This paper presents a simple but novel solution to enhance the image contrast on the screen projected with ambient light. The proposed algorithm is designed to preserve a local image contrast based on a luminance ratio of a pixel to its local surround in attention. The projected image loses its visual contrast and color when viewed in ambient light using auxiliary lamp in place of room light, because each pixel RGB value is biased by the additional surround illuminant. First, the proposed algorithm transforms an original image to a projected image on the screen in the dark room. Next, since the dynamic range of the projected image under ambient light is narrowed as compared with the original, the gamma compression is assumed to map the original input range into the displayed output range. Thirdly, the local contrast of the displayed image lowered by ambient light is enhanced to match with that of the original. Finally, the biased luminance level is compensated by linear correction for output RGB signal to shift the ambient luminance offset level into zero level. As a result, the visual impression of the projected image or the motion picture with ambient light is kept as much the same contrast as seen in the dark room.