Strange pixels in dark areas on screen

[Radec]

Hello, yesterday I was watching my first BluRay, "Kingdom of Heaven".

I need your help in cycling in the reason for some pixel-errors I got every time larger black areas appeared on my screen. Im using a PS3, connected to a BenQ E2200HD via HDMI.

So every time a larger area on my screen showed something black, the black itself "pixeled", cubic forms appeared. It was as if this black areas were suddenly reduced in quality. As if while the rest on screen remained Full-HD, everything darker looked like from a Youtube-vid.

Sorry in advance if this is the wrong sub forum, but I currently have now idea if to blame the movie, the PS3 or the monitor...Can you give me a hint? Thank you