Attenuation-Based 3D Display Using Stacked LCDs

Introduction

Unlike traditional 2D displays, attenuation-based 3D displays enable the accurate, high-resolution depiction of motion parallax, occlusion, translucency, and specularity. We have implemented iterative tomographic reconstruction for image synthesis on a stack of spatial light modulators (multiple low-cost iPad LCDs). We illuminate these volumetric attenuators with a backlight to recreate a 4D target light field. Although five-layer decomposition generates the optimal tomographic reconstruction, our two-layer display costs less than $100 and requires less computation

Background

Engineers have promulgated designs for 3D displays, and even automultiscopic displays, as early as the turn of the 19th century. In particular, we consider four types of 3D display technologies that stand in contrast to what we have produced: parallax barriers, integral imaging, volumetric displays, and holograms. What relates these technologies is their shared ability to replicate disparity, motion parallax, and binocular depth cues without the need for special eyewear.

A performance summary of these comparative technologies produced by [Wetzstein et al. 2011] can be found below:

Unencumbered Automultiscopic Display Technologies

Volumetric	Integral Imaging	Parallax Barriers	Hologram	Resolution
Aptina	37	70.8	5.08	720p
e-con	36	68.0	19.0	1080p

Our display relies on multiplicative light absorption across two spatial light modulators to project 3D content without any moving components and with occlusion, specularity, and depth.

Additive Volumetric Displays

Printed Transparencies

Integral Imaging

Parallax Barriers

Multi-Layer and Tensor Displays

Methods

Light Field Acquisition

Layered Attenuation-based Displays

Tomographic Approximation

We implemented the computed tomography techniques decsribed in “Layered 3D” by G. Wetzstein, D. Lanman, W. Heidrich, R. Raskar (SIGGRAPH 2011) to produce two 2048x1536 reconstructed images from many precomputed views of the light field, spanning a 20-degree FOV. We solve these layer decompositions ahead of time, and paint them as static images to the LCDs.

We designed an enclosure such that the stack of LCDs (2048x1536, 9.7”, IPS 60Hz, iPad 3) would be well-fastened and their driver circuitry well-hidden. In this intitial prototype, we attached the front LCD with adhesive so that we could manually adjust the display for approximate pixel alignment. Quarter-wave plate sheet.

File:IG 0159.png

Results

Limitations: • Light Attenuation • Limited Field of View • Temporal Multiplexing Compute • Pixel Alignment • Color Crosstalk

Performance: • High Contrast Halo Artifacts • Depth of Field • Resolution • PSNR

Conclusions

Improvements: • Dynamic Rendering • High-Refresh Rate (>144Hz) • Three Layer Display • Face-Tracking (with OpenCV)

Appendix I

[1] G. Wetzstein, D. Lanman, W. Heidrich, R. Raskar. Layered 3D: Tomographic Image Synthesis for Attenuation-based Light Field and High Dynamic Range Displays. Proc. of SIGGRAPH 2011 (ACM Transactions on Graphics 30, 4), 2011.
[2] G. Wetzstein, D. Lanman, D. Gutierrez, M. Hirsch. Computational Displays. ACM SIGGRAPH 2012 Course, 2012.

Matlab Implementation of Tomographic Light Field Synthesis
Real-Time Implementation of Tomographic Light Field Synthesis