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Python bindings:

To build the swig-generated Python extension code at least Python 2.6 is
required. Python < 2.6 may build with some minor changes to libwebp.swig or the
generated code, but is untested.

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, TIFF or WebP 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
  -z <int> ............... activates lossless preset with given
                           level in [0:fast, ..., 9:slowest]

  -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
  -blend_alpha <hex> ..... blend colors against background color
                           expressed as RGB values written in
                           hexadecimal, e.g. 0xc0e0d0 for red=0xc0
                           green=0xe0 and blue=0xd0
  -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
  -bmp ......... save as uncompressed BMP format
  -tiff ........ save as uncompressed TIFF format
  -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
  -nodither .... disable dithering
  -dither <d> .. dithering strength (in 0..100)
  -alpha_dither  use alpha-plane dithering if needed
  -mt .......... use multi-threading
  -crop <x> <y> <w> <h> ... crop output with the given rectangle
  -scale <w> <h> .......... scale the output (*after* any cropping)
  -flip ........ flip the output vertically
  -alpha ....... only save the alpha plane
  -incremental . use incremental decoding (useful for tests)
  -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
  -dither <int>  dithering strength (0..100), default=50
  -noalphadither disable alpha plane dithering
  -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

Animated GIF conversion:
========================
Animated GIF files can be converted to WebP files with animation using the
gif2webp utility available under examples/. The files can then be viewed using
vwebp.

Usage:
 gif2webp [options] gif_file -o webp_file
Options:
  -h / -help  ............ this help
  -lossy ................. encode image using lossy compression
  -mixed ................. for each frame in the image, pick lossy
                           or lossless compression heuristically
  -q <float> ............. quality factor (0:small..100:big)
  -m <int> ............... compression method (0=fast, 6=slowest)
  -kmin <int> ............ min distance between key frames
  -kmax <int> ............ max distance between key frames
  -f <int> ............... filter strength (0=off..100)
  -metadata <string> ..... comma separated list of metadata to
                           copy from the input to the output if present
                           Valid values: all, none, icc, xmp (default)
  -mt .................... use multi-threading if available

  -version ............... print version number and exit
  -v ..................... verbose
  -quiet ................. don't print anything

Building:
---------
With the libgif development files installed, gif2webp can be built using
makefile.unix:
$ make -f makefile.unix examples/gif2webp

or using autoconf:
$ ./configure --enable-everything
$ make

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>