Service manual

STP 11-25R13-SM-TG
S - 12
S-11. Luminosity Curve.
The fact that the human eye does not perceive each color with equal efficiency is due in some way
to the physical construction of the eye. It is believed that the cones of the retina respond to color stimuli
and that each cone is terminated by three receptors. Each receptor responds to a different portion of the
spectrum, with peaks occurring in the red, green, and blue regions. An average color response curve
was developed by eye tests conducted on a number of people. This average is shown in Figure S-10
and is referred to as the luminosity curve.
Figure S-10. Luminosity Curve
a. The curve is a plot of response versus wavelength, with the maximum response occurring at
approximately 555 nanometers and that less response is indicated on either side of that point.
b. From this information you can see that the average person is most sensitive to yellow-green
light.
S-12. Qualities of Color.
There are three qualities that are used to describe any one color. These qualities are hue,
saturation, and brightness.
a. Hue
is a quality that is used to identify any color under consideration, such as red, blue or
yellow. Hue, which defines the wavelength of the color, would be synonymous with frequency, which
defines the wavelength of the radio wave.
b. Saturation
is a measure of the absence of dilution by white light and can be expressed with
terms such as rich, vivid, or pure. Saturation, which defines the purity of the color, would be synonymous
with signal-to-noise (S/N) ratio, which defines the purity of the radio wave. A 100-percent saturated color
contains no white light.
c. Brightness
defines the amount of light energy that is contained within a given color. Brightness
is synonymous with amplitude, which defines the amount of energy in the radio wave. Brightness is a
characteristic of both white light and color; hue and saturation are characteristics of color only. The
brightness of a color can be affected without changing the saturation. The reverse is also true.