For a display device needing to show both an image and the background therebehind, a transparent or translucent reflecting screen (glass window or windshield) is usually used for reflecting images. For example, the display device is a head-up display (HUD) or shows a commercial advertisement, and the image is provided by a projecting device or a display. However, an observer may receive the same image reflected by different surfaces of the reflecting screen, which generates a ghost image caused by overlapping the reflected images and greatly affects the image quality.
Please refer to FIG. 1 illustrating a conventional head-up display. As shown in FIG. 1, a projecting device 4 generates an image light M1 projected toward a transparent screen 2, such as a glass window or a windshield. A portion of the image light M1 is directly reflected by a reflecting surface 2a and produces a reflecting image light M2. Another portion of the image light M1 enters the transparent screen 4 and is reflected by a reflecting surface 2b. Then, the portion of the image light M1 passes through the reflecting surface 2a and produces a reflecting image light M3. When the observer receives both the reflecting image light M2 and M3, an overlapping ghost image is generated, which causes difficulty in identifying the image.
Therefore, it is important to reduce the ghost image resulted from multi-reflection for improving the image quality of such kind of display device.