Now is as good a time as there ever will be to go and check out the Art Institute of Chicago. A new exhibit, “Invisible Man: Gordon Parks and Ralph Ellison in Harlem,” combines the photography of Parks, who eventually went on to gain a measure of fame in the ’70s as a Hollywood movie director, and the writing of Ralph Ellison, in an attempt to offer a portrait of Harlem in the post-World War II years.