X-Mask: Improving Soft-Edge Occlusion in Optical See-Through Displays with Cross-Shaped Pinholes

Placing a transparent liquid crystal display (LCD) into the light path is a simple approach to create occlusion-capable optical seethrough head-mounted displays (OST-HMDs) that suffers from defocused (soft-edge) occlusion where the mask leakage partially occludes surrounding content as well. Creating a focused (hard-edge) occlusion that does not suffer from mask leakage requires complicated, bulky optical setups. We present X-Mask, a pinhole-arraybased OST-HMD that creates a sharp occlusion mask without the need for a bulky setup requiring only two transparent LCD layers. By rendering a pinhole array on the layer closer to the user's eye, our system functions as a programmable aperture layer that extends the effective depth of field and improves the sharpness of the occlusion mask rendered on the second LCD layer. Utilizing a conventional circular pinhole would result in non-uniform brightness and contrast. By changing the pinhole shape to a cross enables nearoptimal retinal tiling with reduced overlaps and gaps. To accommodate pupil size variation, focus distance, and gaze direction, our system design allows for gaze-contingent adjustment of both LCD layers. We validate X-Mask in simulations and a physical prototype showing improved occlusion sharpness and visual uniformity.