image-convert

#!/bin/bash
set -euo pipefail

usage() {
    cat >&2 <<EOM
usage: $(basename "$0") [options] FILE [OUTPUT]

Batch convert image files, with various options.

To choose the output filename, you must either specify the OUTPUT file or the
output extension with -e/--ext.

The output extension will also control the output image format used, if you
want to convert from one format to another.

See also: jhead(1), convert(1), ImageMagick(1)

Options:

    -h, --help          Display this help text
    -q, --quality NUM   Use JPEG quality level NUM
    -r, --resize RES    Resize image to WxH resolution
    -f, --force         Overwrite existing output files
    -e, --ext EXT       Use EXT as the output file extension (and image format)
    -o, --out-dir DIR   Write output files to DIR
    --mtime             Set mtime of output files to match input

Examples:

    # Convert input.JPG quality and resolution, save as output.jpg
    image-convert -q 90 -r 640x480 -e jpg input.JPG

    # Convert a whole directory of files in parallel
    parallel image-convert -q 90 -e jpg -- *.JPG

    # Write files to directory \`output/'
    parallel image-convert -q 90 -o output/ -- input/*.jpg

    # Convert png files to jpg
    parallel image-convert -q 95 -o output/ -e jpg -- *.png

    # Convert png files to lossy webp
    parallel image-convert -q 95 -o output/ -e webp -- *.png

EOM
}

run() {
    echo >&2 "+ $*"
    "$@"
}

opts=()
force=
out_dir=
out_ext=
mtime=

while [ $# -gt 0 ] && [[ $1 == -* ]]; do
    case "$1" in
        -h|--help)
            usage
            exit
            ;;
        -e|--ext)
            out_ext="$2"
            shift
            ;;
        -q|--quality)
            opts+=(-quality "$2")
            shift
            ;;
        -r|--resize)
            opts+=(-resize "$2")
            shift
            ;;
        -f|--force)
            force=1
            ;;
        -o|--out-directory)
            out_dir="$2"
            shift
            ;;
        --mtime)
            mtime=1
            ;;
        *)
            usage
            echo >&2 "Unknown option '$1'"
            exit 1
            ;;
    esac

    shift
done

case $# in
    1)
        input="$1"

        # split on final '.'
        ext="${input##*.}"
        basename="${input%.*}"


        if [ -n "$out_dir" ]; then
            # use out_dir as output directory
            mkdir -vp "$out_dir"
            if [ -n "$out_ext" ]; then
                # user-specified output extension
                output="$out_dir/$basename.$out_ext"
            else
                # default to input extension for output
                output="$out_dir/$basename.$ext"
            fi
        else
            # must specify output extension if output directory is not given
            if [ -z "$out_ext" ]; then
                usage
                echo >&2 "error: Where should output go? Must pass OUTPUT, --out-dir, or --ext"
                exit 2
            fi
            output="$(dirname "$input")/$basename.$out_ext"
        fi

        ;;
    2)
        if [ -n "$out_dir" ]; then
            usage
            echo >&2 "error: cannot pass OUTPUT and --out-dir"
            exit 1
        fi
        if [ -n "$out_ext" ]; then
            usage
            echo >&2 "error: cannot pass OUTPUT and --ext"
            exit 1
        fi
        input="$1"
        output="$2"
        ;;
    *)
        usage
        exit 1
        ;;
esac

if [ -z "$force" ] && [ -e "$output" ]; then
    echo >&2 "error: output file already exists: '$output'"
    exit 3
fi

run convert "${opts[@]}" "$input" "$output"

if [ -n "$mtime" ]; then
    touch --no-create --reference "$input" "$output"
fi