woocommerce_gallery_image_size │ filter-hook │ WC 1.0

Usage

add_filter( 'woocommerce_gallery_image_size', 'wp_kama_woocommerce_gallery_image_size_filter' );

/**
 * Function for `woocommerce_gallery_image_size` filter-hook.
 * 
 * @param  $string 
 *
 * @return 
 */
function wp_kama_woocommerce_gallery_image_size_filter( $string ){

	// filter...
	return $string;
}

$string

-

Where the hook is called

$image_size      = apply_filters( 'woocommerce_gallery_image_size', 'woocommerce_single' );

$image_size        = apply_filters( 'woocommerce_gallery_image_size', $flexslider || $main_image ? 'woocommerce_single' : $thumbnail_size );

Where the hook is used in WooCommerce