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 and gflags. 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 libgflags-dev.
   • On Arch Linux, do pacman -S libpng gflags.
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 and gflags using vcpkg: .\vcpkg install libpng gflags.
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.

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.

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

Note that Guetzli is designed to work on high quality images (e.g. that haven't been already compressed with other JPEG encoders). 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.