Optimize pdf files for screen resolution.

pdf-screen-res

#!/usr/bin/env bash

# vim: ft=sh

set -o errexit
set -o pipefail
shopt -s nullglob

usage () {
    echo "Usage: $0 "
    echo "Optimize pdf files for screen resolution."
    echo "Original pdf files are taken from the current directory."
    echo "The resulting files are written to ./out-{TIMESTAMP}"
    echo "The output directory contains a manifest of the processed files."
    echo "Options:"
    echo "  -h      Print this help"
    exit 0
}

case "$1" in
    -h|--help) usage;;
esac

command -v gs >/dev/null 2>&1 \
    || { echo "Please install ghostscript (https://www.ghostscript.com)." >&2; exit 1; }

# Ghostscript options
PDFRES="/ebook"         # /ebook=150dpi, /screen=72dpi
PAPERSIZE="a4"          # a4, letter ...

opts=("-sDEVICE=pdfwrite")
opts+=("-sPAPERSIZE=$PAPERSIZE")
opts+=("-dPDFSETTINGS=$PDFRES")
opts+=("-sColorConversionStrategy=Gray")
opts+=("-dProcessColorModel=/DeviceGray")
opts+=("-dCompatibilityLevel=1.4")
opts+=("-dNOPAUSE" "-dBATCH")

# Look for pdf files in the current working directory.
cwd="$(pwd)"
files=(*.pdf)

(( ${#files[@]} )) \
    || { echo "No pdf files found in $cwd!" >&2; exit 1; }

# The processed files go into $CURRENT_WORKING_DIR/out_$TIMESTAMP.
ts="$(date +%s)"
od="out_$ts"
mkdir -p "$cwd/$od" \
    && echo "▶ Created directory $cwd/$od ..."

for f in "${files[@]}"; do
    eval "gs ${opts[*]} -sOutputFile=$cwd/$od/$f $f"
done

# Check success.
cd "$cwd/$od"
new_files=(*.pdf)
cd "$cwd"
miss_files=( $(printf '%s\n' "${files[@]}" "${new_files[@]}" "${new_files[@]}" \
    | sort | uniq -u) )
if (( ${#miss_files[@]} )); then
    echo "❌ Some files could not be written:" >&2
    printf '%s\n' "${miss_files[@]}" >&2
fi

# The processed files are listed in manifest.txt.
printf '%s\n' "${new_files[@]}" > "$cwd/$od/manifest.txt" \
    && echo -n "▶ ${#new_files[@]} file(s) processed." \
    && echo " Please check ./$od/manifest.txt for details."