Melvin Van Peebles' 1998 documentary, Classified X, explores racist stereotypes of African Americans in the history of cinema, beginning with the silent film era.
Van Peebles narrates throughout; you are highly recommended to see it if haven't done so by now. The documentary, directed by Mark Daniels, is quite compelling and provides a poignant and relatively thorough insight on the historical portrayal of African Americans on screen in both non-black and black films.
It's now streaming on Netflix; feel free to watch it there. However, I was able to find it in full on YouTube, although divided in six parts; which I've embedded below.