Sony G90 - Manual (Page 66)

V I D E O
olor is critical to the performance of any home the-
ater. Most of us instantly recognize the problem with
our neighbor’s TV, orange faces that look painted for
Halloween or dull washed-out colors in a parade. We may
not have problems like that in our equipment, but even sub-
tle errors in color accuracy will produce unnatural flesh-
tones or destroy the carefully painted vision of a master cin-
ematographer. So I want to discuss some basics of color
that apply to video – the factors that are required for a dis-
play to achieve accurate color and how we measure and
present color accuracy to you.
1. The Physics of Color
The subject of color science could easily fill this book. But
all we need to know is that color is a characteristic of light
defined by its spectral content, i.e., the distribution of ener-
gy at different wavelengths. The visible wavelengths of light
are roughly from about 380 nm (nanometers) to 780 nm. An
example of one color of light is shown in Figure 1.
2. Human Color Perception
In the human eye, light enters through the pupil and forms
an image on the retina, which has photoreceptors that con-
vert light into signals that are processed by the eye’s neural
circuits, which then transmit information to the brain.
Vision in normal lighting depends on photoreceptors called
cones
. (Our vision at night depends on photoreceptors
called rods that have no color-discrimination capability, so
we are all colorblind in dim light.)
There are three types of cones with different spectral
responses that are sensitive to long, medium, and short
wavelengths of light. They roughly match the spectral dis-
tributions of the colors red, green, and blue. Their respons-
es are shown in Figure 2. These response plots have been
VIDEO INSIGHTS
. . . . . . . . .
An Introduction to Digital Video
Part 2: Video Color Concepts
G R E G R O G E R S
Two conditions are necessary
to achieve perfect display
color accuracy. The grayscale
must maintain a perfect D65
color temperature across the
entire brightness range of
the display, and the CRT
phosphors must match the
SMPTE C standards…For this
reason, the blue-filter
method [of calibration] must
be considered an approxima-
tion for consumer monitors.
Fig. 1