Improving a time-sequential autostereoscopic 3D display

Hee-Jin Choi and his colleagues from the International Society for Optics and Photonics (SPIE) have suggested a new method to show glasses-free 3D (autostereoscopic, or AS3D) on an LCD display.

Existing AS3D displays effectively show two frames at once, offset from each other and with half the maximum resolution, to produce the 3D effect. Display resolution falls proportional to the increase in viewing positions: a non-ideal scenario, as both factors are important.

A proposed solution in the past has been to use a time-sequential 3D system with a directional backlight unit (DBLU) and an LCD with a high (120Hz) frame rate. In a time-sequential system, different sub-images are shown one after another, fast enough that they appear simultaneously present to the human eye. The LCD, and how it is backlit by the DBLU, control what can be seen from different viewing positions. The choice of the ‘master’ image and what portions of it are visible (controlled by the DBLU) produces an AS3D image. However, a low refresh rate (roughly sub-60Hz) will cause an unpleasant flicker effect.

Choi and his colleagues had previously suggested using dot dithering to reduce the flicker problem. Dot dithering divides the spatially overlapping sub-images into dot-shaped regions, each formed by light from a different path; each region is intended to be viewed from a different viewing point. The effect is to prevent flickering from being noticeable by the human visual system, by reducing the required overall refresh rate for each viewpoint.

However, a disadvantage to dot dithering is that the image data and light paths from the DBLU do not match up in the side lobes (regions either side of the center, each with four viewpoints). The image is distorted, as portions of the image appear in the wrong order. Improving image quality in the side lobes would enable more viewing positions.