Image filter for Wordpress (Source: http://ottopress.com/2011/customizing-wordpress-images/ )

Image filter for wordpress

add_action('after_setup_theme','themename_bw_size');
function themename_bw_size() {
    add_image_size('themename-bw-image', 100, 100, true);
}

add_filter('wp_generate_attachment_metadata','themename_bw_filter');
function themename_bw_filter($meta) {
    $file = wp_upload_dir();
    $file = trailingslashit($file['path']).$meta['sizes']['themename-bw-image']['file'];
    list($orig_w, $orig_h, $orig_type) = @getimagesize($file);
    $image = wp_load_image($file);
    imagefilter($image, IMG_FILTER_GRAYSCALE);
    switch ($orig_type) {
        case IMAGETYPE_GIF:
            imagegif( $image, $file );
            break;
        case IMAGETYPE_PNG:
            imagepng( $image, $file );
            break;
        case IMAGETYPE_JPEG:
            imagejpeg( $image, $file );
            break;
    }
    return $meta;
}