Adaptive predictive coding system for television signals

An adaptive predictive television signal coding system comprising:

• a memory having a capacity capable of storing an input television signal of at least one field and one picture element at all times;
• an intra-field predictive coder which, when supplied with a value X.sub.1 of the latest input picture element of the television signal, reads out from the memory a picture element value in the same field as the input signal to produce a predictive value X.sub.11 of the latest input picture element and provides the predictive value as a decoded value X.sub.11 of the latest picture element value X.sub.1 ;
• an intra-field difference quantizing coder which, when supplied with the value X.sub.1 of the latest picture element, reads out from the memory a picture element value in the same field as the input signal to produce a predictive value X.sub.12 of the latest input picture element and quantizes a difference between the predictive value and the latest picture element value to produce a difference quantized value Z.sub.12 and provides a decoded value X.sub.12 of the latest picture element as X.sub.12 =X.sub. 12 +Z.sub.12 ;
• an inter-field predictive coder which, when supplied with the value X.sub.1 of the latest picture element, reads out from the memory picture element values in the same field as the input signal and in a field immediately preceding it to produce a predictive value X.sub.13 of the latest input picture element and provides the predictive value as a decoded value X.sub.13 of the latest picture element value X.sub.1 ;
• an inter-field difference quantizing coder which, when supplied with the value X.sub.1 of the latest picture element, reads out from the memory picture element values in the same field as the input signal and a field immediately preceding it to produce a predictive value X.sub.14 of the latest input picture element and quantizes a difference between the predictive value and the latest picture element value to produce a difference quantized value Z.sub.14 and provides a decoded value X.sub.14 of the latest picture element as X.sub.14 =X.sub.14 +Z.sub.14 ;
• an adaptive predictive coding control part which compares errors in magnitude between the decoded values X.sub.11 and X.sub.13 of the intra-field predictive coder and the inter-field predictive coder and the true picture element value X.sub.1 and, if the error value of the predictive coder of a smaller error value is smaller than a predetermined threshold value T.sub.H, selects the predictive coder for coding the latest picture element and, if the error value of the predictive coder is larger than the threshold value T.sub.H, compares again the errors in magnitude between the decodes values X.sub.12 and X.sub.14 of the intra-field and inter-field predictive coders and the picture element X.sub.1 and selects the predictive coder of a smaller error value for coding the latest picture element, thereby to select one of the four coders for coding the latest picture element;
• and a coding device of the transmitting side including a transmission signal coder which converts to transmission signals a mode indicating signal indicating the selected one of the four coders and the difference quantized value Z.sub.12 or Z.sub.14 in dependence upon whether the intra-field or inter-field difference quantizing coder, and a buffer control part which stores in a buffer memory the mode indicating signal and the transmission signal coded by the transmission signal coding part and provides them on the transmission line at a constant rate and, at the same time, changes the threshold value T.sub.H for selecting the predictive coder or difference quantizing coder in accordance with the amount of data stored in the buffer memory.