Adaptive DCT coding for home digital VTR

The authors investigate fixed adaptive discrete cosine transform (FADCT) coding for use in digital VTRs (video tape recorders). The image is divided into 8×8-pixel subblocks, and a two-dimensional DCT is performed on each of them. The quantization scheme is adapted to input image data, thereby increasing coding efficiency. The scheme is designed, however, to keep the output data rate fixed. Computer simulation showed that FADCT coding improves the SNR (signal/noise ratio) from 1 dB to 3 dB as compared to nonadaptive DCT coding, and a high-quality image with SNR over 40 dB can be obtained at 3 bits/pixel. Reallocations of the extra bits from the higher to the lower AC energy subblocks allow the application of adaptive coding to the digital VTR, with a high tolerance for channel errors