1.1 Why do I need to know about basic color perception?
1.2 What are "aperture" and "surface" color?
1.3 What is color?
1.4 How are lights and colors classified?
1.5 How many primaries are there?
1.6 What is the difference between luminance and brightness?
1.7 What is the difference between color and brightness contrast?
1.8 What are Trichromatic and Opponent Process Theory
1.9 What are The Basic Color Vision Tasks?
1.1 Why do I need to know about basic color perception?
"When you believe in things you don't understand, then you suffer."
-Noted philosopher Little Stevie Wonder.
Practitioners in any field can work in one of two ways, "cookbook science" or "explanatory science" (Gale, 1979). The "cookbook science" approach uses a set of rules, i.e., "IF this is true THEN do that." In cognitive circles, this is called "heuristic" or "shallow knowledge" because there is no deep understanding. The "explanatory science" approach uses "deep knowledge" or "first-principles." There is an understanding of "why" rather than merely an application of "that."
The cookbook science approach may suffice in the majority of routine problems. But it fails with more complex or extreme problems or when there is a shift in the context. For example, using bird migrations might provide a good rule for when to plant crops. It may work beautifully, so there is no need to understand weather patterns, soil conditions, etc. But if the birds changed their patterns, became extinct or if you moved to a different hemisphere, the rules would no longer work. If you understood about weather and soil, however, then you could still know when to plant.
Time and money constrain people working in applied fields, so many people prefer cookbook science. When encountering a problem, the optimal solution is a single number: neat, efficient and requiring a minimum amount of time to obtain and mental resource to apply. Many fields have books of tables and standards which a designer can directly apply to a wide variety of situations. Problem solved, now let's go on. There's no need to understand; just turn the cookbook to the right recipe.
When it comes to designing computer interfaces, information displays or other artifacts involving visual perception, this cookbook science "just give me one number" (or at least a simple IF-THEN rule) strategy is only partly successful. Most aspects of perception are highly dependent on context. In any given situation, there are a large number of complex, interacting variables. Few numbers or guidelines hold true over many circumstances.
Of course, some guidelines are more robust. For example, monitor update
rate should be at least 60 Hz to avoid serious flicker. But even this
simple rule depends on the age and visual condition of the viewer, the
display's size, brightness, colors, phosphor decay characteristics, ambient
illumination plus a few more. Most problems are far more complex: How
many colors should there be in a computer interface? It depends on what
the colors are, how they relate, their location on the screen, the user's
goals, the user's eyesight and on, and on and on.
The designer must also frequently extrapolate and interpolate his/her
past experience as well as guidelines and rules. Not only do circumstances
and goals vary, but the rules change when faced with special needs groups
(color deficients, the elderly and the handicapped), a new technology
or a new medium. Moreover, blindly following ill-understood rules will
cause designers to misapply guidelines and make counterproductive choices.
For example, people frequently make incorrect assertions, such as "blue
is bad for text" because they are misapplying a rule from typography
to CRT screens. As I explain, this mistake would be obvious with a little
knowledge about chromatic aberration, contrast levels of CRT's and a magnifying
glass. In other cases, people waste time desperately seeking guidelines (what
color text is most readable?, etc.) in circumstances where the question
is simply irrelevant. People often ask the wrong questions because they
don't even understand the issues that are involved.
An alternative to finding a guideline is to pore through the library
stacks looking for research that can solve your problem. This can be extremely
time-consuming and the studies, if you ever find the right ones, are almost
certainly performed with equipment, methods, goals and/or users which
differ from those in your current situation. Do these the data generalize
to solve your problem? You need to evaluate the study, decide whether
it was properly performed and how to relate it your situation. A designer
cannot solve these problems without a good background in basic perception
so that s/he can interpret, extrapolate and interpolate as necessary.
More often than not, however, applied studies don't generalize well, so
all you have left to fall back on is either 1) trial and error or 2) a
good understanding of basic color vision.
Lastly, understanding basic color perception provides greater creative
freedom. If you want to manipulate color in predictable ways, then you
need to know what factors affect color discrimination and color appearance,
how various perceptual dimensions vary together, the effect of size and
spatial layout on color etc. Color is a tool and, like any tool, the more
you understand how it works, the better you will use it.
1.2 What are "aperture" and
There are two worlds of color vision,
aperture and surface color. Although this distinction is important for understanding color
science, it is seldom made explicit. Beginners often become confused because experts use
different terminology and subtle variations in concepts when the context changes from one
world to the other.
The world of aperture color is about lights and wavelength. It is typically studied by
scientists examining the most basic aspects of color vision in the laboratory. In this
world, people view small, disembodied patches of color which are usually seen on a black
backdrop with no other objects visible. Moreover observers are dark adapted, at a neutral
adaptation state, etc. to further remove extraneous factors. (Artists also have a similar
term, "local color," to denote color isolated from influences of background and
lighting.) Aperture color is good for isolating the effects of wavelength on color vision,
and explaining color matching and discrimination, the effect of light on cones, etc. But
it is not very good at predicting color appearance under more natural viewing
The world of surface color is concerned with more typical viewing conditions. We
normally see colors as belonging to the surface of objects which are embedded in a scene
and viewed under some form of illumination. Under these conditions, backgrounds and other
objects in a scene can greatly influence perceived color. In fact, colors which appear
identical in aperture viewing can look very different in a scene and vice versa. To
understand color appearance in normal scenes, it is necessary to go beyond the world of
aperture color and wavelength into the more complex world of surface color. Here,
wavelength becomes only one of many factors which determine apparent color.
There is also a rough correlation between aperture and basic color vision on the
one hand and surface and applied color work on the other. People working in aperture
color are usually interested in fundamental limits and properties of human color vision.
The surface color world is often concerned with an applied problem where the medium
constrains human color vision potential. As a result, the answer to many questions, such
as the number of discriminable colors, etc., will differ depending on context. But if you
know the absolute limits of visual capability, then you can always at least make an
Unfortunately, even experts casually move back and forth between the two worlds when
discussing color. For example, in one breath someone might say that "lights of 580
nm. appear yellow" and in the next say "the background can change the apparent
color of an object." These statements would appear somewhat contradictory if you
didn't understand that the first statement referred to aperture color and the second to
surface color. Some other distinctions, notably lightness vs. brightness and saturation
vs. chroma, make more sense when viewed through the aperture-surface dichotomy.
Computer graphics, especially user interfaces, fall in the middle of these two worlds
because they are just patches of color rather than real world scenes or identifiable objects.
Still, backgrounds, illuminants, chromatic adaptation, etc. may be important.