Good Colour Maps: How to Design Them

TL;DR

This paper discusses the design of perceptually uniform colour maps, emphasizing the importance of uniform perceptual lightness changes, and introduces new design principles, evaluation tools, and basis colours for improved data visualization.

Contribution

It provides detailed requirements for various types of colour maps, critiques existing approaches, and introduces new basis colours for ternary images to enhance visual consistency.

Findings

Identifies issues with existing colour maps, such as flat spots and discontinuities.

Develops specific design requirements for different colour map types.

Proposes new basis colours for ternary images that maintain structure salience.

Abstract

Many colour maps provided by vendors have highly uneven perceptual contrast over their range. It is not uncommon for colour maps to have perceptual flat spots that can hide a feature as large as one tenth of the total data range. Colour maps may also have perceptual discontinuities that induce the appearance of false features. Previous work in the design of perceptually uniform colour maps has mostly failed to recognise that CIELAB space is only designed to be perceptually uniform at very low spatial frequencies. The most important factor in designing a colour map is to ensure that the magnitude of the incremental change in perceptual lightness of the colours is uniform. The specific requirements for linear, diverging, rainbow and cyclic colour maps are developed in detail. To support this work two test images for evaluating colour maps are presented. The use of colour maps in combination with relief shading is considered and the conditions under which colour can enhance or disrupt relief shading are identified. Finally, a set of new basis colours for the construction of ternary images are presented. Unlike the RGB primaries these basis colours produce images whereby the salience of structures are consistent irrespective of the assignment of basis colours to data channels.