A fast and memory efficient algorithm for down-conversion of an HDTV bitstream to an SDTV signal

In the future of the digital television (DTV) broadcasting, a standard definition television (SDTV) decoder should have the function of receiving a high definition television (HDTV) signal and display it on its monitor. In order to do so, it is required to convert an HDTV bitstream down to an SDTV signal. In this paper, we propose a fast and memory efficient algorithm for the down-conversion. The proposed algorithm saves lots of computation of the down-conversion by combining inverse discrete cosine transform (IDCT) with the pixel-domain down-conversion. It also requires a smaller memory by performing motion compensation (MC) after the down-conversion, compared to the conventional scheme where MC is performed before the down-conversion. In the brute-force IDCT case, the computation savings of our proposed algorithm are 62%, 74% and 84% for down-sampling ratios of 2:1, 8:3, and 4:1, respectively, with the same picture quality compared to the conventional memory efficient pixel-domain approach. In the case of using a fast IDCT algorithm, the computational savings are respectively 25%, 31% and 37% for down-sampling ratios of 2:1, 8:3, and 4:1.