from-jxl

Decode JPEG XL Images

Extract images from JPEG XL (.jxl) files using djxl. Outputs PNG or JPEG, with optional recovery of original JPEG bitstream if the source JXL was a lossless JPEG transcode.

When to use

• Converting JXL files back to PNG for general use or compatibility.
• Recovering the original JPEG bitstream from a lossless-transcoded JXL file via djxl --jpeg.
• Batch-decoding a JXL archive to portable formats.

Inputs to gather

• Input .jxl file or directory — single file or folder.
• Output format — png (default) or jpeg. If the user has a JXL that came from a lossless JPEG transcode and wants to recover the original JPEG byte-exact, offer the jpeg format and explain the --jpeg flag.
• Output directory — optional. Default: same directory as input.

Procedure

1. Check tooling

command -v djxl || echo "djxl not installed — install with: sudo apt install libjxl-tools"

Abort if missing.

2. Determine scope and format

• Single file: direct conversion.
• Directory (non-recursive): loop over all .jxl files.
• Recursive: use find to locate .jxl files in the tree.

Confirm the output format with the user.

3. Decode

Single file to PNG (default):

djxl input.jxl output.png

Single file to JPEG (standard):

djxl input.jxl output.jpg

Single file to original JPEG (lossless transcode recovery):

If the JXL was created via cjxl in.jpg out.jxl, this recovers the original JPEG bitstream byte-exact:

djxl --jpeg input.jxl recovered.jpg

Batch (folder or recursive):

find <target> -maxdepth <1|999> -type f -iname '*.jxl' \
  -exec djxl {} {.}.<format> \;

(Replace <format> with png or jpg, or —jpeg flag for JPEG recovery.)

4. Report

After decoding:

• Count of files decoded, skipped, failed.
• Output file sizes and locations.
• If batch, show a summary of converted files.

Output / side effects

• New PNG or JPEG files created in the output directory.
• Original .jxl files remain unchanged.

Notes

• Lossless JPEG recovery: Only use djxl --jpeg if you are confident the .jxl source was created via lossless JPEG transcode (i.e., cjxl original.jpg encoded.jxl). For JXL files created from PNG or other sources, --jpeg may produce incorrect results.
• Alpha channels: JXL alpha is preserved when decoding to PNG. JPEG does not support transparency, so any alpha will be lost if decoding to JPEG.
• Color profile: JXL can carry ICC color profiles; djxl preserves them in the output.
• Depends: apt install libjxl-tools.