Originally Posted by Onkyoman
The masking combined with zoom the big black bars away just covers the black bars in CinemaScope movies. The result looks the same as the screenshot I posted.
In terms of pixel dimensions, every consumer video source will have the same width (1920 or 3840) and only the height is scaled to fit any aspect ratio wider than 16:9. The top and bottom cropping is supposed to give you the correct pixel height within the projector panel for widescreen sources with some minor cropping.
The problem is when 2.40:1 video is put through his horizontal stretch anamorphic lens (even though it's being vertically stretched by the projector first to fill the whole 16:9 panel), it becomes even wider, like 2.5:1 or so, because it's an imperfect lens.
If we just zoom the projector's lens to line up the image with sides with the screen sides, then there are black bars on top and bottom of even a 2.4:1 screen and that is not wanted. Instead we zoom the projector so that the top and bottom of the image line up with the top and bottom of the screen. This leaves a large spill over the left and right sides of the screen frame.
So all that we needed to do was to cover up the sides of the video image with some black pixels so that the spill over is not seen on the wall. A JVC or Sony or Epson projector normally allow this with the masking feature built into the projector, but he just got a BenQ Laser projector, and it did not have this masking feature.
None of the crop, mask, zoom, black border, etc in madVR would achieve this simple result of just covering up some of the sides of the video with black to narrow the video's aspect ratio.
Anything that involves madVR "zooming" or scaling the picture was already wrong as that breaks the 1:1 pixel mapping of the video to the projector as well as introduces extra rendering time that is unwanted and unneeded. Masking has nothing to do with zooming or scaling, it's simply a cover, that's what the term mask means in the first place.