downsample a PDF file using ghostscript

downsample.sh

#!/bin/bash
# Copyright 2018 Johan Hidding
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

usage() {
    exec_name=$(basename "$0")
    exec_spac=$(echo ${exec_name} | sed -e 's/./ /g')
    echo "Downsample PDF file."
    echo "usage: ${exec_name} [-h|--help]"
    echo "     | ${exec_name} <input-file>"
    echo "       ${exec_spac} [-dpi|--dpi <dpi>] [-q|--quiet]"
    echo "       ${exec_spac} [-o|--output] <output-file>"
    echo
    echo "-dpi|--dpi   <dpi>         Defaults to 150."
    echo "-o|--output  <output-file> Defaults to the <input-file> with a '-downsampled'"
    echo "                           suffix, in the same folder as the input PDF."
    echo "-q|--quiet                 Suppress output of ghostscript (-dQUIET)."
    echo "-h|--help                  Print this help."
    exit
}


if [[ $# -lt 1 || "$1" =~ -h|--help ]]; then
    usage
fi

input_file="$1"
if [[ ! -f "$input_file" ]]; then
    echo "File not found: ${input_file}"
    usage
fi
shift

dpi=150
quiet=""
output_file="$(dirname "${input_file}")/$(basename "${input_file}" .pdf)-downsampled.pdf"

while [[ $# -gt 0 ]]; do
    key="$1"
    case ${key} in
        -dpi|--dpi)
            dpi="$2"
            shift; shift
            ;;
        -q|--quiet)
            quiet="-dQUIET"
            shift
            ;;
        -o|--output)
            output_file="$2"
            shift; shift
            ;;
        *)
            echo "unexpected argument: ${key}"
            exit
            ;;
    esac
done


echo "Downsampling ${input_file} -> ${output_file} ... this may take a while"
stat --printf="%n: %s bytes\n" ${input_file}

gs  -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 \
    -dPDFSETTINGS=/screen -dNOPAUSE ${quiet} -dBATCH \
    -dEmbedAllFonts=true \
    -dSubsetFonts=true \
    -dColorImageDownsampleType=/Bicubic \
    -dColorImageResolution=${dpi} \
    -dGrayImageDownsampleType=/Bicubic \
    -dGrayImageResolution=${dpi} \
    -dMonoImageResolution=${dpi} \
    -sOutputFile="${output_file}" "${input_file}"

stat --printf="%n: %s bytes\n" "${output_file}"