Design of Quantizers for Real-Time Hadamard-Transform Coding of Pictures

Abstract

A methodology is developed to obtain subjectively optimum quantizers for Hadamard-transformed still pictures. To exploit the perceptual redundancies that depend upon the local properties of the picture, a small block (2 × 2 × 2, horizontal-vertical-temporal) is used. A series of subjective tests was carried out to determine the visibility of impairment in the reconstructed picture when noise, which simulated the quantization noise, was added to the Hadamard coefficients in the transform domain (H-noise). A design procedure for quantizers was developed using these visibility functions. These quantizers minimize the “mean-square subjective distortion” (mmssd) due to quantization noise. The resulting picture Quality and entropy were compared with that of Max-type quantizers which minimize the “mean-square error” (mmse). This comparison indicates that the mmssd quantizers based on subjective visibility of the quantization noise are less companded than the MMSE quantizers. Also for the same number of quantization levels, pictures coded with mmssd quantizers have better quality and less entropy than the pictures coded with minimum mean-square quantizers.