The Scientist’s Rainbow

How many colors do you need? Color costs money to print, and disappears when you laser print, fax, or photocopy a graphic, and some people (like me) have trouble seeing it. This is why I use grayscale graphics wherever possible, saving color for emphasis (I’ll say more about this in a future post).

The opposite of this approach is a graphic that uses every color in the visible spectrum for no apparent reason. One finds this so often in computer-generated charts in scientific publications that I call it The Scientist’s Rainbow. Once identified, you’ll see it everywhere. Here’s a good example.


The original had no key to the colors, and they seem to correspond only to the scale on the y-axis. One way of testing whether color is conveying any information is to convert the graphic to grayscale.


So this color was just for decoration—yes, rainbows are pretty. But sometimes the Scientist’s Rainbow is actually impeding communication. The visual spectrum isn’t arranged in an intuitive order, and if there’s a scattering of colors it can be pretty hard to extract values for the mess.


We sould start by extracting the meaningful stuff from the empty space. I expanded the vertical scale until the pixels were squares, not rectangles, converted everything to grayscale, blurred away the sharp edges, and messed with the contrast a little.


Note that the lightest areas are not the highest intensity, but correspond to yellow and green in the middle of the spectrum. The highest values on the colored graph are reds, which are as dark as the blues at the other end (so the original would be meaningless as soon as it was photocopied). We’d be best to plot the raw data again using a black-to-white scale, although some clever color substitution in Photoshop could also convert a rainbow to shades of gray. That sort of work is best left to interns though, with their love of drudgery.