Graphics Reference
In-Depth Information
• The eye is approximately logarithmic: Each time you double the light
energy (without altering the spectral distribution) arriving at your eye, the
brightness that you perceive will increase by the same amount (i.e., the
brightness difference between one unit of energy and four units of energy
is the same as the brightness difference between 16 units and 64 units).
Most of what a majority of people “know” about color is false, or at the very
least, it is true only under very restrictive conditions of which they are unaware.
Try to read this chapter with an open mind, forgetting what you've learned about
color in the past.
Before we discuss the physical and perceptual phenomena involved in color, let's
consider some implications of color: Because objects have different colors, and
because you can tell the difference, you can use color in a user interface to encode
certain things. For instance, you might choose to make all the icons in a text editor
having to do with high-lighting be based on a yellow background, reflecting the
idea that many highlighter markers are yellow. Similarly, you might choose to
make all the high-priority items (or all the items with significant consequences,
like “Close this document without saving changes”) be drawn in red, to attract the
user's attention.
But a significant number of people are colorblind (or, more accurately, color-
perception deficient)—they perceive different wavelength mixes in a different way
from the rest of us, and two lights that appear red and green to most people appear
to be the same color to a red-green colorblind person. About 8% to 10% of men
are red-green colorblind; there's also yellow-blue colorblindness (quite rare), and
even total colorblindness, but this is very rare. Colorblindness is very rare (less
than 1%) in women.
From a computer graphics point of view, the critical consequence of color-
blindness comes in interface design: If you rely solely on color-coding to indicate
things, about 5% of your users will miss the idea you're trying to indicate.
The effects of individual colors are important, but even more significant is the
challenge of selecting groups of colors that “work well together.” Such selections
are in the domain of art and design rather than science. As you design a color
palette for a user interface, consider the following.
• Someone else may have already developed a good set of colors; try starting
from interfaces that you like and working with
their
colors.
• Use a paint program to see how each of your colors looks when placed atop
or near each of your other colors, or in groups of three.
• Consider how your colors will look on various devices; certain colors that
look good on an LCD screen may look bad when printed. If this matters in
your application, you'll want to design with this in mind from the start.
We begin our discussion of color with the physical aspects. As we described
in Chapter 26, light is a form of electromagnetic radiation; visible light has
wavelengths between 400 and 700 nanometers. An ordinary fluorescent lamp
