New article on color management

Started Apr 26, 2013 | Discussions thread
Detail Man
Detail Man Forum Pro • Posts: 16,710
Re: Does Melissa "Gloss Over" Image Noise ?

Jeff Schewe wrote:

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.

My apologies, Jeff. I see now that I missed the significance of your statement (below):

... the ONLY place where Melissa RGB is used is for the Develop histogram and the color readouts.

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.

So, the gamma-correction function that is applied to the Adobe CR/LR preview display-screen corresponds to whatever particular color-space that the OS recognized "system display profile" is ?

If that is the case, then it would seem that a system having an sRGB color-space "system display profile" would not be able to accurately reflect the gamma-correction function that results in cases when the output images are rendered in ProPhoto RGB or Adobe RGB 1998 color-spaces ?

It seems that it would be useful for the preview-display to have the operational capacity to reflect the low-level gamma-correction functionality of those other (and differing) color-spaces - in that user's rely upon judgments surrounding image-noise levels in deciding upon the settings of various processor/editor controls.


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:

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