Friday, November 11, 2011

Mister Biv

kw: observations, colors

I am reading a book about the history of Indigo dye, which I'll review in a day or two. Meanwhile, I was thinking about the influence that indigo had on Isaac Newton. While the essential blue dye of the Anglo-Saxons was woad, indigo from India and Africa was becoming better-known. While the two dyes are chemically similar, indigo is longer-lasting, though both run and stain.

Newton enshrined the deep blue of a strong tincture of indigo in his spectrum, leading to the name for the "color man": Roy G. Biv. I suspect if he hadn't had theological reasons to prefer the number seven to the number six, he'd have left indigo off the list.

The other colors are all quite distinct, and seem to have their places in the spectrum. The continuous spectrum image on the left is a rendering intended to appear as much like a natural spectrum as is possible on a monitor screen. The color blocks I placed near it are, in the case of Red, Yellow and Green, pure rgb colors (r, r+g and g), while the color I labeled Indigo is actually the rgb Blue (b).

The "Orange" is r+0.5g, the "Blue" is b+0.5g, and the "Violet" is b+0.5r. It is likely that "Blue" to Newton was even closer to Cyan (b+g), but it is clear he demarcated a range of color very near the spot in the spectrum at which the R cone in the eye has minimum reaction, the purest blues the eye can see, and labeled it Indigo. The purplish look of the violet range is because the R cone has an extra response peak there.

Isaac Newton did pretty well, having as yet no scientific basis for the colorimetry of the normal eye. We can be sure, though, that he had pretty normal (or "ordinary") vision, because had he been color blind or color-anomalous, he'd have been unable to distinguish this many major hues. Now that we know more about color opposition and have more scientific colorimetry available, old Mr. Biv is giving way to RyGcBm, which is pretty hard to render as a name!

No comments: