webp转换工具（第2次修改）

__ __ ____ ____ ____ / \\/ \/ _ \/ _ )/ _ \ \ / __/ _ \ __/ \__\__/\____/\_____/__/ ____ ___ / _/ / \ \ / _ \/ _/ / \_/ / / \ \ __/ \__ \____/____/\_____/_____/____/v0.3.0 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