jpegoptim vs MozJPEG

jpegoptim can optimize JPEGs losslessly without re-encoding, while MozJPEG re-encodes with a more efficient encoder.

Lossless Optimization vs Re-Encoding

jpegoptim can strip metadata and optimize Huffman tables without touching the image data at all, guaranteeing identical pixels, while MozJPEG re-encodes the image entirely with its improved encoder, achieving larger savings but introducing a generational quality step.

jpegoptim can optimize Huffman tables and strip metadata losslessly
This guarantees the decoded pixels remain completely identical
MozJPEG re-encodes entirely, saving more but adding a generational step

Choosing Based on the Source Image

For an already well-encoded JPEG, jpegoptim's lossless mode captures modest savings with zero risk, while MozJPEG makes more sense when encoding from an original source like a PNG or RAW file, where no generational quality loss is introduced at all.

jpegoptim's lossless mode suits already well-encoded existing JPEGs
MozJPEG makes most sense when encoding from an original source
Encoding from PNG or RAW avoids any generational quality loss

Frequently Asked Questions

Does jpegoptim always compress losslessly?

It offers a lossless mode that optimizes Huffman tables and strips metadata, but it also supports a lossy quality-targeting mode that does re-encode the image.

Is re-encoding an existing JPEG with MozJPEG a bad idea?

It introduces a generational quality step, so it's better to encode from an original source when possible — though the practical impact is often minor at high quality settings.

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