Losslessly Transcode JPEG to JPEG XL

Walk a directory of JPEG files and convert them to JPEG XL (.jxl) format using lossless encoding. cjxl automatically detects JPEG bitstream and preserves it without re-compression. Reports byte savings; explains how to recover the original JPEG if needed.

When to use

• Archiving JPEG photo libraries to save space (typically 15–25% reduction) without image degradation.
• Preparing a photo collection for long-term storage where compatibility with JPEG is not required.
• Building a smaller-footprint JXL archive that can still yield the original JPEG via djxl --jpeg.

Inputs to gather

• Source directory — folder containing JPEG files (.jpg or .jpeg). Default: current directory.
• Recursive? Ask whether to process subdirectories. Default: no (flat, current folder only).
• Output location — optional. Default: same directory as originals (.jxl files sit alongside .jpg).
• Dry run first? Recommend a preview pass showing the count and byte savings estimate, before committing to the conversion.

Procedure