Humongous (1982)

A horror directed by Paul Lynch.
A woman is raped at a party and dogs kill the assailant. Years later, a group of teenagers crash their boat on the island on which the woman had lived. Rumor had it that there were dogs protecting the island, but no living dogs are found by the teens. They find the woman's diary in which she writes about her son, whom she kept secluded on the island. The son was not normal and this explains the fact that their friends are missing when they split up.
The son is either black (of 2 white parents) or invisible because he is never seen. I would have thought my computer had black-screened me several times during the film if it didn't look so grainy. There is a lot of spooky music and some gruesome visible scenes involving skeletal remains of the dogs. Also, one of the teenage girls has a high quality upper torso (if you know what I mean). I'm rating this poor based on quality. If I could have seen what was going on, it may have gotten a better rating.