Ever notice that gray screens somehow appear to be white when a picture is projected onto them? Ever notice that you can see actual black areas on a screen that has some incident light falling on it? Well, the color and brightness of a projection screen when the projector is off is the darkest the screen will ever be, so it is said that this brightness level is the black that people will see when you then turn on a projector.

It ain't so.

I've noticed and tested for myself that parts of an image that are supposed to be black look darker than the screen did when not illuminated. This is especially obvious in the occasional setup where a white painted wall is used as the screen -- black inside the picture is darker than the area around the screen.

I just ran across an optical illusion that ilustrates this nicely. It's at [Link: mydailyviral.com] where there are several other interesting illusions.

The gray bar is one color and does not change colors:








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