Register thumbnail size only for specific post type (WP)

gistfile1.php

function set_different_post_type_sizes()
{
	if (!empty($_REQUEST['post_id']) && ctype_digit($_REQUEST['post_id'])) {

		if ('pedagogues' == get_post_type($_REQUEST['post_id'])) {
			add_image_size('pedagogues-normal', 207, 250, true);
		}
		if ('slider' == get_post_type($_REQUEST['post_id'])) {
			add_image_size('slider-normal', 891, 310, true);
		}
		if ('gallery' == get_post_type($_REQUEST['post_id'])) {
			add_image_size('gallery-normal', 252, 252, true);
		}
		if ('groups' == get_post_type($_REQUEST['post_id'])) {
			add_image_size('groups-normal', 200, 200, true);
		}
		if ('projects' == get_post_type($_REQUEST['post_id'])) {
			add_image_size('projects-normal', 209, 196, true);
			add_image_size('projects-big', 584, 584);
		}
		if ('news' == get_post_type($_REQUEST['post_id'])) {
			add_image_size('news-normal', 209, 192, true);
			add_image_size('news-big', 584, 584);
		}
	}
}

add_action('after_setup_theme', 'set_different_post_type_sizes');