Exchange of Spatial and Temporal Resolution in Television Coding

Television coders are usually designed to meet simultaneously the worst contingencies with respect to contrast, sharpness and movement. T h a t is, a fast moving subject can be reproduced with the full spatial resolution afforded a stationary subject and with the full contrast resolution afforded a low detail subject. By contrast resolution we mean the accuracy with which the coded signal represents the amplitude of the input signal for a particular picture element. We want to reduce the channel capacity required for transmitting television signals by coding the signal so that full spatial resolution is only available in stationary areas of the picture and full temporal resolution is only available in moving areas of the picture. Exchange of spatial and contrast resolution has been appreciated and demonstrated for some time. 1 One of the first examples of a coder that exchanged spatial and contrast resolution was demonstrated by E. R. Kretzmer 2 ; more quantizing levels were assigned to low frequency signal components and fewer levels were assigned to high frequency signal components. 191