Visibility of DCT quantization noise: spatial frequency summation

Abstract

In DCT-based compression the image is divided into blocks of pixels, the DCT is applied to each block, and the resulting coefficients are quantized and encoded to form the compressed version of the image. In this paper we report psychophysical measurements of summation across DCT frequencies, and compare the results to area summation results. These measurements provide useful information for optimal DCT quantization. All experiments were performed using the same equipment and viewing conditions as in Peterson et al. We found a decrease in threshold of approximately 5 dB due to summation of quantization error over spatial frequency. This result lies between that predicted by probability summation and that predicted by linear summation (3 dB < 5 dB < 12 dB).