WordPress image orientation detection

functions.php

function ns_single_image_filter($size){
  $tn_id = get_post_thumbnail_id( $post->ID );
  $img = wp_get_attachment_image_src( $tn_id, $size );
  $width = $img[1];
  $height = $img[2];
    if (has_post_thumbnail($post->ID )){
        if ($width > $height){  ?>
            <?php the_post_thumbnail($size, array( 'class'  => "ns-landscape") ); 
        }else{ ?>
            <?php the_post_thumbnail($size, array( 'class'  => "ns-portrait") ); 
        }
    } 
}