3D display systems might be broadly grouped as those requiring visual viewing aids or those that do not. The ones not requiring any viewing aids are sometimes referred to as autostereoscopic displays. The autostereoscopic systems may be further classified as stereoscopic systems, holographic systems, multiviewer systems, viewer adaptive systems, etc. The stereoscopic systems, generally referenced as autostereoscopic simply present two views, a left-eye view and a right-eye view to the left and right eyes respectively. Holographic systems present a sufficient number of views, not only different for each eye, but enough views from different directions that the viewer may roam around the image region and see the imaged object from different positions. The holographic systems may provide holographic views with parallax only in the horizontal direction, or in both the horizontal and vertical directions. Multiviewer systems may be grouped as two types: (1) a fixed viewing system that provides fixed viewing positions for each of several viewers and (2) an adaptive system that tracks the viewer positions so that viewers are not limited to fixed positions in the viewing area.
A Brief Listing of Various Types of 3D Display Systems
    I—VIEWING AIDS REQUIRED    Polarized Systems            Polarized passive glasses            TIME SEPARATION SYSTEMS            Active glasses with alternating shutters            II—Viewing Aids not Required    INTEGRATED SCREEN CONFIGURATION            lenticular lenses with diffused backlight        parallax barrier with diffused backlight            DISPLAYS WITH Separated Backlight (A)            Small multi-backlight sources illuminating a large lens which re-directs images into small viewing zones for individual eyes: Field (image) sequential **            DISPLAYS WITH SEPARATED BACKLIGHT (B)            Array of vertical line light sources        Vertical image-line sequential **            DISPLAYS CONTAINING A LARGE NUMBER OF LIGHT OR IMAGE SOURCES EQUAL TO FULL RESOLUTION            Hologram like            REFLECTION DISPLAY:            Lit from front or side **            HOLOGRAPHIC            Horizontal parallax only        Horizontal plus vertical parallax            ** With optional head/eye tracking to eliminate blank or pseudoscopic viewing zones.
The invention to be described herein fits into the above mentioned class:    DISPLAYS WITH SEPARATED BACKLIGHT (B)            Array of vertical line light sources.        Vertical image-line sequential        
A configuration which would be most suitable for in-home television would be:    autostereoscopic,    multi-viewer, and    adaptive (head/eye tracking)
Creating a 3D display system that produces a near realistic view of a scene remains an elusive achievement. Many factors come into play and based on the technology available at any point in time, compromises are necessary. Systems requiring viewing aids have encountered strong market rejection. Parallax barrier systems place restrictions on viewer position. Brightness and image fidelity at reasonable cost are difficult to achieve with most of the current approaches.
The techniques to be described herein describe an approach which overcomes the deficiencies of the systems mentioned above. This invention uses an array of light sources behind an SLM, spatial light modulator, such as a transparent LCD image panel. Separate, narrow vertical columns of the image are selected, and together with selected light sources in the light-source array, cause vertical sheets of light rays to be projected toward the viewer. An entire vertical picture line is thus projected to be visible to any eyeball (generally a single eyeball) within the vertical plane containing the selected LCD column and the selected light source. Because a relatively large number of light sources are employed in the light array, it is possible to direct selected narrow picture columns, a small number at a time, with very high precision towards the individual viewers. The individual image columns are projected a few, generally one or two at a time, in succession, at high speed into each viewing eyeball so that all columns in the scene reach each eyeball in less than a persistence-of-vision interval of time and so a smooth representation of the scene in achieved.
Thus, with the required number of light sources, careful dynamic alignment between the light sources, the selected vertical LCD columns and a viewing eyeball, it becomes possible to achieve the precision and brightness required to overcome many of the problems with other autostereoscopic display systems.
Numerous patents disclose approaches to autostereoscopic displays based on flat screens which are physically integrated with lenticular lenses or with barrier shutters or both in order to direct separated images to the left and the right eyes. These systems are very limited in their ability to provide multi-viewer capability with high resolution images free of pseudoscopic zones and blank zones. Integrated, flat screens are also limited in their ability to provide multi-viewer tracking
A better approach than integrated screens is achieved by using displays where separate light sources are arranged to produce controlled directional images. Discounting elaborate holographic displays and considering autostereoscopic (left/right only) image displays, autostereoscopic displays have been achievable, in one approach, using means to rear project entire images through large lenses into the viewer's eyes. The image to be projected may be formed in an SLM, either behind the projection lens, or directly in front of the lens, and with proper image or eye placement, the viewed image fills the entire lens. Tracking is achievable by forming the image at different places on the SLM image panel, or by moving the SLM light source so as to maintain the focus point of the lens in the viewing eye. This approach requires, for TV, large lenses and a very deep projection system as well as an image screen which must produce high resolution images on small regions of the active image area. Systems of the type mentioned here are disclosed, for example, in patents such as U.S. Pat. No. 5,132,839, U.S. Pat. No. 7,753,529, U.S. Pat. No. 6,215,590, U.S. Pat. No. 6,172,807 and many others.
The problems associated with autostereoscopic systems of the type mentioned above, which have prevented commercial application, are avoided with the approach used in the presently disclosed invention. Lenses are avoided and the depth of the display device is kept at a few inches. The goal of;
(1) producing a high resolution autostereoscopic image using the full resolution capability of the image panel, and
(2) producing autostereoscopic images free of pseudoscopic and blank zones, and
(3) accommodating multiple viewers with bright images may be realized using the approach disclosed herein.
The main underlying principle of this invention is based on the projection of selected vertical picture columns from the image panel, a small number at a time, into viewer's eyes with high positional precision. Precise projection aiming results from using selected light sources from an array of sources and selected screen image columns where the lights are dynamically chosen for alignment with the viewer's eyes and the columns. Eye tracking technology is employed to provide the control signals to maintain the alignment.
The discussion to follow will primarily focus on a basic configuration which displays the same right-eye (or left-eye) image into the respective eyes of each viewer. In the basic embodiment, eye-tracking is employed for each viewer and each viewer will observe a stereoscopic three dimensional scene with no viewing aids.
In what follows, references will be made to certain components, or to certain sub-systems used in this invention, which are either available standard functional units, or which are sub-components which can be assembled according to the requirements spelled out in this disclosure by one skilled in the appropriate art. These items will therefore not be accorded the same detailed explanations as the completely novel elements of this invention, which include the assemblage and special configuration making use of these sub-units. This includes such items as an LCD panel, or digital video graphics circuitry such as one that separates a left-eye video stream from a right-eye video stream, or an eye tracking imager with eye tracking processing circuitry.
Glossary of Terms Used in the Disclosure:
LCD Panel, SLM Image Panel:
These and similar terms will be used herein in a general sense to mean a flat panel image screen, or a spatial light modulator, not necessarily liquid crystal, with the following features:
1. It has no backlight panel.
2. It must be transparent, that is to say light which passes through the screen is modulated by the color/intensity vales of the screen pixels but does not, appreciably, change direction or get diffused when leaving the screen.
VPL, Vertical Picture Line:
This defines a narrow, vertical, picture element, of full screen height, which may be one or several horizontal resolution elements wide. For convenience of explanation, later, a VPL will generally be considered to be a single pixel wide. Thus, for example, the high definition format referred to as 720p which has 1280H×720V lines of resolution, will have 1280 “vertical picture lines”, VPL's, each of which is one pixel wide and has 720 pixels arranged vertically in a column. In general, however, for very high resolution screens, it is feasible to configure VPL's which are several pixels wide while still keeping left/right scenes separated for the appropriate viewing eyes,
Transmissive VPL, Opaque VPL:
Refers to the light transmissive states of a VPL; when it is “transmissive” it allows the color values of the pixels in the VPL column to modulate the light passing through VPL. For the remainder of the SLM, all VPL's are opaque, or alternatively blocked by a shutter, if not specifically noted as being transmissive.
Selected VPL's:
Refers to VPL's which are made transmissive. When not selected, or un-selected or de-selected, VPL's are opaque.
Light Array, Array Lights, Light Array Panel, Strobe Lights Etc.:
Refers to an array of selectable, individual sources of light of generally small horizontal dimension closely spaced and extended vertically. They might be point sources of light but a preferred embodiment would have thin vertical profiles of light. The term “strobe lights” will also be used herein because these lights must supply bright flashes of short duration. The lights might be xenon or similar discharge lamps or a solid state array of vertical lines of flashable lights or of discreet LED lamps arranged in an array of columns where each column consists of one or several LED lamps or thin vertical rods of glass or acrylic or similar material with lights at one or both ends and treated so as to emit light along its length.
Frame Time:
The time required to display 2 complete pictures (right-eye and left-eye) which produces a full stereoscopic image.
Scan Time, Also Field Time:
The time to complete one picture, or one field, (either right-eye or left-eye). This is one half the frame time.
720p Picture Format:
For purposes of explanation herein, the TV picture format will be assumed to be what is commonly referred to as 720p. This format has 1280 lines of horizontal resolution and 720 lines of vertical resolution. A frame time of 1/30 sec will be assumed and two fields, the right-eye image and the left-eye image, will each take 1/60 sec. These numbers may be departed from and other formats may be used without in any way departing from the spirit or scope of this invention.
Placement of Display Components:
When object A is to the rear of object B, or A is behind B then it is understood that object A is further from the viewer than B. Object A is in front of object B if A is nearer to the viewer.
Vertical and Horizontal:
These refer to conventional screen coordinates and not necessarily to Earth coordinates.