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Digital photographs are made up of hundreds of thousands or millions 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 of pixels. It then uses the
values stored in the digital photograph 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.
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Here you see a portrait of Amelia
Earhart done entirely in jelly beans. Think of each jelly bean as a pixel
and it's easy to see how dots can form images. Jelly Bean Spirit of ’76
courtesy of Herman Goelitz Candy Company Inc. Makers of Jelly Belly jelly
beans. |
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 and sharpen edges.
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
more pixels there are in an image, the more it can be enlarged before
pixelization occurs.
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The photo of the face (right) looks
normal, but when the eye is enlarged too much (left) the pixels begin to
show. Each pixel is a small square made up of a single color. |
The size of a 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 1800 x 1600 pixels (where "x" is pronounced "by" as in "1800
by 1600"), or to contain 2.88-million pixels (1800 multiplied by 1600).
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This digital image of a Monarch
butterfly chrysalis is 1800 pixels wide and 1600 pixels tall. It's said to
be 1800x1600 |
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Image size
