http://wiki.panotools.org/Hugin_FAQ#Enblend_error:_Mask_is_entirely_black.2C_but_white_image_was_not_identified_as_redundant
http:// wiki.panotools. org/Hugin_ FAQ#Enblend_ error:_ Mask_is_ entirely_ black.2C_ but_white_ image_was_ not_identified_ as_redundant