function wpc_remove_parent_theme_function() {

	remove_action( 'after_setup_theme', 'extra_add_image_sizes' );
}

function wpc_extra_add_image_sizes() {
	$sizes = array(
		'extra-image-huge'          => array(
			'width'  => 1280,
			'height' => 768,
			'crop'   => true,
		),
		'extra-image-single-post'   => array(
			'width'  => 1280,
			'height' => 640,
			'crop'   => true,
		),
		'extra-image-medium'        => array(
			'width'  => 9999,
			'height' => 9999,
			'crop'   => false,
		),
		'extra-image-small'         => array(
			'width'  => 440,
			'height' => 264,
			'crop'   => true,
		),
		'extra-image-square-medium' => array(
			'width'  => 440,
			'height' => 440,
			'crop'   => true,
		),
		'extra-image-square-small'  => array(
			'width'  => 50,
			'height' => 50,
			'crop'   => true,
		),
		'extra-image-730'	=> array( 
			'width' => 730,
			'height' => 450,
			'crop' => true,
		),
		'extra-image-220'	=> array(
			'width' => 220,
			'height' => 132,
			'crop' => true,
		),
		'extra-image-150'	=> array(
			'width' => 150,
			'height' => 90,
			'crop' => true,
		),	
	);

	foreach ( $sizes as $name => $size_info ) {
		add_image_size( $name, $size_info['width'], $size_info['height'], $size_info['crop'] );
	}
}

add_action( 'after_setup_theme', 'wpc_remove_parent_theme_function', 0 );
add_action('after_setup_theme' , 'wpc_extra_add_image_sizes');