Good Colour Maps: How to Design Them Peter Kovesi Centre for Exploration Targeting School of Earth and Environment The University of Western Australia Crawley, Western Australia, 6009
[email protected] September 2015 Abstract Many colour maps provided by vendors have highly uneven percep- tual 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 discon- tinuities 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 incre- mental 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. Fi- nally, a set of new basis colours for the construction of ternary images arXiv:1509.03700v1 [cs.GR] 12 Sep 2015 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. 1 Introduction A colour map can be thought of as a line or curve drawn through a three dimensional colour space.