Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Issues with color spaces and perceptual brightness

johnaustin.io

Post reply on HN
Print view View original

51–60 of 67 posts

Re: Issues with color spaces and perceptual brightness

#51

Post by andrewla »

hatthew wrote: post #47
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

I think this is likely, but easily validated -- you'd probably see a couple of clusters or some latent variables, but the raw data would still likely be useful for getting average response characteristics.

Re: Issues with color spaces and perceptual brightness

#52

Post by vanderZwan »

PaulHoule wrote: post #35

There's the strange phenomenon that people like to say "bright red" as much as it is an oxymoron. #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.

... have you ever checked if you might be colorblind? Speaking as someone with protanomaly who used to think "bright red" wasn't bright until he got functioning colorblindness-correcting lenses (as I explained in a comment elsewhere in this discussion).

[0] https://news.ycombinator.com/item?id=42737700

Re: Issues with color spaces and perceptual brightness

#53

Post by boulos »

Amy Gooch's Color2Gray and various follow-on work has better coverage of the OP's actual goal:

> 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.

Re: Issues with color spaces and perceptual brightness

#54

Post by 01HNNWZ0MV43FF »

lieks wrote: post #27
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 have a theory that this generalizes to some extent. Pitch perception is also logarithmic; an octave in music is a 2x ratio. Memory is sort of logarithmic; you'd say a thing happened 1-2 days ago or 1-2 years ago, but not 340-341 days ago. Same with age; someone being 10 years older than you is a much bigger deal when you're 10 than when you're 80.

It does! https://en.wikipedia.org/wiki/Stevens's_power_law

> Stevens' power law is an empirical relationship in psychophysics between an increased intensity or strength in a physical stimulus and the perceived magnitude increase in the sensation created by the stimulus

Re: Issues with color spaces and perceptual brightness

#55

Post by tshaddox »

Animats wrote: post #8

This is part of "tone mapping"[1] in high dynamic range rendering. The idea is that pixels are computed with a much larger range of values than screens can display. 16 bits per color per pixel, or even a floating point value. Then, to generate the displayed image, there's a final step where the pixel values are run through a perceptual transformation to map them into 8 bit RGB (or more, if the hardware is is availabl…

> 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.

Or, very famously 20 years ago in Half-Life 2: Lost Coast, which was released as a tech demo for HDR rendering.

Re: Issues with color spaces and perceptual brightness

#56

Post by tshaddox »

PaulHoule wrote: post #35

There's the strange phenomenon that people like to say "bright red" as much as it is an oxymoron. #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.

> 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.

Right. Just the extremely common cases where humans deliberately use red lights because of the fact that they are perceived as being very bright. Stop lights, brake lights, tail lights, emergency vehicle lights, aviation obstruction lighting, emergency flairs, emergency exit lights, etc.

Re: Issues with color spaces and perceptual brightness

#57

Post by tshaddox »

hatthew wrote: post #47
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

True, but the results would likely still be useful, particularly when choosing colors for web sites which will be displayed on the same distribution of screens.

Re: Issues with color spaces and perceptual brightness

#58

Post by dragonwriter »

PaulHoule wrote: post #35

There's the strange phenomenon that people like to say "bright red" as much as it is an oxymoron. #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.

> There's the strange phenomenon that people like to say "bright red" as much as it is an oxymoron.

It's not. Reds can be dark or bright relative to other reds, and "bright red" -- as you would expect from the way that adjectives work -- refers to a red that is bright relative to other reds.

Re: Issues with color spaces and perceptual brightness

#59

Post by dragonwriter »

tshaddox wrote: post #56
PaulHoule wrote: post #35

There's the strange phenomenon that people like to say "bright red" as much as it is an oxymoron. #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.

> 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. Right. Just the extremely common cases where humans deliberately use red lights because of the fact that they are perceived as being very bright. Stop lights, brake lights, tail lights, emergency vehicle lights, aviation obstruction lighting, emergency flairs, em…

> Just the extremely common cases where humans deliberately use red lights because of the fact that they are perceived as being very bright. Stop lights, brake lights, tail lights, emergency vehicle lights, aviation obstruction lighting, emergency flairs, emergency exit lights, etc.

Green lights have the greatest perceived brightness, and green is used as the go signal in traffic lights for that reason. Red light (1) has a common cultural association with danger stemming from its association with natural fire, (2) has the least impact on night vision because of the relative insensitivity of human eyes to it; the former is the reason it is used or things like stop/warning/etc. lights that might be used in any background lighting conditions, and the latter is the reason it is used for emergency guide lighting and signage that are likely to be used in dark background conditions especially where people would be at substantial likelihood of transitioning the illuminated area to an even darker environment (such as one without or with nonfunctional emergency lighting.)

Re: Issues with color spaces and perceptual brightness

#60

Post by Kleptine »

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...

This is an incredible reference, thanks.
Post reply on HN