Overwrite default thumbnails sizes after WooCommerce installation

woocommerce-overwrite-default-thumbnail-sizes.php

<?php
add_action( 'after_setup_theme', 'mytheme_woocommerce_set_image_dimensions' );
function mytheme_woocommerce_set_image_dimensions() {
	// Do not set sizes multiple times
	if ( ! get_option( 'mytheme_shop_image_sizes_set' ) ) {
		$catalog = array(
			'width' 	=> '768',	// px
			'height'	=> '',		// px
			'crop'		=> 0 		// no-crop
		);

		$single = array(
			'width' 	=> '595',	// px
			'height'	=> '',		// px
			'crop'		=> 0 		// no-crop
		);

		$thumbnail = array(
			'width' 	=> '',		// px
			'height'	=> '127',	// px
			'crop'		=> 0 		// no-crop
		);

		// Image sizes
		update_option( 'shop_catalog_image_size', $catalog ); 		// Product category thumbs
		update_option( 'shop_single_image_size', $single ); 		// Single product image
		update_option( 'shop_thumbnail_image_size', $thumbnail ); 	// Image gallery thumbs

		// Set "images sizes set" option
		add_option( 'mytheme_shop_image_sizes_set', 1 );
	}
}