Ticket #14106: demo-plugin.php

<?php
add_image_size( 'mythumb_bw', 200, 50, true );
add_image_size( 'mythumb', 200, 50, true );
add_filter( 'image_resize_mythumb_bw', 'bw' );
function bw( $image ) {
        imagefilter( $image, IMG_FILTER_GRAYSCALE );
        return $image;
}
add_filter( 'image_resize_suffix_mythumb_bw', 'bwfilename' );
function bwfilename( $suffix ) {
        return "$suffix-bw";
}