You can express every black-and-white photograph as a table of numbers. Each number in the table represents the darkness of a different point — the higher the number, the darker the point. The “darkness numbers” are called gray levels. To feed a picture into the computer, type in the table of gray levels. Or aim a special camera at the object you want pictured; the camera system will automatically compute the gray levels and send them to the computer via a wire.
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