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Description:
============
WebP codec: library to encode and decode images in WebP format. This package
contains the library that can be used in other programs to add WebP support,
as well as the command line tools 'cwebp' and 'dwebp'.
See http://developers.google.com/speed/webp
Latest sources are available from http://www.webmproject.org/code/
It is released under the same license as the WebM project.
See http://www.webmproject.org/license/software/ or the
file "COPYING" file for details. An additional intellectual
property rights grant can be found in the file PATENTS.
Files:
======
cwebp.exe : encoding tool
dwebp.exe : decoding tool
vwebp.exe : webp visualization tool
lib/ : static libraries
include/webp : headers
test.webp : a sample WebP file.
test_ref.ppm : the test.webp file decoded into the PPM format.
Encoding tool:
==============
The package contains tools for encoding (cwebp) and decoding (dwebp) images.
The easiest use should look like:
cwebp input.png -q 80 -o output.webp
which will convert the input file to a WebP file using a quality factor of 80
on a 0->100 scale (0 being the lowest quality, 100 being the best. Default
value is 75).
You might want to try the -lossless flag too, which will compress the source
(in RGBA format) without any loss. The -q quality parameter will in this case
control the amount of processing time spent trying to make the output file as
small as possible.
A longer list of options is available using the -longhelp command line flag:
> cwebp -longhelp
Usage:
cwebp [-preset <...>] [options] in_file [-o out_file]
If input size (-s) for an image is not specified, it is assumed to be a PNG,
JPEG or TIFF file.
options:
-h / -help ............ short help
-H / -longhelp ........ long help
-q <float> ............. quality factor (0:small..100:big)
-alpha_q <int> ......... Transparency-compression quality (0..100).
-preset <string> ....... Preset setting, one of:
default, photo, picture,
drawing, icon, text
-preset must come first, as it overwrites other parameters.
-m <int> ............... compression method (0=fast, 6=slowest)
-segments <int> ........ number of segments to use (1..4)
-size <int> ............ Target size (in bytes)
-psnr <float> .......... Target PSNR (in dB. typically: 42)
-s <int> <int> ......... Input size (width x height) for YUV
-sns <int> ............. Spatial Noise Shaping (0:off, 100:max)
-f <int> ............... filter strength (0=off..100)
-sharpness <int> ....... filter sharpness (0:most .. 7:least sharp)
-strong ................ use strong filter instead of simple (default).
-nostrong .............. use simple filter instead of strong.
-partition_limit <int> . limit quality to fit the 512k limit on
the first partition (0=no degradation ... 100=full)
-pass <int> ............ analysis pass number (1..10)
-crop <x> <y> <w> <h> .. crop picture with the given rectangle
-resize <w> <h> ........ resize picture (after any cropping)
-mt .................... use multi-threading if available
-low_memory ............ reduce memory usage (slower encoding)
-map <int> ............. print map of extra info.
-print_psnr ............ prints averaged PSNR distortion.
-print_ssim ............ prints averaged SSIM distortion.
-print_lsim ............ prints local-similarity distortion.
-d <file.pgm> .......... dump the compressed output (PGM file).
-alpha_method <int> .... Transparency-compression method (0..1)
-alpha_filter <string> . predictive filtering for alpha plane.
One of: none, fast (default) or best.
-alpha_cleanup ......... Clean RGB values in transparent area.
-noalpha ............... discard any transparency information.
-lossless .............. Encode image losslessly.
-hint <string> ......... Specify image characteristics hint.
One of: photo, picture or graph
-metadata <string> ..... comma separated list of metadata to
copy from the input to the output if present.
Valid values: all, none (default), exif, icc, xmp
-short ................. condense printed message
-quiet ................. don't print anything.
-version ............... print version number and exit.
-noasm ................. disable all assembly optimizations.
-v ..................... verbose, e.g. print encoding/decoding times
-progress .............. report encoding progress
Experimental Options:
-jpeg_like ............. Roughly match expected JPEG size.
-af .................... auto-adjust filter strength.
-pre <int> ............. pre-processing filter
The main options you might want to try in order to further tune the
visual quality are:
-preset
-sns
-f
-m
Namely:
* 'preset' will set up a default encoding configuration targeting a
particular type of input. It should appear first in the list of options,
so that subsequent options can take effect on top of this preset.
Default value is 'default'.
* 'sns' will progressively turn on (when going from 0 to 100) some additional
visual optimizations (like: segmentation map re-enforcement). This option
will balance the bit allocation differently. It tries to take bits from the
"easy" parts of the picture and use them in the "difficult" ones instead.
Usually, raising the sns value (at fixed -q value) leads to larger files,
but with better quality.
Typical value is around '75'.
* 'f' option directly links to the filtering strength used by the codec's
in-loop processing. The higher the value, the smoother the
highly-compressed area will look. This is particularly useful when aiming
at very small files. Typical values are around 20-30. Note that using the
option -strong/-nostrong will change the type of filtering. Use "-f 0" to
turn filtering off.
* 'm' controls the trade-off between encoding speed and quality. Default is 4.
You can try -m 5 or -m 6 to explore more (time-consuming) encoding
possibilities. A lower value will result in faster encoding at the expense
of quality.
Decoding tool:
==============
The sample decoding program dwebp will take
a .webp file and decode it to a PNG image file (amongst other formats).
This is simply to demonstrate the use of the API. You can verify the
file test.webp decodes to exactly the same as test_ref.ppm by using:
dwebp test.webp -ppm -o test.ppm
diff test.ppm test_ref.ppm
The full list of options is available using -h:
> dwebp -h
Usage: dwebp in_file [options] [-o out_file]
Decodes the WebP image file to PNG format [Default]
Use following options to convert into alternate image formats:
-pam ......... save the raw RGBA samples as a color PAM
-ppm ......... save the raw RGB samples as a color PPM
-pgm ......... save the raw YUV samples as a grayscale PGM
file with IMC4 layout.
-yuv ......... save the raw YUV samples in flat layout.
Other options are:
-version .... print version number and exit.
-nofancy ..... don't use the fancy YUV420 upscaler.
-nofilter .... disable in-loop filtering.
-mt .......... use multi-threading
-crop <x> <y> <w> <h> ... crop output with the given rectangle
-scale <w> <h> .......... scale the output (*after* any cropping)
-alpha ....... only save the alpha plane.
-h ....... this help message.
-v ....... verbose
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conver2webp.zip (23个子文件)
conver2webp.exe 964KB
说明.txt 599B
libwebp
test_ref.ppm 48KB
cwebp.exe 279KB
dll
msvcr110.dll 838KB
freeglut.dll 206KB
gif2webp.exe 348KB
image.webp 796KB
dwebp.exe 206KB
include
webp
decode.h 22KB
encode.h 23KB
types.h 1KB
mux_types.h 3KB
mux.h 15KB
demux.h 9KB
Readme.txt 18KB
test.webp 5KB
lib
libwebp.lib 535KB
_RF01-_0004.png 991KB
webpmux.exe 144KB
vwebp.exe 264KB
Readme-mux.txt 6KB
main.cpp 4KB
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