Skip to main content

compressJPG

Path: build/compressJPG | Language: Bash | Lines: ~51

JPEG compression helper that rewrites files only when savings exceed a threshold.

Overview​

compressJPG optimizes .jpg / .jpeg files with a two-step pipeline:

  1. jpegtran for progressive/optimized re-encoding with metadata stripping
  2. mogrify -quality 60 for additional size reduction

It computes size ratio (original / new) and only replaces the original if ratio is greater than 1.2 (roughly >20% savings).

Input Behavior​

  • If file arguments are provided, it processes those files.
  • If no arguments are provided, it auto-discovers JPEG files in the current directory (non-recursive).
  • If neither yields files, it exits with an error.

Processing Steps​

For each file:

  1. Copy original to a temp file
  2. Run jpegtran -copy none -progressive -optimize
  3. Run mogrify -quality 60 on the temp result
  4. Compare byte sizes with wc -c
  5. Replace original only if compression gain is sufficient

Temporary files are cleaned up at the end of each iteration.

Dependencies​

  • jpegtran
  • mogrify
  • bc
  • standard POSIX tooling (find, wc, mktemp, cp, mv, rm)

Notes​

  • Uses set -e for fail-fast behavior.
  • Color helper functions are inlined for portability (instead of sourcing build/bash.sh).
  • Uses a conservative replacement threshold to avoid unnecessary churn on low-gain recompressions.

See Also​