Use Filtered for data produced by a filter (or
predictor). Filtered data consists mostly of small
values with a somewhat random distribution. In this
case, the compression algorithm is tuned to compress
them better. The effect of Z_FILTERED is to force more
Huffman coding and less string matching; it is
somewhat intermediate between DefaultStrategy and
HuffmanOnly.
HuffmanOnly
Use HuffmanOnly to force Huffman encoding only (no
string match).