Modified IDCT kernel for down-conversion of MPEG-2 compressed video

A traditional method for down conversion of MPEG-2 video is to perform low- pass-filtering and subsampling after full decompression. However, this meth od has two shortcomings; large memory requirement and high computational co mplexity. To overcome these drawbacks, down conversion in the DCT domain ha s been preferred. Previous methods need only a quarter of the full frame me mory because completely reduced frames are stored in the frame memory. But the loss of field information often causes significant errors during motion compensation. To avoid this problem, recent schemes adopt a hybrid structu re where field information is preserved by performing down conversion in th e DCT domain only for the horizontal direction, and down conversion in the spatial domain for the vertical direction. In this paper, we propose a nove l technique for the horizontal down conversion in the DCT domain where a mo dified 4-IDCT kernel is adopted, and apply it to the hybrid down conversion decoder. The proposed 4-IDCT kernel outperforms the conventional 4-IDCT ke rnel in that it performs efficient low-pass filtering and sub-sampling conc urrently. We apply the proposed technique to down conversion of MPEG-2 comp ressed videos. Experimental results show that the proposed scheme provides high visual quality while maintaining reasonable complexity.