COLOR IN STEREO 121our color perception changes to transform this golden yellow
into “white.”
“White” might be defined as the color of the predominating
illumination.
Now with such a change as that, is it any wonder that the
color value of daylight can change without our being aware of
it? In fact even training cannot teach us to perceive such changes
by our unaided visual sense, unless the change is relatively great.
But any change perceptible to the most delicate color perception,
is many times as great as the amount of change necessary to throw
the color film off balance.
So, if you want to make good color films, the best way is to do
what you can to assist the film in its job.
COLOR TEMPmTuRE.-Under certain laboratory conditions,
there is a very close relationship between the temperature of an
object and the exact color of the light which it emits. This rela-
tionship has been studied and the color-temperature scale worked
out. The color is designated in degrees of the Kelvin scale and
is usually written “K.” We are not going into such factors as
a “black body” nor “absolute temperature.” It is enough to know
there is a scale of color temperature which we can use, and which
is reliable.
In this scale we have a constant change characteristic of a hot
body growing steadily hotter. The first appearance is red, as the
temperature rises, so does the predominant hue, and with green
added to red we have the yellow of incandescence. Later the
growth of blue produces a true “white” and as this is raised, the
red decreases and the color becomes definitely blue-white, then
blue. Note that in all of these changes, we do not have a hap-
hazard scramble of colors, but simply a changing balance of red
and blue, the colors which represent the lowest and the highest
heat of incandescence.
Because this is true, all we need is a set of filters divided into
two categories; one set to absorb blue the other to absorb red.
If these are graduated in strength, you can convert the photo-
graphic color balance of any common light to that of any other.
You can run the scale with Kelvin degrees. You can use any type
or make of color film with any ordinary kind or color of light (of