DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Boynton, Robert M., Human
Color Vision (New York: Holt,
Rinehart and Winston, 1979).
Wandell, Brian A., Foundations
of Vision (Sunderland, Mass.:
Sinauer Associates, 1995).
Perception and
visual acuity 19
Properties of human vision are central to image system
engineering. They determine how many bits are necessary
to represent luminance (or tristimulus) levels, and
how many pixels need to be provided per degree of
picture angle. This chapter introduces the intensity
discrimination and spatial properties of vision.
Retina
The human retina has four types of photoreceptor cells
that respond to incident radiation with different spectral
response curves. A retina has about 100 million rod
cells, and about 5 million cone cells (of three types).
Rods are effective only at extremely low light levels.
Since there is only one type of rod cell, what is loosely
called night vision cannot discern colors.
The cone cells are sensitive to longwave, mediumwave,
and shortwave light – roughly, light in the red, green,
and blue portions of the spectrum. Because there are
just three types of color photoreceptors, three numerical
components are necessary and sufficient to describe
a color: Color vision is inherently trichromatic. To
arrange for three components to mimic color vision,
suitable spectral sensitivity functions must be used; this
topic will be discussed in The CIE system of colorimetry,
on page 211.
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