Wordpress - get all defined thumbnail sizes

list_thumbnail_sizes.php

<?php
function list_thumbnail_sizes($type = 'all', $name = '') {
    global $_wp_additional_image_sizes;
    $sizes = array();
    $rSizes = array();
    foreach (get_intermediate_image_sizes() as $s) {
        $sizes[$s] = array(0, 0);
        if (in_array($s, array('thumbnail', 'medium', 'large'))) {
            $sizes[$s][0] = get_option($s . '_size_w');
            $sizes[$s][1] = get_option($s . '_size_h');
        } else {
            if (isset($_wp_additional_image_sizes) && isset($_wp_additional_image_sizes[$s]))
                $sizes[$s] = array($_wp_additional_image_sizes[$s]['width'], $_wp_additional_image_sizes[$s]['height'],);
        }
    }


    foreach ($sizes as $size => $atts) {
        if ($type == 'width') {
            $rSizes[$size] = $atts[0];
        }
        elseif ($type == 'height') {
            $rSizes[$size] = $atts[1];
        }
        else {
            $rSizes[$size] = $size . ' ' . implode('x', $atts);
        }
    }
    if ($name && isset($rSizes[$name])) {
        return $rSizes[$name];
    }
    return $rSizes;
}