1. Colormaps 101 Sources – Russell Taylor Comp 290 course notes Colin Ware – Perception for Design IBM Web Site An Excellent Paper: A Rule-based Tool for Assisting Colormap Selection, L. Bergman, B. Rogowitz and L. Treinish. Proceedings of the IEEE Computer Society Visualization '95 pp. 118-125, October 1995. Rachael Brady Visualization Friday Forum November 22, 2002

2. Color is useful for classification Color is not needed to understand shape, spatial relationships of objects, movement Laboratory assistant went 21 years without realizing he was color- blind

3. Color Space: RGB Taken from Russell Taylor II, UNC CS 290 Course Notes

4. Colorspace: HSV Taken from Russell Taylor II, UNC CS 290 Course Notes

5. Opponent Process Theory (Hering 1920) The six elementary colors are paired on 3 orthogonal axis: Black-White, Red-Green, Yellow-Blue Modified from Russell Taylor II, UNC CS 290 Course Notes

6. Color Category Perception Task: Name the colors Regions same > 75% Nonuniform sizes Why “rainbow scale” is so nonuniform The fact that only 8 hues were named out of 210 different colors indicates that there may be only a few colors available for labeling. Taken from Russell Taylor II, UNC CS 290 Course Notes

7. Other Color Issues Color Blindness –Most red/green color blind (10% of males, 1% females) Field Size –Avoid small spots, especially in yellow/blue –Small areas: strong, highly-saturated colors –Large areas: low saturation with slight differences Conventions –U.S.: Red = danger, Green = life –China: Red = life, Green = death –Some scientific domains have color conventions Taken from Russell Taylor II, UNC CS 290 Course Notes

8. Designing of a colormap Perceptually Ordered Sequence is required, such as black- white, red-green, blue-yellow, or saturation (dull->vivid) Note: a perceptually ordered sequence will result from a series of colors that monotonically increase or decrease with respect to one or more of the color opponent channels Use a Luminance Ordered Sequence for High Spatial Frequency Data Use a Saturation Ordered Sequence for Low Spatial Frequency Data Use several discrete colors when it is necessary to read back values (to avoid contrast effects)

9. Example Colormaps Source: Ware, Perception for Design

10. Not ordered (red at both ends) Taken from Russell Taylor II, UNC CS 290 Course Notes

11. Luminance (Gray) Scale Taken from Russell Taylor II, UNC CS 290 Course Notes

12. Saturation Scale Taken from Russell Taylor II, UNC CS 290 Course Notes

13. Hue Scale Taken from Russell Taylor II, UNC CS 290 Course Notes

14. Hue+Luminence Taken from Russell Taylor II, UNC CS 290 Course Notes

15. Hue+Saturation Taken from Russell Taylor II, UNC CS 290 Course Notes

16. Black Body Radiation Taken from Russell Taylor II, UNC CS 290 Course Notes

17. Colormap Choice Should be Linked to Task Atmospheric Motion Bergman, Rogowitz, Treinish, IEEE Vis ‘95

18. Colormap Choice Should be Linked to Task Pollution Levels Bergman, Rogowitz, Treinish, IEEE Vis ‘95

19. Color Interaction Bergman, Rogowitz, Treinish, IEEE Vis ‘95

20. Color Interaction Bergman, Rogowitz, Treinish, IEEE Vis ‘95

21. Trumbo’s Principles Univariate –Order: ordered values should be represented by perceptually-ordered colors –Separation: significantly different levels should be represented by distinguishable colors Modified from Russell Taylor II, UNC CS 290 Course Notes

22. Ordered (and double-ended) Tufte ‘97, pg. 76. Taken from Russell Taylor II, UNC CS 290 Course Notes

23. Not ordered Tufte ‘97, pg. 77. Taken from Russell Taylor II, UNC CS 290 Course Notes

24. Double-ended Scale Two distinct scales joined at neutral middle Characteristics –segments values into two groups –can emphasize both extremes of data range Taken from Russell Taylor II, UNC CS 290 Course Notes

25. Double-Ended Income Olson ‘97, fig. 11-8. Taken from Russell Taylor II, UNC CS 290 Course Notes

26. In Summary Interesting values? –Position striking colors at interesting values Zero in range? –Double-ended scale High spatial frequency? –Vary lightness in addition to hue Taken from Russell Taylor II, UNC CS 290 Course Notes

27. Color Theory in Cartography is well developed. Cynthia Brewer at Penn State has a great color creator for discrete, monotonic color sequences. http://www.personal.psu.edu/faculty/c/a/cab38/ColorBrewerBeta.html