Guetzli: Perceptually Guided JPEG Encoder

TL;DR

Guetzli is a perceptually guided JPEG encoder that significantly reduces file size while maintaining visual quality by optimizing quantization and DCT coefficients using a perceptual distance metric, Butteraugli.

Contribution

It introduces a novel JPEG encoding method that incorporates a perceptual model to achieve higher compression efficiency than existing encoders.

Findings

Achieves 29-45% size reduction at constant perceptual quality.

Uses Butteraugli as a feedback metric for optimization.

Currently slow but demonstrates potential for perceptually optimized compression.

Abstract

Guetzli is a new JPEG encoder that aims to produce visually indistinguishable images at a lower bit-rate than other common JPEG encoders. It optimizes both the JPEG global quantization tables and the DCT coefficient values in each JPEG block using a closed-loop optimizer. Guetzli uses Butteraugli, our perceptual distance metric, as the source of feedback in its optimization process. We reach a 29-45% reduction in data size for a given perceptual distance, according to Butteraugli, in comparison to other compressors we tried. Guetzli's computation is currently extremely slow, which limits its applicability to compressing static content and serving as a proof- of-concept that we can achieve significant reductions in size by combining advanced psychovisual models with lossy compression techniques.