New article on color management

Started Apr 26, 2013 | Discussions
gollywop
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New article on color management
Apr 26, 2013

For better or for worse, I have just published a new article: Color Management - a Walkthrough. It can be found at

http://www.dpreview.com/articles/7270088913/color-management-a-walkthrough

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Roy Sletcher
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Re: New article on color management
In reply to gollywop, Apr 26, 2013

gollywop wrote:

For better or for worse, I have just published a new article: Color Management - a Walkthrough. It can be found at

http://www.dpreview.com/articles/7270088913/color-management-a-walkthrough

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gollywop

Thank you - A quick skim of the contents indicate valuable clarification of the subject matter for people like me who have large gaps in their understanding of the subject.

Of course this is DP Review and no good deed goes unpunished. Expect an onslaught of critics questioning the content, your qualifications to write this, and pointing out in great detail any minor flaw or grammatical error.

However, I for one, am very grateful you did it.

Roy Sletcher

I shoot people with a big Canon and frequently cut off their heads and limbs.

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Great Bustard
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Excellent!
In reply to gollywop, Apr 26, 2013

gollywop wrote:

For better or for worse, I have just published a new article: Color Management - a Walkthrough. It can be found at

http://www.dpreview.com/articles/7270088913/color-management-a-walkthrough

This is a subject I need a great deal of education in -- I'm glad to see such a comprehensive article on the subject!

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gollywop
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Re: New article on color management
In reply to Roy Sletcher, Apr 26, 2013

Roy Sletcher wrote:

gollywop wrote:

For better or for worse, I have just published a new article: Color Management - a Walkthrough. It can be found at

http://www.dpreview.com/articles/7270088913/color-management-a-walkthrough

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gollywop

Thank you - A quick skim of the contents indicate valuable clarification of the subject matter for people like me who have large gaps in their understanding of the subject.

Of course this is DP Review and no good deed goes unpunished. Expect an onslaught of critics questioning the content, your qualifications to write this, and pointing out in great detail any minor flaw or grammatical error.

Ah, yes, to be sure.

However, I for one, am very grateful you did it.

Thanks, Roy, very much.

Roy Sletcher

I shoot people with a big Canon and frequently cut off their heads and limbs.

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gollywop
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Re: Excellent!
In reply to Great Bustard, Apr 26, 2013

Great Bustard wrote:

gollywop wrote:

For better or for worse, I have just published a new article: Color Management - a Walkthrough. It can be found at

http://www.dpreview.com/articles/7270088913/color-management-a-walkthrough

This is a subject I need a great deal of education in -- I'm glad to see such a comprehensive article on the subject!

Turnabout's fair play.

many thanks, GB

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Great Bustard
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Since I have you here...
In reply to gollywop, Apr 26, 2013

gollywop wrote:

Great Bustard wrote:

gollywop wrote:

For better or for worse, I have just published a new article: Color Management - a Walkthrough. It can be found at

http://www.dpreview.com/articles/7270088913/color-management-a-walkthrough

This is a subject I need a great deal of education in -- I'm glad to see such a comprehensive article on the subject!

Turnabout's fair play.

many thanks, GB

...let me ask you a question.  If someone worked entirely in sRGB to produce a print, under what circumstances might working in a different color space result in a "significantly better" print?

For example, let's say I'm taking a pic of a bunch of red roses, which, obviously, has lots of hues of heavily saturated reds.  Might working in a colorspace other than sRGB produce a "significantly better" photo, assuming, of course, that the printer worked in that color space?

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gollywop
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Re: Since I have you here...
In reply to Great Bustard, Apr 26, 2013

Great Bustard wrote:

gollywop wrote:

Great Bustard wrote:

gollywop wrote:

For better or for worse, I have just published a new article: Color Management - a Walkthrough. It can be found at

http://www.dpreview.com/articles/7270088913/color-management-a-walkthrough

This is a subject I need a great deal of education in -- I'm glad to see such a comprehensive article on the subject!

Turnabout's fair play.

many thanks, GB

...let me ask you a question.  If someone worked entirely in sRGB to produce a print, under what circumstances might working in a different color space result in a "significantly better" print?

Am I to assume here that the shot was taken as a jpeg in sRGB, or are we shooting raw?  If it starts out life as an 8-bit sRGB jpeg, there isn't much sense in going anywhere else.

If you've shot raw and your printer has a gamut larger than sRGB, then you'll do better, when processing images that have saturated red, oranges, and/or blues, using a wider space, at least Adobe RGB.  This would often be the case for your red roses or dayglo orange graffiti or cobalt blue underwear.

If you've got a wide-gamut monitor that is capable of a broader gamut than sRGB (otherwise forget it), you can see just what is likely to happen by opening your Adobe RGB-processed file in PS, duplicating it and soft proofing the duplicate using the sRGB profile.  Toggling between the two will give you an idea of what is possible. Or, even more simply, use the Convert (to sRGB) dialog and toggle the Preview checkbox.  If you see no important changes, then using the wider gamut hasn't bought you much, if anything.

Clearly, if your monitor's gamut is roughly sRGB, you'll not be able to see any effect even if it exists.  This is even more true for a gamut like ProPhoto RGB. No monitor is going to let you see a lot of what might be happening by using this space.  Similarly, if your printer's gamut is close to sRGB, there is not likely to be any advantage in using a wider working space.  The conversion will be done by the printer's profile and you'd be better off controlling it yourself prior to printing.

I've got a number of sunset shots with saturated oranges that I've processed with both sRGB and Adobe RGB, and the differences are quite noticeable from my Canon PixmaPro 9000 II (particularly when using Red River papers).  The sRGB results are dull and disappointing.

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Detail Man
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Re: New article on color management
In reply to gollywop, Apr 26, 2013

gollywop wrote:

For better or for worse, I have just published a new article: Color Management - a Walkthrough. It can be found at

http://www.dpreview.com/articles/7270088913/color-management-a-walkthrough

So I reiterate. You describe a situation:

You've just taken a shot of a fire engine, and, behind the scenes, it is captured in the raw data. But you want an OOC jpeg to show Junior. ...

Who the hell is Junior ?  The arsonist who started the fire ? That toothless giggling fellow over there ? If so, I would shoot it in RAW to make sure that the authorities had a decent image of the bloke !


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gollywop
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Re: New article on color management
In reply to Detail Man, Apr 26, 2013

Detail Man wrote:

gollywop wrote:

For better or for worse, I have just published a new article: Color Management - a Walkthrough. It can be found at

http://www.dpreview.com/articles/7270088913/color-management-a-walkthrough

So I reiterate. You describe a situation:

You've just taken a shot of a fire engine, and, behind the scenes, it is captured in the raw data. But you want an OOC jpeg to show Junior. ...

Who the hell is Junior ?

Junior's inevitably a jerk, but we all love him if he's ours.  

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Detail Man
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Re: New article on color management
In reply to gollywop, Apr 26, 2013

gollywop wrote:

Detail Man wrote:

gollywop wrote:

For better or for worse, I have just published a new article: Color Management - a Walkthrough. It can be found at

http://www.dpreview.com/articles/7270088913/color-management-a-walkthrough

So I reiterate. You describe a situation:

You've just taken a shot of a fire engine, and, behind the scenes, it is captured in the raw data. But you want an OOC jpeg to show Junior. ...

Who the hell is Junior ?

Junior's inevitably a jerk, but we all love him if he's ours.  

I get it, then ... JPGs are for jerks. RAW is for "real" captures like big shiny fire engines. Sheesh !

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gollywop
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Re: New article on color management
In reply to Detail Man, Apr 26, 2013

Detail Man wrote:

gollywop wrote:

Detail Man wrote:

gollywop wrote:

For better or for worse, I have just published a new article: Color Management - a Walkthrough. It can be found at

http://www.dpreview.com/articles/7270088913/color-management-a-walkthrough

So I reiterate. You describe a situation:

You've just taken a shot of a fire engine, and, behind the scenes, it is captured in the raw data. But you want an OOC jpeg to show Junior. ...

Who the hell is Junior ?

Junior's inevitably a jerk, but we all love him if he's ours.  

I get it, then ... JPGs are for jerks. RAW is for "real" captures like big shiny fire engines. Sheesh !

Finally !!!

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Detail Man
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Re: Does Melissa "Gloss Over" Image Noise ?
In reply to gollywop, Apr 27, 2013

The raw processor's working space varies from one processor to another. In ACR, for example, you have a choice among sRGB, Adobe RGB, ProPhoto RGB, or ColorMatch RGB, although a linearized version (gamma = 1.0) of the very broad ProPhoto RGB appears to be its native intermediate space. In others, such as LightRoom or PhotoNinja, there is no choice: they use a linearized version ProPhoto RGB (although the image as displayed on the monitor and the histograms have a 2.2 gamma applied to make them appear more in line with human perception).

"Color Management - a Walkthrough", Section 3b., Raw Processor:

http://www.dpreview.com/articles/7270088913/color-management-a-walkthrough

It occurs to me that since the "Melissa" gamma-corrected color-space (used only for user-interface previewing, histograms, and color readouts) contains the same linearized region at low levels that sRGB does (at an input value existing 5.767 EV below maximum input):

.

From quoted text attributed by Sean McCormack to Adobe's Jeff Schewe:

Lightroom (and Camera Raw) uses a "working space" (meaning the processing
color space) of Pro Photo chomaticities (colors) and a linear gamma (1.0 gamma).
Martin is correct to call LR's working space as linear, but (and this is
where it gets confusing), "Melissa RGB" (the color space coined by Mark
Hamburg) isn't the processing space of LR/CR but the display space in Develop.
Melissa RGB does indeed have the Pro Photo chomaticities but the gamma is
actually that of sRGB and the ONLY place where Melissa RGB is used is for
the Develop histogram and the color readouts.
So, Lightroom's internal processing space is ProPhoto RGB in a linear gamma
(1.0), but Melissa RGB is ProPhoto RGB with an sRGB tone curve. Also note
that the sRGB tone curve is not a simple gamma curve but is a tweaked curve
based on gamma 2.2 but with the toe adjusted.
Jeff Schewe

- Sean Mccormack, 11 May 2008, 1:55 am: http://www.lightroomforums.net/showthread.php?1758-LR-ProPhotoRGB-Gamma-1-8-and-monitor-calibration&s=5ff4347babf64107e62cd96b95f60288

.

... unlike Adobe RGB (which does not utilize any low-level linearized region at all), and ProPhoto RGB (which by definition does at an input value existing 7.105 EV below maximum input):

http://en.wikipedia.org/wiki/ProPhoto_RGB_color_space

... and which is stated here by Eric Chan to precisely comport with that ProPhoto RGB specification, but has been measured by Bill Janes using Imatest to appear to not comport:

http://forums.adobe.com/message/4895109

While it is the case that the perceivable range of human vision when viewing preview displays may be limited to around a 100:1 ratio or so (around 6.64 EV), it seems that the use of the sRGB low-level linearized region (at an input value existing 5.767 EV below maximum input) in Adobe Melissa RGB previews appears to provide something of an over-optimistic picture of image-noise that exists in the lowest (around) 1 EV of perceptability.

Thus, if and when the user happily renders a previewed and processed image in either Adobe RGB 1998 or ProPhoto RGB (particularly as it was measured when implemented in ACR 7.2 by Bill Janes using Imatest) color-spaces, they will find that "Melissa" has (at least to some extent) glossed-over and "fibbed" to them regarding the amount of image-noise present in such images (when those images are presented in either Adobe RGB 1998 or ProPhoto RGB color-spaces).

They will also discover that the numerical values of RGB color readouts at low levels are erroneous.

The only apparent work-around would be to use sRGB color-space as the working color-space (if using Adobe Camera RAW, whereas Lightroom users are not afforded such color-space options).

DM ...

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gollywop
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Re: Does Melissa "Gloss Over" Image Noise ?
In reply to Detail Man, Apr 27, 2013

Detail Man wrote:

They will also discover that the numerical values of RGB color readouts at low levels are erroneous.

The only apparent work-around would be to use sRGB color-space as the working color-space (if using Adobe Camera RAW, whereas Lightroom users are not afforded such color-space options).

As I understand it, Melisa is essentially ProPhoto RGB with an sRGB gamma, but it is not sRGB.  It's also not clear in what sense the RGB color readouts at low levels are "erroneous."  They are what they are, and as long as they are converted meaningfully into the output space, it doesn't make too much difference how they're used as a working space.  I would assume that the ProPhoto RGB output space is legitimately ProPhoto RGB.

As to using sRGB as a work-around, I wouldn't want to limit myself to that in many circumstances.

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Detail Man
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Re: Does Melissa "Gloss Over" Image Noise ?
In reply to gollywop, Apr 27, 2013

gollywop wrote:

Detail Man wrote:

They will also discover that the numerical values of RGB color readouts at low levels are erroneous.

The only apparent work-around would be to use sRGB color-space as the working color-space (if using Adobe Camera RAW, whereas Lightroom users are not afforded such color-space options).

As I understand it, Melisa is essentially ProPhoto RGB with an sRGB gamma, but it is not sRGB.

Granted. All that has been stated is that Melissa RGB uses sRGB's gamma-correction function.

It's also not clear in what sense the RGB color readouts at low levels are "erroneous."

Because they (according to Adobe's Jeff Schewe) report tone-level values within Melissa RGB's linearized low-level region that do not accurately reflect ProPhoto RGB or Adobe RGB values ...

They are what they are, and as long as they are converted meaningfully into the output space, it doesn't make too much difference how they're used as a working space.

But that is precisiely the point being made - that the "Melissa" preview display, histograms, and color values reflect sRGB (tone-level) values only - and do not reflect ProPhoto RGB or Adobe RGB.

I would assume that the ProPhoto RGB output space is legitimately ProPhoto RGB.

In terms of color-gamut, yes. In terms of preview appearance, histograms, and color values, no.

As to using sRGB as a work-around, I wouldn't want to limit myself to that in many circumstances.

Who would ? That is my point.

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gollywop
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Re: Does Melissa "Gloss Over" Image Noise ?
In reply to Detail Man, Apr 27, 2013

Detail Man wrote:

gollywop wrote:

They are what they are, and as long as they are converted meaningfully into the output space, it doesn't make too much difference how they're used as a working space.

But that is precisiely the point being made - that the "Melissa" preview display, histograms, and color values reflect sRGB (tone-level) values only - and do not reflect ProPhoto RGB or Adobe RGB.

I would assume that the ProPhoto RGB output space is legitimately ProPhoto RGB.

In terms of color-gamut, yes. In terms of preview appearance, histograms, and color values, no.

But, isn't this only as a working space?  If so, that's not great, but it's not the same as saying that the conversion on "export" is not to a proper ProPhoto RGB output space.  Is that what you're saying?  As far as I know, Melissa is not used as an output space.

As to using sRGB as a work-around, I wouldn't want to limit myself to that in many circumstances.

Who would ? That is my point.

understood.

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Detail Man
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Re: Does Melissa "Gloss Over" Image Noise ?
In reply to gollywop, Apr 27, 2013

gollywop wrote:

Detail Man wrote:

gollywop wrote:

They are what they are, and as long as they are converted meaningfully into the output space, it doesn't make too much difference how they're used as a working space.

But that is precisiely the point being made - that the "Melissa" preview display, histograms, and color values reflect sRGB (tone-level) values only - and do not reflect ProPhoto RGB or Adobe RGB.

I would assume that the ProPhoto RGB output space is legitimately ProPhoto RGB.

In terms of color-gamut, yes. In terms of preview appearance, histograms, and color values, no.

But, isn't this only as a working space?  If so, that's not great, but it's not the same as saying that the conversion on "export" is not to a proper ProPhoto RGB output space.  Is that what you're saying?

What I am saying is that the Adobe CR and LR preview displays, histograms, and color value readouts (which are provided using "Melissa RGB") do not (within the linearized low-level region of sRGB and Melissa RGB) accurately correspond (in terms of RGB tone-levels) to what will actually exist if/when the in-process image is then rendered into ProPhoto RGB or Adobe RGB 1998 (but not sRGB).

The failure to accurately preview and report low-level signal and image-noise seems rather undesirable as a characteristic - because it provides an overly optimistic preview of existing image-noise levels.

As to using sRGB as a work-around, I wouldn't want to limit myself to that in many circumstances.

Who would ? That is my point.

understood.

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gollywop
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Re: Does Melissa "Gloss Over" Image Noise ?
In reply to Detail Man, Apr 27, 2013

Detail Man wrote:

gollywop wrote:

Detail Man wrote:

gollywop wrote:

They are what they are, and as long as they are converted meaningfully into the output space, it doesn't make too much difference how they're used as a working space.

But that is precisiely the point being made - that the "Melissa" preview display, histograms, and color values reflect sRGB (tone-level) values only - and do not reflect ProPhoto RGB or Adobe RGB.

I would assume that the ProPhoto RGB output space is legitimately ProPhoto RGB.

In terms of color-gamut, yes. In terms of preview appearance, histograms, and color values, no.

But, isn't this only as a working space?  If so, that's not great, but it's not the same as saying that the conversion on "export" is not to a proper ProPhoto RGB output space.  Is that what you're saying?

What I am saying is that the Adobe CR and LR preview displays, histograms, and color value readouts (which are provided using "Melissa RGB") do not (within the linearized low-level region of sRGB and Melissa RGB) accurately correspond (in terms of RGB tone-levels) to what will actually exist if/when the in-process image is then rendered into ProPhoto RGB or Adobe RGB 1998 (but not sRGB).

That could very well be the case.  I'm not sure why they would be doing that.  It is clear that the monitor rendering and histograms would have to be "gamma-ed" from the underlying linearized ProPhoto RGB, but it's not clear why it shouldn't properly reflect that working space.  I can't say that the issue has ever caused me any particular problems -- but that's really beside the point.  It would be an even worse situation if the output spaces were not accurate, but I don't believe that's the case.

Meanwhile, I get the feeling that ACR, for all the time it has been with us, is still trying to get its feet on the ground.  But they do seem to be making progress.  The current version is a far cry better than what was around even one version past.

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gollywop
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Re: New article on color management
In reply to Detail Man, Apr 27, 2013

Detail Man wrote:

gollywop wrote:

For better or for worse, I have just published a new article: Color Management - a Walkthrough. It can be found at

http://www.dpreview.com/articles/7270088913/color-management-a-walkthrough

So I reiterate. You describe a situation:

You've just taken a shot of a fire engine, and, behind the scenes, it is captured in the raw data. But you want an OOC jpeg to show Junior. ...

Who the hell is Junior ?

By the way, do you like it better now?

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gollywop

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Detail Man
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Re: Does Melissa "Gloss Over" Image Noise ?
In reply to gollywop, Apr 27, 2013

gollywop wrote:

Detail Man wrote:

gollywop wrote:

Detail Man wrote:

gollywop wrote:

They are what they are, and as long as they are converted meaningfully into the output space, it doesn't make too much difference how they're used as a working space.

But that is precisiely the point being made - that the "Melissa" preview display, histograms, and color values reflect sRGB (tone-level) values only - and do not reflect ProPhoto RGB or Adobe RGB.

I would assume that the ProPhoto RGB output space is legitimately ProPhoto RGB.

In terms of color-gamut, yes. In terms of preview appearance, histograms, and color values, no.

But, isn't this only as a working space?  If so, that's not great, but it's not the same as saying that the conversion on "export" is not to a proper ProPhoto RGB output space.  Is that what you're saying?

What I am saying is that the Adobe CR and LR preview displays, histograms, and color value readouts (which are provided using "Melissa RGB") do not (within the linearized low-level region of sRGB and Melissa RGB) accurately correspond (in terms of RGB tone-levels) to what will actually exist if/when the in-process image is then rendered into ProPhoto RGB or Adobe RGB 1998 (but not sRGB).

That could very well be the case.  I'm not sure why they would be doing that.

Clearly, it has involved a conscious decision on Adobe's part to specifically proceed in that manner.

It is clear that the monitor rendering and histograms would have to be "gamma-ed" from the underlying linearized ProPhoto RGB, but it's not clear why it shouldn't properly reflect that working space.

Probably so that the preview displays would appear to have a consistency in appearance regardless of the chosen working (and the chosen output) color-spaces (in the case of CR, where the user does have a choice of working color-space, that is). Thus, they chose the lowest common denominator of sRGB (which also happens to provide the "rosiest" view where it comes to low-level image-noise).

The LR interface was likely kept the same in order to maintain operational consistency with CR.

What would obviously make the most sense would be to apply the particular gamma-correction that corresponds to the user's chosen output color-space, so that what the user sees accurately represents what the user is actually going to get upon output. The histogram displays and reported RGB tone-level values are arguably a less critical (though not at all undesirable) thing to get right where it comes to what represents the lowest typically visible EV on the preview display screen.

They (probably) have shied away from that because users might likely not be aware of that particular operational functionality, and then become frustrated when they (later) realize that their (albeit accurate) previewing depends upon "developing" for a given output color-space. Probably a rigor that they may (reasonably) assume surpasses the desire of (most) users ?

I can't say that the issue has ever caused me any particular problems -- but that's really beside the point.

I would not say so. If it is not something that (most) users notice, then why should they care ?

It would be an even worse situation if the output spaces were not accurate, but I don't believe that's the case.

Right. But the preview display appearance, histograms, and RGB tone-values are not accurate.

Meanwhile, I get the feeling that ACR, for all the time it has been with us, is still trying to get its feet on the ground.  But they do seem to be making progress.  The current version is a far cry better than what was around even one version past.

Adobe being such a new, small company (in sales and personnel), they do deserve our patience.

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Jeff Schewe
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Re: Does Melissa "Gloss Over" Image Noise ?
In reply to Detail Man, Apr 27, 2013

Detail Man wrote:

It's also not clear in what sense the RGB color readouts at low levels are "erroneous."

Because they (according to Adobe's Jeff Schewe) report tone-level values within Melissa RGB's linearized low-level region that do not accurately reflect ProPhoto RGB or Adobe RGB values ...

Just to be clear, Melissa RGB is ONLY used for the Histogram display and the color readouts...not you image preview display. The image preview goes from raw>ProPhoto RGB Linear>Display profile. The sRGB tone curve has no impact on your image preview display. So, the only impact of the sRGB tone curve would be color readouts in 0-100% (which don't relate to 0-255) and the way the levels are displayed on the histogram.

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Jeff Schewe

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