Catalyzes the introduction of a C-3,4 double bond into 1'-hydroxy-gamma-carotene and rhodopin (1-hydroxylycopene) to yield 1'-hydroxytorulene and (3E)-3,4-didehydrorhodopin, respectively. Can also 1-hydroxy-all-trans-1,2-dihydro-neurosporene, 1,1'-dihydroxy-1,1',2,2'-tetrahydroneurosporene and 1,1'-dihydroxy-1,1',2,2'-tetrahydrolycopene (PubMed:15251462). Probably involved in the synthesis of myxol, a gamma-carotene derivative (Probable). May use FAD as a proton acceptor (By similarity). A + rhodopin = (3E)-3,4-didehydrorhodopin + AH2 1'-hydroxy-gamma-carotene + A = 1'-hydroxytorulene + AH2 1-hydroxy-all-trans-1,2-dihydro-neurosporene + A = AH2 + demethylspheroidene 1,1'-dihydroxy-1,1',2,2'-tetrahydroneurosporene + A = 1'-hydroxy-demethylspheroidene + AH2 1,1'-dihydroxy-1,1',2,2'-tetrahydrolycopene + A = 1,1'-dihydroxy-3,4-didehydro-1,2-dihydrolycopene + AH2 Carotenoid biosynthesis. Monomer. Belongs to the carotenoid/retinoid oxidoreductase family.