An architecture for hybrid coding of NTSC TV signals

A hardware feasible architecture for DCT/DPCM hybrid coding of color television (TV) signals has been developed. The coding system is based on formatting four horizontal scan lines into blocks of the same subcarrier phase elements. The samples in each block are rearranged and transformed by a FDCT processor. Based on its average energy, a given transform block is compared with its adjacent blocks and the nearest block is selected as its estimate. The difference between the actual and the estimated values of the (DCT) coefficients are then quantized and encoded using nonuniform quantizers and a variable length coder. Furthermore, the maximum number of different wordlengths is assumed to be five. Therefore, five sets of 256-byte encoding ROMs are used to store the quantization tables. To reduce the redundancy in the code words, an adaptive coding scheme is used. The coding scheme is based on setting two threshold levels.