Improved optical see-through head mounted display using transmittance variable display

Abstract

The state of the art optical see through head mounted displays OST HMD s) typically rely upon a beam splitter to uniformly blend the light from the real scene with the virtual objects, and lack th e ability to selectively block out the light of the real world from reaching the eye. As a result, the digitally rendered virtual objects viewed through OST HMDs typically appear “ghost like”. Actually such transparent objects degrade the contrast ratio an d color expression, which eventually harm the sense of realism. There are a few potential problem of the difficulty in resolving objects and perceiving colors in OST HMDs In order to solve this problem, we introduced a new transmittance variable display at the front of OST HMDs’ display area. The additional display blocks light from the external enviro nment. We used g uest h ost l iquid c rystal (GHLC) layer which has a clear initial state without volt application, and an opaque state under voltage application. In the proposed method, the aperture ratio of the GHLC layer should be high and transmittance of GHLC is set to be maximized in situations where “ghost like” effect can be ignored. Relatively bright objects or darker background scene may be such cases. In contrast, the transmittance of the GHLC layer can be minimized for the cases with objects with mi ld or dark brightness in comparison with the environmental irradation level. Operating the GHLC layer only in the desired envrionment may be helpful to reduce power consumption of the OST HMD. For the verification of the suggested method, we designed an ex periment using a DC power supply to drive the GHLC layer, an OST HMD (EPSON Moverio BT 300) and an optical probe connected to a spectrometer (GL Spectis 1.0 Touch, GL Opti Probe 5.0 luminance) on an optical breadboard. F igure 1. shows the experiment setup. We verified the validity of the proposed method through experiments including the evaluation of image qualities with the GHLC layer in clear and opaque states. We will repeat similar experiments on some other OST-HMDs to further verify if the proposed method is generally applicable to OST-HMD systems.