a method of producing an image drive signal which is free of skew . disclosure is made of a point of sale merchandising system having a transparent digitizer mounted on an lcd module . a stylus is used to draw a signature on the digitizer , and the signature is displayed on the lcd module in registration with the moving stylus . skew effects are eliminated by performing a mapping transformation using a set of 6 transformation constants . these constants are derived from data obtained while placing the stylus over three reference spots on the display .