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docs: clarify level 0/1 filter heuristic

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kyc001 2026-02-26 00:01:27 +08:00
parent ea9caac249
commit c081f1f873
1 changed files with 12 additions and 2 deletions
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14
MANUAL.txt
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@ -13,8 +13,8 @@ Options:
compression. Lower levels are faster, higher levels provide better compression, though
with increasingly diminishing returns.
0 => --zc 5 --fast (filter chosen heuristically)
1 => --zc 10 --fast (filter chosen heuristically)
0 => --zc 5 --fast (single filter, chosen heuristically)
1 => --zc 10 --fast (single filter, chosen heuristically)
2 => --zc 11 -f 0,1,6,7 --fast
3 => --zc 11 -f 0,7,8,9 --brute-level 1 --brute-lines 3
4 => --zc 12 -f 0,7,8,9 --brute-level 1 --brute-lines 4
@ -22,6 +22,13 @@ Options:
6 => --zc 12 -f 0-9 --brute-level 5 --brute-lines 8
max => (stable alias for the maximum level)
For levels 0 and 1, the heuristic currently chooses exactly one filter based on bit depth:
bit depth >= 8 => Bigrams (7)
bit depth < 8 => None (0)
Since only one filter is enabled by default at these levels, '--fast' is usually a no-op
unless you manually enable additional filters, e.g. '-o0 -f 0,7'.
Manually specifying a compression option (zc, f, etc.) will override the optimization
preset, regardless of the order you write the arguments.
@ -137,6 +144,9 @@ Options:
Perform a fast compression evaluation of each enabled filter, followed by a single main
compression trial of the best result. Recommended if you have more filters enabled than
CPU cores.
On preset levels 0 and 1 this is typically a no-op, because only one filter is enabled
by default at those levels.
--zc <level>
Deflate compression level (0-12) for main compression trials. The levels here are defined