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Hearing has a few quirks too:

- When we measure sound pressure, we measure it in log (so, every 3dB is a doubling in sound pressure), but our hearing perceives this as a linear scale. If you make a linear volume slide, the upper part will seem as if it barely does anything.

- The lower the volume, the less perceivable upper and lower ranges are compared to the midrange. This is what "loudness" intends to fix, although poor implementations have made many people assume it is a V-curve button. A proper loudness implementation will lessen its impact as volume increases, completely petering off somewhere around 33% of maximum volume.

- For the most "natural" perceived sound, you don't try to get as flat a frequency response as possible but instead aim for a Harman curve.

- Bass frequencies (<110Hz, depending on who you ask) are omnidirectional, which means we cannot accurately perceive which direction the sound is coming from. Subwoofers exploit this fact, making it seem as if deep rich bass is coming from your puny soundbar and not the sub hidden behind the couch :).

> evaluate relative brightnesses between art assets, and improve overall game readability

The method in Color2Gray is trying to enhance salience, but the paper does a good job of comparing the problems (including red / blue examples in particular).

Like other commenters, I think oklab would look better than CIELAB on the example given in the OP. https://bottosson.github.io/posts/oklab/#comparison-with-oth... and the Munsell data below it show it to be a lot more uniform than either CIELAB or CIELUV.

https://keithjgrant.com/posts/2023/04/its-time-to-learn-oklc...

This has issues. When you go from a dark space to a bright space, the eye's iris stops down. But not instantaneously. It takes a second or two. This can be simulated. Cyberpunk 2077 does this. Go from a dark place in the game to bright sunlight and, for a moment, the screen becomes blinding, then adjusts.

In the other direction, go into a dark space, and it's dark at first, then seems to lighten up after a while. Dark adaptation is slower then light adaptation.

Tone mapping is not just an intensity adjustment. It has to compensate for the color space intensity problems the OP mentions. Human eyes are not equally sensitive to the primary colors.

Some visually impaired people hate this kind of adjustment, it turns out.

Here's a clip from Cyberpunk 2077.[2] Watch what happens to screen brightness as the car goes into the tunnel and then emerges into daylight.

[1] https://en.wikipedia.org/wiki/Tone_mapping

[2] https://youtu.be/aWlX793ACUY?t=145

Accurate color reproduction on uncalibrated consumer devices is just wishful thinking and will not be fixed in the forseeable future.

So unless you work in a color controlled and calibrated environment it's hard to make any reliable statements about perception.

I simply would not worry too much about optimizing perceptual color spaces at this point.

https://library.imaging.org/cic/articles/31/1/36

A benefit of doing it this way is you account for color blindness and accessibility e.g. all colors at L=50 will have the same WCAG contrast ratio against all colors at L=25. This helps when finding colors with the contrast you want.

Related, I'm working on a color palette editor based around creating accessible palettes where I use the HSLuv color space which has the above property:

https://www.inclusivecolors.com/

You can try things like maxing out the saturation of each swatch to see how some some hues get more bold looking at the same lightness (the Helmholtz-Kohlrausch effect mentioned in the article I think). You can also explore examples of open source palettes (Tailwind, IBM Carbon, USWDS), where it's interesting to compare how they vary their saturation and lightness curves per swatch e.g. red-700 and green-700 in Tailwind v3 have different lightnesses but are the same in IBM Carbon (the "Contrast > View colors by luminance only" option is interesting to see this).

Y = 0.299 * R + 0.587 * G + 0.114 * B

A Better Default Colormap for Matplotlib | SciPy 2015 | Nathaniel Smith and Stéfan van der Walt https://www.youtube.com/watch?v=xAoljeRJ3lU

It was actually quite shocking how much more sense most color choices in art and design made to me, which was a much bigger reason for me to keep wearing the glasses than being able to distinguish red, green and brown better than before. The world just looks "more balanced" color-wise with them.

While it was very obvious early on in my life that I experienced most green, red and brown colors as ambiguously the same (I did not know peanut butter was not green until my early thirties), the fact that there also were differences in perceptual brightness had stayed completely under the radar.

¹ And yes, these lenses do work, at least for me. They're not as scummy as enchroma or other colorblind-"correcting" lenses, for starters you can only buy them after trying them out in person with an optometrist, who tests which type of correction you need at which strength. Ironically their website is a broken mess that looks untrustworthy[0]. And their list of scientific publications doesn't even show up on Google Scholar, so they probably have near-zero citations[1]. But the lenses work great for me.)

[0] https://www.colorlitelens.com/

[1] https://www.colorlitelens.com/color-blindness-correction-inf...

OSA-UCS takes the Helmholtz-Kohlrausch effect into consideration.

#ff0000 is, in terms of brightness, pretty dark compared to #ffffff yet there is a way it seems to "pop out" psychology. It is unusual for something red to really be the brightest color in a natural scene unless the red is something self-luminous like an LED in a dark night.

https://youtu.be/fv-wlo8yVhk