Wai Keung Cheung

Holographic video at 40 frames per second for 4-million object points.

We propose a fast method for generating digital Fresnel holograms based on an interpolated wavefront-recording plane (IWRP) approach. Our method can be divided into two stages. First, a small, virtual IWRP is derived in a computational-free manner. Second, the IWRP is expanded into a Fresnel hologram with a pair of fast Fourier transform processes, which are realized with the graphic processing unit (GPU). We demonstrate state-of-the-art experimental results, capable of generating a 2048 x 2048 Fresnel hologram of around 4 × 10(6) object points at a rate of over 40 frames per second.

Intensity image-embedded binary holograms.

Past research has demonstrated that, by downsampling the source object scene in multiple directions, a binary Fresnel hologram can be generated to preserve favorable quality on the reconstructed image. In this paper, we will show that a binary hologram generated with such an approach is also insensitive to noise contamination. On this basis, we propose a method to embed an intensity image into the binary hologram. To prevent the embedded information from being tampered or retrieved with unauthorized means, scrambling is applied to relocate each pixel to a unique position in the binary hologram according to a random assignment that is only known with the availability of a descrambling key. Experimental results demonstrate that our proposed method is capable of embedding an intensity image that is one quarter the size of the binary hologram without causing observable degradation on the reconstructed image. In addition, the embedded image can be retrieved with acceptable quality even if the binary hologram is damaged and contaminated with noise.

Fast Generation of Hologram Sub-Lines Based on Field Programmable Gate Array

An economical hardware solution based on Field Programmable Gate Array (FPGA) for generating horizontal-parallax-only (HPO) hologram sub-lines at a rate of over 100M pixels per second is reported.

Near computation-free compression of Fresnel holograms based on adaptive delta modulation

Delta modulation (DM) is a classical technique that is generally applied to compress audio signals with a negligible amount of computation. Recently, it has been demonstrated that a similar approach can be applied to provide a moderate degree of compression, and at the same time maintain favorable coding fidelity, in compressing digital Fresnel holograms. The downside of this method is that it is necessary to determine an optimal step size for each of the source holograms through a trial and error process. In this paper we attempt to overcome this problem with adaptive delta modulation (ADM). Being different from the classical DM, the step size in ADM is automatically adjusted according to the intensity variation of the hologram. Experimental evaluation reveals that our proposed method is capable of attaining a compression ratio of 32 times without the need of determining the step size for each hologram. Hence, the proposed technique is useful for any holographic video system where holograms are needed to refresh at video rate. In addition, the proposed technique maintains favorable fidelity on the reconstructed images, and the complexity of both the encoding and decoding process is so small that they can be regarded as near computation-free operations.

Decoding Ambisonic Signals to Irregular Loudspeaker Configuration Based on Artificial Neural Networks

This paper present a novel scheme which applies Artificial Neural Network (ANN) for determining the decoding parameters of a first order ambisonic system so that the three dimensional sound field can be reconstructed with an arbitrary quad speaker configuration. Differ from approaches based on the Modified Tabu Search (MTS) and the Heuristic Genetic Algorithm (HGA) which involve large number of iterations, the proposed method provides a significant reduction in computation. Experimental evaluation demonstrates that our method is significantly faster than existing schemes, and also exhibit higher accuracy and stability than the MTS.

Fast generation of hologram from range camera images based on the sub-lines and holographic interpolation

The intensity image and the depth images of a three-dimensional object scene can be captured with a commodity range camera, and converted into a Fresnel hologram. However, for some cameras, the images are subject to radial distortion, and too small to be visible in optical reconstruction. Moreover, the conventional hologram generation process with numerical means is significant. In this paper, we present a fast method to overcome the above-mentioned problems. First, the intensity and the depth images are transformed to reduce the radial distortion. Next, the images are interpolated horizontally, and converted into a sequence of sub-lines. Finally, the sub-lines are swiftly converted into a Fresnel hologram through padding along the vertical direction. The pair of interpolation process effectively increases the size and visibility of the reconstructed image. Although our method can be applied to different kinds of range cameras, we have selected the Swissranger model as a showcase to demonstrate the feasibility of the approach.

Low Complexity Compression of Hologram Sub-Lines

In this paper we propose a low complexity scheme for compressing hologram sub-lines based on Predictive coding. Our method can attain a compression ratio of 16 times with only slight artifacts on the reconstructed images.