Have you ever wondered how digital camera works. Digital cameras start out very much like their 35mm film camera ancestors. Both have a lens, an aperture, and a shutter. The purpose of the lens is to bring light from the scene into focus inside the camera where the image is exposed. The aperture is the hole the can expand and contract to control how much light enters the camera. The shutter controls the length of time the light enters the aperture. Once you get past those similarities though, the digital camera is in a class of its own.

Every time that you snap a photo, millions of calculations have to be made in just seconds in order for the camera to preview, capture, compress, filter, store, transfer, and display the image. In order to pull this off, the camera has a microprocessor inside that's very similar to the one in a personal computer.

Digital photographs are made up of hundreds of thousands or millions of tiny squares called pixels, which is short for picture elements. Your computer and printer uses 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. Controlling, or addressing a grid of individual pixels is called bit mapping and digital images are called bit-maps.

In order to get the image converted into pixels, the camera uses a solid-state device called an image sensor, or CCD, (charge-couple device) to receive the incoming image. The CCD takes the place of film and is made up of fingernail-sized silicon chips that each contain a grid made up of hundreds of thousands or millions of photosensitive diodes called photosites, photoelements, or pixels. Each photosite captures one picture of what will be the complete photograph. The more pixels that the CCD contains, the better the quality of the picture.

Pressing the shutter release causes the shutter to open and lets light stream through the lens and into the aperture. A metering cell measures the amount of light that is coming through the lens and sets the aperture and shutter speed for the correct exposure. Each pixel CCD records the intensity of the light that hits it by building up a corresponding electrical charge. The more light that hits a pixel, the higher the electrical charge. When the shutter closes, no more light strikes the pixels, and the camera then converts the accumulated charge on each pixel into a number. This series of numbers is then used to build the image by setting the color and brightness of matching pixels and saving them to the camera's memory device.

The memory device performs the second function that we typically think of film performing, and that is saving the image so it can be developed later. In the digital camera's case, however, the picture does not need to be developed. You simply download it to your computer or, if your camera supports this option, you can download it directly to a printer.

So, now you know how digital camera works. Digital photography is the next logical step in photography. As prices continue to fall, and the number of pixels that a camera is capable of storing and rendering rises, there will come a time when the film-based camera becomes obsolete and are relegated to cardboard boxes stored in the attic. (By Len Dozois)

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