A Survey of Color for Computer Graphics

A Survey of Color for Computer Graphics SIGGRAPH 2001
red or to see green is impaired. This type of deficiency appears in approximately 10% of
men. A much smaller percentage (1-2%) are weaknesses in the blue-yellow channel, with
very few people actually “color blind,” or unable to see any hues at all. While most color
vision problems are genetic, they can also appear as a side-effect of medication or illness.
Opponent color theory was first proposed by Herring, in 1878, but was not accepted until
Dorthea Jameson and Leo Hurvich performed controlled experiments in 1955 that verified
the theory. It is now accepted as the first-level processing of the color vision signal
after the cone response. Leo Hurvich has written a textbook, Color Vision, that is based
on this theory. It is also the best technical reference I have found for the modalities of
color vision deficiencies.
Color appearance phenomenon are caused by the relationship between colors, by adaptation
and by cognitive effects based on our knowledge about lights and objects in the real
world. Simultaneous contrast describes the influence of surrounding colors on the perception
of a color. There are several simultaneous contrast examples in the slides. The
simplest model for simultaneous contrast is that the afterimage of the surrounding color is
added into the perception of the surrounded color. Therefore, a gray patch on a dark
background looks lighter (add white) than a gray patch on a white background (add
black). However, the real answer is more complex. In the slides are a set of colored
patches on a background of alternating colored bars. Which bar the patch appears on
changes its appearance, even though the actual surround is identical. Clearly the cognitive
effect, in which we see a patch as being “on” a particular colored bar, is contributing in
this example.
Even a thin outline of a different color can make a big difference in the appearance of a
colored region. The slide labeled the “Bezold Effect” demonstrates this. The only difference
between the two patterns is the color of the outlines; white in one case and black in
the other. But, the overall difference in appearance is quite dramatic. This effect was
named for a 19 th century rug designer, who was able to reuse his designs by this simple
alteration.
Size, or spatial frequency, has a strong impact on the perception of a color. The higher
the spatial frequency, the less saturated the color. This is why the paint on the sample
chip looks less vivid than it does on the wall. In the slide, the two colors really are identical.
Human vision is very adaptable. We are capable of seeing in both very dim and very
bright light. When we move from bright to dim lighting, or vice versa, we can feel our
visual system adapt. Think of this as a gain control on the visual system. For dim lighting,
we turn up the sensitivity. For bright lights, we need to damp it. These phenomena
are called dark adaptation and light adaptation, respectively. In many cases, it is valid to
assume that color appearance is relative to the current black/white levels, and is not effected
by the absolute luminance. However, increasing luminance can produces a
measurable increase in colorfulness (Hunt Effect) and contrast (Stevens Effect).
Chromatic adaptation describes the visual system’s ability to adapt to the color of the
light illuminating the scene. Most color is created by shining light off of objects. While
the reflected spectrum can be measured with colorimetric instruments, changing the light
will change the measured color, sometimes dramatically. But, as we view the world, we
Maureen C. Stone 8
StoneSoup Consulting