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How digital cameras work

Digital camera block diagram

A digital camera is similar to a 35mm film camera in that it has a body, lens and light sensitive recording ability. The major difference is of course that instead of silver halide film there is an electronic semiconductor sensor. This needs rather comples control electronics, and differently sized optics compared to a film camera. The advantages include compactness and the abilites to preview the images and store them on computer.

The amount of light falling on the sensor is controlled by camera shutter speed, aperture size and lens, just as in film photography. The simple block diagram below shows the basic structure of a digicam:

Bayer filter and demosaicing

A conventional CCD or CMOS sensor can see only in shades of grey. In other words it senses the brightness of the light falling on it. Colour is given by putting a filter in front of the sensor, with a particular pattern of red, green and blue filters, one for each sensor pixel. This is known as a Bayer Filter and is represented diagrammatically in the image below.

There are more green filters because the human eye is most sensitive to changes in green.

The filter and sensor produces a mosaic of red, green and blue light levels. Powerful computer routines (unsurprisingly called de-mosaicing algorithms) in the camera circuitry then convert this into an image that can be interpreted by the human eye.

Before the image is stored further in-camera processing deals with white balance, contrast and edge sharpness. The final computer readable file is then placed on the camera storage card.