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

1. Get a copy of the source code, either by cloning this repository, or by downloading an archive and unpacking it.
2. Install Bazel by following its installation instructions.
3. Run bazel build -c opt :guetzli in the directory this README file is in.

Using

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:

bazel-bin/guetzli [--quality Q] [--verbose] original.png output.jpg
bazel-bin/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.