Catalyzes the NADPH-dependent reduction of 1,3,6,8-tetrahydroxynaphthalene (T4HN) into (+)-scytalone and 1,3,8-trihydroxynaphthalene into (-)-vermelone. This enzyme is the biochemical target of several commercially important fungicides which are used to prevent blast disease in rice plants. NADP(+) + scytalone = H(+) + NADPH + naphthalene-1,3,6,8-tetrol Pigment biosynthesis; melanin biosynthesis. Homotetramer. Belongs to the short-chain dehydrogenases/reductases (SDR) family.