Original Image size in Lighbox

Hey,

I want to use the original size of an image in the gallery lighbox, cause the large – version is a bit blurry.

I have the same problem in multiple websites with many pictures, so defining “large” new and uploading the pictures again is not an option (I have read this solution in an other topic).

I would prefer a solution where you can define “full size Image” as the lighbox image in the functions.php or gallery.php in the child-theme.

I have tried this code in the functions.php:

add_filter( 'avf_avia_builder_masonry_lightbox_img_size', 'enfold_customization_change_popup_size' );
function enfold_customization_change_popup_size( $size ) {
	return 'fullsize';
}

but it did not worked out.