KEYSTONE CORRECTION CIRCUIT

PROBLEM TO BE SOLVED: To provide a keystone correction circuit which corrects distortion in a video image on a screen by the correction operation of an optical system without burdening the control of a CPU. SOLUTION: The keystone correction circuit is used in a projector. The keystone correction circuit comprises: a coordinates calculator for calculating coordinates positions on the LCD panel at four vertexes of the video image distorted reversely, so that the distortion of a video image region on the screen is canceled out based on parameters, such as a vertical pitch angle θ and a horizontal one determined according to user's operation; an addition processor for adding an external parameter that is inputted from an external parameter input terminal, and consists of each displacement of the coordinates positions of four vertexes to the coordinates positions of four vertexes obtained by the coordinates calculator; and a parameter calculator for calculating a parameter required for arranging each pixel in video image data in the coordinates positions on the LCD panel of four vertexes to which the external parameters are added by the addition processor. COPYRIGHT: (C)2007,JPO&INPIT