Picture coding

A critical view is presented of the development of certain picture coding systems. An attempt is made to unify the treatment of these systems by emphasizing the reaction of the observer to the types of alteration introduced into the transmitted signal, on the basis of what is known about vision. For the purpose of casting a number of apparently different techniques into similar forms, the relationship between differential quantizing and PCM is discussed in detail. We conclude that the pre- and post-quantizing filters play a key role in these systems. Optimum choice of such filters is shown to improve both quality and efficiency. Two-dimensional and dual-mode systems are seen to be outgrowths of these considerations. Recent results are described and a method of comparison between systems is proposed.