Hirohito Nishi

Rendering of specular surfaces in polygon-based computer-generated holograms

A technique is presented for realistic rendering in polygon-based computer-generated holograms (CGHs). In this technique, the spatial spectrum of the reflected light is modified to imitate specular reflection. The spectral envelopes of the reflected light are fitted to a spectral shape based on the Phong reflection model used in computer graphics. The technique features fast computation of the field of objects, composed of many specular polygons, and is applicable to creating high-definition CGHs with several billions of pixels. An actual high-definition CGH is created using the proposed technique and is demonstrated for verification of the optical reconstruction of specular surfaces.

Simple wave-field rendering for photorealistic reconstruction in polygon-based high-definition computer holography

A simple and practical technique is presented for creating fine three-dimensional (3D) images with polygon-based computer- generated holograms. The polygon-based method is a technique for computing the optical wave-field of virtual 3D scenes given by a numerical model. The presented method takes less computation time than common point-source methods and produces fine spatial 3D images of deep 3D scenes that convey a strong sensation of depth, unlike conventional 3D systems providing only binocular dis- parity. However, smooth surfaces cannot be reconstructed using the presented method because the surfaces are approximated by planar polygons. This problem is resolved by introducing a simple rendering technique that is almost the same as that in common computer gra- phics, since the polygon-based method has similarity to rendering techniques in computer graphics. Two actual computer holograms are presented to verify and demonstrate the proposed technique. One is a hologram of a live face whose shape is measured using a 3D laser scanner that outputs polygon-mesh data. The other is for a scene including the moon. Both are created employing the proposed rendering techniques of the texture mapping of real photo- graphs and smooth shading.

Advanced rendering techniques for producing specular smooth surfaces in polygon-based high-definition computer holography

Novel techniques is proposed for rendering specular smooth surfaces in polygon-based computer holography that features reconstruction of fine 3D images accompanied with strong sensation of depth. The technique is an improvement of the conventional technique for rendering flat specular surfaces. In this technique, phase distribution that works as a diffuser is divided into small rectangular segments and the reflection direction is controlled for each segment. In addition, this new method increases freedom for lighting the object. Two high-definition CGHs are calculated by the proposed method. One of them is fabricated and demonstrated for verifying the technique.

New techniques for wave-field rendering of polygon-based high-definition CGHs

Four novel techniques are introduced into polygon-based high-definition CGHs (PBHD-CGH) that feature the true-fine spatial 3D image accompanied with a strong sensation of depth. The first is algorithm for creating specular surfaces based on Phong reflection model. This is very useful for providing a feel of material to polygonal surfaces. The second technique is called digitized holography that replaces the entire processes of classical holography by their digital counterparts. The wave-field of real-existent objects can be optically reconstructed by the digitized holography. This technique makes it possible to edit the 3D scene of holograms or create mixed 3D scene of the real and virtual objects. Another technique for creating PBHD-CGH of real-existent objects is also proposed by a CG-like method using a 3D laser scanner that measures the 3D shape of the object. Finally, a prototype PBHD-CGH is demonstrated for creating landscape scenery. This CGH is intended to reconstruct a scene as if the viewers see mountain scenery through the window given by the CGH.

Rendering of specular curved objects in polygon-based computer holography

A realistic rendering technique is presented for creating large-scale computer-generated holograms. The technique is based on the polygon-based method, but allows specular curved surfaces to be reconstructed without increasing the number of polygons. In this technique, specular flat surfaces are transformed into curved surfaces. This is achieved by controlling the direction of reflected light, using fragmentary plane waves. An actual large-scale computer-generated hologram is created, and is used to verify the validity and practicality of the technique.

Computer holography: 3D digital art based on high-definition CGH

Our recent works of high-definition computer-generated holograms (CGH) and the techniques used for the creation, such as the polygon-based method, silhouette method and digitized holography, are summarized and reviewed in this paper. The concept of computer holography is proposed in terms of integrating and crystalizing the techniques into novel digital art.

A Novel Method for Rendering Specular and Smooth Surfaces in Polygon-Based High-Definition CGH

A new rendering method is proposed for smooth shading of specular surfaces in the polygon-based CGH. In the method, surface functions are divided into rectangular segments and the spectral envelopes are modified in order to produce metal-like specular reflection.

Computer holography: 3D imaging of virtual and real objects

In classical holography, light waves from a real object are recorded on light-sensitive films by interference with reference waves. Object waves are reconstructed by diffraction of the interference fringes after chemical processing of the films. Thus, classical holography requires a real object to create its 3D holographic image. It is, therefore, impossible to create holograms of virtual 3D scenes—such as provided by modern computer graphics—and edit the 3D scene after recording the interference fringes. An interference fringe is just a 2D image, and the reference wave can be expressed by a simple theoretical framework. In principle, therefore, we could easily produce the fringe pattern by numerical simulations of optical interference if we could obtain numerical data of the object waves from the 3D scene. However, calculating object waves from virtual 3D scenes is very hard work, even for modern computers. It sometimes takes several hundreds of hours or days to calculate object waves by conventional methods. Capturing light waves from real objects is also not easy, because the resolution and sizes of currently available image sensors do not meet the requirements for computer holography. We recently developed a novel computer algorithm1 that enables synthesis of holograms of completely virtual, computergenerated 3D scenes in only several tens of hours. In addition, we developed a technique2 to capture light waves from real objects at high resolution and over a wide area to meet computer-holography conditions. This enables digitization of the entire process of classical holography. The resulting computer holograms give viewers a strong sensation of depth that has never been achieved with conventional 3D images. Figure 1. Optical reconstruction of the computer hologram ‘Moai II,’3 which contains 65; 536 65; 536 pixels with a pixel pitch of 1 1 m2. The camera is focused on (a) the near and (b) the far moais.

Smooth shading of specular surfaces in polygon-based high-definition CGH

High-definition computer-generated holograms (CGH) created by the polygon-based method feature reconstruction of very fine 3D image accompanied with strong sensation of depth. However, rendering technique for specular surfaces has not been established. We propose a novel technique for smooth shading of specular surfaces in the polygon-based method. This technique divides the surface function of polygons into some segments and controls the spectral envelopes.