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How to choose a good colormap

How to choose a good colormap

Damon McDougall sharing information about how to choose a good colormap.

Kristen Thyng

July 10, 2014

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  1. How to choose a good colour map Damon McDougall Institute

    for Computational and Engineering Sciences, UT Austin, USA 10th July 2014 1/19
  2. Introduction Most of the content is taken from this excellent

    article: http://www.research.ibm.com/people/l/lloydt/color/color.HTM 2/19
  3. Introduction • Data is a huge aspect of science •

    By and large we (scientists) treat data well. . . • . . . and we visualise it poorly. Why? • Colour maps • Data is of some field f : Ω ⊂ R2 → [0, 1] • A colour is assigned to the output of f (a scalar). Seems reasonable. • Colour map is a function g : [0, 1] → Ω ⊂ R3 • Mismatch in dimensions: R3 versus R • The point? Colour maps can be misleading. 3/19
  4. Hating on the jet colour map Did anybody see Florida?

    • Left: Linear interpolation in RGB space between red and blue. • Right: Changes in data are perceived as proportional changes in colour (subjective) • Right: Domain specific knowledge used to reveal important features 5/19
  5. What have we learned? • Jet is not a great

    colourmap (or is it?) • Two types of information one can glean from a colourmap1 • ‘Value’ or ‘metric’ information • ‘Form’ or ‘structure’ information • Jet is not bad for value information (but not everywhere) • Jet is awful for form information • Jet is not alone—but it is very commonly used • How to pick a good colour map? It depends! 1C. Ware, Color sequences for univariate maps: theory, experiments, and principles, IEEE Computer Graphics and Appliations, 1998. 11/19
  6. What is good for form/structure information? • Colour has 3

    dimensions: hue, saturation, and luminance • Saturation-varying colourmaps are good for low-frequency data • Luminance-varying colourmaps are good for high-frequency data • The human brain is very bad at interpolating hue2 • Perceptually-based colourmaps • Equal steps in data are perceived as equal steps in the colour space 2Conclusion from psychophysical experiments by S. S. Stevens (formerly at Harvard) 12/19
  7. Thank you. Pssst. Jet is the default colourmap in matplotlib.

    Anybody want to fix it? Submit a PR! Link to slides: https://github.com/dmcdougall/scipy14-colormaps 19/19