Digital photographs are made up of tiny squares
called picture elements—or just pixels.
Like the impressionists who painted wonderful scenes with small dabs of paint,
your computer and printer can use these tiny pixels to display or print photographs.
To do so, the computer divides the screen or printed page into a grid containing
hundreds of thousands or millions of of pixels. The computer or printer then
uses the values stored in the digital photograph's file to specify the brightness
and color of each pixel in this grid—a form of painting by number. Controlling,
or addressing a grid of individual pixels in this way is called bit
mapping and digital images are called bit-maps.
The quality of a digital image, whether printed
or displayed on a screen, depends in part on the number of pixels used to
create the image (sometimes referred to as resolution). More
pixels add detail to an image, sharpen edges, and increase resolution.
If you enlarge any digital image enough, the
pixels will begin to show—an effect called pixelization.
This is not unlike traditional silver-based prints where grain begins to show
when prints are enlarged past a certain point.
The size of a digital photograph is specified
in one of two ways—by its dimensions in pixels or by the total number of pixels
it contains. For example, the same image can be said to have 1600 × 1200 pixels
(where "×" is pronounced "by" as in "1600 by 1200"), or to contain 1.92 million
pixels (1600 multiplied by 1200).
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