Estimating Laplacian Parameters of DCT Coefficients for Requantization in the Transcoding of MPEG-2 Video

This paper addresses bit-rate reduction of MPEG-2 compressed video and presents a method to reduce requantization errors in transcoding. The proposed method assumes Laplacian distributions for the original AC coefficients of the DCT. A Laplacian parameter for each coefficient is estimated at the transcoder from the quantized input DCT coefficients. These parameters are then used in requantization to improve the quality of the transcoded video. The algorithm provided in this paper to estimate the Laplacian parameters of the original DCT coefficients is simple to implement and may be adapted to other DCT-based coding schemes.