README

Introduction

Guetzli is a JPEG encoder that aims for excellent compression density at high
visual quality. Guetzli-generated images are typically 20-30% smaller than
images of equivalent quality generated by libjpeg. Guetzli generates only
sequential (nonprogressive) JPEGs due to faster decompression speeds they offer.



 Building

 On POSIX systems

1.  Get a copy of the source code, either by cloning this repository, or by
    downloading an
    archive and
    unpacking it.
2.  Install libpng.
    If using your operating system
    package manager, install development versions of the packages if the
    distinction exists.
       On Ubuntu, do apt-get install libpng-dev.
       On Fedora, do dnf install libpng-devel. 
       On Arch Linux, do pacman -S libpng.
       On Alpine Linux, do apk add libpng-dev.
3.  Run make and expect the binary to be created in bin/Release/guetzli.

 On Windows

1.  Get a copy of the source code, either by cloning this repository, or by
    downloading an
    archive and
    unpacking it.
2.  Install Visual Studio 2015 and
    vcpkg
3.  Install libpng using vcpkg: .\vcpkg install libpng.
4.  Cause the installed packages to be available system-wide: .\vcpkg integrate
    install. If you prefer not to do this, refer to vcpkg's
    documentation.
5.  Open the Visual Studio project enclosed in the repository and build it.

 On macOS

To install using Homebrew:
1. Install Homebrew
2. brew install guetzli

To install using the repository:
1.  Get a copy of the source code, either by cloning this repository, or by
    downloading an
    archive and
    unpacking it.
2.  Install Homebrew or MacPorts
3.  Install libpng
       Using Homebrew: brew install libpng.
       Using MacPorts: port install libpng (You may need to use sudo).
4.  Run the following command to build the binary in bin/Release/guetzli.
       If you installed using Homebrew simply use make
       If you installed using MacPorts use CFLAGS='-I/opt/local/include' LDFLAGS='-L/opt/local/lib' make

 With Bazel

There's also a Bazel build configuration provided. If you
have Bazel installed, you can also compile Guetzli by running bazel build -c opt //:guetzli.

 Using

Note: Guetzli uses a large amount of memory. You should provide 300MB of
memory per 1MPix of the input image.

Note: Guetzli uses a significant amount of CPU time. You should count on
using about 1 minute of CPU per 1 MPix of input image.

Note: Guetzli assumes that input is in sRGB profile with a gamma of
2.2. Guetzli will ignore any color-profile metadata in the image.

To try out Guetzli you need to build or
download the Guetzli binary. The
binary reads a PNG or JPEG image and creates an optimized JPEG image:

bash
guetzli [--quality Q] [--verbose] original.png output.jpg
guetzli [--quality Q] [--verbose] original.jpg output.jpg


Note that Guetzli is designed to work on high quality images. You should always
prefer providing uncompressed input images (e.g. that haven't been already
compres