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How a digital camera works, briefly

In a digital camera, light-sensitive electronic circuits serve the function of light-sensitive grains on film

The individual light-sensitive circuits are called pixels (short for picture element)

Pixels are arranged in rows and columns

In a 6-megapixel sensor there are approximately 2000 rows by 3000 columns (2000 x 3000 = 6 million)

Each pixel has a filter for red, green, or blue, typically populated in the ratio of 1: 1: 2.

When exposed, an electrical charge accumulates on each pixel, proportional to the light intensity and exposure time

Carol Williams

(Even when not exposed, some charge tends to accumulate. This is called "dark current" and is the cause of hot pixels. In addition, a random component adds to the light-induced charge, the cause of noise in images.)

After exposure, the electrical charges are passed to analog-to-digital converters, typically of 12 bits (4096 levels)

Optionally, the 6 million numbers are recorded for later processing (RAW mode)

Or, the numbers are converted in camera to a JPEG image (8 bits/color, or 24-bit color)

Image data is stored on one of several types of flash memory card

 Pluses and Minuses of Digital SLRs            © Robert Harrington 2004
Page updated 8/31/05