Mathematical Topics from 3D Graphics - 3D Math Primer for Graphics and Game Development - page 354

phenomena. The RGB basis is not the only color space, nor is it necessarily
the best one for many purposes, but it is a very convenient basis because
it is the one used by most display devices. In turn, the reason that this
basis is used by so many display devices is due to the similarity to our own
visual system. Hall [29] does a good job of describing the shortcomings of
the RGB system.
Since the visible portion of the electromagnetic spectrum is continuous,
an expression such as f( x , ω out ,λ) is continuous in terms of λ. At least

it should be in theory. In practice, because we are producing images for
human consumption, we reduce the infinite number of different λs down to
three particular wavelengths. Usually, we choose the three wavelengths to
be those perceived as the colors red, green, and blue. In practice, you can
think of the presence of λ in an equation as an integer that selects which
of the three discrete “color channels” is being operated on.

ω in ,

Key Points about Color

• To describe the spectral distribution of light requires a continuous

function, not just three numbers. However, to describe the human
perception of that light, three numbers are essentially su cient.

• The RGB system is a convenient color space, but it's not the only one,

and not even the best one for many practical purposes. In practice,
we usually treat light as being a combination of red, green, and blue
because we are making images for human consumption.

You should also be aware of the different ways that we can measure
the intensity of light. If we take a viewpoint from physics, we consider
light as energy in the form of electromagnetic radiation, and we use units
of measurement from the field of radiometry. The most basic quantity is
radiant energy, which in the SI system is measured in the standard unit
of energy, the joule (J). Just like any other type of energy, we are often
interested in the rate of energy flow per unit time, which is known as power.
In the SI system power is measured using the watt (W), which is one joule
per second (1 W = 1 J/s). Power in the form of electromagnetic radiation is
called radiant power or radiant flux. The term “flux,” which comes from the
Latin fluxus for “flow,” refers to some quantity flowing across some cross-
sectional area. Thus, radiant flux measures the total amount of energy that
is arriving, leaving, or flowing across some area per unit time.