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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: