Sony G90 manual An Introduction to Digital Video, Part 2 Video Color Concepts, Physics of Color

V I D E O

VIDEO INSIGHTS

G R E G R O G E R S

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An Introduction to Digital Video

Part 2: Video Color Concepts

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.

Fig. 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.

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.

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