Custom image size not regenerating when image editted

To regenerate custom image size when image is edited in image editor , You have to add following options in wp_options table using update_option function along with add_image_size.

Example :

$img_size_name="custom-size"; // The new image size name.
if ( function_exists( 'add_theme_support' ) )
add_image_size($img_size_name, 100, 100 , true);

update_option($img_size_name.'_size_w', 100);
update_option($img_size_name.'_size_h', 100);
update_option($img_size_name.'_crop', 1);