CET Perceptually Uniform Colours

The University of Western Australia's Centre for Exploration Targeting (CET) provide a collection of perceptually uniform colour palettes, which can be used to display geological, geophysical, and geochemical data that vary over a continuous range.

Perceptually uniform means that the visible difference between any two colours in a palette only depends on how far apart they are on the palette. The actual hue, saturation, or brightness of each colour is irrelevant.

In other words, the difference between two colours at the dark end of a palette, separated by 10 units (in the colour space), will appear to be the same as two colours separated by 10 units at the bright end of the palette.

The advantages of this uniformity are to:

• Avoid flat spots, where locally low perceptual contrast can hide small but important details
• Avoid false anomalies, where locally high contrast can appear to represent a structure that isn't really there

Palettes are divided into the following categories:

• Linear: colour ramps suitable for general purpose use
• Diverging: suitable for data with values that lie above and below a reference value
• Rainbow: for general purpose use; better suited to presentation maps than technical mapping
• Cyclic: colours match at each end. Best for angular (e.g. azimuth) data
• Isoluminant: colours in these palettes have a constant perceptual lightness. Best used in conjunction with relief shading

Colours by Peter Kovesi. Good Colour Maps: How to Design Them:

[arXiv:1509.03700 [cs.GR] 2015|https://arxiv.org/abs/1509.03700]

The University of Western Australia, Centre for Exploration Targeting (CET): Perceptually Uniform Colour Maps