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Monday, July 7, 2003

Remember the colorblind test, those circular images made up of a bunch of tiny circles that formed a number in a distinctive color? Or, uh, maybe you see a nice random pattern? The Ishihara test [1] uses colors that can be confused, such as unsaturated greens, pinks, and beige's to identify color vision anomalies.

Go try this Ishihara Quickie Test to see how it works.

Plate 21 presents an interesting phenomenon. Deuteranopes can see a figure, while "normal" eyes cannot. The distinctive color we see in that image is synthesized from dichromatic data coming from two (instead of three) types of cones. You can see more synthesized colors with the after image effect, color fringing and my filtration experiment.

In order to explain this, the opponent color space has been devised, with three axes: red/green, blue/yellow and black/white (which is also called luminance.) Opponent color explains synthesized colors: yellow comes about by removing blue and green results from reducing red's contribution to the overall brightness. In this way, colorblind people can see a whole range of colors that tricolor theory would suggest cannot be seen by someone without M (green sensitive) cones. [2]

Opponent colors can be translated to tricolor coordinates:

[r,g,b] = C X [r/g, b/y, w/b]

where C is an appropriate 3X3 matrix. [3]

adapted from a diagram at York U.

The new color space arises from the interconnections between neurons within each eye. The diagram at right is a schematic of those connections. You can think of the output channels as the red channel, the blue channel and the white channel. Although deuteranopes lack M cones, thus cannot code green directly, it is synthesized by being not blue, yet not red. The green we see, however is not qualitatively the same as yours.

The red, blue, white colorspace reminds me of the starting point for this exploration. Did Goethe really see this colorscheme through his prism? Stay tuned, I'll try to recreate his observations in the conclusion (continued...)


1. How the Ishihara test is made.

2. A. Orazem and H. Scheibner A, Der Ophthalmologe volume 94, number 3, March 25, 1997 - a perceptual mapping of the deuteranopic colorspace as a subset of the CIE chromaticity diagram.

3. RGB to opponent channel conversion matrices (B. A. Wandell, Foundations of Vision, 1995)

Hurvich and Jameson, recreated the spectrum by mixing opponent colors in 1955 and Ewald Hering translated the color wheel into the four opponent colors in 1920

There is an alternative process that may also explain color synthesis, rod cone interactions:

Brenton and Cowen ( J Opt Soc Am. 1981 Oct;11(10):1220-3) Rod-cone interactions account for wide field trichromacy

Kilavik and Kremer (Retinal Physiology preprint 1999) Rod and L-cone Interactions in a Deuteranopic Observer

Kremers and Scholl (Vis Neurosci. 2001 May-Jun;18(3):339-51) more rod cone interactions




Speaking of Dave Winer (below), Google has 'de-appreciated' his website when searching for "rss". Maybe Andrew Orlowski is gonna get his way after all. Dave asks the interesting question, whether Google is downgrading blogs consistently.

About a month ago, search results pointing to this blog were de-appreciated, in fact I am now Google's #4 Chris 101.

So I thought, maybe "Heilman Gallery", nope - I'm behind non-blogs by the paperweight guy, my sister, and a Heilman who shoots his HVAC.

Hey! I can do ducts:


Wu wu.

When I read Andrei Linde's 1990 book on quantum inflation (with cartoons,) I was hooked. I corresponded with Frank Reed and others on the sci.astro newsgroup to cook up my own interpretation of the theory. I stuck it on a back page of another website, and promptly forgot it.

This afternoon, I (finally) read Max Tegmark's May 2003 Scientific American article about parallel universes, and BAM!, there it was. I lacked the mathematical sophistication to sort it out then, and still do. But I've been playing with linear algebra lately, what with the color and wine experiments, so I'm once again encouraged. (Oh boy! Obscure blogging material!)

In a tangental, yet illustrative coincidence, Giordano Bruno, who posed a universe of many worlds in 1584, reminds me of Dave Winer. Does this give us an insight into where information science will be in 431 years?

© Copyright 2004 by Chris Heilman.