Shoaib R. Soomro

Design, fabrication and characterization of transparent retro-reflective screen

A transparent retro-reflective screen, which can be used as head-up-display (HUD) or a see-through screen for head mounted projection displays (HMPD) is proposed. The high optical gain of screen enables the use of low power projectors to produce very bright content. The screen assembly is based on retro-reflective microspheres, patterned on an optically clear substrate using steel stencil as a shadow mask. The incident light is retro-reflected as a narrow angular cone to create an eyebox for the viewer. The optical gain and transparency of screen is varied by changing the fill factor of the mask. The optical design and fabrication of the screen is presented. The retro-reflective and transmission characteristics of screen are evaluated. The impact of fill factor on screen luminance and transparency is studied. The screen provides high luminance (up to 280cd/m2 with 50% transparency) from about 40cm to >3m when used with a low power (15 lumen) mobile projector. Unlike regular diffusers, luminance remains nearly constant with projection distance. Furthermore, the screen offers prominent see-through capability with small degradation in modulation transfer function for transmitted light. For a particular camera and imaging configuration, MTF10 (10% cutoff) for 50% transparent screen is reduced from 37 cyc/deg to 30 cyc/deg when screen is inserted at an intermediate distance.

Augmented reality 3D display using head-mounted projectors and transparent retro-reflective screen

A 3D augmented reality display is proposed that can provide glass-free stereo parallax using a highly transparent projection screen. The proposed display is based on a transparent retro-reflective screen and a pair of laser pico projectors placed close to the viewer’s head. The retro-reflective screen directs incident light towards its source with little scattering so that each of the viewer’s eyes only perceives the content projected by the associated projector. Each projector displays one of the two components (left or right channel) of stereo content. The retro-reflective nature of screen provides high brightness compared to the regular diffused screens. The partially patterned retro-reflective material on clear substrate introduces optical transparency and facilitates the viewer to see the real-world scene on the other side of screen. The working principle and design of the proposed see-through 3D display are presented. A tabletop prototype consisting of an in-house fabricated 60×40cm2 see-through retro-reflective screen and a pair of 30 lumen pico-projectors with custom 3D printed housings is demonstrated. Geometric calibration between projectors and optimal viewing conditions (eye box size, eye-to-projector distance) are discussed. The display performance is evaluated by measuring the brightness and crosstalk for each eye. The screen provides high brightness (up to 300 cd/m2 per eye) using 30 lumens mobile projectors while maintaining the 75% screen transparency. The crosstalk between left and right views is measured as <10% at the optimum distance of 125-175 cm, which is within acceptable range.

Head Mounted Projection Display & Visual Attention: Visual Attentional Processing of Head Referenced Static and Dynamic Displays while in Motion and Standing

The Head Mounted Projection Display (HMPD) is a growing interest area in HCI. Although various aspects of HMPDs have been investigated, there is not enough information regarding the effect of HMPDs (i.e., head referenced static and dynamic displays while a user is in motion and standing) on visual attentional performance. For this purpose, we conducted a user study (N=18) with three experimental conditions (control, standing, walking) and two visual perceptual tasks (with dynamic and static displays). Significant differences between conditions were only found for the task with dynamic display; accuracy was lower in walking condition compared to the other two conditions. Our work contributes an empirical investigation of the effect of HMPDs on visual attentional performance by providing data-driven benchmarks for developing graphical user interface design guidelines for HMPDs.

Integrated 3D display and imaging using dual purpose passive screen and head-mounted projectors and camera

We propose an integrated 3D display and imaging system using a head-mounted device and a special dual-purpose passive screen that can simultaneously facilitate 3D display and imaging. The screen is mainly composed of two optical layers, the first layer is a projection surface, which are the finely patterned retro-reflective microspheres that provide high optical gain when illuminated with head-mounted projectors. The second layer is an imaging surface made up of an array of curved mirrors, which form the perspective views of the scene captured by a head-mounted camera. The display and imaging operation are separated by performing polarization multiplexing. The demonstrated prototype system consists of a head-worn unit having a pair of 15 lumen pico-projectors and a 24MP camera, and an in-house designed and fabricated 30cm × 24cm screen. The screen provides bright display using 25% filled retro-reflective microspheres and 20 different perspective views of the user/scene using 5 × 4 array of convex mirrors. The real-time implementation is demonstrated by displaying stereo-3D content providing high brightness (up to 240 cd/m2) and low crosstalk (<4%), while 3D image capture is demonstrated by performing the computational reconstruction of the discrete free-viewpoint stereo pair displayed on a desktop or virtual reality display. Furthermore, the capture quality is determined by measuring the imaging MTF of the captured views and the capture light efficiency is calculated by considering the loss in transmitted light at each interface. Further developments in microfabrication and computational optics can present the proposed system as a unique mobile platform for immersive human-computer interaction of the future.

Dual purpose passive screen for simultaneous display and imaging

Advanced imaging and display techniques are widely explored for realistic content capture and visualization but cannot fully follow the miniaturization and mobility trends in technology. Wide field-of-view displays require large surfaces and image capture requires separate installation of cameras having separate footprints and perspective views. Here we propose a novel, portable dual purpose passive screen that can simultaneously facilitate display and imaging with unprecedented features and performance. The optical design of the screen is presented. A prototype of the dual-purpose screen paired with a camera and a low power mobile projector is demonstrated. The developed screen has size of 28×21cm2 to facilitate capture of eye contacted perspective view and displays high-quality images with high-brightness (>100cd/m2 ) using only 15 lumen pico projector.

Wearable Augmented Reality Displays

Wearable augmented reality displays and associated light efficient screens are presented. We review three recent developments in augmented reality displays: head-mounted projection display, retro-reflective augmented reality screen and light efficient 3D augmented reality display.