Beom-Ryeol Lee

Holographic display based on a spatial DMD array.

The image space of the reconstructed image from the hologram displayed on a digital micromirror device (DMD) is defined by the diffraction pattern induced by the 2D pixel pattern of the DMD, which works as a 2D blazed grating. Within this space, a reconstructed image of 100 mm × 20 mm is spatially multiplexed by a 2 × 5 DMD array that is aligned on a board, without using any extra optics. Each DMD chip reconstructs an image piece of the size 20 mm (width) × 10 mm (height). The reconstructed image looks somewhat noisy but regenerates the original object image faithfully.

A floating type holographic display

A floating image type holographic display which projects an electronically generated holographic image together with a background image displayed on a monitor/TV to enhance the visual effects of the former image is introduced. This display can display a holographic image with a spatial volume floating in the front space of the display with use of PDLC sheets as the focused plane of the image. This display can preserve and enhance the main property of holographic image from a display chip, i.e., a spatial image with a volume. This property had not been appealed by the previous holographic displays due to the much brighter active surface image accompanied with the reconstructed image and the diffuser used for viewing the image.

Characteristics of composite images in multiview imaging and integral photography

The compositions of images projected to a viewers eyes from the various viewing regions of the viewing zone formed in one-dimensional integral photography (IP) and multiview imaging (MV) are identified. These compositions indicate that they are made up of pieces from different view images. Comparisons of the composite images with images composited at various regions of imaging space formed by camera arrays for multiview image acquisition reveal that the composite images do not involve any scene folding in the central viewing zone for either MV or IP. However, in the IP case, compositions from neighboring viewing regions aligned in the horizontal direction have reversed disparities, but in the viewing regions between the central and side viewing zones, no reversed disparities are expected. However, MV does exhibit them.

Properties of DMDs for holographic displays

Digital micromirror device’s (DMD) properties as being a display device for holographic displays are investigated. High speed, a large separation between reconstructed image and reconstruction beam, two symmetric diffraction patterns, and low intensity (0,0)th-order beam at a blazed grating condition are the desired properties for the displays. The blazed grating condition of a DMD can reconstruct images with higher diffraction efficiency than the line grating condition. DMD’s high speed enables to present colors and gray levels to the reconstructed image. However, reconstructed images from a gray-level computer-generated hologram (CGH) and its binary form hologram reveal no noticeable difference between them, except the background noise in the image from the CGH.

Basic image cell in contact-type multiview three-dimensional imaging systems

Abstract. The viewing zone of a contact-type multiview three-dimensional imaging system are divided into nine viewing regions by assuming that at least n−2 pixel cells can be viewed at each of the regions, where n is the total number of pixel cells in horizontal direction of a display panel. Each of these regions consists of m2 subregions, where m is the number of pixels in the horizontal of a pixel cell. The image viewed at each of the subregions reveals a disparity of 1 pixel distance with that viewed at its adjacent subregion. Hence, each subregion is defined as a basic image cell that can provide the disparity of a pixel distance with its immediate neighbors. The width of the cell is independent of the focal length of the viewing zone forming optics but highly sensitive to the pixel size. It can be smaller than viewers’ pupil sizes by decreasing the pixel size.

A holographic display based on spatial multiplexing

A DMD chip is capable of displaying holographic images with a gray level and of reconstructing its image only in the space defined by the diffraction pattern induced from its pixel arrangement structure. 2 X 5 DMD chips are combined on a board to generate a spatially multiplexed reconstructed image of 10cmX2cm. Each DMD chip generates an image piece with the size of 2cm (Horizontal) X 1cm (vertical). The reconstructed image reveals the features of original object image including the gray level but noises from several sources are also laden with it.

Resolution of electro-holographic image

The resolution of the reconstructed image from a hologram displayed on a DMD is measured with the light field images along the propagation direction of the reconstructed image. The light field images reveal that a point and line image suffers a strong astigmatism but the line focusing distance differences for lines with different directions. This will be astigmatism too. The focusing distance of the reconstructed image is shorter than that of the object. The two lines in transverse direction are resolved when the gap between them is around 16 pixels of the DMD’s in use. However, the depth direction is difficult to estimate due to the depth of focus of each line. Due to the astigmatism, the reconstructed image of a square appears as a rectangle or a rhombus.

Holographic and Light-Field Imaging as Future 3-D Displays

Light-field imaging and holographic imaging are currently the two mostly investigated 3-D imaging technologies because of their potentials to create the viewing environment conforming to a natural viewing condition. The basic optical geometries for image display in these imaging are not different from that of integral photography. The images in the two type of imaging are a set of different view images. These images are arranged as a 2-D point image array, and each point image is expanded with a certain angle to form a viewing zone. The differences between the two types of imaging are the number of point images in the array and the physical entities forming the images. Holographic imaging has many more point images than light-field imaging, and each image in the array consists of coherent right rays from different positions of an object. In light-field imaging, an array of pixels represents a direction view of the object. Despite these differences, they share the same goal of providing a continuous parallax to viewers and require display panels of almost the same characteristics. It is expected that in the future these two imaging techniques will be integrated into the same flat panel along with the plane image.

Increasing the depth of field in Multiview 3D images

A super-multiview condition simulator which can project up to four different view images to each eye is introduced. This simulator with the image having both disparity and perspective informs that the depth of field (DOF) will be extended to more than the default DOF values as the number of simultaneously but separately projected different view images to each eye increase. The DOF range can be extended to near 2 diopters with the four simultaneous view images. However, the DOF value increments are not prominent as the image with both disparity and perspective with the image with disparity only.

Increasing the depth of field for multiview 3D images

One of the overarching goals for 3D displays is allowing viewers to perceive depth. This can be achieved through ‘continuous parallax,’ which is provided by the displays themselves. Indeed, the concept of continuous parallax is the principal factor that governs the creation of natural viewing conditions with a 3D display. It is also the reason why eyes do not suffer from the vergence-accommodation conflict when people view natural scenes and objects. Continuous parallax can be achieved with a type of 3D display known as a ‘super-multiview display’ (a concept first introduced in the 1990s1). In super-multiview displays it is necessary for at least two different image views to be provided simultaneously to each eye of a viewer. Through this process, it is possible for a viewer to perceive a hologram with a sense of depth. In other words, a monocular sense of depth is achieved by simultaneously projecting two different-view images to each pupil of a viewer’s eyes. Although the realization of a monocular sense of depth, with 26 continuously projected different-view images directed to the eyes of viewers, was reported in 2011,2 no additional information on this subject has since been published. We have therefore been investigating ways to verify the effects of increasing the number of simultaneously projected differentview images to each eye of a subject. As part of this work we have developed a super-multiview condition simulator that can be used to project up to four different-view images to each eye simultaneously.3 With our simulator we can address a number of important questions that need to be answered before a commercial super-multiview display is built. For instance, is it possible to obtain a monocular sense of depth with more than two simultaneously projected images? In addition, does the focusable depth range increase proportionally with the number of different-view images that are simultaneously projected to the pupils? Figure 1. Schematic illustration of the super-multiview effect simulator concept. Up to four different-view images can be simultaneously projected onto each pupil of a viewer. The depth of field (DOF) of the different projection configurations, expressed in units of diopter (D), is known for stereo image and two different-view image situations, but has not previously been obtained for three or four different-view projections.