How does a camera take a picture?


The image a camera takes is formed in several stages as follows;

  • First a lens focusses the image onto an electronic chip – made of silicon.
  • The chip is divided into many tiny light-sensitive regions – each region less than one hundredth of a millimetre across. There are at least three of these sensors for each ‘pixel’
  • Each light sensor is covered by a filter – either red, green or blue. Light passes through this filter and makes an electrical current flow whose strength is proportional to the brightness of the light.
  • A computer measures the brightness of every red, green and blue sensor from the chip and calculates the colour and brightness of that pixel.
  • It then lists the colour and brightness of each pixel in a specified order to make a ‘raw’ camera data file.

This data allows the image to be re-created on a screen or in print. This corresponds to around 6 million numbers for every frame of HD television, and there are 25 frames every second. Which is a very high number to cope with.

Typically most pictures are only changed a little from the previous picture 1/25th of a second before, and so HD televisions generally only send
the difference between each frame and the next which corresponds to much less data.