| 摘要 |
A composite color television signal codec combines modified folded, hybrid differential pulse code modulation (H-DPCM) encoding and band-limiting decimation and interpolation filters to enhance encoding resolution without a reduction in signal quality of the reconstructed signal. The codec encodes, at five bits per sample, an NTSC 4.2 MHz composite color video signal for transmission over a 44.736 Mb/s communication channel. As in a conventional (H-DPCM) encoding scheme, a digital code value that is associated with a previous (quantized) jth sample of the signal and the difference between that digital code value and a digital code value of an ith sample are combined to produce an output code value for the ith sample. However, unlike the conventional hydrid approach, in which the predictor for the ith value is the immediately previous sample, the present invention uses a jth sample located in the second previous line of the frame from the line in which the ith sample is located, and at a point that is both color phase-matched and aligned with the ith sample of interest. Because the 44.736 Mb/s data rate limitation of the communication link will not readily accommodate a 4.2 MHz NTSC signal that is represented by more than four bits per sample by a fixed rate encoder, the passband of an anti-aliasing, decimation filter is narrowed to 4.0 MHz, which does not effectively impair the quality of the reconstructed video at the receiver. |
