Bash script resize image easily

#!/bin/bash
#Filename: image_help.sh
#Description: A script for image management
if [ $# -ne 4 -a $# -ne 6 -a $# -ne 8 ];
then
echo Incorrect number of arguments
exit 2
fi
while [ $# -ne 0 ];
do
case $1 in
-source) shift; source_dir=$1 ; shift ;;
-scale) shift; scale=$1 ; shift ;;
-percent) shift; percent=$1 ; shift ;;
-dest) shift ; dest_dir=$1 ; shift ;;
-ext) shift ; ext=$1 ; shift ;;
*) echo Wrong parameters; exit 2 ;;
esac;
done
for img in `echo $source_dir/*` ;
do
source_file=$img
if [[ -n $ext ]];
then
dest_file=${img%.*}.$ext
else
dest_file=$img
fi
if [[ -n $dest_dir ]];
then
dest_file=${dest_file##*/}
dest_file="$dest_dir/$dest_file"
fi
if [[ -n $scale ]];
then
PARAM="-resize $scale"

elif [[ -n $percent ]];
then
PARAM="-resize $percent%"
fi
echo Processing file : $source_file
convert $source_file $PARAM $dest_file
done

The following is a sample output, to scale the images in the directory sample_dir to 20% size:
$ ./image_help.sh -source sample_dir -percent 20%
Processing file :sample/IMG_4455.JPG
Processing file :sample/IMG_4456.JPG
Processing file :sample/IMG_4457.JPG
Processing file :sample/IMG_4458.JPG
In order to scale the images to width 1024 use:
$ ./image_help.sh -source sample_dir –scale 1024x
Change the files to PNG format by adding –ext png along with the above commands.
Scale or convert files with specified destination directory as follows:
$ ./image_help.sh -source sample -scale 50% -ext png -dest newdir
# newdir is the new destination directory

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