An image display system includes a light source for projecting an illumination light. The image display system further includes a light source control unit that controls the light source to adjust the illumination intensity and/or light emission time of the illumination light. The display system further includes an SLM (Spatial Light Modulator) having a plurality of pixel elements. The SLM modulates the incident illumination light to generate gray scales. The light source control unit controls the light source during at least one time slice in one frame period, and the SLM uses that time slice to control a minimum adjustable gray scale.