This program tries to recover the lost precision of DCT coefficients based on a quantization table from a JPEG image. The result is saved as a JPEG image with quantization set to 1 (like a JPEG saved at 100% quality).
You may not notice jpeg artifacts on the screen without zooming in, but you may notice them after printing. Also, when editing compressed images, artifacts can accumulate, but if you use this program before editing - the result will be better.
JPEG files can be transformed into the JPEG XL form without quality loss, while reducing their size by 22%. JPEG XL preserves all the data in a more efficient container, where the integrity of an original photograph is maintained byte-by-byte — without damage to our digital cultural heritage.
On this page you can be one of the first to try out the new compression technology on your photographs. The conversion process runs locally in your browser using WebAssembly technology, no images are uploaded to servers. This demo only works with .jpg files, there is no .png nor .gif support at the moment.
Lossless recompression improves JPEG XL’s compatibility with existing clients such as older generation phones and browsers not yet having dedicated JPEG XL support. The lossless recompressing feature simplifies the ecosystem migration to JPEG XL: servers can store a single JPEG XL file to serve both JPEG and JPEG XL clients, and multiple efficiency and transfer speed improvements will be available in an ecosystem having a rich mixture of old and new clients. The format has several flexibility considerations for interoperability and migration of JPEG to JPEG XL, and incremental steps of quality improvement can be taken while remaining compatible with both the old and new formats.
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.