@afre - Yes, my first question is how to get as close as possible to “no change”. I’m not all that interested in dealing with what the image will look like as displayed on some “other device” because at the point where I want to use the CIECAM02 module, I’m still editing the image.
I like to understand the tools that I use in my digital darkroom. The RT CIECAM02 module seems pretty powerful, and I’d like to understand something of what’s really happening when using this module, rather than just twiddle dials and hope that eventually I see something that I like.
As part of figuring out how the the RT CIECAM02 module works, my first goal is to figure out what specific settings for the “Scene Conditions”, “Viewing Conditions”, and “Colors/White Balance” result in “no change at all”, or at least minimal change, before I actually start using the algorithms provided under “Image Adjustments”. Here’s what I’ve found so far:
There are three parts to the RT CIECAM02 module:
- Scene Conditions
- Image Adjustment
- Viewing Conditions
The CIECAM02 module does interact with the White Balance set on the Color tab.
Whether for a raw file or an already processed file from disk, these CIECAM02 settings seem to produce minimal change:
A. Under “Preferences/Color Management” set:
B. Set the Colors/White Balance to Temperature 6490/Tint 1.002 and leave the B/R equalizer at 1.000. Of course this won’t be the correct White Balance for most raw files.
C. Activate the CIECAM02 module and make these changes:
- Scene Conditions:
* Set CAT02 adaptation to 100%
* Don't check "Dark surround" (use an appropriately lighter theme, which RT doesn't currently seem to provide)
* Choose WP Model: WB[RT+CAT02]+[output]
* Move "Scene luminosity" to maximum value: 16384.000
Image Adjustments: Of course don’t make any image adjustments.
* Viewing luminosity: Move to maximum value: 1000.0
* Surround: Average
* My test image has a small color gamut and Gamut control seemed to make no difference. For the raw file, under the Raw tab I used the Hot/Dead pixel filters, so I wouldn't expect the Hot/bad pixel filter to do anything, and it didn't seem to.
FWIW, at least with the above settings, the Color tab Input, Working and Output Profiles seem to make no difference. This is true regardless of whether the Scene Conditions degree of adaptation is 0% or 100%. So the “ICC profile” variables probably can be eliminated as affecting the workings of the CIECAM02 module, at least as far as the Scene and Viewing Conditions go.
Question 1: The “minimal changes” produced by activating the CIECAM02 module with the above settings almost looks “as if” a small amount of a really good (artifact-free) sharpening algorithm had been applied or maybe “as if” there were more micro-contrast. The LCH Lightness and Chroma are slightly higher (measured in GIMP using the LCH color picker), and there are very small LCH Hue changes.
Where do these nice “minimal changes” come from?
Question 2: If the Scene Conditions degree of adaptation is set to 0%, then the image looks very different with and without the CIECAM02 module being activated: Moving the degree of adaptation slider to 0 produces a cyan color cast, even if a conversion to black and white is done using the RT “Colors/Black-and-White module”.
Where does this cyan color cast come from? Are source and destination white points somehow different? I keep coming back to this question. Or is there something else going on in the CIECAM02 module that produces the cyan color cast when the adaptation slider is moved to 0%?