Question regarding: Custom Header

The custom header is really hard to understand.

Im trying to resize the area to 299px x 223px.

Therefore, I have changed the following lines in functions.php:

// The height and width of your custom header. You can hook into the theme's own filters to change these values.
	// Add a filter to twentyten_header_image_width and twentyten_header_image_height to change these values.
	define( 'HEADER_IMAGE_WIDTH', apply_filters( 'twentyten_header_image_width', 299 ) );
	define( 'HEADER_IMAGE_HEIGHT', apply_filters( 'twentyten_header_image_height', 223 ) );

However, when i upload an image of that size it defaults back to the else statement (default image ‘path.jpg’).

Any ideas?