A convolution model and a cepstral filtering algorithm for the reduction of blocking artifacts
Proposes a convolution model and a cepstral filtering algorithm for reducing the blocking artifacts in compressed images and videos. Since each of the horizontal or vertical lines of the compressed image has abrupt changes at almost every 8th sample, images can be modeled as a convolution of the original sequence with an excitation signal of periodicity 8. Comparison of the cepstrums also shows that the multiples of 8th samples of the compressed signal's cepstrum usually have larger magnitudes than those of the original. The proposed filtering algorithm is to reduce the magnitudes of every 8th sample of the cepstrum, and disperse the reduced values to the neighboring samples. The algorithm is conducted in the cepstrum domain for reducing only the excitation signal which is the cause of blocking artifacts. Hence, the high frequency contents are not reduced by the postprocessing, whereas the conventional lowpass filtering blurs the image.