APPLIED COLOR SCIENCE
There are three distinct kinds of concepts relating to applied color perception: physical, psychological, and psychophysical. A lot of confusion can be avoided by knowing which kind we're talking about as we go along. While a few physical concepts occasionally crop up, and the user's perceptions are the goal of the display, most of the technical content of applied color perception is in the psychophysical category.
From a purely physical standpoint light is not colored. While there are physical optics dimensions (e.g., wavelength, frequency, quantum energy) that are closely connected with the effect of the light on the human visual system, the color is in the visual system, not in the light. Consequently, physical concepts show up in design of color graphics mostly in their subordinate role within the psychophysical concepts.
In purely physical terms, display primaries are described by their energy spectra, the radiant power at each wavelength of the light.
Color is part of the user's mental response to the light entering the eyes from the display and its surroundings. The mental imagery stimulated by the display is private to the user, which poses challenges to scientific study. Debate about the structure of visual experience started early in the history of philosophy and continues to the present. For our immediate concern, applied color design, we can start with a few highly simplified attempts to describe the structure of color experience.
Most (but not all) color experience can be described within three dimensions. There are several alternative three-dimensional descriptions, but probably the most familiar is hue, saturation, and brightness.
In color graphics design, as in other applied color disciplines, we are mainly interested in how to manipulate physical lights to produce desired perceptual responses in our users. This means we are mostly dealing with psychophysical concepts, concepts that bridge the gap between physical stimuli and psychological responses. Luminance and chromaticity, for example, are psychophysical concepts.
Applied color scientists and basic color scientists both use psychophysical concepts but they have different approaches. The applied science is engineering oriented and need only be concerned with reliable prediction and control. The basic science has the added task of explaining the underlying visual processes.
The psychophysical concepts used in applied work are necessarily approximations. To achieve a standard, shared technical description of the psychological effects of light stimuli, international organizations have developed a "standard observer". This is a hypothetical typical visual system that is described in terms of equations relating its quantitative visual responses to measurable physical statistics of light stimuli. The equations that define the standard observer are based on averages of laboratory measurements of the visual responses of real human subjects to particular light stimuli under particular viewing conditions.
The nature of the
standard observer imposes at least two concerns
for us to keep in mind when designing from psychophysical
Display Hardware and Software. Display hardware issues such as gamut, gamma, and calibration are related to visual psychophysics and affect design of color graphics.
Contrast in Color Graphics. Control of luminance contrast is a
major concern in design of graphics. It is much more difficult in
color graphics than in grayscale graphics.