Complex sentence: The main personages in the Hermitage painting are shown dressed as characters of the commedia dell'arte: the quack wears the mask and costume of Il Dottore while the guitar player has the costume of a Zanni (madcap servant).
Split into simpler sentences: The main personages in the Hermitage painting are shown with the disguise of characters of the commedia dell'arte. The charlatan wears the mask and costume of Il Dottore while the figure with the guitar wears the costume of a Zanni (madcap servant).