Magenta Error in Wikipedia

[Andrea B.]

Does anyone have a proper Wikipedia login to correct an error?

 

Out of simple curiosity, I just went to see what the Wick had to say about Magenta (was discussing it elsewhere) and found this in the section entitled In optics and color science.

 

The errors are bolded in color.

 

"If the spectrum is wrapped to form a color wheel, magenta (additive secondary) appears midway between red and violet. Violet and red, the two components of magenta, are at opposite ends of the visible spectrum and have very different wavelengths. The additive secondary color magenta, as noted above, is made by combining violet and red light at equal intensity; it is not present in the spectrum itself."

 

Elsewhere, the correct magenta components of blue & red are referred to. Sometimes I think people tamper with Wikipedia to see if anyone is actually reading it. Or perhaps I should say proof-reading it.

[Cadmium]

Andrea, your "Magenta" link doesn't work.

 

What you quote is correct. It means that Magenta is not found in a rainbow, because red and blue/violet don't connect in a rainbow, unless wrapped around to connect in a wheel.

Magenta has no wavelength in the electromagnetic spectrum. It is a mixture of two wavelengths that are not next to each other, and are at opposite ends of the visual spectrum.

Are you questioning what term should be used for the edge of the rainbow? blue or violet? Is that the problem with the quote?

Violet is the far edge of the visual spectrum, and the far edge of blue. Unless you want to further define the visual spectrum to more than 3 colors, then violet is part of the blue section of visual.

In any case, violet is at the very edge of the rainbow, and the very edge of human vision.

In a wheel type representation of a rainbow (as illustrated in an example below the quote), magenta is shown half way between red and blue (blue/violet).

https://en.wikipedia...olour_wheel.svg

[Andrea B.]

link fixed.

***

 

The two sentences should correctly read as follows ---

 

"If the spectrum is wrapped to form a color wheel, magenta (additive secondary) appears midway between red and blue."

 

"Blue and red, the two components of magenta....."

 

**********

 

Then we must note that while it is indeed true blue & red are on opposite ends of the spectrum, we typically name violet to be the left-most color of the visible spectrum. So there is another sentence which is problematic that appears as a label under the color wheel image.

 

"Visible spectrum wrapped to join violet and red in an additive mixture of magenta."

 

There it is indeed true that the visible spectrum can be wrapped to join violet and red but that does not create magenta which is an additive mixture of blue and red.

 

***********

 

An additive mix of blue & red = magenta.

Because (255,0,0) + (0,0,255) = (255,0,255).

 

But an additive mix of violet & red = ???

However an additive mix of purple & red = purple.

Because (255,0,0) + (128,0,255) = (128,0,255).

 

 

 

removed bad ref to red-violet.

[OlDoinyo]

The red channel of the retina has a secondary peak of sensitivity at the short end of the visible spectrum--thus certain mixtures of blue light with small amounts of red can appear metameric to deep blue light--sort of. Some early color separation schemes did not accurately reproduce this feature of human vision, leading to the "violet-magenta problem," wherein certain things appearing blue-violet in real life end up looking magenta in photos. More recent film emulsions and sensors have largely corrected this problem.

 

It is true that hues in the magenta range of tristimulus values cannot be evoked with any single wavelength of monochromatic light. There is thus a sector of the color wheel that has this curious property.

 

There are also tristimulus values that cannot be evoked with any physical light at all, though they would be theoretically possible on neurological grounds. Due to the overlap of sensitivity curves in the retina for example, a deep red monochromatic light will probably produce a visual sensation equivalent to something like (255,30,0) and that is as red as it gets. But if we could stimulate the nerves directly, we could achieve "redder than red" hues.

[Cadmium]

Colors in the rainbow

 

Violet

 

Blue - Science and nature

 

Magenta is between red and violet on the color wheel.

https://upload.wikim..._wheel_1908.png

 

Glad you worked it out. :)

 

By the way, prepare yourself, because your UG2A has a magenta label...

[Andrea B.]

So how do I go correct this Wikipedia thing? Are there instructions somewhere?

[JCDowdy]

Click on the Edit tab and you will get a message at the top of the page.

 

You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to a user name, among other benefits.

 

The Talk tab has some discussion of your point.

[Andrea B.]

Thanks JD. I guess I'll create a login and fix that little error.