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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:

guetzli [--quality Q] [--verbose] original.png output.jpgguetzli [--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
compressed with any JPEG encoders, including Guetzli). While it will work on other
images too, results will be poorer. You can try compressing an enclosed sample
high quality
image.

You can pass a --quality Q parameter to set quality in units equivalent to
libjpeg quality. You can also pass a --verbose flag to see a trace of encoding
attempts made.

Please note that JPEG images do not support alpha channel (transparency). If the
input is a PNG with an alpha channel, it will be overlaid on black background
before encoding.