#!/bin/bash
# part of ImageMagick

ext=jpg
for i in *.$ext;
   do convert -resize 600x450 -background gray10 -compose Copy -gravity center -extent 600x450 -quality 92 $i `basename $i .$ext`-600.$ext;
done

#convert -scale 600x450 $1 `basename $1 .$ext`-ext.$ext;