Black and White in Photoshop I - Black and White in Photoshop CS4 and Photoshop Lightroom - page 128

Mixed Filters
photographers often use orange and red i lters to cancel blue and green,
making skies dark and foliage rich in tone. Careful selection of these color
i lters allows the photographer to decide which colors in the image will
produce the brightest or darkest tones.
How color i lters in black and white make color i lm
Even when photography was only black and white, visionaries were already
laying the foundations to move photography into color. In the 1860s, less than
30 years after the introduction of Daguerreotype, the method of using color
i lters with black and white i lm was utilized by James Clerk Maxwell, who
experimented with a three-image projection process to create a color image
from black and white i lm. He presumed that a color image could be created
by exposing three monochrome images of the same subject, exposing each
using a dif erent color i lter before the lens. Each of the red, blue and green
i ltered exposures was then projected using three lanterns, each equipped
with the corresponding colored i lter. The red and green i lter together
created a yellow image, and all the three colors together created a white
image. The i nal image, although far from perfect, included all of the original
colors in the subject. This experimentation laid the foundation for not only
color photography but also the Technicolor process used well into the
21st century to create movies in color.