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Author Topic: Some questions about working with Absolute Colorimetric intents  (Read 1878 times)

andrewrodney

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Forget about sRGB--I only brought that up because Chrome as of yet is not color managed while Firefox and Safari are. I use chrome.
Which has absolutely nothing to do with what you wrote and I had to keep asking you to explain! Again, you really seem the correct candidate I discussed below in terms of not using Absolute Colorimetric intent....
Chrome is color managed!
https://www.color-management-guide.com/web-browser-color-management.html

The reason there's so much ignorance on the subject of color management, is that those who have it are so eager to regularly share it! - The Digital Dog
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Andrew Rodney
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Doug Gray

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Yes. But again, in Photoshop, I see zero differences in how Absolute vs. RelCol convert from ProPhoto RGB let alone Adobe RGB (1998) with ACE. When I toggle to Apple CMM, the differences noted are absolutely awful appearing so I can't fathom why anyone would do so. Can you? A
Sure. I can explain what's going on with Microsoft and Apples (now I know Apple also isn't abiding by the ICC's clarification) engines.

When you have an image in an RGB D50 media space, like ProPhoto, the convert to Adobe RGB or sRGB the Absolute Intent in Apple and Microsoft's engines attempts to create the same "colors" that are would occur if the displays were switched from D50 to D65. To do that they strongly yellow tint the image. It's highly problematic since most people set their monitors independently of the working space's "media whitepoint" and usually at the same CCT regardless of working space. The ICC recognizes this. Apple and Microsoft apparently do not.

The only possible use of something like that is if you have an image you want to paste into a printable image, possibly inserted into a "monitor" screen and want it to reflect the difference between the D50 of a print and the D65 of a typical monitor. In that case you would convert the image from sRGB to ProPhoto using Abs. Col. with either the Microsoft or Apple engine then paste it into the "monitor's" face.

That extreme corner case aside, it's still problematic. Any full white (RGB 255,255,255) will be luminance clipped because either the reds or blues would need to go above 255 it get the same luminance of "white" post conversion.  You can see this by converting from sRGB to ProPhoto and back again to sRGB using Abs. Col and one of these screwy engines. The white is no longer 255,255,255.  In the case of ProPhoto->sRGB->ProPhoto the white is changed to 245,253,253.  It's not even a neutral color because of the conversion clipping at 255. Pretty obvious why the ICC indicated color engines should not do this.
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andrewrodney

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Sure. I can explain what's going on with Microsoft and Apples (now I know Apple also isn't abiding by the ICC's clarification) engines.

When you have an image in an RGB D50 media space, like ProPhoto, the convert to Adobe RGB or sRGB the Absolute Intent in Apple and Microsoft's engines attempts to create the same "colors" that are would occur if the displays were switched from D50 to D65. To do that they strongly yellow tint the image. It's highly problematic since most people set their monitors independently of the working space's "media whitepoint" and usually at the same CCT regardless of working space. The ICC recognizes this. Apple and Microsoft apparently do not.

The only possible use of something like that is if you have an image you want to paste into a printable image, possibly inserted into a "monitor" screen and want it to reflect the difference between the D50 of a print and the D65 of a typical monitor. In that case you would convert the image from sRGB to ProPhoto using Abs. Col. with either the Microsoft or Apple engine then paste it into the "monitor's" face.
 
That extreme corner case aside, it's still problematic. Any full white (RGB 255,255,255) will be luminance clipped because either the reds or blues would need to go above 255 it get the same luminance of "white" post conversion.  You can see this by converting from sRGB to ProPhoto and back again to sRGB using Abs. Col and one of these screwy engines. The white is no longer 255,255,255.  In the case of ProPhoto->sRGB->ProPhoto the white is changed to 245,253,253.  It's not even a neutral color because of the conversion clipping at 255. Pretty obvious why the ICC indicated color engines should not do this.
Agreed on all points above. And the results are also ugly. But it appears, this has nothing to do with what BobDavid was writing about. His text about conversions from RGB working spaces was just confused. And incorrect  :(
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Andrew Rodney
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Doug Gray

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Agreed on all points above. And the results are also ugly. But it appears, this has nothing to do with what David was writing about. His text about conversions from RGB working spaces was just confused. And incorrect  :(

Yes. Conversions of sRGB <> Adobe RGB do not change whites in any of the color engines. But it's possible David had run across the Apple or Microsoft weirdness converting between spaces that had differing media white points and has confused this with Adobe RGB / sRGB. It might also show up if for some reason one of the conversion spaces was a monitor's profile space instead of a standard RGB working space and he was using the Apple/Microsoft engine. Sometimes it's hard to remember exactly what one did 5 years ago and it could just be something fuzzy in his memory.
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BobDavid

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Re absolute: So you do not see more shadow detail in the sky area, meaning the trees. The color of the auto is also slightly punchier.  Perhaps we're missing each other's points.

Anyway, for whatever reason, printing with the rendering intent set to Absolute is working fine. Soft proofing in Absolute and then toggling soft proof to aRGB matches closely, much better than with Relative with or without black point compensation.

In the end, it's what a print shows or hides that matters. Outside of studio work, I typically photograph scenes I'm familiar with. I've been observing that shack for six months. It often takes me months to figure out how to photograph a scene. The print looks as I'd imagined it would.

It took about an hour to process the file for print. I made an 8.5" X 11" test and then a final 24" X 36" exhibition print.
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Doug Gray

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Here are three screen shots: Absolute, Relative with Black Point Compensation, and Relative (soft proofs for Epson Ultra Premium Luster Photo Paper). Photos were taken with an Olympus Pen F in 8-shot mode for color fidelity and to control moire. The three RAW files were minimally processed as one batch with all adjustment in sync.
I see the differences between Rel. Col. and Abs. and they are exactly what I would expect. The Rel. Col. soft proof is slightly bluer and less luminous. This is to be expected as Abs. Col. prints will be brighter because Rel Col drops the print density and shifts tint so that L*=100 matches the paper white. Another side effect is that when the black point is reached, Abs Col typically undergoes larger a* and b* changes than Rel. Col. this can create the impression of more texture in deep shadows, or it can produce less desirable effects.

The basic problem with Abs. is that white gradients will clip when you go from smooth RGB 220 to 255. Try it. You don't have those in this image but this is a big reason Abs. Col. is discouraged for the normal photo printer.
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andrewrodney

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Yes. Conversions of sRGB <> Adobe RGB do not change whites in any of the color engines. But it's possible David had run across the Apple or Microsoft weirdness converting between spaces that had differing media white points and has confused this with Adobe RGB / sRGB. It might also show up if for some reason one of the conversion spaces was a monitor's profile space instead of a standard RGB working space and he was using the Apple/Microsoft engine. Sometimes it's hard to remember exactly what one did 5 years ago and it could just be something fuzzy in his memory.
I can’t read his mind nor can I read his memories. Bottom line is the text that he wrote about the two RGB working spaces and an absolute colorimetric conversion is either wrong or confused or both.  ::)
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Andrew Rodney
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BobDavid

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There is discord re whether Chrome is color managed or not.

Chrome Okay



Chrome not Okay
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andrewrodney

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There is discord re whether Chrome is color managed or not.

Chrome Okay

Chrome not Okay
Either way IF you use a non color managed product, you get what you deserve.The larger point, is that what you wrote about the two working spaces and an absolute called metric conversion is incorrect and has nothing to do with a color managed or non color managed web browser! Nice try at a digression, not going to fly here. A professional photographer and technician knows better ;D
« Last Edit: May 10, 2018, 06:57:01 PM by andrewrodney »
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Andrew Rodney
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Doug Gray

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I can’t read his mind nor can I read his memories. Bottom line is the text that he wrote about the two RGB working spaces and an absolute colorimetric conversion is either wrong or confused or both.  ::)

No, it's simply wrong. He may also be confused or just mistaken.

Edit: It appears he has edited his posts. He states that he may have been unclear, and was not claiming a difference in converting Adobe RGB <> sRGB using Abs. v. Rel Col.

In any case he seems to be focusing on the soft proofing and Abs. v Rel.  I've pointed out the risks and issues of using Abs. Col. but if he tweaks it soft proofing as he indicated he did then he may well like the results and that's fine. There are cases where Abs. Col. can create a nice effect in deep shades as a result of the a* and b* shift that occurs at the black point. I've seen it maybe once or twice but it's rare. The negatives of having high key clipping are the major reason I don't use Abs. for photos. I only use Abs. for repro work.
« Last Edit: May 10, 2018, 06:52:55 PM by Doug Gray »
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BobDavid

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I can’t read his mind nor can I read his memories. Bottom line is the text that he wrote about the two RGB working spaces and an absolute colorimetric conversion is either wrong or confused or both.  ::)

...never wrote anything about converting aRGB to Absolute or sRGB or anything else. I may have stumbled while trying to explain that soft proofing an image and then photographing that soft proof from the screen and then posting that photo of the photo on on the web to be viewed on another screen is problematic.

What I did write is that when soft proofing paper, Absolute intent rather than Relative matches how the original file looks on the screen as opposed to a print.
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BobDavid

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This is a good facsimile of what the print looks like. It's the same picture I posted hours ago. So back to the beginning, if for whatever reason one is able to get a better print via Absolute intent rather than Relative intent, so be it.
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andrewrodney

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...never wrote anything about converting aRGB to Absolute or sRGB or anything else. I may have stumbled while trying to explain that soft proofing an image and then photographing that soft proof from the screen and then posting that photo of the photo on on the web to be viewed on another screen is problematic.
You did very much so stumble:
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It's also streamlines the process of going from aRGB to sRGB for screen display.
« Last Edit: May 10, 2018, 07:00:05 PM by andrewrodney »
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Andrew Rodney
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Doug Gray

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This is a good facsimile of what the print looks like. It's the same picture I posted hours ago. So back to the beginning, if for whatever reason one is able to get a better print via Absolute intent rather than Relative intent, so be it.

As long as you soft proof it pick whatever intent produces the most appealing results. It's your eyes. Just be particularly aware of the high key clipping issue in Abs. Col. due to the luminance increase between Rel. Col and Abs. Col.
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BobDavid

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As long as you soft proof it pick whatever intent produces the most appealing results. It's your eyes. Just be particularly aware of the high key clipping issue in Abs. Col. due to the luminance increase between Rel. Col and Abs. Col.

Exactly! Bravo, well spoken! ... Yes it's often necessary to add a curve layer to maintain detail in the highlights.
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andrewrodney

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Yes it's often necessary to add a curve layer to maintain detail in the highlights.
How do you accomplish that when, as Doug suggests, the highlights are clipped:
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Just be particularly aware of the high key clipping issue in Abs. Col. due to the luminance increase between Rel. Col and Abs. Col.
Curves layers can't bring back clipped detail or data, only make them less than RGB 255 (Lstar 100).
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Andrew Rodney
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BobDavid

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You did very much so stumble:

Tenacity, extraordinary self-confidence, and infallibility are great traits. ... So, is Chrome a color managed browser? There's a good amount of dissension on that issue. And somehow things got muddy along the way when discussing how an aRGB image when displayed on an sRGB device often doesn't look the same.

Quite a mashup of red herrings and garden paths today...
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Doug Gray

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Here's what happens with a neutral gradient from RGB 200 to 255:

As you can see, the AbsCol tone curve is more luminous until it reaches the clipping point, about 240 with this paper then the RelCol exceeds it by about 1 L*. There are reasons why AbsCol is discouraged for normal photo work and this is a major one.
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andrewrodney

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Tenacity, extraordinary self-confidence, and infallibility are great traits. ... So, is Chrome a color managed browser?
You really don't know, do you. Or how to check. Would you like me to teach you how to confirm if it's color managed or not? Ask.
I don't have an answer yet for you because I don't use Chrome and I don't run Windows. But I know how one can easily check if it is or isn't. Since you admit you use it, then tell us it's not color managed, then ask if it is, all I can do is wonder how much you don't know about this subject....

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There's a good amount of dissension on that issue.

It would take a knowledgeable technical savvy person about 1 minute to figure it out.
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And somehow things got muddy along the way when discussing how an aRGB image when displayed on an sRGB device often doesn't look the same.
Muddy like this: It's also streamlines the process of going from aRGB to sRGB for screen display.
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Quite a mashup of red herrings and garden paths today...
Who joined this discussion today? « Reply #21 on: Today at 02:35:48 PM »
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Andrew Rodney
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BobDavid

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How do you accomplish that when, as Doug suggests, the highlights are clipped:Curves layers can't bring back clipped detail or data, only make them less than RGB 255 (Lstar 100).

If there is data in the highlights, use a curve to ensure the data doesn't get crushed. If there isn't any data to begin with (255, 255, 255), paint it in if so desired 30 years of retouching and a high degree of competency in drawing helps, a lot.

Stills photography is about rendering three dimension onto a two dimensional plain. As for fine art and commercial photography, if one is able to "draw" or "paint" credible detail into a scene using Photoshop, GREAT! Not being a photo journalist or a forensics photographer, what difference does it make?

I'd love to see some of your work. How about putting some up?
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