From drawing to stained-glass window, 1

Why can't a drawing be transformed as it is into a stained-glass window? This first video explains it to you, by going from an icon to a stained-glass window, and more precisely from the icon of the Protection of Mary contained in the cathedral of Chartres to the stained glass window made by Paul Challan Belval and the Catholic-Orthodox team that helped him in his stained glass workshop.