# Relationship between color theory and spectrum **URL:** \ **Category:** Factual Questions\ **Created:** [June 15, 2010, 12:55am UTC](https://boards.straightdope.com/t/relationship-between-color-theory-and-spectrum/543231 "2010-06-15T00:55:31Z")\ **Posts on this page:** 15\ **Page:** 3
**Author:** ![septimus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/septimus/32/410_2.png) [@septimus](https://boards.straightdope.com/u/septimus)\ **Post date:** [June 16, 2010, 9:35pm UTC](https://boards.straightdope.com/t/relationship-between-color-theory-and-spectrum/543231/41 "2010-06-16T21:35:56Z")
> [@thelurkinghorror](#): > > Incidentally, blue on CRTs seems dimmer because it **is**. Green is the brightest. Let’s clarify one possible confusion. CRT Blue is generally _brighter_ relative to CRT Green than daylight blue is to daylight green. CRT Blue is dim only in the sense that _all_ blue is dim. Blue is dim because in daylight the output of red and green cones is summed to produce the retina’s luminance signal, but the blue cone output does not affect this detected luminance. (At night, rod outputs are substituted for R+G cones.) ---
**Author:** ![thelurkinghorror](https://avatars.discourse-cdn.com/v4/letter/t/7c8e57/32.png) [@thelurkinghorror](https://boards.straightdope.com/u/thelurkinghorror)\ **Post date:** [June 16, 2010, 9:42pm UTC](https://boards.straightdope.com/t/relationship-between-color-theory-and-spectrum/543231/42 "2010-06-16T21:42:12Z")
> [@njtt](#): > > Many hues that we experience cannot be found in the spectrum (i.e., cannot be produced by any unmixed wavelength of light), but are only produced by certain mixtures of wavelengths. Indeed, IIRC,\* the color that most people judge to be the best, most pure and unmixed looking red, cannot be produced by any single wavelength of light. snip > [@](#): > > \*My uncertainty here is over whether this applies to red, as opposed to one or other of the other so-called “primary” colors. I think it is red, but it might possibly be subjectively pure green or blue (or perhaps even all of them, or two out of the three) that corresponds to no monochromatic wavelength. If anyone knows about this, and can provide a cite, I would be grateful. > > This does not sound right to me, but I am not certain. Does anyone know better, or have a cite? This agrees with you: [Glossary](http://www.yorku.ca/eye/glossary.htm) about red, at bottom. Sounds like you’re talking about unique hues? Hering said that RYGB were 470, 500, 570, and 700 nm respectively. [handprint : the geometry of color perception](http://www.handprint.com/HP/WCL/color2.html#uniquehues) scroll down a few lines. Scroll down a bunch more (search for “what about unique red”), and see the graph right above that. Please note than in a physiological color space, this may not apply. The “red-green” and “blue-yellow” axes do not correspond to colors that we would consider unique. Red is actually the most physiologically-determined color in this case. ---
**Author:** ![njtt](https://avatars.discourse-cdn.com/v4/letter/n/ecd19e/32.png) [@njtt](https://boards.straightdope.com/u/njtt)\ **Post date:** [June 16, 2010, 9:46pm UTC](https://boards.straightdope.com/t/relationship-between-color-theory-and-spectrum/543231/43 "2010-06-16T21:46:24Z")
> [@TriPolar](#): > > Yes, I’m familiar with that. But good CRTs can adjust the level for each color. I have the effect until blue is at the max (without excessive bleed, more allowed if its only me looking), and red and green brought down below standard matched levels. Then everyone brings up blue phosphors and blue receptors and I just ignored it. Recently I saw a test image online and couldn’t read the numbers. I figured it was just an artifact of the plasma screen, but then recalled all the ways blue colors seemed ‘different’ for me and tried a photographic image, and still couldn’t pick out the numbers. A specialist is supposed to have a whole range of similar test images for a better diagnosis. It’s not like I’m can’t distinquish blue from green altogether, so it hasn’t had much affect on my life. > Brown is a more interesting color. Its all in the post processing. Very interesting because almost everybody distinquishes brown easily, but it requires all the cones and maybe the rods as well to provide input. njtt mentioned you can’t perceive brown without contrasting samples. If this processing is occuring in the eye or optic nerve, that supports the statement made by someone that the eyes are part of the brain and not a seperate organ (paraphrasing). It is hard to say for certain from your description, but it sounds as though you might have tritanomaly, which is very rare. It occurs when the peak response of the “blue” cones is shifted a bit toward longer wavelengths, so although blues and greens will still be distinguishable, they will not be as different as they are for most. It might also make the far violet darker than normal, or even invisible altogether. Rods, incidentally, play no significant role in color vision at all. In conditions that are bright enough to see color properly, the highly sensitive rods are, essentially, all maxed out, and not doing anything for you. The rods function to give you monochromatic vision in low light, when it is not bright enough for the cones to function. I guess there must be an intermediate range of dim light where you are getting some rod and some (diminished) cone function, but I do not think the rods are contributing anything to color discrimination even then. There is not any actual “processing” going on in the optic nerve, but you are right that a lot of visual processing goes on in the retina, over and above the mere transduction of light into nerve signals by the 4 types of receptor. Not only color processing, but also quite a bit of the work of edge detection and even motion processing is done there too, before the signal ever reaches the brain. There may be more too. After all, discovery of motion processing in the retina is fairly recent, but it has been shown (in some species, at least) that the retina distinguishes between object motion and motion of the whole image caused by eye or head motion, and that the retina can directly detect a rapidly approaching object. (Crudely speaking, one of the signals the retina can send to the brain means SOMETHING IS COMING RIGHT AT YOU! MOVE NOW!) It is hard to demonstrate these sorts of retinal processing directly in human beings, but there is no reason to think that our retinas do not do similar sorts of things. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 16, 2010, 10:25pm UTC](https://boards.straightdope.com/t/relationship-between-color-theory-and-spectrum/543231/44 "2010-06-16T22:25:37Z")
> [@](#): > > Rods, incidentally, play no significant role in color vision at all. In conditions that are bright enough to see color properly, the highly sensitive rods are, essentially, all maxed out, and not doing anything for you. Ah, so that’s why we have a three-dimensional color space, even though we have four kinds of receptors. I’ve wondered about that. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [June 16, 2010, 11:51pm UTC](https://boards.straightdope.com/t/relationship-between-color-theory-and-spectrum/543231/45 "2010-06-16T23:51:07Z")
> [@thelurkinghorror](#): > > ETA: In response to TriPolar’s last post. > > The first page I found with a search shows respective RGB luminances of 13.5, 43.1, and 5.22 cd/m^2. You can lower G down to B, then it would be at about 12%, which may limit the gamut. I’m not sure how the adjustment you describe works (brightness matching?). > > It would be cool to figure out what you have, but then it doesn’t affect you much and probably costs more than it’s worth. They would run a full battery of tests. We were usually lowering green to get the best balance with red, and sometimes raising blue to suit individuals. This was 1970’s technology, 3 gun with RGB triads, higher res than television and most data monitors. The objective was to get satisfactory yellow variations, and the overall brightness wanted by the users. We only had an 8 color interface, so software adjustment wasn’t possible. I think the red phosphors were brighter than other displays. In addition, we were changing the aspect ratio of the screen from the design spec, which could lead to bleed and focus problems. We were going from 4:3 to 1:1 to make the pixels square. We could only get close though, around 1.2:1. If insurance covers it, I’ll see the specialist, otherwise, I have little to gain. Apparently my father said he couldn’t distinquish between green and grey. I don’t have a way to get more detail. My brothers don’t seem to have any symptoms. My eyes are fine otherwise, even after staring at a CRTs and other displays for much of the past 40 years. Not so sure about the effect on my brain:) ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [June 16, 2010, 11:58pm UTC](https://boards.straightdope.com/t/relationship-between-color-theory-and-spectrum/543231/46 "2010-06-16T23:58:54Z")
> [@njtt](#): > > Rods, incidentally, play no significant role in color vision at all. In conditions that are bright enough to see color properly, the highly sensitive rods are, essentially, all maxed out, and not doing anything for you. The rods function to give you monochromatic vision in low light, when it is not bright enough for the cones to function. I guess there must be an intermediate range of dim light where you are getting some rod and some (diminished) cone function, but I do not think the rods are contributing anything to color discrimination even then. I haven’t worked in graphics for a long time, and some questions have been answered since then, but there was a theory about the involvement of rods in some color vision, especially in ‘brown’ perception. No idea if that proved out in any way. Do you have any info on various ‘illusions’? I’ve heard of explanations that include ideas like ‘cone saturation’ and ‘overload’ that sound fuzzy at best. The contrast and motion illusions may involve retinal processing. I’m sure some of them happen further down the line in the brain. ---
**Author:** ![panamajack](https://avatars.discourse-cdn.com/v4/letter/p/47e85d/32.png) [@panamajack](https://boards.straightdope.com/u/panamajack)\ **Post date:** [June 17, 2010, 12:20am UTC](https://boards.straightdope.com/t/relationship-between-color-theory-and-spectrum/543231/47 "2010-06-17T00:20:57Z")
Slightly related, I’m kind of curious whether color-blind people see a picture like [this](http://people.msoe.edu/~taylor/eisl/land.htm) in the same way someone with normal color vision does. (What I see is a cheeseburger, properly colored but the overall photograph has a red cast, as if taken with a filter). In case you don’t want to read more about it - the image is entirely created with red and shades of grey, meaning the only physical color information is red. But the brain compensates by filling in the colors, so that you see green lettuce and yellow cheese. It’s the same way that a tinted or faded photograph (which might have an overall color cast) has okay color on its own, but if you were to compare it side by side with another one with a different cast, it’d really stick out. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [June 17, 2010, 12:31am UTC](https://boards.straightdope.com/t/relationship-between-color-theory-and-spectrum/543231/48 "2010-06-17T00:31:28Z")
> [@panamajack](#): > > Slightly related, I’m kind of curious whether color-blind people see a picture like [this](http://people.msoe.edu/~taylor/eisl/land.htm) in the same way someone with normal color vision does. (What I see is a cheeseburger, properly colored but the overall photograph has a red cast, as if taken with a filter). > > In case you don’t want to read more about it - the image is entirely created with red and shades of grey, meaning the only physical color information is red. But the brain compensates by filling in the colors, so that you see green lettuce and yellow cheese. It’s the same way that a tinted or faded photograph (which might have an overall color cast) has okay color on its own, but if you were to compare it side by side with another one with a different cast, it’d really stick out. I didn’t see any green or yellow. Brown is primarily red, and black isn’t a color, its the absence of light. I don’t know what was meant by white light, white contains red, green and blue. It looks like a hamburger with green and blue filtered out. I doubt my problems with blue have any effect. ---
**Author:** ![thelurkinghorror](https://avatars.discourse-cdn.com/v4/letter/t/7c8e57/32.png) [@thelurkinghorror](https://boards.straightdope.com/u/thelurkinghorror)\ **Post date:** [June 17, 2010, 1:09am UTC](https://boards.straightdope.com/t/relationship-between-color-theory-and-spectrum/543231/49 "2010-06-17T01:09:11Z")
> [@panamajack](#): > > Slightly related, I’m kind of curious whether color-blind people see a picture like [this](http://people.msoe.edu/~taylor/eisl/land.htm) in the same way someone with normal color vision does. (What I see is a cheeseburger, properly colored but the overall photograph has a red cast, as if taken with a filter). > > In case you don’t want to read more about it - the image is entirely created with red and shades of grey, meaning the only physical color information is red. But the brain compensates by filling in the colors, so that you see green lettuce and yellow cheese. It’s the same way that a tinted or faded photograph (which might have an overall color cast) has okay color on its own, but if you were to compare it side by side with another one with a different cast, it’d really stick out. [Color constancy](http://en.wikipedia.org/wiki/Color_constancy). As far as a color blind person goes, they would most likely see the “right” colors, although it is of course based upon their own visual system and may not correspond to a trichromat’s percept of the cheeseburger. A color blind person is not _incapable_ of seeing red, green, or blue depending on their particular form. Their ability to discriminate is limited. In the cheeseburger’s case, it may be very possible for them to recognize “phantom” colors, depending on how different the green and red are. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [June 17, 2010, 2:58am UTC](https://boards.straightdope.com/t/relationship-between-color-theory-and-spectrum/543231/50 "2010-06-17T02:58:22Z")
> [@thelurkinghorror](#): > > [Color constancy](http://en.wikipedia.org/wiki/Color_constancy). > > As far as a color blind person goes, they would most likely see the “right” colors, although it is of course based upon their own visual system and may not correspond to a trichromat’s percept of the cheeseburger. A color blind person is not _incapable_ of seeing red, green, or blue depending on their particular form. Their ability to discriminate is limited. In the cheeseburger’s case, it may be very possible for them to recognize “phantom” colors, depending on how different the green and red are. Interesting. The pink card cited stays the same for me, but the green card on the left, and the purple on the right change color. ---
**Author:** ![njtt](https://avatars.discourse-cdn.com/v4/letter/n/ecd19e/32.png) [@njtt](https://boards.straightdope.com/u/njtt)\ **Post date:** [June 17, 2010, 4:38am UTC](https://boards.straightdope.com/t/relationship-between-color-theory-and-spectrum/543231/51 "2010-06-17T04:38:18Z")
> [@panamajack](#): > > Slightly related, I’m kind of curious whether color-blind people see a picture like [this](http://people.msoe.edu/~taylor/eisl/land.htm) in the same way someone with normal color vision does. (What I see is a cheeseburger, properly colored but the overall photograph has a red cast, as if taken with a filter). That doesn’t work for me, and I am reasonably confident that I have normal color vision. The lettuce looks gray to me, and the cheese looks the same color as the bun (I seem to be able to somehow recalibrate so I imagine it as yellow or white, but it is really pink, of course). However, a lot of these color vision tests do not work consistently online, because of the limitations of RGB monitors, and variations in their settings. It may be that under better conditions it is possible to create a much more distinct illusion of green and yellow this way. I wonder if it matters whether you “know” that the lettuce should be green, etc. I suspect it is. ---
**Author:** ![njtt](https://avatars.discourse-cdn.com/v4/letter/n/ecd19e/32.png) [@njtt](https://boards.straightdope.com/u/njtt)\ **Post date:** [June 17, 2010, 4:47am UTC](https://boards.straightdope.com/t/relationship-between-color-theory-and-spectrum/543231/52 "2010-06-17T04:47:33Z")
> [@TriPolar](#): > > Do you have any info on various ‘illusions’? I’ve heard of explanations that include ideas like ‘cone saturation’ and ‘overload’ that sound fuzzy at best. The contrast and motion illusions may involve retinal processing. I’m sure some of them happen further down the line in the brain. There are an awful lot of illusions, with many different mechanisms, and some of them are still not very well understood. Certainly some of them depend on retinal mechanisms and some on processing in the brain proper (or even a combination of the two). You can’t really generalize. Incidentally, I did not mean to imply that _all_ the motion, color, and edge processing gets done in the retina - it certainly does not - just that a significant part of it gets done there before the information is passed on to the brain for further work. ---
**Author:** ![SlowMindThinking](https://avatars.discourse-cdn.com/v4/letter/s/dc4da7/32.png) [@SlowMindThinking](https://boards.straightdope.com/u/SlowMindThinking)\ **Post date:** [June 17, 2010, 3:47pm UTC](https://boards.straightdope.com/t/relationship-between-color-theory-and-spectrum/543231/53 "2010-06-17T15:47:14Z")
> [@njtt](#): > > Well, yes, if you are missing your “red” cones, reds can look very dark, besides being indistinguishable in hue from greens and yellows. Indeed, such people can sometimes use this difference in experienced shade to guess that what they are looking at is red rather than green, even though they do not seem to differ in hue. … > A deuteranope (someone lacking functional green cones) will presumably, for similar reasons, experience some darkening of greens relative to cyans, although this effect is not nearly as marked because the “red” cones are, in fact, still responsive to light far into the green, and even the blue regions of the spectrum. Still, this might give them a slightly enhanced shade contrast between greens and cyans. But why should a camouflager paint his tank cyan, when green paint is readily available? I agree with you, but I’d love to test my officemate. Being in a male dominated field, I’ve met my share of colorblind people, but never anyone like him. He calls himself red-green colorblind, and as far as I can tell, he really is blind to those colors and can see neither red nor green. As I said earlier, he can’t find a stationary, red laser pointer on a white background. To him, a bright, light green display looks yellow. One day we went to the wikipedia page on colorblindness, and he couldn’t see the numbers in either the protanopia and the deuteranopia example. But, he picked out the tritanopia number more easily than the rest of us. The glare and the angle from which we viewed the screen weren’t optimal, causing the rest of us to stare for a bit to see it. It jumped out at him, but no matter how hard he tried, he couldn’t see the other two numbers. And in looking at plots I can tell you that the rest of us are generally better at discerning which data goes with which source, but occasionally, as with reds and purples, he gets irritated that we tell him to change the colors. I’ve got to believe that there are those who have an advantage looking at pictures that may or may not contain camouflaged objects in a forest. And the incidence would be higher amongst those that have already been identified as colorblind. It is hard for me to believe though, that just any colorblind person would have an advantage. ---
**Author:** ![thelurkinghorror](https://avatars.discourse-cdn.com/v4/letter/t/7c8e57/32.png) [@thelurkinghorror](https://boards.straightdope.com/u/thelurkinghorror)\ **Post date:** [June 17, 2010, 6:05pm UTC](https://boards.straightdope.com/t/relationship-between-color-theory-and-spectrum/543231/54 "2010-06-17T18:05:30Z")
I assume the tritan image you’re talking about is the “56.” I put it on both of my monitors, and it is much easier to see on the CRT. I’m sure you saw the note about how viewing it on monitors screws it up? For accurate diagnosis, color tests should always be run using paper or cardboard plates, lights, or CRT monitors connected to special video cards. ---
**Author:** ![SlowMindThinking](https://avatars.discourse-cdn.com/v4/letter/s/dc4da7/32.png) [@SlowMindThinking](https://boards.straightdope.com/u/SlowMindThinking)\ **Post date:** [June 17, 2010, 8:07pm UTC](https://boards.straightdope.com/t/relationship-between-color-theory-and-spectrum/543231/55 "2010-06-17T20:07:11Z")
Yes and yes, but I wasn’t trying to diagnose him, we were passing time during a lull at work. Given his inability to see a red laser on a white background, and his claim that “purple is his favorite shade of blue”, he would seem to be at least a protanope. I also know that, in addition to his not seeing either number on Wikipedia, his description of colors does not match any of those on a web site for designing computer user interfaces for the colorblind, and that he has occasionally remarked something along the lines of the deuteranope sentence on that same wiki page: “Similarly, violet, lavender, purple, and blue, seem to be too many names to use logically for hues that all look alike to him.” So, I suspect he has at least two forms of colorblindness, but whether they are both “Xnopes”, or a “Xnope” with a “Xanomaly” would undoubtedly require a doctor’s exmaination. [Previous page](https://boards.straightdope.com/t/relationship-between-color-theory-and-spectrum/543231.md?page=2)