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__ __ ____ ____ ____ / \\/ \/ _ \/ _ )/ _ \ \ / __/ _ \ __/ \__\__/\____/\_____/__/ ____ ___ / _/ / \ \ / _ \/ _/ / \_/ / / \ \ __/ \__ \____/____/\_____/_____/____/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. Building: ========= Windows build: -------------- By running: nmake /f Makefile.vc CFG=release-static RTLIBCFG=static OBJDIR=output the directory output\release-static\(x64|x86)\bin will contain the tools cwebp.exe and dwebp.exe. The directory output\release-static\(x64|x86)\lib will contain the libwebp static library. The target architecture (x86/x64) is detected by Makefile.vc from the Visual Studio compiler (cl.exe) available in the system path. Unix build using makefile.unix: ------------------------------- On platforms with GNU tools installed (gcc and make), running make -f makefile.unix will build the binaries examples/cwebp and examples/dwebp, along with the static library src/libwebp.a. No system-wide installation is supplied, as this is a simple alternative to the full installation system based on the autoconf tools (see below). Please refer to makefile.unix for additional details and customizations. Using autoconf tools: --------------------- When building from git sources, you will need to run autogen.sh to generate the configure script. ./configure make make install should be all you need to have the following files /usr/local/include/webp/decode.h /usr/local/include/webp/encode.h /usr/local/include/webp/types.h /usr/local/lib/libwebp.* /usr/local/bin/cwebp /usr/local/bin/dwebp installed. Note: A decode-only library, libwebpdecoder, is available using the '--enable-libwebpdecoder' flag. The encode library is built separately and can be installed independently using a minor modification in the corresponding Makefile.am configure files (see comments there). See './configure --help' for more options. SWIG bindings: -------------- To generate language bindings from swig/libwebp.i swig-1.3 (http://www.swig.org) is required. 2.0 may work, but has not been tested. Currently the following functions are mapped: Decode: WebPGetDecoderVersion WebPGetInfo WebPDecodeRGBA WebPDecodeARGB WebPDecodeBGRA WebPDecodeBGR WebPDecodeRGB Encode: WebPGetEncoderVersion WebPEncodeRGBA WebPEncodeBGRA WebPEncodeRGB WebPEncodeBGR WebPEncodeLosslessRGBA WebPEncodeLosslessBGRA WebPEncodeLosslessRGB WebPEncodeLosslessBGR Java bindings: To build the swig-generated JNI wrapper code at least JDK-1.5 (or equivalent) is necessary for enum support. The output is intended to be a shared object / DLL that can be loaded via System.loadLibrary("webp_jni"). Encoding tool: ============== The examples/ directory 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: ============== There is a decoding sample in examples/dwebp.c which 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: cd examples ./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 (e.g. print encoding/decoding times) -noasm ....... disable all assembly optimizations. Visualization tool: =================== There's a little self-serve visualization tool called 'vwebp' under the examples/ directory. It uses OpenGL to open a simple drawing window and show a decoded WebP file. It's not yet integrated in the automake build system, but you can try to manually compile it using the recommendations below. Usage: vwebp in_file [options] Decodes the WebP image file and visualize it using OpenGL Options are: -version .... print version number and exit. -noicc ....... don't use the icc profile if present. -nofancy ..... don't use the fancy YUV420 upscaler. -nofilter .... disable in-loop filtering. -mt .......... use multi-threading. -info ........ print info. -h ....... this help message. Keyboard shortcuts: 'c' ................ toggle use of color profile. 'i' ................ overlay file information. 'q' / 'Q' / ESC .... quit. Building: --------- Prerequisites: 1) OpenGL & OpenGL Utility Toolkit (GLUT) Linux: $ sudo apt-get install freeglut3-dev mesa-common-dev Mac + XCode: - These libraries should be available in the OpenGL / GLUT frameworks. Windows: http://freeglut.sourceforge.net/index.php#download 2) (Optional) qcms (Quick Color Management System) i. Download qcms from Mozilla / Chromium: http://hg.mozilla.org/mozilla-central/file/0e7639e3bdfb/gfx/qcms http://src.chromium.org/viewvc/chrome/trunk/src/third_party/qcms ii. Build and archive the source files as libqcms.a / qcms.lib iii. Update makefile.unix / Makefile.vc a) Define WEBP_HAVE_QCMS b) Update include / library paths to reference the qcms directory. Build using makefile.unix / Makefile.vc: $ make -f makefile.unix examples/vwebp > nmake /f Makefile.vc CFG=release-static \ ../obj/x64/release-static/bin/vwebp.exe Encoding API: ============= The main encoding functions are available in the header src/webp/encode.h The ready-to-use ones are: size_t WebPEncodeRGB(const uint8_t* rgb, int width, int height, int stride, float quality_factor, uint8_t** output); size_t WebPEncodeBGR(const uint8_t* bgr, int width, int height, int stride, float quality_factor, uint8_t** output); size_t WebPEncodeRGBA(const uint8_t* rgba, int width, int height, int stride, float quality_factor, uint8_t** output); size_t WebPEncodeBGRA(const uint8_t* bgra, int width, int height, int stride, float quality_factor, uint8_t** output); They will convert raw RGB samples to a WebP data. The only control supplied is the quality factor. There are some variants for using the lossless format: size_t WebPEncodeLosslessRGB(const uint8_t* rgb, int width, int height, int stride, uint8_t** output); size_t WebPEncodeLosslessBGR(const uint8_t* bgr, int width, int height, int stride, uint8_t** output); size_t WebPEncodeLosslessRGBA(const uint8_t* rgba, int width, int height, int stride, uint8_t** output); size_t WebPEncodeLosslessBGRA(const uint8_t* bgra, int width, int height, int stride, uint8_t** output); Of course in this case, no quality factor is needed since the compression occurs without loss of the input values, at the expense of larger output sizes. Advanced encoding API: ---------------------- A more advanced API is based on the WebPConfig and WebPPicture structures. WebPConfig contains the encoding settings and is not tied to a particular picture. WebPPicture contains input data, on which some WebPConfig will be used for compression. The encoding flow looks like: -------------------------------------- BEGIN PSEUDO EXAMPLE #include <webp/encode.h> // Setup a config, starting form a preset and tuning some additional // parameters WebPConfig config; if (!WebPConfigPreset(&config, WEBP_PRESET_PHOTO, quality_factor)) return 0; // version error } // ... additional tuning config.sns_strength = 90; config.filter_sharpness = 6; config_error = WebPValidateConfig(&config); // not mandatory, but useful // Setup the input data WebPPicture pic; if (!WebPPictureInit(&pic)) { return 0; // version error } pic.width = width; pic.height = height; // allocated picture of dimension width x height if (!WebPPictureAllocate(&pic)) { return 0; // memory error } // at this point, 'pic' has been initialized as a container, // and can receive the Y/U/V samples. // Alternatively, one could use ready-made import functions like // WebPPictureImportRGB(), which will take care of memory allocation. // In any case, past this point, one will have to call // WebPPictureFree(&pic) to reclaim memory. // Set up a byte-output write method. WebPMemoryWriter, for instance. WebPMemoryWriter wrt; pic.writer = MyFileWriter; pic.custom_ptr = my_opaque_structure_to_make_MyFileWriter_work; // initialize 'wrt' here... // Compress! int ok = WebPEncode(&config, &pic); // ok = 0 => error occurred! WebPPictureFree(&pic); // must be called independently of the 'ok' result. // output data should have been handled by the writer at that point. -------------------------------------- END PSEUDO EXAMPLE Decoding API: ============= This is mainly just one function to call: #include "webp/decode.h" uint8_t* WebPDecodeRGB(const uint8_t* data, size_t data_size, int* width, int* height); Please have a look at the file src/webp/decode.h for the details. There are variants for decoding in BGR/RGBA/ARGB/BGRA order, along with decoding to raw Y'CbCr samples. One can also decode the image directly into a pre-allocated buffer. To detect a WebP file and gather the picture's dimensions, the function: int WebPGetInfo(const uint8_t* data, size_t data_size, int* width, int* height); is supplied. No decoding is involved when using it. Incremental decoding API: ========================= In the case when data is being progressively transmitted, pictures can still be incrementally decoded using a slightly more complicated API. Decoder state is stored into an instance of the WebPIDecoder object. This object can be created with the purpose of decoding either RGB or Y'CbCr samples. For instance: WebPDecBuffer buffer; WebPInitDecBuffer(&buffer); buffer.colorspace = MODE_BGR; ... WebPIDecoder* idec = WebPINewDecoder(&buffer); As data is made progressively available, this incremental-decoder object can be used to decode the picture further. There are two (mutually exclusive) ways to pass freshly arrived data: either by appending the fresh bytes: WebPIAppend(idec, fresh_data, size_of_fresh_data); or by just mentioning the new size of the transmitted data: WebPIUpdate(idec, buffer, size_of_transmitted_buffer); Note that 'buffer' can be modified between each call to WebPIUpdate, in particular when the buffer is resized to accommodate larger data. These functions will return the decoding status: either VP8_STATUS_SUSPENDED if decoding is not finished yet or VP8_STATUS_OK when decoding is done. Any other status is an error condition. The 'idec' object must always be released (even upon an error condition) by calling: WebPDelete(idec). To retrieve partially decoded picture samples, one must use the corresponding method: WebPIDecGetRGB or WebPIDecGetYUVA. It will return the last displayable pixel row. Lastly, note that decoding can also be performed into a pre-allocated pixel buffer. This buffer must be passed when creating a WebPIDecoder, calling WebPINewRGB() or WebPINewYUVA(). Please have a look at the src/webp/decode.h header for further details. Advanced Decoding API: ====================== WebP decoding supports an advanced API which provides on-the-fly cropping and rescaling, something of great usefulness on memory-constrained environments like mobile phones. Basically, the memory usage will scale with the output's size, not the input's, when one only needs a quick preview or a zoomed in portion of an otherwise too-large picture. Some CPU can be saved too, incidentally. -------------------------------------- BEGIN PSEUDO EXAMPLE // A) Init a configuration object WebPDecoderConfig config; CHECK(WebPInitDecoderConfig(&config)); // B) optional: retrieve the bitstream's features. CHECK(WebPGetFeatures(data, data_size, &config.input) == VP8_STATUS_OK); // C) Adjust 'config' options, if needed config.options.no_fancy_upsampling = 1; config.options.use_scaling = 1; config.options.scaled_width = scaledWidth(); config.options.scaled_height = scaledHeight(); // etc. // D) Specify 'config' output options for specifying output colorspace. // Optionally the external image decode buffer can also be specified. config.output.colorspace = MODE_BGRA; // Optionally, the config.output can be pointed to an external buffer as // well for decoding the image. This externally supplied memory buffer // should be big enough to store the decoded picture. config.output.u.RGBA.rgba = (uint8_t*) memory_buffer; config.output.u.RGBA.stride = scanline_stride; config.output.u.RGBA.size = total_size_of_the_memory_buffer; config.output.is_external_memory = 1; // E) Decode the WebP image. There are two variants w.r.t decoding image. // The first one (E.1) decodes the full image and the second one (E.2) is // used to incrementally decode the image using small input buffers. // Any one of these steps can be used to decode the WebP image. // E.1) Decode full image. CHECK(WebPDecode(data, data_size, &config) == VP8_STATUS_OK); // E.2) Decode image incrementally. WebPIDecoder* const idec = WebPIDecode(NULL, NULL, &config); CHECK(idec != NULL); while (bytes_remaining > 0) { VP8StatusCode status = WebPIAppend(idec, input, bytes_read); if (status == VP8_STATUS_OK || status == VP8_STATUS_SUSPENDED) { bytes_remaining -= bytes_read; } else { break; } } WebPIDelete(idec); // F) Decoded image is now in config.output (and config.output.u.RGBA). // It can be saved, displayed or otherwise processed. // G) Reclaim memory allocated in config's object. It's safe to call // this function even if the memory is external and wasn't allocated // by WebPDecode(). WebPFreeDecBuffer(&config.output); -------------------------------------- END PSEUDO EXAMPLE Bugs: ===== Please report all bugs to our issue tracker: http://code.google.com/p/webp/issues Patches welcome! See this page to get started: http://www.webmproject.org/code/contribute/submitting-patches/ Discuss: ======== Email: webp-discuss@webmproject.org Web: http://groups.google.com/a/webmproject.org/group/webp-discuss

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