How do our colour-blind cones achieve colour vision? • Hacker News Board

Re: How do our colour-blind cones achieve colour vision?

#11

Post by neurosphere » Tue, Feb 23, 2016, 5:07 PM UTC

pluteoid wrote: post #5

logicrook wrote: post #2

I'm always surprised to see barely high-school level science articles get on the front page. An alternative title to this article could be "how spaceless numbers achieve defining space"? Like you just have a basis, and this defines space. Mind blown. Really, how do these magnets work?

It's not even an article I'd want to present to a high school class. An RGB pixel on your monitor is not emitting red, green and blue monochromatic (single wavelength) light. Same goes for the light reflected from a CYM pigment. Metamerism is at play, just like in the "real world". The author confuses the need to choose three primaries with a requirement those primaries be monochromatic. And since when have painters…

Painters don't stick to just three pigments, but all the pigments they use CAN be created by mixing three primaries in different proportions. I'm quite sure that's the whole basis for Thomas Young's colour mixing experiments performed in the 1800s, finding that every colour we see can be made with mixtures of three lights. Any more than that is redundant. Similarly, while an RGB pixel on your monitor may not emit all single-wavelength light, it doesn't negate the validity of the statement that three single wavelengths can be used to recreate all colours visible to the human eye. I'm quite sure that some RGB pixels are indeed single wavelength, though I would love to hear from those of you who know better about this because I don't know for sure...

Re: How do our colour-blind cones achieve colour vision?

#12

Post by neurosphere » Tue, Feb 23, 2016, 5:14 PM UTC

KingMob wrote: post #10

As a former neuroscientist who studied perceptual awareness, there's lots of little things wrong with this article. 1) The RGB palette used in monitors most certainly does not span the whole gamut of human vision. Not even the wide-gamut monitors used professionally can do that yet. 2) The diagram showing each cone type's peak spectral sensitivity is a bit misleading, too. The M- and L-cones are colored red and green…

I'm the author of the article, and I'm quite happy to see a response from a neuroscientist who studied this topic in the past. I wanted to ask you about point 3, because obviously I could have made a mistake. From what I understand (and what I have studied) retinal ganglion cells computing the S vs M and S vs M+L dimensions are the critical ones underlying coding of colour information along the blue-yellow and red-green axis. The additive axis, featuring amplitude information, from what I understand primarily concerns luminosity rather than colour discrimination. Without any of the ratio information, colour discrimination would not exist. Am I wrong? Would genuinely love to hear from you on this.

Re: How do our colour-blind cones achieve colour vision?

#13

Post by logicrook » Tue, Feb 23, 2016, 5:38 PM UTC

neurosphere wrote: post #11

pluteoid wrote: post #5

Earlier quoted context omitted.

It's not even an article I'd want to present to a high school class. An RGB pixel on your monitor is not emitting red, green and blue monochromatic (single wavelength) light. Same goes for the light reflected from a CYM pigment. Metamerism is at play, just like in the "real world". The author confuses the need to choose three primaries with a requirement those primaries be monochromatic. And since when have painters…

Painters don't stick to just three pigments, but all the pigments they use CAN be created by mixing three primaries in different proportions. I'm quite sure that's the whole basis for Thomas Young's colour mixing experiments performed in the 1800s, finding that every colour we see can be made with mixtures of three lights. Any more than that is redundant. Similarly, while an RGB pixel on your monitor may not emit all…

>Painters don't stick to just three pigments, but all the pigments they use CAN be created by mixing three primaries in different proportions.

No. Paint is not light, and has physical properties that constrain what you can do with them. Some colors just don't mix well together, so you'll find recommendation on what exact type of pigment work best for specific mixes.

Re: How do our colour-blind cones achieve colour vision?

#14

Post by neurosphere » Tue, Feb 23, 2016, 6:24 PM UTC

logicrook wrote: post #13

neurosphere wrote: post #11

Earlier quoted context omitted.

Painters don't stick to just three pigments, but all the pigments they use CAN be created by mixing three primaries in different proportions. I'm quite sure that's the whole basis for Thomas Young's colour mixing experiments performed in the 1800s, finding that every colour we see can be made with mixtures of three lights. Any more than that is redundant. Similarly, while an RGB pixel on your monitor may not emit all…

>Painters don't stick to just three pigments, but all the pigments they use CAN be created by mixing three primaries in different proportions. No. Paint is not light, and has physical properties that constrain what you can do with them. Some colors just don't mix well together, so you'll find recommendation on what exact type of pigment work best for specific mixes.

Yeah, that's true, paint is subtractive, as opposed to light. But isn't it still the case that all pigments can be achieved by mixing three primaries? Whereas in light mixing the primaries are considered to be red, green, blue, in pigment mixing they are considered to be cyan, magenta, yellow. Obviously please correct me if I'm wrong (no sarcasm implied), links would be useful.

Re: How do our colour-blind cones achieve colour vision?

#15

Post by logicrook » Tue, Feb 23, 2016, 6:47 PM UTC

neurosphere wrote: post #14

logicrook wrote: post #13

Earlier quoted context omitted.

>Painters don't stick to just three pigments, but all the pigments they use CAN be created by mixing three primaries in different proportions. No. Paint is not light, and has physical properties that constrain what you can do with them. Some colors just don't mix well together, so you'll find recommendation on what exact type of pigment work best for specific mixes.

Yeah, that's true, paint is subtractive, as opposed to light. But isn't it still the case that all pigments can be achieved by mixing three primaries? Whereas in light mixing the primaries are considered to be red, green, blue, in pigment mixing they are considered to be cyan, magenta, yellow. Obviously please correct me if I'm wrong (no sarcasm implied), links would be useful.

No, I meant some pigments won't mix well because of other physical properties. The only example I can think of from the top of my head is in the Quiller, Color choices. It is mainly concerned with watercolors, and some colors mix uniformly (so blue+yellow -> green) and some look like an emulsion (so not green, but yellow with blue bubbles inside). Which can be interesting, because the mixing of colors is thus done by the eye instead of the paint, and is in fact one of the major painting effects used by impressionists.

Re: How do our colour-blind cones achieve colour vision?

#16

Post by rspeer » Tue, Feb 23, 2016, 11:40 PM UTC

neurosphere wrote: post #14

logicrook wrote: post #13

Earlier quoted context omitted.

>Painters don't stick to just three pigments, but all the pigments they use CAN be created by mixing three primaries in different proportions. No. Paint is not light, and has physical properties that constrain what you can do with them. Some colors just don't mix well together, so you'll find recommendation on what exact type of pigment work best for specific mixes.

Yeah, that's true, paint is subtractive, as opposed to light. But isn't it still the case that all pigments can be achieved by mixing three primaries? Whereas in light mixing the primaries are considered to be red, green, blue, in pigment mixing they are considered to be cyan, magenta, yellow. Obviously please correct me if I'm wrong (no sarcasm implied), links would be useful.

No. No matter whether you're doing additive or subtractive color, there will be perceivable colors that you can't reach just by mixing a finite number of primaries. In fact, CMYK printing has a rather small gamut, with more colors that are clearly unreachable than RGB has.

Perceivable colors are a three-dimensional space, and colors you can make out of three primaries are a three-dimensional space, but they're different shapes. Mixing primary colors is a way of interpolating between them linearly, and the space of perceivable colors doesn't have convenient linear edges.

Here's an example. Your printer has cyan, magenta, and yellow ink (and also black for convenience). So it can print any color, right? It should be able to print bright lime green, something that looks like RGB #00ff00, right?

No, in fact, you can't print that color without "spot color" ink. When you mix cyan and yellow to make green, it will necessarily get darker. If you use enough cyan and yellow to get full-saturation green, it'll be too dark. If you use less ink, it won't be saturated enough.

Lime green is outside of the CMYK gamut. Similarly, the deep cyan you'd get by printing with lots of cyan ink is outside of the RGB gamut.