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Issues with color spaces and perceptual brightness

johnaustin.io

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Re: Issues with color spaces and perceptual brightness

#41

Post by ttoinou »

jorvi wrote: post #18

I've always found these "perceptual vs absolute" things about human senses very interesting. 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 a…

    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
Its the other way around : we perceive logarithmically so we created the logarithmic decibel scale

Re: Issues with color spaces and perceptual brightness

#42

Post by mattdesl »

cccbbbaaa wrote: post #6
weinzierl wrote: post #4

"Unfortunately, I haven’t been able to find any perceptually uniform color spaces that seem to include these transformations in the final output space. If you’re aware of one, I would love to know." OSA-UCS takes the Helmholtz-Kohlrausch effect into consideration.

That, or the more recent darktable UCS: https://eng.aurelienpierre.com/2022/02/color-saturation-cont...

Although the article is intimidating, the implementation appears pretty simple and flexible. Has anyone tried using this either in the Darktable app or in their own libraries? I might like to try porting it to JS to compare it for web based color picker GUIs.

Re: Issues with color spaces and perceptual brightness

#43

Post by jorvi »

mark-r wrote: post #22
jorvi wrote: post #18

I've always found these "perceptual vs absolute" things about human senses very interesting. 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 a…

I can't remember the last time I saw a "loudness" button. My receiver from 1980 had one but my receiver from 2000 does not.

Sonos has a loudness toggle! Sadly its much too aggressive and applies even at 50% volume.

Re: Issues with color spaces and perceptual brightness

#44

Post by andrewla »

jorvi wrote: post #18

I've always found these "perceptual vs absolute" things about human senses very interesting. 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 a…

I've played around with this a little bit while trying to engineer the "perceptually loudest ringtone sound". I thought a square wave or pulsed white noise would work well, but I found that the bell-like "telephone ring" seemed perceptually louder.

I now have to read up on the Harman curve because I'm curious about this and it has a direct practical application.

Re: Issues with color spaces and perceptual brightness

#45

Post by andrewla »

It seems that this would be well-suited to a simple online test -- show a square with one color and a square inside of that with a different color, and ask the user whether the inner square is brighter (or too close to call). Aggregate this across users and assess the fit to the CEILAB or other color spaces. It seems like you could get almost all hn users to take a stab at this for a bit before they get sick of it.

Re: Issues with color spaces and perceptual brightness

#47

Post by hatthew »

andrewla wrote: post #45

It seems that this would be well-suited to a simple online test -- show a square with one color and a square inside of that with a different color, and ask the user whether the inner square is brighter (or too close to call). Aggregate this across users and assess the fit to the CEILAB or other color spaces. It seems like you could get almost all hn users to take a stab at this for a bit before they get sick of it.

precise results would depend heavily on screen calibration

Re: Issues with color spaces and perceptual brightness

#49

Post by cccbbbaaa »

mattdesl wrote: post #42
cccbbbaaa wrote: post #6

Earlier quoted context omitted.

That, or the more recent darktable UCS: https://eng.aurelienpierre.com/2022/02/color-saturation-cont...

Although the article is intimidating, the implementation appears pretty simple and flexible. Has anyone tried using this either in the Darktable app or in their own libraries? I might like to try porting it to JS to compare it for web based color picker GUIs.

This colorspace is used internally by the color balance RGB module of Darktable (and Ansel).

Re: Issues with color spaces and perceptual brightness

#50

Post by TinkersW »

viggity wrote: post #34

I once had an app that used a lot of colored bars with text labels on top of them, and I wanted a programmatic way to determine if a color should use black text or white text because R+G+B over some threshold was not working. I stumbled upon the YIQ color space where Y is the perceived luminance. Under 128 got a white text, over 128 got black text. Worked like a charm. Y = 0.299 * R + 0.587 * G + 0.114 * B

That is the standard approach, but if you try to tonemap using it, you will quickly realize it really really sucks.
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