoshop, normal can work fine assuming you like the hue and sat shift that was designed to work this way. Luminance blending (I wish they would stop using that term luminance) for just altering Lightness sometimes produces a flat unattractive image and sometimes its just what the doctor ordered.
Got to say, this has been debated for a long time, yet I don't find I have issues in either product producing a desired color appearance. There's so much other stuff that I wished sucked less (HDR, the lack of a true Saturation Curve ala LinoColor, printing out of PS).
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If you need to convert to L*a*b more than once to improve your image, then you're probably not doing an effective job while you're there. The whole point of converting to L*a*b is that you are improving the look of the image. The histogram is not really important and a single round trip will simply not harm your image.
There are excellent reasons for using L*a*b for certain image improvements. There are moves to the "a" and "b" channels especially that can't be duplicated elswhere - if you know how to exploit them.
When you did your 14 round trips, did you have dithering turned on in your Color Settings? If so, try the test again.
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I typically make a conversion to LAB and back to aRGB once. What is the practical application of converting to LAB 14 times?
I'd really like to see what the full image (instead of just the 100% crop) you posted looked like after 14 conversions.
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No-one needs more than one RGB-Lab-RGB round-trip; if you do then re-consider your workflow. And when converting from Lab back to RGB then make sure your working colour space matches that of the original RGB image because in Lab mode, the information about the original RGB colour space gets lost, so when switching back to RGB mode the working colour space will get applied.
Any change in the representation of a digital image that requires some kind of calculation inevitably will incur some losses, that's only natural. After all, any math done with a limited number of bits cannot be perfectly accurate. Even when 16-bit arithmetics are way more accurate than 8-bit arithmetics, there still is no infinite accuracy. So don't switch modes more often than required.
-- Olaf
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If you need to convert to L*a*b more than once to improve your image, then you're probably not doing an effective job while you're there.
I'd say you didn't do an effective job of rendering the Raw (or making the scan). But yes, if you have to, have to go to Lab, do it once and do it in high bit.
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If you need to convert to L*a*b more than once to improve your image, then you're probably not doing an effective job while you're there. The whole point of converting to L*a*b is that you are improving the look of the image. The histogram is not really important and a single round trip will simply not harm your image.
There are excellent reasons for using L*a*b for certain image improvements. There are moves to the "a" and "b" channels especially that can't be duplicated elswhere - if you know how to exploit them.
When you did your 14 round trips, did you have dithering turned on in your Color Settings? If so, try the test again.
I know, I just wanted to make sure that there are real reasons to keep Lab conversions to a minimum.
pfigen, could you explain some of those useful a-b strategies? I would like to investigate.
The dithering option was set off, however doesn's it only apply to 8-bit images? that's what my PS says.
BR
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For fun, try ProPhoto RGB. I suspect its even "worse".
Of course, there's at least one industry "pundit" who tells everyone to ignore Histograms and convert to and from Lab as often as you wish, there's no visible damage (in 8-bit no less).
I did my own test using a full scale image rendered into 16 bit ProPhotoRGB with ACR 5.3.
Here is the image:
(http://bjanes.smugmug.com/photos/485115770_ZvTPv-O.jpg)
And here are the histograms of the original file (on the top) and of the file after 15 round trips to L*a*b and back to ProphotoRGB (on the bottom):
(http://bjanes.smugmug.com/photos/485115759_BxVCC-O.gif)
And here is the difference view of the superimposed layers and the stats on the differences:
(http://bjanes.smugmug.com/photos/485115775_wL5iC-O.gif)
The differences are minimal. Perhaps the experts can explain why my findings are different from Guillermo's.
Bill
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Bruce Lindbloom, a well-respected color geek and scientist, has a very useful Levels Calculator,which allows you to enter values to determine the actual number of levels lost to quantization (see the “Calc page”at http://www.brucelindbloom.com) (http://www.brucelindbloom.com)).
And here is the difference view of the superimposed layers and the stats on the differences:
This is a better way to view the differences:
In Photoshop, open both images.
Go to Image > Apply Image.
Set whichever image isn't listed as the target as the source. Set the Channel as RGB. Set the Blending to Subtract, with an Opacity of 100, a Scale of 1, and an Offset of 128.
If the images were truly identical, every pixel in the image would be a solid level 128 gray. Pixels that aren't level 128 gray are different by the amount they depart from 128 gray. You can use Levels to exaggerate the difference, which makes patterns easier to see.
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Amazing, I get the same result as you Bill, but only when using the Microsoft ICM colour engine for the conversion instead of Adobe (ACE). Which one dis you use?
Funily, I had completely rejected to use Microsoft's ICM because I experienced strong hue shifts in a single conversion to Lab and back. If you remember I showed about this here (http://luminous-landscape.com/forum/index.php?showtopic=28753), and have checked it again with the girl's picture and it happens again: when going to Lab and back just once with the Microsoft ICM engine, clearly highlights become more blue, while the rest of the histogram seems well preserved.
(http://img125.imageshack.us/img125/9054/move.gif)
I am using PS CS2. No idea what's going on here, perhaps others can say.
BR
PS: BTW download a new version of Histogrammar 1.2, some minor things have been improved.
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Bruce Lindbloom, a well-respected color geek and scientist, has a very useful Levels Calculator,which allows you to enter values to determine the actual number of levels lost to quantization (see the “Calc page”at http://www.brucelindbloom.com) (http://www.brucelindbloom.com)).
Andrew,
Thanks for the informative reply. I used the levels calculator for converting from gamma 2.2 and 1.8 spaced to L*. The gamma box for the L* is a bit confusing, since L* doesn't use gamma, but I found that you can enter whatever gamma you want and the results are not affected. Anyway, one loses more levels with a gamma of 1.8 as you predicted.
(http://bjanes.smugmug.com/photos/485140814_77z9f-O.gif)
(http://bjanes.smugmug.com/photos/485140808_Q5vW6-O.gif)
This is a better way to view the differences:
In Photoshop, open both images.
Go to Image > Apply Image.
Set whichever image isn't listed as the target as the source. Set the Channel as RGB. Set the Blending to Subtract, with an Opacity of 100, a Scale of 1, and an Offset of 128.
If the images were truly identical, every pixel in the image would be a solid level 128 gray. Pixels that aren't level 128 gray are different by the amount they depart from 128 gray. You can use Levels to exaggerate the difference, which makes patterns easier to see.
I did use that method and the resulting image was a uniform gray at 128.
Bill
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I did use that method and the resulting image was a uniform gray at 128.
That would indicate no alteration what so ever to every pixle, that doesn't sound kosher. Did you alter levels to see the results?
The results also are influenced by the Dither setting in the Color Settings.
16-bit conversions show very small if any data loss, 8-bit, pretty significant.
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That would indicate no alteration what so ever to every pixle, that doesn't sound kosher. Did you alter levels to see the results?
The results also are influenced by the Dither setting in the Color Settings.
16-bit conversions show very small if any data loss, 8-bit, pretty significant.
The conversions were done with a bit depth of 16. Dither is not enabled in 16 bit mode. I did use levels, but to no avail. I think that the math may have been performed in 8 bit mode rather than 16 bits. To investigate this possibility, I used the freeware program Iris, which uses 16 bit math. I then subtracted the two files using an offset of 500 to avoid negative numbers. The statistics are shown for the RGB channels in the stat box of Iris. The standard deviation of the difference is only about 7 pixels. I then used the threshold settings of Iris to give the best view of the differences. Shown is a crop of the full sized image in the area of the carillon (bell tower). The differences are negliglible.
(http://bjanes.smugmug.com/photos/485173814_prz5K-O-2.png)
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Amazing, I get the same result as you Bill, but only when using the Microsoft ICM colour engine for the conversion instead of Adobe (ACE). Which one dis you use?
Funily, I had completely rejected to use Microsoft's ICM because I experienced strong hue shifts in a single conversion to Lab and back. If you remember I showed about this here (http://luminous-landscape.com/forum/index.php?showtopic=28753), and have checked it again with the girl's picture and it happens again: when going to Lab and back just once with the Microsoft ICM engine, clearly highlights become more blue, while the rest of the histogram seems well preserved.
I am using PS CS2. No idea what's going on here, perhaps others can say.
BR
PS: BTW download a new version of Histogrammar 1.2, some minor things have been improved.
Guilermo,
I used the Adobe ICM engine in CS4 (11.0.1).
Bill
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In Photoshop, open both images.
Go to Image > Apply Image.
Set whichever image isn't listed as the target as the source. Set the Channel as RGB. Set the Blending to Subtract, with an Opacity of 100, a Scale of 1, and an Offset of 128.
If the images were truly identical, every pixel in the image would be a solid level 128 gray. Pixels that aren't level 128 gray are different by the amount they depart from 128 gray. You can use Levels to exaggerate the difference, which makes patterns easier to see.
This thread inspired me to run a test of my own. I won't post extensive results because... you guys are much smarter than I am. But just for the sake of throwing another data point in on the pile, I'll report what I found:
I found that running 20 conversions of an image from ProPhoto RGB to LAB in 16 bit (using CS3, ACE), and I found extremely minimal differences. I actually wasn't able to see any differences whatsoever before I tried the technique quoted above, and even then, only the histogram showed anything. So to me at least, within the parameters of the image editing I usually do, RGB to LAB seems OK enough in 16 bit.
Of course, if I ever needed to use LAB color for anything, I'd probably just contain the needed edits within a smart object anyway as opposed to round-tripping the whole document anyway, so it may be a moot point. Still, good to know.
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I used the Adobe ICM engine in CS4 (11.0.1).
I cheked again and again the histogram degradation is there. Definitively something has changed since CS2, I need an update.
Thanks!
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I found that running 20 conversions of an image from ProPhoto RGB to LAB in 16 bit (using CS3, ACE), and I found extremely minimal differences. I actually wasn't able to see any differences whatsoever before I tried the technique quoted above, and even then, only the histogram showed anything. So to me at least, within the parameters of the image editing I usually do, RGB to LAB seems OK enough in 16 bit.
16-bit, totally AOK. 8-bit, not so good. But that pundit doesn't buy into high bit workflows either.... But heck, if you output to a halftone dot, you really have to go out of your way to mangle the data and see it.
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16-bit, totally AOK. 8-bit, not so good. But that pundit doesn't buy into high bit workflows either...
Regarding "That Pundit", his views on 8-bit editing kinda put me off anything he had to say, including using the LAB color space (of which he seems to be a leading proponent). The testing in this thread is actually making me a little more interested in using messing around with LAB color. Funny how things work sometimes.
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Since I had never heard the word 'pundit' I searched for it and found "‘Pundit‘ means an expert or knowledgeable person, an authority with opinion."
Are you talking about someone (don't remember his name) who had a loooooong discusion with Bruce Lindblom about 16 vs 8 bit image edition?
BR
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Since I had never heard the word 'pundit' I searched for it and found "‘Pundit‘ means an expert or knowledgeable person, an authority with opinion."
Are you talking about someone (don't remember his name) who had a loooooong discusion with Bruce Lindblom about 16 vs 8 bit image edition?
Yes. I should have said, in this context, anti-pundit or something along those lines. That said, it would be totally irresponsible of me to say this fellow isn't an expert or very knowledgeable. We have major disagreements on certain aspects of imaging, but there's no question, there's value added opinions and techniques presented by this person. That's what makes his ideas about Raw processing, high bit, wide gamut imaging so distasteful. He'd be easier to ignore if he didn't have anything useful to say. That's not the case. So lets say, he's a sudo-pundit.
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So lets say, he's a sudo-pundit.
you mean, "sudo" as in "superuser"?
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Since I had never heard the word 'pundit' I searched for it and found "‘Pundit‘ means an expert or knowledgeable person, an authority with opinion."
Are you talking about someone (don't remember his name) who had a loooooong discusion with Bruce Lindblom about 16 vs 8 bit image edition?
BR
For more background, go to Lindbloom's site and click on the info tab and then scroll down to the "Dan Margulies 16 bit challenge"
Bruce Lindbloom Site (http://www.brucelindbloom.com/)
And here is some more background:
Reconsidering 16 bits (http://www.retouchpro.com/forums/input-output-workflow/4826-reconsidering-16-bit.html)
Or it might be more profitable to do 15 iterations of the round trip with 8 bit files and repeat the analysis.
Bill
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For more background, go to Lindbloom's site and click on the info tab and then scroll down to the "Dan Margulies 16 bit challenge"
Bruce Lindbloom Site (http://www.brucelindbloom.com/)
And here is some more background:
Reconsidering 16 bits (http://www.retouchpro.com/forums/input-output-workflow/4826-reconsidering-16-bit.html)
Its a tired debate. Are we supposed to believe that there's no benefit to high bit workflows, capture devices that capture more than 8 bits, printer drives that send more than 8 bits to the printer, software that supports high bit editing but rather, its all a conspiracy and unnecessary? The "pundit" is just down on high bit (and high gamut) workflows to point a light onto himself. Its the Ken Rockwell mode of generating attention by being controversial.
BTW, Lindbloom nailed it here (direct link):http://www.brucelindbloom.com/index.html?DanMargulis.html.
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Wow, so the pundit was Margulis?!? pity it's already 3am in Spain and that means my time to go to bed to enjoy some (printed) reading is nearing. Tomorrow I'll have a look at all that old but interesting stuff.
Thanks.
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"‘Pundit‘ means an expert or knowledgeable person, an authority with opinion."
Well there's a dated definition if I've ever heard one... "generating attention by being controversial" is the main goal of the modern pundit.[/thread drift]
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Its a tired debate. Are we supposed to believe that there's no benefit to high bit workflows, capture devices that capture more than 8 bits, printer drives that send more than 8 bits to the printer, software that supports high bit editing but rather, its all a conspiracy and unnecessary? The "pundit" is just down on high bit (and high gamut) workflows to point a light onto himself. Its the Ken Rockwell mode of generating attention by being controversial.
Andrew,
I repeated the experiment with the same image using 8 bit ProPhotoRGB and then 16 bit ProPhotoRGB and compared the results using the method you suggested. In my first attempt, due to unfamiliarity with the method, I applied the image to itself!
Here is the image:
(http://bjanes.smugmug.com/photos/485374647_ij93D-O.png)
Here is the difference with 16 bit processing. There are a few differences in the shadow areas.
(http://bjanes.smugmug.com/photos/485374566_AgcKf-O.png)
and with 8 bit processing, there is abundant posterization.
(http://bjanes.smugmug.com/photos/485374619_NMW6J-O.png)
How much these differences would show up in a print is yet to be determined, but the differences are quite striking in the analysis.
Bill
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"The testing in this thread is actually making me a little more interested in using messing around with LAB color. Funny how things work sometimes."
Then I highly recommend Dan's Lab book, The Canyon Connundrum. As well as leading you through the ins and outs of Lab, it will also help you learn when Lab is appropriate and when it's not - and it's definitely not always a benefit. Knowing when makes you a better retoucher.
As far as Dan being totally down on hi-bit high gamut workflows, this is somewhat disengenuous. He's not and even advocates that for most processes it won't hurt. What he objects to, and this is my opinion, is that there is a certain constituent that claims it's always beneficial to work in 16 bit large gamut color spaces. You have to actually read his books to understand what his real opinion is and understand where his complaints are based. As far as large gamut, what's larger than Lab - well, mathematically maybe ProPhoto RGB, but not in the real world.
One of the cool things The Canyon Connundrum does is show you examples of how Lab interacts with different RGB workspaces with real world images and how you can take advantage of some of Photoshop's limitations when dealing with severely out of gamut colors
The most important thing to remember is that the typical single round trip into Lab and back does no real damage to the image, and if you're adept at your Lab adjustments, your image will benefit greatly.
On a practical note, I work on hundreds of stock images a year for various clients, getting paid to make some fairly mediocre iStock and Getty Images files look like I might have actually taken them. Every one of those stock images comes to me as an 8 bit (usually) sRGB number eight compressed jpeg, and I'd say that maybe 60 percent make the trip to Lab and either back to RGB or straight to CMYK from there. These are usually printed on high end presses at 175-200 line screen and they all look great, as do the Epson proofs I make prior to going to press. Yes, every once in a while, a blue sky falls apart, but it would have broken apart regardless. So, while it might not be advised, I'm living proof that you can move 8 bit jpegs to Lab and back if you need to.
Sometimes it's not that you can't get similar results in RGB, but it's the fact that I might have to plow through a hundred images in an afternoon and I'm after the fastest most efficient workflow possible. Not everyone "gets" Lab, but for those wiling to spend the time to really learn it, it can be one of the most powerful tools in your color correction/retouching toolkit.
Peter Figen
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"The testing in this thread is actually making me a little more interested in using messing around with LAB color. Funny how things work sometimes."
Then I highly recommend Dan's Lab book, The Canyon Connundrum. As well as leading you through the ins and outs of Lab, it will also help you learn when Lab is appropriate and when it's not - and it's definitely not always a benefit. Knowing when makes you a better retoucher.
As far as Dan being totally down on hi-bit high gamut workflows, this is somewhat disengenuous. He's not and even advocates that for most processes it won't hurt. What he objects to, and this is my opinion, is that there is a certain constituent that claims it's always beneficial to work in 16 bit large gamut color spaces. You have to actually read his books to understand what his real opinion is and understand where his complaints are based. As far as large gamut, what's larger than Lab - well, mathematically maybe ProPhoto RGB, but not in the real world.
One of the cool things The Canyon Connundrum does is show you examples of how Lab interacts with different RGB workspaces with real world images and how you can take advantage of some of Photoshop's limitations when dealing with severely out of gamut colors
The most important thing to remember is that the typical single round trip into Lab and back does no real damage to the image, and if you're adept at your Lab adjustments, your image will benefit greatly.
On a practical note, I work on hundreds of stock images a year for various clients, getting paid to make some fairly mediocre iStock and Getty Images files look like I might have actually taken them. Every one of those stock images comes to me as an 8 bit (usually) sRGB number eight compressed jpeg, and I'd say that maybe 60 percent make the trip to Lab and either back to RGB or straight to CMYK from there. These are usually printed on high end presses at 175-200 line screen and they all look great, as do the Epson proofs I make prior to going to press. Yes, every once in a while, a blue sky falls apart, but it would have broken apart regardless. So, while it might not be advised, I'm living proof that you can move 8 bit jpegs to Lab and back if you need to.
Sometimes it's not that you can't get similar results in RGB, but it's the fact that I might have to plow through a hundred images in an afternoon and I'm after the fastest most efficient workflow possible. Not everyone "gets" Lab, but for those wiling to spend the time to really learn it, it can be one of the most powerful tools in your color correction/retouching toolkit.
Peter Figen
An interesting post. For a long while I have pondered about sending some of my images to a stock library. What has put me off is that numerous magazine and internet posts state that these libraries demand the best images in a technical sense ( there was a post a couple of days ago on this subject ) Yet you state ( no criticism of you ) that you are making poor images look good? My question is why are these libraries accepting them?
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For more background, go to Lindbloom's site and click on the info tab and then scroll down to the "Dan Margulies 16 bit challenge"
Ah, someone has mentioned his name. I thought I knew who was the subject of the discussion, but I had a nagging doubt that it was really Voldemort.
Jeremy
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Every one of those stock images comes to me as an 8 bit (usually) sRGB number eight compressed jpeg, and I'd say that maybe 60 percent make the trip to Lab and either back to RGB or straight to CMYK from there. These are usually printed on high end presses at 175-200 line screen and they all look great, as do the Epson proofs I make prior to going to press. Yes, every once in a while, a blue sky falls apart, but it would have broken apart regardless. So, while it might not be advised, I'm living proof that you can move 8 bit jpegs to Lab and back if you need to.
In that case I think the important thing is not if your source image was 8-bit, but if the conversion process to Lab and back is done in 8 or 16 bits.
If you do that step in 16 bits (regardless the source image was 8 bit), and convert to 8-bit once in sRGB again, the conversion process probably won't affect at all to the quality of the image. It would be only the things you do once in Lab that can affect it, like any other processing being applied to an 8-bit image.
See the third histogram is identical to the first. 16-bit rounding errors don't affect the levels of an 8-bit precision source image:
(http://img110.imageshack.us/img110/6682/evolutionx.gif)
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In that case I think the important thing is not if your source image was 8-bit, but if the conversion process to Lab and back is done in 8 or 16 bits.
If you do that step in 16 bits (regardless the source image was 8 bit), and convert to 8-bit once in sRGB again, the conversion process probably won't affect at all to the quality of the image. It would be only the things you do once in Lab that can affect it, like any other processing being applied to an 8-bit image.
That is especially true if the source space is relatively narrow, such as sRGB or aRGB. Dan stated that ProPhotoRGB is rarely used in professional work, but I think that is changing with the advent of inkjet printers with a wide gamut. Dan is used to working with printing presses.
Bill
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How much these differences would show up in a print is yet to be determined, but the differences are quite striking in the analysis.
Might not show at all. Might show after more edits. That's the issue. Keeping your editing options open.
I suspect something like a smooth blue sky would suffer first. Then the printer would of course play a role. Now that Epson 90 series with HDR and 16-bit drivers are supported under Leopard, we're trying to see when there's an actual benefit of sending 16-bit through the print path. That's starting with high bit and going all the way to output. With 8-bit, I expect one could see banding in many images on such a device unless very careful editing is conducted.
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As far as Dan being totally down on hi-bit high gamut workflows, this is somewhat disengenuous. He's not and even advocates that for most processes it won't hurt. What he objects to, and this is my opinion, is that there is a certain constituent that claims it's always beneficial to work in 16 bit large gamut color spaces. Y
Peter, I've archived all of Dan's silly quotes from his list about high bit, wide gamut, ACR is unfit for professional use etc. So you might wish to call it disingenuous but his words are clear and on the record. I find nothing close to disingenuous when his various rants over the years are placed easily within view and context. I can of course barf up all this nonsense here but much of it is archived already.
It will be interesting to poke my head in one of his PSW world sessions this month and see if he's still using CS2 as he was last show. I guess after he got kicked out of the PS beta, he decided whatever version he had was adequate for the job. Says a lot about this pundit IMHO.
Read the Lindbloom piece again. It shows how a true scientist handles a flat earth mindset.
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An interesting post. For a long while I have pondered about sending some of my images to a stock library. What has put me off is that numerous magazine and internet posts state that these libraries demand the best images in a technical sense ( there was a post a couple of days ago on this subject ) Yet you state ( no criticism of you ) that you are making poor images look good? My question is why are these libraries accepting them?
You hit the nail on the head! Dan's entire life's work is about turd polishing. And he's damn good at it! If you look at his books or sessions, you see the most awful original images you can imagine. Worse, he tells his readers that many are from "Professional" photographers. Well maybe they shot them at 4X the legal alcohol limit. Really, my 85 year old mom takes better snaps.
If Dan had a clue about proper capture and Raw processing, his need for Lab or any of his other exotic fixes would be reduced to nearly zero. Lets not forget, his background (or so he says, I've yet to find anyone who can confirm what he did before becoming a "Photoshop expert" and found at least one person who dismisses his history) was supposedly fixing poor originals in a prepress house. He has a rather low regard for photographers in my opinion, but maybe my skin is thin for this group of which I belong.
If you've got crap images or your job is to make truds look better, I can think of no one else better to study than Dan. If not, he's pretty much a waste of time, especially with so many flat earth theories about high bit and wide gamut workflows.
Now if you're the shooter who under exposes JPEGs with the wrong white balance, Dan's your man. I find it far more effective to teach folks to shoot Raw and process the data appropriately which as Peter appears to desire, is far faster, less damaging and results in far better results. Not as impressive as showing a turd that on a scale from 1 to 10 is a 9, then jumping through 34 Photoshop hoops and 10 minutes later, ending up with a turd that's now only a 6. My advise, stay away from truds in the first place (don't make em)!
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Dan stated that ProPhotoRGB is rarely used in professional work, but I think that is changing with the advent of inkjet printers with a wide gamut. Dan is used to working with printing presses.
Dan likes to make up stat's and history, another area that pisses me off. He would like his readers to believe he really has his pulse on the so called industry (whatever industry that might be). He's pulled the "Rush Limbaugh speaks for the Republicans" for years. And he sees everything as a file going to press. I don't know that he even has a modern ink jet printer and could recognize its qualities over a 133lpi CMYK press. Point is, one can work with high bit, wide gamut workflows as their master archive and spin off either an RGB iteration for CMYK conversions by others (I'd personally convert to ColorMatch RGB), or directly to CMYK. Oh, another of his flat earth ideas a few years ago was the U.S. Web Coated (SWOP) v2 profile in Photoshop was simply no good (I will not go into the silly details but he didn't "get" the fact that, IF you send a U.S. Web Coated (SWOP) v2 separated file to a press that really did conform to TR001, it printed really well, something Chris Murphy, Bruce Fraser and I demo'd years ago at a Seybold seminar). Its just another of his "a copy of Photoshop killed my parents" story that so many on his list believe as truth. I really believe you can lump Dan, Rush and Ken into a group. They all have useful things to say (well I'm a bit hard pressed to say this is true with Rush). What's so upsetting is the huge BS factor you have to edit through to get to the good data.
OK, back to our regularly scheduled posts on Lab conversions.....
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Peter, I've archived all of Dan's silly quotes from his list ....
So why at all ?
Fwiw – I’m sometimes using a fancy technique to repair burned skin tones which works in Lab only (with a given non-Raw image). Something about to make use of "Lab’s impossible colors" due to integer encoding. Clever technique (http://www.dgrin.com/showthread.php?p=190595#post190595) – not more not less.
But that’s it for me.
Peter
(another Peter)
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So why at all ?
Fwiw – I’m sometimes using a fancy technique to repair burned skin tones which works in Lab only (with a given non-Raw image). Something about to make use of "Lab’s impossible colors" due to integer encoding. Clever technique (http://www.dgrin.com/showthread.php?p=190595#post190595) – not more not less.
What is an impossible color (yes I know, its another made up Dan term, like "false profile" and "Invisible color").
As the Chinese proverb says: The first step towards genius is calling things by their proper name. Not sure what to make of the opposite (someone who makes them up).
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What is an impossible color (yes I know, its another made up Dan term, like "false profile" and "Invisible color").
As the Chinese proverb says: The first step towards genius is calling things by their proper name. Not sure what to make of the opposite (someone who makes them up).
Pretty simple:
The integer encoding of Lab by means of three Cartesian coordinates (cuboid space), as given in Photoshop, bears a low Coding efficiency (just 35.1%). Means there are many many combinations of L, a and b which appear to be outside of the blob like Lab space and the gamut of human vision. This is illustrated in full 3D glory on Bruce Lindbloom’s website. The point is that we still can make use of these "not real colors" as Bruce likes to call it, or "impossible colors", based on the given mapping functions applied under the hood, thus turning everything to real-world colors.
For the science part, I recommend to study Bluce Lindbloom’s website (Lab Gamut display > Learn more (http://www.brucelindbloom.com/LabGamutDisplayHelp.html)). If you find a better term for this 3D effect just let us know.
Anyway, driven by your “anti Dan” obsession (as it seems) you missed or ignored the point that above quoted technique was the only motivation I found worth to mention for making an occasional trip to Lab.
Peter
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see above
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The integer encoding of Lab by means of three Cartesian coordinates (cuboid space), as given in Photoshop, bears a low Coding efficiency (just 35.1%). Means there are many many combinations of L, a and b which appear to be outside of the blob like Lab space describing the gamut of human vision. This is illustrated in full 3D glory on Bruce Lindbloom’s website. The point is that we still can make use of these "not real colors" as Bruce likes to call it, or "impossible colors", based on the given mapping functions applied under the hood, thus turning everything to real-world colors.
I would agree we can define 16.7 million colors definitions using 8-bit per colors but not necessarily 16.7 million perceivable colors. Many of these values are totally redundant. Can you see the difference between 0/0/0 and 0/0/1 on a display?
On the other hand, color is a perceptual property. So if you can't see it it's not a color. We define colors based on perceptual experiments. Color is not a particular wavelength of light. It is a cognitive perception that is the end result of the excitation of photoreceptors followed by retinal processing and ending in the visual cortex.
A coordinate in a "color space" outside the spectrum locus is not a color. Some refer to these as "imaginary colors" (Dan of course had to make up his own term) but this is by and large also erroneous (you can't map an imaginary color from one color space to another as the math (and experimental data) for each color space breaks down outside the spectrum locus.
My beef is the made up terms or modified terms that only Dan uses when existing terminology has been in place. The ICC doesn't have any such definition for "False Profile" and I don't know anyone, other than Dan who uses the term "Ultra Wide Gamut Spaces" to describe say ProPhoto RGB but somehow, Adobe RGB (1998) slips under that made up heading. Or "Range-opening routines" (another made up term). Everyone else would call it tone correction.
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On the other hand, color is a perceptual property. So if you can't see it it's not a color. We define colors based on perceptual experiments. Color is not a particular wavelength of light. It is a cognitive perception that is the end result of the excitation of photoreceptors followed by retinal processing and ending in the visual cortex.
A coordinate in a "color space" outside the spectrum locus is not a color. Some refer to these as "imaginary colors" (Dan of course had to make up his own term) but this is by and large also erroneous (you can't map an imaginary color from one color space to another as the math (and experimental data) for each color space breaks down outside the spectrum locus.
The introduction of 'negative' colors goes back to the original color matching experiment by Hermann Grassmann (about 1853; see page 4 of Gernot Hoffmann’s paper (http://www.fho-emden.de/~hoffmann/ciexyz29082000.pdf)). Then, in order to avoid negative RGB numbers, the CIE consortium defined a synthetic master space based on 'imaginary' primary colors. That is CIE XYZ. By means of Grassmann's law (http://en.wikipedia.org/wiki/CIE_1931_color_space) which assumes the "linearity of human perception" it’s easily possible to calculate beyond. This step outside the human gamut is finally needed for this whole concept of computation of colors to make sense.
Peter
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The introduction of 'negative' colors goes back to the original color matching experiment by Hermann Grassmann
Indeed, its discussed early on in Hunt's book on color reproduction yet I can't find anywhere in that book, or the others I have (Giorginsnni/Madden/Fairchild), the term "Impossible Colors"......