Efficient transform domain transcoding: Intra frame of H.264/AVC to JPEG

In this paper, we propose an efficient transform domain method for transcoding an intra frame of H.264/AVC to a JPEG image. First, we show how to obtain the transform domain predictions for various intra modes of H.264/AVC through simplified matrix multiplication. Then, we describe a transform domain operation corresponding to the rounding operation which is performed after computing the weighted average during spatial domain intra prediction. Finally, we convert 4x4 integer transform blocks to 8x8 DCT blocks by defining a transform kernel matrix based on the factorization of transform matrices. Experimental results demonstrate that the proposed algorithm can reduce the total computational complexity about 16% on average as compared with the existing methods, and outperforms them in PSNR by 1.5~2.5dB.