1. Visualization Friday Forum
Rachael Brady
Visualization Friday Forum
November 22, 2002
Colormaps 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 , October 1995.

2. Color is useful for classification
Color is not needed to understand shape, spatial relationships of objects, movement
Some objects differ from their surroundings primarily by color
Food: Is this fruit ripe? Is this meat putrid? What kind of mushroom is this?
Material: What kind of stone is this (for making an axe or knife)?
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
Yet another reason not to use blue to indicate the shapes of objects; it seems to be ignored in the Luminance calculation.
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.
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 Field Size Conventions
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
To enable color-blind people too view these changes as well, avoid maps that differ only in the red/green channel.
Large areas, such as map regions, should use low contrast and vary slightly from one another (but have borders between).
This enables small, vivid-colored targets to be seen against the background.
Conventions: You may not always follow the conventions in a scientific domain, but you want to know when you are not and explicitly state it.
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
XXX This is not the blackbody radiation spectrum
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? Zero in range? High spatial frequency?
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.