Image processing apparatus and method for format conversion

TL;DR: In this paper, the downsampling low-pass filter is designed together with an associated up-sampling lowpass filter, such that the first downsample low pass filter and the upsample low passing filter substantially satisfy perfect reconstruction filter bank condition, and such that a sum of the group delay of the first down-sample low pass and a normalized filter obtained by making the sum of all the coefficients of the upsampling lower pass filter equal to 1 is substantially equal to an integer number at frequency ω=0.

Abstract: A signal processing apparatus converts interlaced 4:2:2-format video signals including a luminance component and two chroma components into interlaced 4:2:0 format video signals. A downsampling low-pass filter has such a group delay that a modulo-1 remainder of the group delay at frequency ω=0 is substantially equal to 0.25. The downsampling low-pass filter is designed together with an associated upsampling low-pass filter such that the first downsampling low-pass filter and the upsampling low-pass filter substantially satisfy perfect reconstruction filter bank condition, and such that a sum of the group delay of the first downsampling low-pass filter and a group delay of a normalized filter obtained by making the sum of all the coefficients of the upsampling low-pass filter equal to 1 is substantially equal to an integer number at frequency ω=0.