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Small, affordable video projectors can produce such bright pictures that many people use them in place of a traditional television. But when placed on a table or shelf, the projector lens is seldom parallel to its screen, so a rectangular picture is warped into a parallelogram, a problem known as keystone distortion. Mitsubishi has patented a way to automate the adjustments needed to restore the image (WO 03/051045). The projector beams a chessboard pattern onto the screen. At the press of a button, it uses a built-in digital camera to compare the grid on the screen to a perfect one…