Why is a yellow line hard to see against a white background?

[Lionel Mandrake]

I have always wondered why yellow is a light color, whereas red and blue are dark colors. Red and blue lines show up well against a white background. They have high contrast. Green is okay. Yellow is a terrible choice. You can hardly see it against a white background. Everyone is familiar with this phenomenon. Can anyone explain it?

As a physicist I can not think of an explanation. I don't even know what kind of expertise is needed to answer this question.

Does anybody have an idea about this?

[Tien1985]

1. Check out

This: http://www.theanswerbank.co.uk/Science/Question86190.html

I don't know how accurate it is, but it's a good starting place.

[Lionel Mandrake]

5. I see I'm not the first to ask this question.

That's good to know. But I'm still in the dark (pun intended) even after reading the answers in the link.

[Tien1985]

6. Could be contrast?

I mean the brain already likes to trick us into seeing what we THINK we see, instead of what is actually there. Maybe because the colors are so similar we have to fight our brain to interrupt them as separate instead of seeing an all white sheet?

[Salviati]

8. Well Gandy's answer sure isn't going to help...

Yellow and white light are not pure colors, they don't have a wavelength.

Here's a link that goes into a fair amount of detail about color vision, the section of Opponency is what I was talking about remembering in my original reply.

http://www.scholarpedia.org/article/Color_vision

[Lionel Mandrake]

13. Wow, that's a good article.

It's succinct and authoritative. I never heard of Scholarpedia before. I'll have to check it out by looking at some more articles. (Not that I have finished this one.)

[unblock]

26. white is not a color at all in fact, but yellow is a pure color.

white is a collection of light of multiple wavelengths. there is no way to make light of any single wavelength appear yellow.

there is a single wavelength of light that is yellow. human eyes do not have cones with peak response at that frequency, so it is not a "primary" color for us, but our perception of light doesn't change the light itself.

for people with normal color vision, red light plus green light is indistinguishable from yellow light. but that doesn't mean yellow light "is" red light plus green light. in fact a single beam of yellow light is different from a combined beam of both red light and green light, even though most people can't tell the difference.

certain color "blind" people can see a difference and of course a spectrograph can certainly detect the difference.

[Lionel Mandrake]

31. Color is not a property of light.

Color is in the eye of the beholder. The same light can have different colors for different people.

A light that appears yellow to me may appear yellow-orange or yellow-green (chartreuse) to you, and vice versa. This is true even if we both have normal color vision, since there are many polymorphisms of the pigments in L and M cones that cause them to peak at slightly different wavelengths. The instrument usually used to measure such differences is called an anomaloscope:

http://arapaho.nsuok.edu/~salmonto/vs2_lectures/Lecture34.pdf

For some people with an extreme form of colorblindness, all light appears to be white or gray.

[Salviati]

2. My guess:

White light stimulates all three cones, Yellow stimulates the long and medium wavelength cones, while red or blue only stimulate either the long or the short wavelength cones.

As I'm typing this though, I'm remembering that the signals that the brain gets don't quite correspond to long, medium, and short. It's some other superposition of the signals, so it's probably not quite that easy. But it's likely something to do with that.

Color vision is pretty crazy stuff. I wonder if tetrachromats have the same difficulty?

[Lionel Mandrake]

9. Good question. Why don't we ask a tetrachromat?

That's not as ridiculous as it sounds. I don't mean ask a fish or a bird. Some women have cones with four or more different pigment types. That's because of X-inactivation and mosaicism in a woman's retina. A few experiments indicate the possibility of tetrachromatism in such women, but this is controversial.

As for yellow stimulating the long and medium wavelength cones, the same can be said of green, but green can be a dark color and thereby show high contrast with a white background. Even chartreuse is an improvement over yellow.

[Salviati]

14. Yeah, but green would stimulate the medium a bit more than the long.

That might explain it, but I might be completely wrong as well.

[Jim__]

37. I tend to agree with you.

Yellow stimulates the green and red cones almost equally. So does white. Of course, white also stimulates the blue cones; but the fovea is only sparsely populated with blue cones and there are none in the center of the fovea. The signals from the cones are combined in the retina before being passed to the brain. The signal between yellow light and white light that comes from the central part of the fovea and gets passed to the brain could be very similar.

[immoderate]

3. Perhaps it has to do with the fact that yellow cuts through the middle of ...

...the visible light range. Red and blue, being at the edges of what constitutes "light" are therefore apparently "dark."

--imm

[Lionel Mandrake]

10. I think you are right in saying

it has to do with the fact that yellow cuts through the middle of the visible light range. But that explanation doesn't distinguish yellow from green, which has much better contrast.

[immoderate]

15. Yellow has a narrow spectral range.

Consider also that some of this may depend on how the eye functions, and what the color "looks like" as opposed to how it is rendered objectively (whatever that means.) Consider that other species see different parts of the spectrum.




--imm

[Lionel Mandrake]

17. Yes and no.

It's true that when you look at a pure spectrum, only a narrow region looks yellow. But you can also get yellow by mixing red and green light, as in an anomaloscope.

So the sensation of yellow is not really a wavelength or even a range of wavelengths.

It's also true that other species can see wavelengths that we cannot. But it's not clear what that has to do with my original question.

[immoderate]

18. It has to do with how the sensation of yellow lines up with human

visual reception. It is a complex composite of sensors that do not behave linearly.

--imm

[Lionel Mandrake]

19. Huh?

The "sensors" are cones with pigments of types S, M, and L, which have absorption peaks at short, medium, and long wavelengths, respectively. Sometimes these cones are called blue, green, and red, respectively. Their outputs are combined linearly, as has been shown by many experiments. Why would you think otherwise?

[immoderate]

21. It's not that simple.

From wiki:

The cones are conventionally labeled according to the ordering of the wavelengths of the peaks of their spectral sensitivities: short (S), medium (M), and long (L) cone types. These three types do not correspond well to particular colors as we know them. Rather, the perception of color is achieved by a complex process that starts with the differential output of these cells in the retina and it will be finalized in the visual cortex and associative areas of the brain.

For example, while the L cones have been referred to simply as red receptors, microspectrophotometry has shown that their peak sensitivity is in the greenish-yellow region of the spectrum. Similarly, the S- and M-cones do not directly correspond to blue and green, although they are often depicted as such. It is important to note that the RGB color model is merely a convenient means for representing color, and is not directly based on the types of cones in the human eye.

The peak response of human cone cells varies, even among individuals with 'normal' color vision;[3] in some non-human species this polymorphic variation is even greater, and it may well be adaptive.[4]
http://en.wikipedia.org/wiki/Color_vision

See?

--imm

[Lionel Mandrake]

22. Nothing in your post, including the quotation, contradicts what I wrote.

The wikipedia article on color vision is okay, but the link in post #8 is even better.

[immoderate]

32. I wouldn't call it linearly.

Once you are into the "opponent process" your information has been translated into red-green and blue-yellow color blobs which complement the trichromatic system you are describing (and which is not linear to begin with.)

I'm not contradicting. I'm augmenting.

--imm

[Lionel Mandrake]

34. Perhaps we are not using "linear" the same way.

When I say linear, I mean that doubling or halving the intensity at all wavelengths changes only the brightness, not the hue or saturation, of the perceived color. This sort of linearity is what makes it possible to draw a chromaticity diagram:


I do not completely understand "opponency" as described, e.g., in post #8. But I'm pretty sure that this theory, too, is linear in the same sense.

[Salviati]

38. Basically opponancy means that it's nto the raw signals that get fed to your brain...

but linear combinations of the S M and L signals that get fed to your brain after processing. But they are _linear_ combinations, so like you said, doubling or halving the intensity at all wavelengths doubles or halves the corresponding output of the linear combinations.

[nenagh]

4. That's because yellow makes such a fine highlighter ...

Orange is too dark and pink is too flamboyant..

Just could not study without a yellow highlighter...

[Lionel Mandrake]

11. Yellow makes a good highlighter because it's light, not vice versa.

My apologies if you were joking.

[PoliticAverse]

7. It has to do with the science of color contrast....

And how our eyes perceive color.

For example yellow on white has a contrast ratio of 1.07:1
Where as blue on white has a contrast ratio of 8.59:1
(From the following contrast analyzer: http://www.colorsontheweb.com/colorcontrast.asp )

For more on contrast:
http://www.colorsontheweb.com/colorcontrasts.asp
https://en.wikipedia.org/wiki/Color_contrast

[Lionel Mandrake]

12. Okay, then let me rephrase my question:

Why does yellow have such a low contrast ratio?

I'm not sure whether this has to do with color contrast or luminance contrast.

[Paulie]

16. There is no yellow on this screen

[tridim]

20. I might know why, pardon the woo.

I did an experiment with light spectrums viewed directly through a slit (directly projected on the retina) and discovered that the left eye sees the spectrum as violet to red and the right eye as red to violet. Red and Violet are out of phase with each other at the opposite ends of each eye's spectrum. Yellow, in the middle of the spectrum is at the same spot for each eye, which in my non-scientific opinion makes it appear brighter (closer to white) to the brain.

I think the brain uses the reversed spectrums to keep track of which eye sees what. Oddly, there is no research that I've found on this phenomenon.

[Lionel Mandrake]

24. No, that's wrong.

In general, a spectrum produced by a prism or diffraction grating can go either way: right to left or left to right. In most experimental setups, it goes the same way both eyes. But this has nothing to do with the question I asked in my OP.

Furthermore, the middle of the visible spectrum is green, not yellow.

[tridim]

28. Same light, same slit, one eye at a time. The spectrums are reversed.

I'm not looking at a projection, I'm looking at the actual spectrum created between the slit, my eye has to be very close to the slit to focus correctly.

Try it! Just make a slit in a black piece of paper with a razor blade, hold it up to a bright light and move your eye close enough to see the spectrum. You can even see the dark spectral lines.

[hunter]

23. Simple answer: Our color vision is a wretched evolutionary kludge achieved mostly in software.

Our little fury nocturnal ancestors lost the wonderful color vision that birds and many reptiles have. We're not true trichromats.

Color vision is useful for omnivores, for example it lets us better see which fruits are ripe. But it had to re-evolve in our lineage from ancestors who had lost all but two color receptors. We got some color vision back by splitting the green/red receptors into slightly-more-red and slightly-more-green receptors.



Most birds have color receptors spread evenly across the spectrum:



Ordinary pigeons can detect a wide range of color contrasts invisible to people. The brightness/contrast and color detection systems of birds are well integrated.

http://en.wikipedia.org/wiki/Trichromacy

http://en.wikipedia.org/wiki/Tetrachromacy

The software trick in great ape color vision is that the "red" and "green" signal inhibit one another across a single red-green color channel. The difference in color sensitivity between our red and green cones isn't great and it has to share a single transmission channel because the other color transmission channels had been lost along with their associated color receptors. What we see as "yellow" is something where the total red-green signal is inhibited, but the brightness signal is still strong. Our ability to distinguish contrast is tied to the brightness signal, not the kludged color processing system.

Messing with the highly sophisticated motion-contrast detection software didn't happen. An evolutionary kludge "good enough" for leisurely searching out ripe fruit is fine, but such a kludge is not good enough for avoiding predators, catching branches when falling, etc. We share the brightness/contrast detection systems of our ancient fury ancestors. If that makes a yellow line on a white background appear bright and indistinct, so what? How often, when you are swinging from branches in the trees, do you have to reach out and grab a bright yellow branch against a white sky? Pretty much never.

[Lionel Mandrake]

25. Interesting post.

I agree with much of what you wrote, but I would use less judgmental language to describe the color vision that we great apes share with other old-world monkeys. It seems to have evolved about 40 million years ago, after the separation of the Americas from other continents. New world monkeys remained dichromats for a while, and have since evolved independently various forms of color vision beyond that of typical extant mammals. I would agree that our color vision is limited by the closeness of the L and M spectra. It is furthermore afflicted by numerous polymorphisms in both the L and M cones, with the result that the spectral separation between them is reduced even in some people considered to have normal color vision, let alone those with red-green colorblindness. This system is far from ideal, but not what I would call a kludge.

There were two key evolutionary events: a gene duplication, and selection for different spectral properties of pigments expressed by the genes in question, which lie near one end of the X chromosome. Nobody knows which happened first. If the gene duplication came second, then for a while our ancestors must have had the kind of color vision enjoyed by many new world monkeys, among whom trichromacy is limited to certain females.

It was also necessary for the brain (including the retina) to develop the capability to compute difference signals between L and M cones; perhaps this is what you mean by software.

I agree that there is no obvious adaptive advantage to distinguishing a yellow line from a white background. I don't disagree with the idea that contrast means primarily luminance contrast as opposed to color contrast, especially when it must be perceived quickly.

But why is the luminance of yellow so close to that of white? That's what I still don't understand.

[hunter]

27. Our language has not the proper tools to discuss evolution.

"Judgmental" is built into it. We are "creatures" because some entity "created" us? It all gets much more tangled from there.

Take your pick, gods or tautologies...

There's another factor in our color perception:

Heat up a chunk of metal. It gets red hot, orange hot, yellow hot, white hot, and then, getting extreme, blue hot. That's the Kelvin scale of lighting.



http://en.wikipedia.org/wiki/Color_temperature

Where's the "green hot?" Look up into a clear sky at night. Where are all the green stars? There are a few, but unusual. Seen through clouds of gas, or stars of unusual composition themselves.

Hmmmmmm...

A greenish-tinged "bright," a perceived "yellow" but greenish star in a prejudiced blue sky. That's our "white." That's the brightness/contrast signal our ancient fury mammal minds are processing.

One of the problems plants have is dumping excess energy. The amount of energy available is rarely the limiting factor in plant growth, instead it's nutrients or water. If this wasn't true plants would be black. So plants dump the green light, and they dump the infrared. Don't need it. So it looks to humans like leaves are green. On my modified digital cameras healthy plants are bright pink.

I started my academic career as an engineering major. So I took this class and there were two women in it and a bunch of guys who talked about "chicks" and cars whenever they were not talking about engineering. The woman who was not a lesbian dropped out. Next semester I changed my major to biology, partly because in biology classes the women outnumbered the men. Potential girlfriends! No, it did not work out that way, the optimism of youth.

My new major's "specialization" (our school didn't have minors) was Evolutionary Biology. I'm still an engineer at heart. That's why I speak of "software." I write software. I was going to say wetware but that's not common language.

[Lionel Mandrake]

29. I can see you're having fun with this.

Whenever I am tempted to say "creature", I say "organism" instead. Same reason I prefer CE to AD, BCE to BC. Why grant anything to creationists?

I will talk about the Intelligent Designer. I'd say he was having a really bad day when he designed the vertebrate retina, what with all them neurons and blood vessels and stuff in front of the rods and cones. The IDer got it right when he started working on cephalopods. As an evolutionary biologist, of course, you know all about this.

About green plants--often they need to get rid of excess heat. Like us, they use evaporation for this purpose when radiation of IR isn't enough to do the job.

Green plants will do anything to get what they want. They even resort to bribery. They bribe us with fruit. They bribe birds and bees with nectar. Their behavior is utterly immoral.

When I talk like that, as if plants had goals and did things on purpose, of course I am being metaphorical. But then all language is metaphorical. There's no way around it.

[hunter]

30. So many things designed on the creator's drunk-binge days...

... do we really want to worship that creator???

So why can't I see a rainbow as pigeons do? Or better??? I know how an optimal eye would work. Hell, humans built better into the Mars explorers. But gods didn't???

I'm a spiritual person but I've little patience for Creationists or "Intelligent Design" people.

The universe is very big, humans are very small. That's the reason we have to look out for one another.

[Lionel Mandrake]

33. Amen!

[Paulie]

35. Ha! Our own star is green but looks white or yellow

Depending if we look through the Earths atmosphere or not.

Now the question is does a pigeon see green or yellow when looking up for raptors?

http://m.

&desktop_uri=%2Fwatch%3Fv%3DBvjeP3SfD1g

[hunter]

36. I'm bookmarking this!

Thanks.

[Lionel Mandrake]

39. The astronomer in the clip is confusing violet with purple.

There are no purple stars, because purple is a combination of red and blue, and there is no temperature at which blackbody radiation looks like that.

A sufficiently hot star should, theoretically, appear violet. I don't know whether any violet stars have been observed.

Our eyes can distinguish violet light (which excites only the S cones) from blue light (which excites S and M cones, but not L cones).

[HereSince1628]

40. I suspect it's about 'edge detectors' in the 'wiring' of nerves in the retina.

Edge detection is incredibly useful to animals.

Humans can "see" missing edges in patterns of black and white splotches (the classic illusion pic of this phenomenon is high contrast black and white figure of a dog (Dalmation?) on a leafy lawn).

My "thing" was population dynamics of parasitic nematodes, so I am not anywhere near up to speed on this topic. But, IIRC, my physiology training suggested that the innervation of the retina included the structure of analog comparators hat responded to differences in adjacent ranges response of tone and contrast in adjacent/nearby photoreceptors.