Use 'find' command to search for PNG files, pipe output to imagemagick for batch conversion

Question

I've got a directory with thousands of image files, mostly JPG but some PNG. The files have no extension, they're just numbered. I need to convert all of them to JPG.

Using find I can get a list of all the files with their types, and from that I can use Imagemagick to convert from PNG to JPG by specifying their type:

convert png:10020 jpg:10020.jpg

But I'd like to do this as a batch across all the files. How can I pipe the output of find and convert all the PNG files to JPG?

Answer 1

find . -type f | while read IN; do
  if [ "x$(file -b --mime-type $IN)" = "ximage/png" ]; then
    convert png:$IN jpg:$IN.jpg;
  fi;
done;

Meaning of arguments:

1. .
   Find in the current directory

2. -type f
   Just find files, not directories/sockets/etc.

3. while read IN; do
   Put each filename into the variable IN and run the loop on it.

4. if [ "x$(file -b --mime-type $IN)" = "ximage/png" ]; then
   Check if the file is a PNG...

5. convert png:$IN jpg:$IN.jpg;
   ...and if it is, convert it.

6. fi; done;
   We are done!

I have tested it this time, and it works, converting a directory full of PNG's without the .png extension to JPG's.