Motion detection method and apparatus

Display standards in common use for the display of computer or television images on high resolution displays, commonly assume that the output image will be displayed on an output device having a high refresh rate. A high refresh rate is normally required to avoid the viewer observing flicker, stilted motion or other visual artifacts if a lower refresh rate were used. It is difficult to drive some displays (5) at a high refresh rate. Apparatus (16) is disclosed for detecting areas (33,36) of an input image (2,24) that are changing over time, even where the input image may be subject to some degree of noise. A priority value is determined for providing a measure of this change for use with a system to determine which areas of the image may need changing as a matter of high priority.