Ms. Raz-Russo then initiated an effort in 2014 to identify the works. She called it part scavenger hunt and part research: There were clues, including information about the overlapping Harlem projects, drafts of photo captions and more, but no way to verify which projects the photos belonged to. When Jean-Christophe Cloutier, an assistant professor of English at the University of Pennsylvania, found two manuscripts related to “Harlem Is Nowhere,” both Ms. Raz-Russo and Mr. Cloutier were able to complete the puzzle and identify the images. As luck and hard work through research would have it, the Library of Congress had what was known to be the only surviving photograph taken by Parks from inside the clinic.

Ellison and Parks were not alone in their efforts to push the boundaries of mainstream news media and expose racial disparities in the United States. Other prominent artists from various genres who collaborated in the mid-1900s included Richard Wright and Edwin Rosskam, whose 1941 book, “12 Million Black Voices,” depicted the lives of black citizens in the 1930s, and James Baldwin and Richard Avedon, who produced a photography book, “Nothing Personal,” with text condemning the bleakness of life in 1960s America.

Parks and Ellison’s “A Man Becomes Invisible” was conceived as a response to the publication of Ellison’s novel, about a man who lives in a hidden world because of his invisibility to others. Beyond the professional work, the show also offers glimpses of their personal connection.

“There was a solitary quality about each of them,” said John Callahan, Ralph Ellison’s literary executor. “As Ralph would talk about it, he would say, ‘I could just walk with Gordon, and he wouldn’t expect me to say anything and I wouldn’t expect him to say anything.’ I have a sense that there was an electricity and a casualness to their relationship.”

Mr. Bradley elaborated. “In some ways, their collaboration is akin to a great songwriting duo,” he said. “One handles the music, the other lyrics, and there’s never something that comes completely first. They understood that the sum of their art would be greater than its individual parts.”