Speeding up Imagemagick convert by using it in conjunction with Ghostscript

Using the script below resulted in the Imagemagick convert taking 7.5 seconds, compared with the 2 pronged approach taking just over 0.5 seconds


#!/bin/bash

echo "---------------------------------------------------------"
echo "Use ImageMagick to convert PDF to 450x307 jpg"
echo "---------------------------------------------------------"
TT="$(date +%s%N)"

convert -resize 450x307 test.pdf test_resized.jpg

T="$(($(date +%s%N)-TT))"
# Seconds
S="$((T/1000000000))"
# Milliseconds
M="$((T/1000000))"
printf "Run time: %02d:%02d:%02d:%02d.%03d\n" "$((S/86400))" "$((S/3600%24))" "$((S/60%60))" "$((S%60))" "${M}"

echo "---------------------------------------------------------"
echo "Use Ghostscript to convert PDF to 450x307 jpg"
echo "---------------------------------------------------------"
TT="$(date +%s%N)"
gs -sDEVICE=jpeg -dNumRenderingThreads=4 -dNOGC -o test.jpg -dJPEGQ=95 test.pdf 2>&1
convert -resize 450x307 test.jpg test_resized.jpg
T="$(($(date +%s%N)-TT))"
# SecondsS="$((T/1000000000))"

# Milliseconds
M="$((T/1000000))"
printf "Run time: %02d:%02d:%02d:%02d.%03d\n" "$((S/86400))" "$((S/3600%24))" "$((S/60%60))" "$((S%60))" "${M}"
echo "---------------------------------------------------------"