Recently, some real 3D display technologies have been developed to display a life-like 3D image in the real space having an image quality comparable to that of the high-definition 2D image without requiring the viewer to wear any special glasses. As a promising real 3D display technology, holographic 3D, volumetric 3D and spatial 3D displays have been actively researched and developed. Among them, holographic 3D displays already discussed in the previous column, so that volumetric and spatial 3D displays are introduced in this column.
Floating 3D displays is one of the spatial 3D display systems. In general, the floating 3D display system can provide a floated image with a real depth in the real space. That is, in this system, the floated image can be viewed directly in a free space without a need of any special glasses.
This floating 3D display system mostly uses the 2D image as an input signal contrary to that of the conventional stereoscopic display system, in which two-view or multi-view images are employed. Therefore, existing software packages and video cameras can be used for generating the input pictures for the floating 3D display system. The common 2D images can be displayed as a natural and optically interactive floating image with a realdepth in a free space through a LCD panel and a Fresnel lens.
Generally, this floating 3D display system can be easily implemented by combined use of a LCD panel and a Fresnel lens having a positive focal length. The Fresnel lens serves to direct and cause light rays from the source image from the LCD panel to converge at locations in the backfocal image plane, so that a floated real 3D image appears in space.
3DRC developed the '3DRC-60' system, which can project a floated image into the air with a depth of 1 meter and the '3DS-II' system, which can provide a floated image having a 3D background image. Also, Pioneer developed Haruka, which is the name of a virtual receptionist, by using a pair of microlens array, which can project an image into the space with some depth. There is no doubt that this floating 3D display system will make a big business in the advertisement market in the near future, because the floated 3D images on space can attract all of the customers' eyes and give them a deep impact on the advertised goods contrary to the conventional flat and mean 2-D images of commercial products on screen.
Virtual 3D display so-called a virtual showcase is another spatial 3D display system. The virtual showcase has the same form as a real showcase making it compatible with traditional museum displays. Real scientific and cultural artifacts are placed inside the virtual showcase allowing their threedimensional graphical augmentation.
Inside the virtual showcase virtual representations and real artifacts share the same space providing new ways of merging and exploring real and virtual content. The virtual part of the showcase can react in various ways to a visitor enabling intuitive interaction with the displayed content. These interactive showcases represent a step towards ambient intelligent landscapes, where the computer acts as an intelligent server in the background and visitors can focus on exploring the exhibited content rather than on operating computers.
A virtual showcase consists of two main parts: a convex assembly of half-silvered mirrors and one or multiple graphics display. So far, many different versions of virtual showcases have been developed. Some of them apply a large projection display and curved, cone-shaped mirror optics, and others use multiple monitors in addition with planar pyramidshaped mirror optics. While the pyramid- shaped prototypes simultaneously supports up to four viewers, the cone-shaped prototypes provides a seamless surround view onto the displayed artifact for less viewers.
Optional components of the virtual showcase are additional video projectors that are used for a pixel-precise illumination of the real content and video cameras to receive feedback from the inside of the display. The pyramid-like virtual showcase prototype can support up to four observers simultaneously. Looking through the mirror optics allows seeing the reflection of the corresponding screen portion at the same time and within the same spatial space as the real object inside the showcase.
Since convex mirror assemblies unequivocally tessellate the object space into mirror individual reflection zones which do not intersect or overlap, a single object that is displayed within the object space appears exactly once within the image space. Consequently, a definite one-to-one mapping between the object space and the image space is provided by convex mirror assemblies. Observed from a known viewpoint, the different images optically merge into a single consistent image space by reflecting the projection plane, whereby this image space visually equals the image of the untransformed image space geometry. 3DRC developed a new type of virtual 3D display system using a dual-view flat panel display.
Cheoptics360 XL system was also developed as a new product for showing products and films in Denmark, which can revolve video images that can be viewed 360° under all ambient light conditions.
In addition to spatial 3D displays, volumetric 3D displays are also actively researched. One of them is the integral 3D display. Especially, this integral 3D display has been regarded as one of the most promising real 3D display system, because it can provide full parallax, continuous viewing and full-color 3D images.
Integral 3D display is a technology that uses lenslet (microlens) arrays to make a series of small elemental images from various perspectives on a detector such as a camera sensor or a photographic plate. This technology was first demonstrated in 1911 in Moscow, where Professor P. P. Sokolov made a 3D image of a filament of an incandescent light bulb on a photographic plate using a pinhole array instead of a lenslet array. In modern practice, a set of elemental images of a 3D scene are obtained by use of a lenslet array and a 2D image sensor such as a CCD camera. Elemental images contain information on the direction and intensity of spatially sampled light rays coming from a scene.
To reconstruct a 3D image of the scene, the set of 2D elemental images are displayed by placing the lenslet array in front of a 2D display panel. Then, the rays coming from the pixels in the elemental image converge to form a 3D real image through the lenslet array. This image can include both horizontal and vertical parallax, depending on the design of the lenslet array. But this technology still suffers from a couple of same problems such as low resolution, narrow viewing- angle, etc. Toshiba developed a new integral 3D display known as a flatbed 3D display last year, and NHK is implementing a system to capture and reproduce 3D integral images in real-time for 3DTV application.
