The loss of violet

[steuard]

I was thinking about color this morning (yes, I do these things), and I was struck by a disturbing thought: when did I last see violet? Not purple, which I see all the time, but actual violet. [I'm not the first person to wonder this: here's a very thorough discussionPurple, as you no doubt recall, is a compound color: it's what we perceive when we

Comments

[nemene]

seems you are not the only one thinking about this:
http://www.rottenbrains.com/?p=121

[nemene]

I just found in this link a discussion on how the red receptors have a secondary sensitivity a little above 400 nm. This means the wavelengths in the violet region excite both the blue and the red receptors, just like purple. So visually it should be possible to construct a purple mix which is INDISTINGUISHABLE from actual violet, awesome.

[steuard]

Oh, interesting: I hadn't spotted a clear discussion of the red cones' secondary peak in the article that you (and I, actually) linked to earlier, but the discussion in this article gives a nice clear explanation (and a good graph, too). That explains why violet and purple look similar (and why we perceive a color circle rather than a color line)... I wonder to what degree it really is possible to trigger the visual system to perceive violet (or, more broadly, what hues out there we just don't see).

Also, unless digital camera sensors mimic that secondary peak (do they??), we'll still wind up missing out on violet in most photographs these days. (As kirinn's photo would seem to show.)

[nemene]

had you found that link first, sorry, was in a rush but you had peaked my interest and that was what I found

[kirinn]

I'm doing pretty well by this measure, since I happened to get to see a really bright rainbow in person just a few weeks ago.

But presumably you could also reset your clock with a decent prism...

Hmm, I wonder if true-violet LEDs are commercially available? Can you get a cellophane filter that's true violet pass-through? Are most purplish flowers violet or mixtures? I'd bet there's at least some that reflect true violet strongly, given there are some that reflect ultraviolet patterns...

[kirinn]

...and after reading some of the linked article, I suddenly realized I have *experimental evidence* of true-violet flowers. There's a certain kind of Iris I've found growing around here several times that looks deep purple (err, violet) to the eye but inevitably comes out deep blue on my iPhone camera. Bingo!

[steuard]

Oh, awesome! Or disappointing, depending on how you look at it. (The whole time I've been thinking about this, I've had to keep fighting back the urge to say, "I'll just find a picture with Google..." or, just now, "Send me a picture of what they really look like!")

[kirinn]

Well, I can upload the picture of what they *don't* really look like. The one below is definitely a deep violet in person. And meanwhile, I noticed I also have several pictures of flowers on my phone that *do* look purple, meaning that unlike the Iris they're reflecting red wavelengths.

[prock]

This image from wikipedia illustrates the problem from the perspective of gamuts:

[steuard]

That's a really nice illustration: thanks! (To be honest, I'm surprised that it gets as far down into the violet/purple corner as it does. But come to think of it, I realize that I don't know nearly enough about color theory to really grok the details anyway: what are the axes, and how are they scaled? I should probably avoid spending the time it would take to figure all this out right now. :) )