to-jxl

Convert Images to JPEG XL

Encode images to JPEG XL (.jxl) format using cjxl. Supports lossless, visually lossless, and web quality presets, with optional effort (compression) tuning.

When to use

• Converting photos to JXL for archival, where file size matters and quality must be preserved.
• Lossless-transcoding existing JPEG files to save ~20% file size without re-compression artifacts.
• Creating web-optimized JXL variants with controlled visual loss.

Inputs to gather

• Input file or directory — single image, folder, or recursive tree. If omitted, ask for the path.
• Quality preset — ask which tier: lossless (full fidelity, -d 0), visually-lossless (imperceptible loss, -d 1.0, default), or web (visible compression acceptable, -d 3.0). Default: visually-lossless.
• Effort level — optional, range 1–9 (1 = fastest, 9 = slowest/best compression). Default: 7. Only ask if the user is concerned about speed vs file size.

Procedure

1. Check tooling

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

Abort if missing.

2. Map quality presets to distance

• lossless → -d 0
• visually-lossless → -d 1.0
• web → -d 3.0

Set effort=7 unless the user overrides.

3. Determine scope

• Single file: run one conversion.
• Directory (non-recursive): ask before processing, then loop over image files in the folder.
• Recursive: use find to locate all images in the tree.

Ask for confirmation before batch operations.

4. Convert

Single file:

cjxl -d <distance> -e <effort> input.jpg output.jxl

Batch (folder or recursive):

find <target> -maxdepth <1|999> -type f \
  \( -iname '*.jpg' -o -iname '*.jpeg' -o -iname '*.png' \
     -o -iname '*.gif' -o -iname '*.webp' -o -iname '*.tif' \) \
  -exec cjxl -d <distance> -e <effort> {} {.}.jxl \;

Show progress (file count, time remaining estimate if batch is large).

5. Report

After conversion:

• Count of files converted, skipped, failed.
• Original vs. converted file sizes; report total bytes saved.
• If any conversions failed, list them and suggest manual inspection.

Output / side effects

• New .jxl files created in the same directory as originals (or in a user-specified output folder).
• Original files remain unchanged.

Notes

• Lossless JPEG→JXL transcoding: cjxl auto-detects JPEG bitstream and preserves it. To recover the original JPEG bit-exact later, use djxl --jpeg input.jxl recovered.jpg. This is the killer feature for photo archives.
• Effort vs. speed: Effort 7 is a good default (reasonable compression in 1–2 seconds per MP). Effort 9 can take minutes on large files. Only use 9 for final archival encodes, not batch preview work.
• Alpha channels: JXL supports them natively. PNGs with transparency will retain it.
• Depends: apt install libjxl-tools.