Highly programmable chrominance filter for 4:2:2 to 4:2:0 conversion during MPEG2 video encoding

A filter for downsampling input video having a first chrominance sampling to a second chrominance sampling, the input video comprising a Bitstream of data representing a sequence of picture frames, each picture frame comprising a plurality of video lines, the filter comprising:

• a programmable mode register defining a list of available downsampling modes;
• means for transmitting control data to the mode register to choose one of the downsampling modes from the list of available downsampling modes for the downsampling of the first chrominance sampling,
• a means for dividing each picture frame into video line sets according to predetermined criteria for the particular downsampling mode chosen, each video line set comprising at least two video lines,
• a means for assigning default downsampling coefficients for each of the video lines in the video line sets based upon the downsampling mode chosen, and
• a means for downsampling each video line set to a single video line having the second chrominance sampling according to the following equation:
• L0={(C1*L1)+(C2*L2)+ . . . (Cn*Ln)}
• where L0 is the downsampled video line with the second chrominance sampling, C is the downsampling coefficient for line L, and where the subscripts denote the video line number of the video line set having a total of n video lines.