Why Video Artifacts Occur in High Speed Digital Video Images

All high speed digital video cameras, in common with most digital stills cameras, have a single image sensor, the surface of which is divided into a grid of light sensors. These sensors are only 'black & white' - they only measure brightness. To 'see' colour a red, green or blue filter is fixed in front of each sensor. On our cameras, the colour arrangement of these filters is in a particular pattern known as a 'Bayer' pattern. The light falling on each sensor, through its own colour filter, is measured by electronics to produce a 'raw' computer data file of red, green and blue values. In the case of the Phantom HD, the file format is called 'cine raw'. Subsequent to downloading the .cine file, the raw data is converted (de-Bayered) into a sequence of colour images, usually .tif files, using a particular algorithm (a sophisticated mathematical recipe for interpreting the colour information in a RAW file into ‘real’ colour).

A consequence of this technique is that when viewing finely detailed scenes, some algorithms are better than others at interpreting the fine detail: all algorithms generate 'artifacts' or errors of these finely detailed areas. At Pirate, we actually use this inherent fault for focusing - by using a focus chart containing fine lines the appearance of these artifacts on the chart indicates pin-point focus.

A great explanation of the Bayer Pattern by Sean McHugh, with pictures(!), can be found here.

Wikipedia entry with more links and info is here.