A gamma variation of image intensity is created by varying the illumination intensity during a pulse width modulated display time period. During the pulse width modulated display time period a ramp signal may be compared with the image data to determine when pixel electrodes of the pixel array are switched. The illumination intensity may be varied in concert with ramp signal to produce a quadratic variation of displayed intensity on image data value. The illumination source could be an LED illumination source and intensity of the LED illumination source could be controlled using pulse width modulation.