Color Huamin Qu Hong Kong University of Science and Technology
Outline Color and Color Space Color for information visualization Color harmonization
Visible Light Visible Spectrum of Light Wavelength
Human Vision – Human Cone Response to Color three cone types (S,I,L) correspond to B,G,R Wavelength (nm) Relative response BlueCyanGreenRed 490 ILS Slide Courtesy of Chester F. Carlson Center for Imaging Science
Color Matching Process From “Foundations of Vision” by B. Wandell
The Tristimulus Theory Any perceived color could be generated by some combination of three primary colors RGB Curve Negative Intensity Figure courtesy of D. Forsyth
CIE XYZ CIE (Commission Internationale d’Éclairage) CIE tristimulus values XYZ Y is luminance All positive curves Figure courtesy of D. Forsyth
Color Spaces Use color matching functions to define a coordinate system for color. Each color can be assigned a triple of coordinates with respect to some color space (e.g. RGB). Devices (monitors, printers, projectors) and computers can communicate colors precisely.
CIE XY Chromaticity Diagram
RGB Color Space
Some Colors Cannot Be Displayed
CIE LUV Color Space A uniform color space used to illustrate or quantify relative color differences. The Euclidean distance between two points is a measure of the difference between the colors.
1976 CIE u'v' Chromaticity Diagram
HSV Color Space HSV: Hue Saturation Value - Hue: the color type - Saturation: the “ vibrancy ” of the color - Value: the brightness of the color From Wikipedia
Color Wheel
Combining Colors Additive (RGB) Shining colored lights on a white ball Subtractive (CMYK) Mixing paint colors and illuminating with white light
Usage of Color for Visualization To label To quantify
Nature of your data -Sequential -Diverging -Qualitative
Qualitative
Rules for Qualitative Color Scheme The maximum number of colors which can be used is usually between 6 to 12 The 12 recommended colors 1.Red 2. Green 3. Yellow 4. Blue 5. Black 6. White 7. Pink 8. Cyan 9. Gray 10 Orange 11. Brown 12. Purple
Color Family
Color for Sequential Data
Use a sequence that varies monotonically on at least one of the opponent color channels Examples are – red to green – yellow to blue – dark to light – low saturation to high saturation
Divergent Color Scheme
Color Harmonization 3Z6Q 3Z6Q
Color Harmonization
Monochromatic
Analogous
Complementary
Triadic
Tetradic
Color Used in Tableau
Color from DataWatch
Bad Color: Red + Blue
Colorblind
Logo color
Red = Adventure. Energy. (Coca Cola) Pink = Compassion. Nurturing. (Breast Cancer Research Foundation; Barbie) Orange = Cheerful. Warm. Optimistic. (Amazon) Yellow = Happy. Bright. Sunny. (McDonalds) Green = Health and Healing. Environment. Organic. (Whole Foods Market; Starbucks) Blue = Honesty. Trust. Dependability. (Facebook; Pfizer) …
Using Color for Visualization Coding qualitative vs. quantitative data - use differing hues for qualitative data - use continuous variation for quantitative data Use familiar color coding - “ red ” for hot, dangers, cautions, & warnings >> watch for culture conflicts (e.g., red in Asian cultures)
Coding Information with Colors Limit color numbers - (5- 10) Don ’ t have blue and red together Be careful with blue (small blue objects, blue objects on dark background). Our eyes are not sensitive to blue Red-Green are good color combinations. For people with red-green color blindness, Yellow- blue are usually OK.