Icons, Electrons, Photons and Neurons - Color Science for Computer-Human Interface Designers

Charles A. Poynton, Sun Microsystems

Seminar on People, Computers, and Design
Stanford University April 15, 1994


Interface designers select colors for use in computer systems, but often have limited knowledge of the color reproduction capabilities of those systems. Interface designers often have to design icons or acquire images on one system, but deliver the icons or images to a user on another system whose color capability is different.

In this presentation, I will outline -- and demonstrate -- how color is reproduced in the digital domain. I will expose some of the problems of color interchange in computing, and outline some solutions.

VISUAL PERCEPTION. I will begin the presentation by explaining the features of perception that are important to color, such as contrast ratio and surround conditions. I will show you pictures of some pixels in various media, and explain how their structure influences image quality.

REPRODUCTION. I will explain how the spectral energy distribution of physics relate to perceived color, and show how a color can be expressed as three numbers. You were taught in grade school that red, yellow and blue are the primary colors, but those primaries can't be mixed to produce a full-color image. I will explain -- and demonstrate, using three slide projectors -- how red, green and blue light can be mixed to produce full color. I will outline why some scanners have good color reproduction and others don't, and tell you how it is that a specific set of RGB values can produce one set of colors on one system and a different set of colors on another system.

CODING. I will explain the properties of visual perception that allow color images to be represented in compact coding systems such as YUV and YCbCr that have a limited number of bits per pixel.

USER INTERFACE. Finally, I will explain how concepts of visual perception, color reproduction and color coding can be used to improve the appearance of icon, display elements and images. I will outline some issues of color selection in the computer-human interface, and explain the failings of the HSB and HSV systems for color selection. Scientists often scoff at statements such as "blue is a receding color", but I will introduce the scientific basis for that statement, and begin to bridge the gap between the art and the science of color in user interface design.


Charles A. Poynton is a Staff Engineer at Sun Microsystems Computer Corporation in Mountain View, California, where he is working to integrate television technology -- particularly HDTV and accurate color technology -- into computer workstations. He's Canadian, eh: he sometimes spells colour with a "U".


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