Parameter estimation for image/video transcoding

In most of the current image/video compression standard, such as JPEG, MPEG, H.263, etc, the DCT is used. The DCT coefficients for every AC frequency component usually have Laplacian distribution. Such a distribution is critical in the image or video transcoding system. Therefore, the parameter in the distribution should be well estimated. Different from the normal parameter estimation, in the transcoding system, the original DCT value is unavailable, and only the dequantized value is available. In this paper, we propose 3 estimation methods based on the dequantized value for the transcoding system. The simulation demonstrates that they can yield very good results. In addition, under a fixed bit rate, they can work even better than estimation with the original DCT value in the sense of image/frame's PSNR.