Chris Willman Senior Music Writer and Chief Music Critic When it comes to coffee-table books that survey the great album covers of the classic rock era, there are generally two kinds: those that include a lot of the work of the 1970s design team called Hipgnosis, and those that consist entirely of Hipgnosis’ work. Virtually any rock superstar who had the cachet to ask his record company to blow hundreds of thousands of dollars on a Hipgnosis cover went for the splurge of commissioning an original piece of art that might join classic LP jackets from Pink Floyd and Led Zeppelin in a renaissance of 12’x12′ photographic surrealism. Only Hipgnosis could shoot a photo of a cow against a blue sky, put it on a Floyd cover (“Atom Heart Mother”), and make it look like an act of mysterious profundity on a level with the greatest works of Magritte.