USL PCA-100 - Manual (Page 7)

- 6 -
PCA I
NSTRUCTION
M
ANUAL
Ultra Stereo Labs, Inc.
Figure 4
Measuring Color
The measurement of length and weight are relatively simple tasks. They are
both one dimensional. The measurement of color is much more difficult, as
is the description of color. It is multi-dimensional. The apparent or subjective
color of an object or surface is also affected by many things. The color or
spectral content of the light on the surface strongly affects the apparent color.
For instance, sunlight, fluorescent light and tungsten light all make the color
look different. There is also a significant difference in the color sensitivity of
the eyes of various people. The size of the object and the colors in the
background also make a difference in the apparent color.
An international commission called the CIE established a system for accurately
quantizing color in 1931. This system establishes the basic attributes of color
as hue, saturation and lightness. Hue refers to the actual color classification
as we know it, as green, blue, red, etc. Saturation is the amount of color, or
the “brightness” or vividness of that color. For instance, a subdued rust red
has a lower red saturation than the bright red paint that a sports car might
have. Lightness refers to the light or dark characteristics of the color. A dark
blue would have lower lightness than a sky blue color, given the same hue.Based
on a large amount of experimental evidence, the CIE established the color
sensitivities of the human eye for the primary colors of red, green and blue,
(see figure 4). The tri-color or tristimulus curves are called the color matching
functions of the standard observer.