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Colour perception and colour blindness March 7, 2008

Posted by David Corney in Uncategorized.
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A short post about three of my favourite things: colour vision, Matlab and the Tokyo subway system[1].

I’ve recently been reading Jeff Mather’s blog about photography and in particular, Matlab-based image processing. He describes a recent presentation by Yasuyo Ichihara about colour perception by people who are colour-blind, or “colour confused” as they seem also to be called. She (Ichihara) is part of a not-for-profit group called the “Color Universal Design Organization” (CUDO). They promote the sensible and considerate use of colour for things like presentations, graphs, street signs… and the Tokyo subway system. The same group includes Masataka Okabe and Kei Ito, who have a nice summary about the importance of colour design, including a potential importance to academics: “There is a good chance that [any] paper you submit may go to colour-blind reviewers. Suppose that your paper will be reviewed by three white males (which is not unlikely considering the current population in science), the probability that at least one of them is color-blind is whopping 22%!” Worth bearing in mind!

They also point out that using red and green stains in DNA microarray chips is perhaps not the smartest move, a complaint I’ve heard before. (I used to work in UCL’s bioinformatics group.) I think it’s pretty universal though, so unlikely to change…

The CUDO group promote “three plus one” key principles which I’ll quote verbatim:

1 Choose colour schemes that can be easily identified by people with all types of color vision, in consideration with the actual lighting conditions and usage environment.

2 Use not only different colours but also a combination of different shapes, positions, line types and colouring patterns, to ensure that information is conveyed to all users including those who cannot distinguish differences in colour.

3 Clearly state colour names where users are expected to use colour names in communication.

+1 Moreover, aim for visually friendly and beautiful designs.

There’s some nice pictures back on Jeff’s blog too, showing what a pile of red and green peppers look like, if you’re red-green colour blind. Turns out they look pretty similar…

Finally, because this post about colour has no colour pictures so far, here’s one I prepared earlier (in the best Blue Peter tradition). This is a display of 1250 colours from the Munsell spectraMunsell Book of Colour, or rather the reflectance spectra measured from the book by the Colour Research group at the University of Joensuu (Finland).

Each of the 40 mini-graphs here is one page from the book, and each line is the reflectance spectra of one colour “chip”. The x-axis goes from 400nm (violet/blue) to 700nm (red) for each graph, and each line is drawn in the RGB colour derived from the spectrum using the Stiles and Burch (1959) “10-deg, RGB Color Matching Functions”.

All of which sets me up for a future post about how a repeatedly changing colour of incident light could allow a completely colour blind person to still perceive colours…

[1]I have a t-shirt to prove it. No, seriously, I do…
[2]A full paper by members of the CUDO group is available too.

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