Convert banch of pictures to another format

convert.sh

#!/bin/bash

# http://mywiki.wooledge.org/BashFAQ/001
# http://askubuntu.com/questions/343727/filenames-with-spaces-breaking-for-loop-find-command

function usage {
    echo "Example usage: convert.sh dir base-extension target-extenstion"
}

if [[ -z $1 ]]
then
    echo "What location should I take?"
    usage
    exit 1
fi

if [[ -z $2 ]]
then
    echo "Which file extension should I take?"
    usage
    exit 1
fi

if [[ -z $3 ]]
then
    echo "Which file type should I convert to?"
    usage
    exit 1
fi

find $1 -type f -name "*.$2" -print0 | while IFS= read -r -d '' filename; do
    convert "$filename" "`basename -s .$2 "$filename"`.$3"
done