Why use “advanced” pre-filtering techniques ?
Think of the DCT and quantizer as an A/D converter. Think of the pre-filter as the required anti-alias prefilter found before every A/D. The big difference of course is that the DCT quantizer assigns a varying number of bits per sample (transform coefficient). Judging on the normalized activity measured in the pre-analysis stage of video encoding, and the target buffer size status, you have a fairly good idea of how many bits can be spared for the target macroblock, for instance. Other pre-filtering techniques mostly take into account: texture patterns, masking, edges, and motion activity. Many additional advanced techniques can be applied at different immediate layers of video encoding (picture, slice, macroblock, block, etc.).
