v6.7.0

Features

• JPEG XL support, read and write, using the internal
  pillow-jxl-plugin module.
• JXL is now optimized by default. .jxl files that previous versions ignored
  are re-encoded on a plain picopt -r run. Only lossless JXL is touched; lossy
  (XYB encoded) JXL is left alone, as lossy WebP is.
• Lossless images convert to JXL with -c JXL, which now leads the preference
  order for still images ahead of WEBP and PNG.
• New --convert-jpeg-to-jxl converts JPEG to JXL losslessly and reversibly:
  the JXL stores the original JPEG bitstream and can restore it byte for byte.
  Files carrying that reconstruction data are never re-encoded, so the original
  JPEG stays recoverable.
• New --convert-webp-to-jxl converts lossless WebP to JXL. Off by default
  because JXL support is still much thinner than WebP's.
• Both flags require -c JXL as well. JPEG and WEBP are formats picopt already
  processes by default, so unlike BMP or TIFF they cannot be gated by naming
  them with -x. A plain -c JXL still converts only GIF and PNG