Normalize images in CBZ file for e-Reader. Fixes contrast issues for manga.

batch-fix-cbz.sh

#!/usr/bin/env bash

# usage:
# batch-fix-cbz.sh comic1.cbz [comic2.cbz ...]

# WARNING: overwrites original file

die() {
    EXIT_CODE=$?
    echo "$*" >&2
    exit $EXIT_CODE
}

for cbz in "$@"; do
    echo "Normalizing $cbz..."
    test -f "$cbz" || die "Not a file: $cbz"
    cbz_dir=$(mktemp -d) || die "Failed to make temp dir"
    unzip -q "$cbz" -d "$cbz_dir" || die "Failed to unzip archive"

    find "$cbz_dir" -type f \( -iname '*.jpg' -o -iname '*.png' \) -print0 | xargs --null -r -P "$(("$(nproc)"*3/2))" \
        mogrify -level 5%,95% -contrast-stretch 10%,15% || die "Failed to equalize images"

    cp -a "$cbz" "$cbz.old" || die "Failed to backup original CBZ"
    zip -q -j -r "$cbz" "$cbz_dir" || die "Failed to replace original CBZ"
    echo "Done"
done