errors in "convert" (image magick)

fwc · 02-16-2009, 01:57 AM

Hello, I was trying to reduce the quality of a folder of images (batch) to put on the web and wasn't sure which command to use. I downloaded image magick and went to the folder where the images were.

I had used mogrify to change the dimensions but then to change the quality I used "convert -quality 80% *.JPG" So I thought it was converting the quality of the images in that folder but after about 30 mins of processing with no sign of stopping I decided to abort (restart button, because screen was greyed out).

So when I came back none of the images in the folder had been changed. Can someone please help explain what actually happened? Thanks very much for any support.

colucix · 02-16-2009, 02:39 AM

The convert command accept both the input file name and the output file name as arguments:

Code:

convert input-file [options] output-file

Most likely the first image has been converted and the output has been overwritten onto the second image and so on. Hence to process multiple files better to use a for loop, like this:

Code:

for file in *.JPG
do
  convert "$file" -quality 80 "$file"
done

Moreover you don't need to apply the mogrify command before processing with convert, since you can use the -resize option of convert to achieve the same result.

fwc · 02-16-2009, 04:15 AM

Quote:

Originally Posted by colucix

The convert command accept both the input file name and the output file name as arguments:

Code:

convert input-file [options] output-file

Most likely the first image has been converted and the output has been overwritten onto the second image and so on. Hence to process multiple files better to use a for loop, like this:

Code:

for file in *.JPG
do
  convert "$file" -quality 80 "$file"
done

Moreover you don't need to apply the mogrify command before processing with convert, since you can use the -resize option of convert to achieve the same result.

Thank you very much. I did not mean to imply that one has to use mogrify, but that was just the command I found online. It didn't seem to overwrite any files, but I am surprised it used so much processing power.
I converted the quality with mogrify and it seems to work better so I think I will use that. Thanks very much, and my main concern was that it had converted files outside the directory I was in.