Hmm, I'm not sure that my use of CIECAM to make a night scene from a day scene is all that special. CIECAM is about changes in color appearance, and the way we perceive colors changes as the light level changes. The RT CIECAM02 Image Adjustment options seem well-suited for emulating such changes, but not until the Scene and Viewing Conditions are modified to not affect the image appearance all by themselves.
My apology for stating the obvious, but one thing that changes how we perceive colors is when viewing the same scene under different "colors of light", which is addressed by chromatic adaptation. Currently the RT CIECAM02 chromatic adaptation code is specialized to handle one very specific instance of chromatic adaptation, which is how the colors need to change to make the colors "look the same" if the white point of the intended display device differs from the white point of the device on which the image is being edited.
But what if the user wants to change the "color of light" in the image itself as part of an editing workflow, completely apart from how the image will look as displayed on some hypothetical future display device?
I put an example of using the CIECAM02 module to "change the color of the light in the image" on my website, and my first question is does my procedure even make sense? And if not, why not? and is there a better way to use CIECAM02 to change the color of the light in the image?
I think the particular example I posted looks pretty good, but maybe this is by pure chance:
Using (misusing?) RawTherapee's CIECAM02 to capture the color of the light
Here's a photograph of a lamp lit only by the lamp's tungsten bulb, shot raw, opened with RT, and custom white-balanced on the PVC plastic shown in the image, using "Colors/White Balance":
My actual goal for the image wasn't to "white balance away" the tungsten color of light, but instead keep the ight looking like tungsten light. A common approach to "keeping the colors" is to use Daylight white balance instead of custom white balancing on a neutral white or gray object. Daylight white balance produces the following, which compared to the actual "real life" lamp is too orange and too saturated:
Keeping the custom white balance and using the CIECAM02 module to chromatically adapt the color of the light back to Tungsten (assuming my procedure actually makes sense) produces this (imho nicer, and definitely much closer to reality) rendition of tungsten light:
It would be nice if instead of just "Tungsten", there was an option to dial in specific Temperature/Tint combinations as real-life light sources seldom exactly match presets.
I want to experiment further with different scenes and different source and destination "colors of light". But this is made a bit difficult because currently the destination "color of light" is limited to just a few options, and changing this color requires accessing the Color Management options and then reloading the image.
I did try changing the color of the light in the test image from tungsten to D65, but lacking a D65 light bulb for the lamp, I'm not sure how close the result might be to what would be seen in reality, and I wasn't sure of what combination of CA models and display device color temperatures to use (I tried several other combinations, but the colors came out considerably more and probably too saturated):
It might be nice if the current RT CIECAM02 chromatic adaptation options were enhanced to include user control over the source and destination "color of light" - not just for an eventual display device that's different from the display device used for editing - but also for changing colors in the actual image itself. I've had the relevant code files open in the geany code editor for the last week, trying to suss out the logic, but I'm not very good at reading c++ code.