Involved in the biosynthesis of the 2,6-deoxysugar, dTDP-L-rhodinose, attached to the benzoisochromane quinone chromophore to produce the aglycone antibiotics granaticin and granaticin B. Catalyzes the reduction of the C-3 keto moiety of dTDP-3,4-diketo-2,6-dideoxy-alpha-D-glucose to yield dTDP-4-keto-2,6-dideoxy-alpha-D-glucose. NADPH is the better reductant, however NADH can also be used. dTDP-4-dehydro-2,6-dideoxy-alpha-D-glucose + NADP(+) = dTDP-3,4-didehydro-2,6-dideoxy-alpha-D-glucose + H(+) + NADPH Antibiotic biosynthesis; granaticin biosynthesis. Belongs to the Gfo/Idh/MocA family.