Color Choosing Paradox, also Warmer vs Cooler

[briend (Brien Dieterle)]

@Elle

When you talk about “colorants” I’m not sure what you mean. To me “colorants” usually refers to the xyY/XYZ values that define a given RGB matrix color space.

I’m guessing that you are using the term “colorants” as the RGB equivalent of picking real-world paint pigments that will be mixed together to make various colors (which is basically what an RGB matrix profile is, a set of colorants, plus black and white, that can be mixed together to make various colors)? So one colorant combined with mixing with black and white would result in a monotone image? One or more colorants might be specified to define a palette? Or (and/or?) is there a “spectral rendering” meaning?

I think we have the same meaning. When I say “spectral” I just mean a whole bunch of colorants (CIE xy coordinates). If I pick a “real world” blue paint, ignoring a lot of other factors I think I’m really just picking a whole bunch of colorants at various intensities (xyYs). In RGB I just have my three colorants at specific xy coordinates. I’m starting to think RGB exists as just three colorants for no other reason than because it was (barely) good enough and saved on bandwidth and cpu, etc.

@Elle

Whereas on the HS"X" color wheels, the “meaning” of any given hue varies from one RGB color space to the next, depending on the relative locations of the colorants.

Doesn’t that only apply for non-color managed applications? That is, HS"X" Hue 0 means the same exact perceived Red in sRGB as it does in any other color space. Without CM we’re totally lost no matter what

@Elle

A second reason why I like LCH for choosing colors is that the “Chroma” of a given RGB color as located on the LCH color wheel is constant, always the same, regardless of what RGB color space the painting or photograph might be painted/edited in

This is pretty neat. I wonder if the same could be achieved by always using the humongous ACES colorspace. As long as you always convert everything to ACES, your HS"X" values would always be on the same scale, no? The problem would be you’d always be using a tiny portion of your interface, but “10% chroma” would have an unchanging meaning. I do find it a bit odd to use color selectors that show you such a huge gamut though. In my example earlier with my tiny slice of pie, I really wanted a way to “zoom in” on that pie slice to make it easier to use. I’m playing around with the GIMP LCH gui, is there a way to just “chop off” or zoom in, or somehow limit the scale to your selected colorspace?

@Elle

The various HS"X" calculations for Saturation vary from one HS"X" color space to another

Very true, but I think each “flavor” is trying to serve a different purpose. The way LCH and HCY (tries to ) keep luma constant seems pretty useful, but maybe HSL or HSV is more useful for some other purpose.

@Elle

and the “same” HS"X" values for a given color in the sRGB color space doesn’t match the HS"X" value for that same color in, for example, Rec.2020

I still don’t really see the problem, as long as you exchange the color space information along with the HSV numbers. When you say “5,20,100” it doesn’t mean anything, even with LCH, unless you also say “those numbers are LCH numbers” Having the values scale with your current color space (likely your display) is probably pretty useful, honestly. You would know 50% is right in the middle of what you can work with, and leave some headroom and bottom end. An absolute number is also useful, but I’m starting to think having 3 or 4 color dialogs open at once might be best, maybe HCY, RGB, and LCH.

@Elle

I spent some time looking at the “Colors/Saturation” code and experimenting with the two ways to increase Chroma in an image, and wrote up the results in a tutorial:

Interesting! Thanks for using my image, actually, feel free to use the actual picture if you’d like. Full size is over here: https://flic.kr/p/Xqa4vZ

@Elle

Like yourself with the straight-line gamut map, I also use straight lines to define a restricted color palette. But my straight lines are drawn on the LCH color wheel to choose a range of hues, a subset of all possible hues.

I think it’d be cool if we could take that limited gamut shape, whatever it may be, and map that to a new color wheel. Makes sense right? The RGB triangle is mapped to a wheel, why not any arbitrary colorants?

@Elle

You know how sometimes the sky looks yellow at the horizon?

That is funny. It’s hard to know what’s real, what’s in the mind, or what is an effect from the camera, etc. So frustrating. I recall trying to study the gradient in the sky just after the sun set. So I knew the sky would get darker as I looked higher and higher, but what I didn’t expect was that for every few degrees I tilted my head back, my vision “reset” and re-calibrated to the new gradient. So, it barely seemed to get any darker!

@Elle

Here is a question: if your portrait is printed and put on a blue wall next to a north-facing window, or a yellow wall next to a south-facing window, how would the surroundings affect the perceived color of the jeans?

I think as long as you included the background in the painting, the effect would remain more or less on the blue wall, but if you cut the figure out of the painting I’m sure that would destroy the effect. The yellow wall… I think that would enhance the effect, maybe. Another fun thing to try would be to create a synthetic ICC profile using the gamut mask or the plot you generated, and set the white point to the center of that triangle. Then load it in gimp w/ that profile assigned and see what happens when you convert it to sRGB. I really have no idea. It’d be interested to adjust saturation, etc, and then convert back to the synthetic profile. I have no idea if that is even a coherent thought