Filter through wordpress and custom image sizes and remove unwanted fields from the array

image_size_by_post_type.php

add_filter( 'intermediate_image_sizes', function($sizes){
    $type = get_post_type($_REQUEST['post_id']);
    foreach($sizes as $key => $value){
        if($type=='post_type'  &&  $value != 'img_size_name'){
            unset($sizes[$key]);
        }
    }
    return $sizes;
});