Interfield Hybrid Coding of Component Color Television Signals

Hybrid coding of color television images at broadcast standards is investigated. This involves two-dimensional discrete cosine transform (2-D DCT) of each field, followed by the differential pulse code modulation (DPCM) between successive fields. Two 22frame sequences of "Water Skier" and "Wheel of Fortune" in component form, i.e., luminanceYand chrominanceIandQ, were utilized as the database. A statistical study of the prediction error in the 2-D DCT domain is carried out. Three different algorithms for the 2-D DCT system are simulated and analyzed. In the first algorithm, optimum (nonuniform) quantizers are used in DPCM loops followed by fixed-wordlength coders. Uniform quantizers along with variablewordlength coders are implemented in the second system. The performances of different deterministic coders are investigated and compared with Huffman coders. The third scheme is an adaptive system. In this system each 8 × 8 block is divided into four subblocks. The activity of each subblock is monitored and when it exceeds some threshold, the subblock is considered to be spatially active. More bits are assigned to active subblocks and the ranges of corresponding quantizers are expanded. The prediction error of the dc coefficient is monitored to determine the temporal activity of a block. For a temporally active block, the number of bits assigned to the two lower frequency subblocks is increased. Performance of these three systems for unmatched statistics and in the case of a scene change are studied. Mean square error (MSE) between the original and reconstructed images, bit rate, entropy, essential maximum, and other parameters are utilized as the performance criteria. Also, a subjective evaluation of the processed images is carried out. It is shown that the interfield adaptive hybrid coding of color TV signals in component form results in significant savings in bit rates for transmission over a digital link.