Yet another question about changing header image size!!!

Working with 20-11 child theme that now has only style.css and header.php files. Not sure I understand this, but…

Can I simply create and upload an 980×320-pixel image, then create a functions.php file with this code?

<?php
remove_filter( 'HEADER_IMAGE_WIDTH', 'twentyeleven_header_image_width' );
remove_filter( 'HEADER_IMAGE_HEIGHT', 'twentyeleven_header_image_height' );
define( 'HEADER_IMAGE_WIDTH', apply_filters( 'child_header_image_width', 980 ) );
define( 'HEADER_IMAGE_HEIGHT', apply_filters( 'child_header_image_height', 320 ) );
?>

Or, if I only want to change the depth of the header image, would this work?

<?php
remove_filter( 'HEADER_IMAGE_HEIGHT', 'twentyeleven_header_image_height' );
define( 'HEADER_IMAGE_HEIGHT', apply_filters( 'child_header_image_height', 320 ) );
?>

Any advice appreciated.