Most likely this is the poster from the Kick Out the Jams: Detroit's Cass Corridor 1963-1977 show at the DIA in 1980. This significant show was a major exhibition of the work of many of the Detroit artists who lived and worked in the Corridor during that period.

Clearly, during that period it was "the Cass Corridor" and not "Midtown." So the work in the show, for the most part, had a very gritty, hard edge to it. These were not pretty pictures that someone's grandmother would buy, although, I guess many of those who bought work by these artists in the 60's are now somebody's grandparents.