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.