Legacy ImageMagick Discussions Archive

Hi,

Is there a way to tell mogrify to change the "-quality" compression level only if the image does not already have a lower quality setting?

i.e.
> mogrify -quality 50% *.jpg
should leave files that are already compressed at quality 20% untouched.

Or in other words, if the file size would increase, do not change the file.

See http://www.imagemagick.org/script/formats.php. Look for the JPEG format:

• Finally, to restrict the maximum file size, use jpeg:extent, for example -define jpeg:extent=400kb.

Thanks!
Can I somehow apply that to all files in a directory with mogrify *.jpg?
something like mogrify -quality 50% -define jpeg:extent $EXISTING_SIZE *.jpg

Ideally I would want to leave files with lower compression level totally untouched, not recompressing them to stay at the same size. I suppose the only way to do that is to first get the current quality of each file with identify and then parse that somehow?

The problem is quality is dependant on indivitual JPG library implementations.
It is also not actually stored with the JPG image, though a 'educated guess' can be made on it.