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1.5x-2x faster encoding for method 3 and up

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using token-buffer (that is: slightly more memory. O(output_size))

This change is ON by default. To return to previous behaviour, use
'cwebp -low_memory' or set config.low_memory to true.

Side-effect of this new mode: it forces 1 partition only (which was
default anyway), and makes some statistics about the bitstream
no longer available. cwebp will no longer report 'intra4-coeffs', etc.

This mode also doesn't work (yet) with multi-pass, and -low_memory
is currently forced for multi-pass.

also: reversed the flag: USE_TOKEN_BUFFER -> DISABLE_TOKEN_BUFFER
also: fixed the kAverageBytesPerMB estimate

Change-Id: I4ea80382038d6df4309663e0cb7bd88d9bca9cf1
This commit is contained in:
skal
2013-03-12 00:37:42 +01:00
committed by James Zern
parent be2fd1735a
commit 9bfbdd144f
10 changed files with 346 additions and 184 deletions
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13
man/cwebp.1
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@ -1,5 +1,5 @@
.\" Hey, EMACS: -*- nroff -*-
.TH CWEBP 1 "February 28, 2013"
.TH CWEBP 1 "March 8, 2013"
.SH NAME
cwebp \- compress an image file to a WebP file
.SH SYNOPSIS
@ -86,6 +86,15 @@ with less visual distortion.
Use multi-threading for encoding, if possible. This option is only effective
when using lossy compression on a source with a transparency channel.
.TP
.B \-low_memory
Reduce memory usage of lossy encoding by saving four times the compressed
size (typically). This will make the encoding slower and the output slightly
different in size and distortion. This flag is only effective for methods
3 and up, and is off by default. Note that leaving this flag off will have
some side effects on the bitstream: it forces certain bitstream features
like number of partitions (forced to 1). Note that a more detailed report
of bitstream size is printed by \fBcwebp\fP when using this option.
.TP
.B \-af
Turns auto-filter on. This algorithm will spend additional time optimizing
the filtering strength to reach a well-balanced quality.
@ -108,6 +117,8 @@ Disable strong filtering (if filtering is being used thanks to the
.BI \-segments " int
Change the number of partitions to use during the segmentation of the
sns algorithm. Segments should be in range 1 to 4. Default value is 4.
This option has no effect for methods 3 and up, unless \fB\-low_memory\fP
is used.
.TP
.BI \-partition_limit " int
Degrade quality by limiting the number of bits used by some macroblocks.