Noise reduction in DCT-coded images by estimating optimal quantized values
Masayuki Tanimoto, Kiyohito Narita, Toshiaki Fujii, Tadahiko Kimoto · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 1996
This paper proposes a new scheme to reduce the quantization noise in DCT coded images by estimating optimal quantized values. In the proposed scheme, the quantized value of DCT coefficients is shifted from the middle of the quantization step to the mean value of the amplitude distribution of DCT coefficients in the quantization step. The values of the shift minimizing the quantization noise power are obtained experimentally. A simple scheme approximating these values is derived so that the modification factors of the quantized values can be estimated at the decoder. About 0.5 dB improvement of SNR is achieved experimentally by the proposed scheme. By smoothing the boundaries of DCT blocks in the decoded images further, 1.0 dB improvement of SNR is achieved and visually better images are obtained.