Magenta is a color | Hacker News Reader

Magenta is a color

arstechnica.com

40 pointsjyothi19 comments

This is an improvement over the earlier submitted post. Wikipedia was always in the background

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

ready to correct many of the errors in that post. "A range of wavelengths of light stimulates each of these receptor types to varying degrees. Yellowish-green light, for example, stimulates both L and M cones equally strongly, but only stimulates S-cones weakly. Red light, on the other hand, stimulates L cones much more than M cones, and S cones hardly at all; blue-green light stimulates M cones more than L cones, and S cones a bit more strongly, and is also the peak stimulant for rod cells; and violet light stimulates almost exclusively S-cones. The brain combines the information from each type of receptor to give rise to different perceptions of different wavelengths of light." The issue is not so much one wavelength versus more than one wavelength mixed, as it is an assignment of "color" to a combination of cone cell responses, subject to further processing by the brain. Farther along in the Wikipedia article it is noted,

"Chromatic adaptation

"An object may be viewed under various conditions. For example, it may be illuminated by sunlight, the light of a fire, or a harsh electric light. In all of these situations, human vision perceives that the object has the same color: an apple always appears red, whether viewed at night or during the day. On the other hand, a camera with no adjustment for light may register the apple as having varying color."

Black is the only non-color. Or more precisely:

The combination of all colors gives white light; the absence of all color is seen as black. (_New York Public Library Science Desk Reference_ p. 288).

I was wondering what kind of crazy bug bit HN the other day with that "Magenta is not a Color" bitty.

Black is the only non-color when working with additive primaries (RGB, light).

Black is the presence of all colors when working with subtractive primaries (RYB/CMYK, pigment).

If you mix pigments of all colors you wont get black, you will probably get some kind of brown. Thats why you need the K in CMYK - you need a specifc black paint, which contains pigment that absorb all colors. But you cant mix colors to get black.

C+M+Y=K in theory, but in practice the pigments are not calibrated precisely enough to be a perfect black when they combine.

I dont think that is true, even in theory. Non-black color pigments absorb some colors but reflect other colors. So even if you mix pigments you get some light reflected, although the color of the light will be mixed.

Just as you cannot mix black, you cannot mix white. However, a color printer can use the white in the paper to create lighter colors.

A color has the color we see because it absorbs all the other colors and only reflects the seen one.

So it's the same soup either way.

Not if you ask a goth teenager what their favorite color is...

I was wondering what kind of crazy bug bit HN the other day with that "Magenta is not a Color" bitty.

Even though the title is not true, the article was still interesting.

This reminds me of my philosophy class, where I learned that it is a significant open question on what color is.

Agreed. A statement like "The truth is, no color actually exists outside of our brain's perception of it." flies in the face of the materialism that is so popular these days. It sounds, rather, a great deal like George Berkeley's idealism: Esse est percipi.

Exactly how would it do that, pray tell?

There is zero contradiction between that statement and materialism.

This brings back memories of green or blue = grue.

The usual meaning ("usual"?! Well...) of "grue" is cleverer than that. Or sillier. Or both. Something is "grue" if it's green before (say) midnight at the start of January 1, 2010, and blue after that. You've observed an object many times and it's looked green. It isn't 2010 yet, so you would equally say that it's looked grue. So how come everyone agrees that it's sensible to say "it's green" and expect it to look green in 2010, but not to say "it's grue" and expect it to look blue in 2010? It turns out that lots of simple easy natural answers to this don't stand up well to philosophical nitpicking, and giving a really convincing answer is tricky. Which may or may not tell us something about what it is we're doing when we make generalizations from what we see.

This, of course, is why philosophers get paid the big bucks.

(What about something that looks blue first, and then green? "Bleen", of course. Hence one person's email signature: "It is very dark and after 2000. If you continue, you are likely to be eaten by a bleen." Nelson Goodman's original paper used 2000 rather than 2010 as the cutoff date.)

I've often wondered "How would you describe colour to a blind person" (obviously, someone who's been blind from birth).

The best I've come up with is comparing it to sound - sharp and dull sounds relate to wavelength, as does colour; loud and soft sounds relate to brightness.

Any better ideas out there? I admit it's a largely pointless exercise, one of many I have to amuse myself.

I'd like to point you to my comment (and its resulting thread) on the other article: http://news.ycombinator.com/item?id=483780

"This article is useless. Magenta is a combination of colors, and is not represented by any single wavelength of light. That doesn't mean it doesn't exist. Saying magenta doesn't exist is like saying green paint doesn't exist, because it's a combination of blue and yellow (within subtractive primaries). [...]"

This is a very good article. There are way too many articles that take some "interesting fact" and then misinterpret into something earth-shattering. "Magenta isn't a color? HOW CAN THAT BE!?"

The original article should have said, "some colors are a single wavelength of light, others are a combination, thanks to how your brain works." Fortunately, this article was written to make up for the inadequacies and sensationalism in the original.

Interesting, but "x" and "y" as labels for the axises on the chart made it really hard for me to understand.

What would you label them instead?

http://en.wikipedia.org/wiki/CIE_1931_color_space#The_CIE_xy...

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