On wordpress, how do i require specific dimensions from user uploads only

I have this filter but it is for minimum upload requirements. I need one for sepcific

add_filter('wp_handle_upload_prefilter','tc_handle_upload_prefilter');
function tc_handle_upload_prefilter($file)
{


$img=getimagesize($file['tmp_name']);
$minimum = array('width' => '640', 'height' => '480');
$width= $img[0];
$height =$img[1];

if ($width < $minimum['width'] )
    return array("error"=>"Image dimensions are too small. Minimum width is {$minimum['width']}px. Uploaded image width is $width px");

elseif ($height <  $minimum['height'])
    return array("error"=>"Image dimensions are too small. Minimum height is {$minimum['height']}px. Uploaded image height is $height px");
else
return $file; 


}

Thanks for the help!