HPO HOLOGRAM SYNTHESIS FOR FULL-PARALLAX RECONSTRUCTION SETUP Martin Janda, Ivo Han´ ak, and V ´ aclav Skala University of West Bohemia Department of Computer Science and Engineering Univerzitn´ ı 8, Pilsen, 306 14, Czech Republic ABSTRACT Digital hologram synthesis is a task that simulates a physical process. Currently, there is no working solution capable of handling continuous surfaces, solving visibility, and applying a local intensity variation efficiently. Due to the computa- tional complexity an approximation is required. Our solution tries to address this issue by extending the most efficient HPO hologram synthesis in such way that the computed hologram does not require a special optical setup for reconstruction. Index Terms— Holography, Computer graphics, Render- ing 1. INTRODUCTION Holography is a scientific area that deals with light field cap- turing using the phenomena of diffraction and interference. It utilizes the wave nature of light as the fundamental build- ing block. If coherent light is used it is possible to capture monochromatic light waves scattered from an object. It is done by interfering the reference wave with the scattered one. The image of the resulting interference pattern captured on a photosensitive material then acts later on as a diffraction grat- ing. This grating, if illuminated by the reference wave, pro- duces a light field which contains the original scattered wave. In the ideal case this can lead to the impression of a real scene even thought only the hologram is present, see [1] for refer- ence. Holography is therefore a promising technology for a genuine 3D display. Digital holography is a numerical version of the optical holography. It employs equations and relations derived for light propagation to numerically simulate the physical phe- nomena [2]. It deals with processing of captured holograms, extracting information stored within, and finally with the nu- merical synthesis of holograms. The latter one is targeted by this paper. Currently, there is no approach to synthesis available that would be able to simulate the physical phenomena accurately This work has been supported by EU within FP6 under Grant 511568 with the acronym 3DTV and by MSMT CR projects CPG No. LC06008 (Centre for Computer Graphics) and No. 1P04LA240. enough in reasonable time. This is because of the computa- tional complexity of the problem. To illustrate the fact, with- out any approximations or assumptions, to numerically simu- late a propagation in a free space between two parallel planes that are sampled by N × N samples an algorithm of the com- putational complexity O(N 4 ) is required. Due to the nature of the problem, it is not possible to reduce the complexity without loosing some information. One of the most drastic approximations used is the re- duction or elimination of the vertical parallax in a hologram. Such holograms are called horizontal parallax only (HPO) holograms and they bring reduction of complexity by one order of magnitude. The HPO hologram is a hologram that lacks vertical parallax, i.e. the wave from a single point is not propagated vertically [3]. Therefore, the viewer does not experience parallaxing of the image if the viewer changes her position relatively to the Y-axis, i.e. up-vector. Nevertheless, the vertical parallax is not so important as the horizontal one. It is because the human eyes are orga- nized horizontally, thus the viewer does experience the binoc- ular disparity in the HPO hologram, hence she does sense the depth. The drawback of HPO holograms is the necessity of a special reconstruction setup composed of cylindrical lenses [4], otherwise the reconstructed image is heavily vertically blurred. Our main goal therefore was including additional infor- mation back into the HPO hologram so that it could be re- constructed on a common reconstruction setup without the need of special lenses or other special display device except the spatial light modulator such as LCD or DMD [2] with reasonably small element pitch. Our extension is therefore a compromise between the performance of the HPO hologram synthesis and the simple optical setup used for reconstructing the full parallax holograms. It should be emphasized again that the actual synthesis approach is not the main topic of this paper but the enrichment of the HPO hologram content is. In order to improve the performance of our approach we used a graphical processing unit (GPU). Currently, the GPU is able to replace a specific part of the graphics pipeline with a user supplied program that can perform various tasks. Thanks to the specialization of the GPU, it offers a greater computa- tional power than the comparable CPU [5]. The GPU has two Authorized licensed use limited to: Univ of West Bohemia in Pilsen. Downloaded on August 13,2010 at 08:26:21 UTC from IEEE Xplore. Restrictions apply. 3DTV Conference proceedings, IEEE ISBN 978-1-4244-0722-4, 2007