In ICC profile color managed editing applications, your eyes are presumed 100% chromatically adapted to your monitor. This assumption might be partially or even completely false given factors like how much of your field of view the monitor fills, the color of other light sources in your field of view, and so on. But for the sake of argument, let’s assume your eyes are adapted to “monitor white”.
Once your eyes have adapted to “monitor white”, that particular white point is a given, and ICC profile color management takes care of “adapting” the colors in the image from D50 (the V2/V4 profile illuminant) to the white point of the monitor profile.
When processing a raw file (painting isn’t photography, but the same principles apply here), the point of white balancing the image is to make it look like it was shot under the same illuminant as the camera input ICC profile, which for V2/V4 color management is D50. What your eyes actually see on the screen (assuming your eyes really are adapted to “monitor white”) are “the same colors except adapted to monitor white”.
So a technically speaking, a properly white balanced image doesn’t look warm or cool. It looks neutral. Even if the image is mostly just one color, say a close-up of a red apple, if the image is technically correctly white balanced, you don’t think, “well, the light on the apple must be warm because the apple is red”. You just assume it’s a red apple.
But what if you really don’t want the “color of the light” in a photograph to be “neutral”, to be the same as the color of white that your eyes are adapted to? What if what you really want to do is capture the color of the light source illuminating the scene, instead of white balance it away? The usual course of action in this circumstance is to use Daylight white balance; another option is to use Ciecam.
In the photograph below of a self-lit candle flame:
- “a” shows the result of “capturing the color of the light” by using Daylight white balance. "
- “b” shows the result of “white balancing the color of the light source away to make a neutral rendition neither warm nor cool” by white balancing on the light source, which in this case the light source is the flame itself.
- “c” shows the result of playing with RT Ciecam sliders to get something less extreme than “a” or “b”, something closer to what I remember seeing when I took the image - less orange and more yellow than the result of using Daylight white balance.
- “d” is just “a” converted to black and white.
OK, I made four “final renditions” of the candle flame, using three different white balances, with the fourth verion not using any white balance at all. Instead it’s a “toned” black and white image. The next image shows two things: the tonality for all four final renditions, and “the color of early morning snow” taken from a photograph of early morning snow - this was quite a bit before the sun came, so no “rosy dawn light”, in fact the sky was completely overcast.
I took the “early morning snow” photograph in the early morning (duh!) and then immediately it processed in RawTherapee, setting the white balance to make the color of the snow on my monitor screen match the color of the snow just outside the window near my monitor. (In reality the blue should probably be a very slight bit more green - when I processed the image my monitor’s “monitor white” was a bit on the green side all by itself - after recalibrating and reprofiling several of my more recent images could use a bit of tweaking back towards green. Sigh.)
OK, here are the four final versions of the candle image:
1 In my opinion, using daylight white balance really didn’t make the finished image look like it was lit by actual candle light, not at all. But this rendition represents an attempt to deliberately convey “a very warm light source (the candle flame itself) is illuminating the scene”.
2 White balancing on the candle flame also didn’t make the finished image look like actual candle light. But it did recover the actual color of the candle wax under “normal daylight” lighting. The candle wax is a sickly shade of purple-blue, one of the ugliest colors in the paint box (personal opinion, labeled as such). This represents a successful attempt to give the image a technically correct white balance. The represented light source is neither warm nor cool, but instead neutral (which looks really weird when the actual light source is the candle flame in the middle of the image).
3 Using RT’s Ciecam module to white balance the candle did fairly well capture what I saw when I photographed the candle flame, including the rather unappetizing “purple-blue wax as lit by the yellow candle flame”. This also is an attempt to deliberately convey “this is very warm light”.
4 Image number 4 shows the result of using “the color of early morning snow” to add color to the black and white version of the final image. This is not an attempt to convey “this scene is illuminated by a very cool light source”. Instead it’s merely an artistic decision to tone a black and white image using a particular blue color. The represented “color of the light illuminating the scene” is neither warm nor cool but rather is just “monitor white”. Or rather, there is no “color of the light” illuminating the scene. It’s just a monotone image that happens to be toned using blue.
OK. Back to paintings. I think it’s fair to say that some paintings represent “neutral light”. Some represent attempts to capture the various colors of ambient natural light sources (Monet’s haystacks). Some paintings use colors for reasons that have very little to do with capturing “colors of light” or “neutral light”, but instead use colors in other ways, for other reasons.
Anyway, for the longest time I assumed that “adapting to a light source” such as direct sunlight or deep shade or the light on an overcast day or candle light, meant that we stop noticing that the light actually has a color, that we only notice “warm or cool light” when the light source is actually changing. But in reality, I’m fairly sure most of us continue noticing the color of the light, at least for many light sources. Leastways, I don’t ever seem to “forget” that on an overcast snowy day (like today is here in Central New York), the light is a cold blue color. And likewise, warm candle light at the dinner table always looks warm even if it’s the only light source.
So I’m guessing that “adapted” really just means we can still make judgements like “the red apple is still red and the yellow banana is still yellow”, even when the color of the light changes fairly drastically across the spectrum from warmest to coolest natural light.
I suppose this implies that somewhere between the cold light of deep shade or an overcast snowy day and the warm light of a candle-lit dinner, there might be “the color of light” most people think of as “neutral” - is there such a thing as "the color of light that everyone or most people think is neutral, neither warm nor cold? Is that color D65 daylight (mix of sky light and direct sunlight)?
Anyway, “warmer and cooler” requires a context. The context is obvious if the goal is representing a particular color of light illuminating a scene. In other contexts, I suppose it just means moving a color’s hue closer to or farther away from some pre-chosen “warmest” and “coolest” colors in the painting’s color palette.
Regarding @briend 's painting, I would guess that there really isn’t a represented color of light illuminating the scene. I say this because the shadows under the chair don’t seem to be using cooler hues than the highlight areas that seem to be illuminated by a presumed directional light source.
So “warmer” for this painting would mean means closer to whatever color is intended by the artist to be the warmest color. Somewhere on the handprint website one of the pages talks about how for some artists yellow is “the warmest” color, and for other artists it might be orange or red. But “warmest color” in @briend 's painting doesn’t seem to mean an “attempted representation of an actual light source, different from some presumed neutral light source”.
I’m sure there is some fuzzy thinking above. Comments, corrections, and insights are very welcome! @jdc - is my explanation of what “chromatically adapted” does and doesn’t mean at least somewhat close to being more or less correct?
but if/when there’s new code in a branch implementing what you just described, I’d be happy to compile and experiment with whatever’s changed.
. But here are a few preliminary questions, and I’m sure there are a bunch of questions that could be added to the list:
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