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.