Concerning this Straightdope classic about 3D movies, there is just one thing I don’t understand. Now I could be wrong, and I could be on the verge of making a fool out of myself with this question. But I don’t think this is the case, so bear with me.
PREMISE: 3D movies work by tricking the brain by sending two separate images to each eye.
MY ASSUMPTION(which could be wrong): The blue side of the blue/red glasses erases the blue image and darkens the red. The red side erases the red and darkens the blue.
ALRIGHT THEN…
So what is the “middle” black and white image for? Shouldn’t there just be two images then: blue and red?
Your premise and assumption are absolutely correct. I have no idea what the “middle” image is – all Anaglyphic 3-D movies (and comics, etc.) I’ve seen only have the two images, as you suggest. Inevitably they overlap somewhat, and the overlapping image (seen without the glasses) arguably looks kinda blurry and black-and-white (although I’d be inclined to call it brown). If the movie isn’t a “black and white movie” (As Creature from the Black Lagoon, Robot Monster, It Came From Outer Space, The Mask are), but attempts to be a color anaglyphic movie (Bride of the Gorilla, the recentSpy Kids 3-D), then the image you see without the glasses looks like a blurry and spread-out color image. Most of these that I’ve seen don’t work really well, since the red-and-green filters mess up the colors of the reeal movie, although SK3D did a pretty decent job of it.
