ImageAlchemyCompression Studio

MozJPEG

Mozilla's improved JPEG encoder — same JPEG format, roughly 10–15% smaller files at equal quality.

Definition

MozJPEG is a JPEG encoder maintained by Mozilla. It improves on the standard libjpeg encoder with trellis quantization (choosing coefficients that compress better at equal visual quality) and progressive encoding, producing JPEGs that are typically 10–15% smaller at the same visual quality while remaining 100% standard JPEG files.

In practice

Because MozJPEG output is a standard JPEG, it works everywhere JPEG works — no browser or tool changes needed. The catch is that few online compressors actually use it. ImageAlchemy uses MozJPEG for its JPEG output path.

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Frequently asked questions

MozJPEG is an improved JPEG encoder. Using trellis quantization and progressive encoding, it produces standard JPEG files that are roughly 10–15% smaller than those from the default libjpeg encoder, at the same visual quality.

No. MozJPEG output is a 100% standard JPEG file — every browser, editor and device reads it. The improvement is purely in how the file is encoded, not in the format itself.

Yes. MozJPEG is open source, maintained by Mozilla, and royalty-free to use. ImageAlchemy uses it as its JPEG encoder.