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By the end of the 20th cent. digital imaging and processing and
computer-based techniques had made it possible to manipulate images
in many ways, creating revolutionary changes in photography. Digital
technology allowed for a fundamental change in the nature of photographic
technique. Instead of light passing through a lens and striking
emulsion on film, digital photography uses sensors and color filters.
In one technique three filters are arranged in a mosaic pattern
on top of the photosensitive layer. Each filter allows only one
color (red, green, or blue) to pass through to the pixel beneath
it. In the other technique, three separate photosensitive layers
are embedded in silicon. Since silicon absorbs different colors
at different depths, each layer allows a different color to pass
through. When stacked together, a full color pixel results. In both
techniques the photosensitive material converts images into a series
of numbers that are then translated back into tonal values and printed.
Using computers, various numbers can easily be changed, thus altering
colors, rearranging pictorial elements, or combining photographs
with other kinds of images. Some digital cameras record directly
onto computer disks or into a computer, where the images can be
manipulated at will.
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