File Exchange Pick of the Week

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Generate Distinct Colors for Your MATLAB Plots

Brett's Pick this week is "Generate Maximally Perceptually-Distinct Colors,", by Tim Holy.

Today, I'm going out on a limb: I'm going to Pick a new file from a new File Exchange author. As of this writing, "Generate Maximally-Perceptually Distinct Colors" (GMPDC)--the author's first File Exchange submission (welcome!)--has been downloaded only three times. (My download was the third.) However, I was excited to see this file, and I know it will come in handy. In fact, I've often considered writing something like this myself--but have never gotten around to it.

So what does GMPDC do? It provides an easy way to generate distinct, differentiable colors in which to plot a long sequence of objects (like lines).

MATLAB ships with several built-in colormaps that are useful in different situations. One of those, "lines," is a repeating array of seven distinct colors. By default, MATLAB axes cycle through these seven different colors when plotting lines:

% You can see the default color order with:


% and you can verify that they are the same as the repeating sequence in
% "lines" with

ans =
         0         0    1.0000
    1.0000         0         0
         0    1.0000         0
         0         0    0.1724
    1.0000    0.1034    0.7241
    1.0000    0.8276         0
         0    0.3448         0
ans =

Sometimes, however, I want to be able to differentiate more than 7 lines or plots. In the past, I've monkeyed about with custom color orders I made up on the fly. Tim makes it easy to standardize those colors; the colors returned by GMPDC are consistent regardless of the number of colors you request. As a bonus, one can specify a background color as an optional input to ensure that your colors differ from the background, as well as from each other:

Tim worked in the L*a*b* colorspace, which was designed to approximate human color perception. His code is solid and well implemented, with nice documentation. I hope this file is a harbinger of more good stuff to come from this author.

Note that the default "colororder" property can be readily modified. In fact, I just added a line to my startup file to set my colororder to be distinguishable_colors(20). Thanks, Tim!

Try GMPDC for yourself; you'll be modifying your own startup files before you know it! let us know what you think, or leave a comment for Tim here.

Published with MATLAB® 7.11

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