According to the present invention, when displaying 4: 3 video signal on a 16: 9 widescreen, the 4: 9 4:16 screen of a liquid crystal projection apparatus can reduce the size of the screen left and right by changing the shift clock frequency of the source driver. A three-screen display method and apparatus therefor. The present invention outputs pulse signals having different frequencies from the variable pulse generator, the fast pulse generator, and the normal pulse generator by using the clock signal generated by the phase-locked loop circuit. The switching unit under the control of the compression mode indicating unit selects one of the pulse signals according to the screen display mode and outputs it as a shift clock signal. In addition, the start time of the start clock signal is controlled differently according to the screen display mode to change the size of the side blank. Accordingly, the center portion of the screen may display a time-compressed image, and the left and right sides of the screen may display an image expanded at a different ratio according to the screen display mode, thereby reducing distortion.
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