Guetzli – perceptual JPEG encoder

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.

Guetzli uses a large amount of memory and significant amount of CPU time. You should provide 300MB of memory per 1MPix of the input image. You should count on using about 1 minute of CPU per 1 MPix of input image.

This is free and open source software.

Features include:

  • Designed to work on high quality images (supports only the top of JPEG’s quality range (quantizer settings 84–100). You should always prefer providing uncompressed input images.
  • Very effective with bigger files.
  • Uses methods to optimize compression efficiency that target mainly the quantization step. It constructs custom quantization tables for each file, decides on color subsampling, and quantizes some adjacent DCT coefficients to zero, balancing benefits in the run-length encoding of coefficients and preservation of perceived image fidelity. Zeroing the right coefficients is the most effective tool in Guetzli, which is used as a makeshift means of spatially adaptive quantization. The optimizations are guided by Butteraugli, a newly introduced objective image quality assessment metric.

Website: github.com/google/guetzli
Support: Photo Compression
Developer: Google Research Europe
License: Apache License 2.0

Guetzli is written in C++. Learn C++ with our recommended free books and free tutorials.

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