Improved Conversion From DCT Blocks to Integer Cosine Transform Blocks in H.264/AVC

Abstract

As adoption of the newly standardized H.264 becomes increasingly more widespread, efforts must be made to transcode video from earlier standards, such as MPEG-2, to the H.264 format. One aspect of transcoding is the conversion from the discrete cosine transform (DCT) used in MPEG-2 to the integer-based DCT of H.264, the integer cosine transform. By investigating the structure of the transform kernels, two efficient schemes are introduced to convert an 8 times 8 DCT block into its corresponding four 4times4 integer cosine transform block8 times 8 DCT block into its corresponding four 4times4 integer cosine transform blockss. An analysis of computational complexity shows a reduction of up to 42% in multiplications over existing conversion schemes, while simulations of the conversion system with pre- and post-quantization show that the proposed methods yield high fidelity in terms of peak signal-to-noise ratio. Further approximation of matrix coefficients in the second proposed method yields additional conversion schemes which require no multiplications. These also provide comparable quality with fewer operations than existing schemes. Thus, the proposed transform conversion methods can potentially contribute to efficient transcoding systems.