WORDPRESS Remove standard image sizes

gistfile1.php

<?php
/**
 * Remove standard image sizes so that these sizes are not
 * created during the Media Upload process
 *
 * Tested with WP 3.2.1
 *
 * Hooked to intermediate_image_sizes_advanced filter
 * See wp_generate_attachment_metadata( $attachment_id, $file ) in wp-admin/includes/image.php
 *
 * @param $sizes, array of default and added image sizes
 * @return $sizes, modified array of image sizes
 * @author Ade Walker http://www.studiograsshopper.ch
 */
function sgr_filter_image_sizes( $sizes) {
		
	unset( $sizes['thumbnail']);
	unset( $sizes['medium']);
	unset( $sizes['large']);
	
	return $sizes;
}
add_filter('intermediate_image_sizes_advanced', 'sgr_filter_image_sizes');