Coding characteristics of the pixel-adaptive DPCM utilizing the variable-length-codes

The coding characteristics of a modified DPCM (differential pulse code modulation) method for data compression of still images for digital still cameras are described. In pixel adaptive DPCM, the pixels are classified into eight groups according to the magnitude of the prediction error of preceding pixels, and the prediction error signals of each group are quantized using eight nonlinear quantizers, each of which is designed optimally to each group. The performance of the pixel adaptive DPCM can be improved by utilizing the variable bit-rate scheme. It is shown in an example that the signal-to-noise ratio can be improved to 48 dB by 6 dB at 3.0 b/pixel, that this improvement is due to the relief of the slope overloading at the edges, and that the spectrum of the coding errors is distributed uniformly in the 2-D spatial frequency region