Google has introduced Jpegli, an advanced JPEG coding library that maintains high backward compatibility while offering enhanced capabilities and a 35% compression ratio improvement at high quality compression settings.

The new library is designed to be faster, more efficient, and more visually pleasing than traditional JPEG. Google says the library provides both a fully interoperable encoder and decoder complying with the original JPEG standard, but images that are compressed or decompressed through Jpegli look clearer because more precise and psychovisually effective computations are performed. 

The developers say Jpegli's coding speed is comparable to traditional approaches, such as libjpeg-turbo and MozJPEG, meaning web developers can integrate Jpegli into their existing workflows without sacrificing coding speed performance or memory use.

Jpegli can be encoded with 10+ bits per component, as opposed to traditional JPEG coding solutions that offer only 8 bit per component dynamics causing visible banding artifacts in slow gradients. The resulting images are still fully interoperable with 8-bit viewers. The images are more dense, so saving on bandwidth and storage space, and speeding up web pages.

Jpegli achieves the improved resuls and performance through a number of new techniques to reduce noise and improve image quality. The first new technique is the use of adaptive quantization to reduce noise and improve image quality. The developers the techniques were originally developed for JPEG XL, and work by spatially modulating the dead zone in quantization based on psychovisual modeling. On noisy parts of the image, quantization thresholds for zero coefficients are higher than on smoother parts of the image.

The next change is improved quantization matrix selection.  Precise intermediate results in Jpegli improve image quality, and both encoding and decoding produce higher quality results. Jpegli can also use JPEG XL's XYB colorspace for further quality and density improvements.

The quality of the output image can be indicated by a distance parameter that is analogous to the distance parameter of JPEG XL. The developers say the quantization tables are chosen based on the distance and the chroma subsampling mode, with different positions in the quantization matrix scaling differently, and the red and blue chrominance channels have separate quantization tables.

Jpegli is available now on GitHub.

More Information

Jpegli On GitHub

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