Optimize PDF files with Ghostscript.

pdfoptim.sh

#!/usr/bin/env bash
# pdfoptim.sh
#
# Optimize a PDF with Ghostscript
#
# Usage: bash pdfoptim.sh FILE.pdf
#
# This will copy the input file to FILE-original.pdf
# And write an optimized file to FILE.pdf
#
# Install dependencies: brew install ghostscript
#
# Learn more about Ghostscript options: https://ghostscript.com/docs/9.54.0/Use.htm

if [[ "$#" -ne 1 ]]; then
  echo "usage: $0 in.pdf"
  exit 1
fi

dpi=300
downsample=0.8
in_file="$1"

out_file="${TMPDIR}pdfoptim.$(uuidgen).pdf"

gs \
  -o"${out_file}" \
  -sDEVICE=pdfwrite \
  -dDownsampleColorImages=true \
  -dDownsampleGrayImages=true \
  -dDownsampleMonoImages=true \
  -dColorImageResolution=${dpi} \
  -dGrayImageResolution=${dpi} \
  -dMonoImageResolution=${dpi} \
  -dColorImageDownsampleThreshold=${downsample} \
  -dGrayImageDownsampleThreshold=${downsample} \
  -dMonoImageDownsampleThreshold=${downsample} \
  "${in_file}"

command mv -f "$in_file" "${in_file%.pdf}-original.pdf"
command mv -f "$out_file" "$in_file"
command rm -f "$out_file"