Batch blur images using multiple cores - r

Question

I'm trying to blur the bottom section of thousands (>50,000) of images using imagemagick. Image resolution is 800x600. The command line code (below) works, but takes a long time. Is there any way that this can be run in parallel, and hopefully called from within R using system()?
I got this code off the internet, so I'm not sure if it's the best way to even achieve this objective? Any help would be greatly appreciated. Thanks in advance!
(OS = OSX El Capitan)
cd /Users/Desktop/test_images
list=$(ls *.jpg)
for img in $list; do
convert $img \
\( -size 800x525 xc:black -size 800x75 xc:white -append \) \
-compose blur -define compose:args=6 -composite \
cd /Users/Desktop/test_images/results/$img
done
cd

Answer 1

I think this command does something very similar to what you are doing but is FAR quicker. See if you like the effect:
convert start.jpg \( +clone -crop +0+525 -blur x4 \) -gravity south -composite result.jpg
If that works, you can use GNU Parallel just as before:
parallel 'convert {} \( +clone -crop +0+525 -blur x4 \) -gravity south -composite results/{}' ::: *.jpg
You can also put that lot in a script called BlurTitle like this:
#!/bin/bash
parallel 'convert {} \( +clone -crop +0+525 -blur x4 \) -gravity south -composite results/{}' ::: *.jpg
and then make it executable with:
chmod +x BlurTitle
and call it from R with:
system("./BlurTitle")
or from the Terminal with:
./BlurTitle
If you get "Argument list too long", you can express it the other way around like this by sending the arguments on stdin rather than after the command:
cd /path/to/images
find . -name \*.jpg -print0 | parallel -0 'convert {} \( +clone -crop +0+525 -blur x4 \) -gravity south -composite results/{}'