imagequant.sh

#!/usr/bin/env bash
# Optimize PNG files larger than 800 KiB without keeping larger results.
# Usage: imagequant.sh [ROOT]
# Requires pngquant, oxipng, GNU find/stat, and awk.
set -euo pipefail

ROOT="${1:-.}"
MIN_SIZE="+800k"

if [[ $# -gt 1 ]]; then
    echo "Usage: $0 [ROOT]" >&2
    exit 2
fi

if [[ "${1:-}" == "-h" || "${1:-}" == "--help" ]]; then
    echo "Usage: $0 [ROOT]"
    echo "Optimize PNG files larger than 800 KiB below ROOT (default: current directory)."
    exit 0
fi

if [[ ! -d "$ROOT" ]]; then
    echo "Error: directory not found: $ROOT" >&2
    exit 2
fi

if ! command -v pngquant >/dev/null 2>&1; then
    echo "Error: pngquant is not installed" >&2
    exit 1
fi

if ! command -v oxipng >/dev/null 2>&1; then
    echo "Error: oxipng is not installed" >&2
    exit 1
fi

find "$ROOT" -type f \( -iname "*.png" \) -size "$MIN_SIZE" -print0 |
while IFS= read -r -d '' file; do
    echo
    echo "File: $file"

    before_size=$(stat -c%s "$file")
    backup="${file}.bak"

    cp -p "$file" "$backup"

    # pngquant reduces the palette with minimal quality loss.
    # --skip-if-larger avoids replacing the file with a larger result.
    if pngquant --quality=90-100 --skip-if-larger --ext .png --force "$file"; then
        :
    else
        echo "pngquant could not process the file; trying oxipng only"
        cp -p "$backup" "$file"
    fi

    # oxipng performs lossless PNG optimization.
    oxipng -o 4 --strip safe "$file" >/dev/null

    after_size=$(stat -c%s "$file")

    if [ "$after_size" -ge "$before_size" ]; then
        cp -p "$backup" "$file"
        rm -f "$backup"
        echo "No size reduction; restored the original"
        echo "Size: $before_size bytes"
    else
        rm -f "$backup"
        saved=$((before_size - after_size))
        percent=$(awk "BEGIN { printf \"%.2f\", ($saved / $before_size) * 100 }")
        echo "Before: $before_size bytes"
        echo "After:  $after_size bytes"
        echo "Saved:  $saved bytes ($percent%)"
    fi
done