Colormaps 101

Sources – Russell Taylor Comp 290 course notesColin 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

Color is useful for classification

Color is not needed to understand shape, spatial relationships of objects, movementLaboratory assistant went 21 years without realizing he was color-blind

Color Space: RGB

Taken from Russell Taylor II, UNC CS 290 Course Notes

Colorspace: HSV

Taken from Russell Taylor II, UNC CS 290 Course Notes

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

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

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

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)

Example Colormaps

Source: Ware, Perception for Design

Not ordered (red at both ends)

Taken from Russell Taylor II, UNC CS 290 Course Notes

Luminance (Gray) Scale

Taken from Russell Taylor II, UNC CS 290 Course Notes

Saturation Scale

Taken from Russell Taylor II, UNC CS 290 Course Notes

Hue Scale

Taken from Russell Taylor II, UNC CS 290 Course Notes

Hue+Luminence

Taken from Russell Taylor II, UNC CS 290 Course Notes

Hue+Saturation

Taken from Russell Taylor II, UNC CS 290 Course Notes

Black Body Radiation

Taken from Russell Taylor II, UNC CS 290 Course Notes

Colormap Choice Should be Linked to TaskAtmospheric Motion

Bergman, Rogowitz, Treinish, IEEE Vis ‘95

Colormap Choice Should be Linked to TaskPollution Levels

Bergman, Rogowitz, Treinish, IEEE Vis ‘95

Color Interaction

Bergman, Rogowitz, Treinish, IEEE Vis ‘95

Color Interaction

Bergman, Rogowitz, Treinish, IEEE Vis ‘95

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

Ordered (and double-ended)

• Tufte ‘97, pg. 76.Taken from Russell Taylor II, UNC CS 290 Course Notes

Not ordered

• Tufte ‘97, pg. 77.Taken from Russell Taylor II, UNC CS 290 Course Notes

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

Double-Ended Income

• Olson ‘97, fig. 11-8.

Taken from Russell Taylor II, UNC CS 290 Course Notes

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

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