Stewart R. Lang

Time-multiplexed color autostereoscopic display

A practical color autostereoscopic display has been developed at Cambridge, and has been in operation since 1994. It provides six view directions at half VGA resolution (640 X 240 pixels) of 24-bit color at a luminance of 100 cd/m2. Each individual view direction is refreshed at standard television rates, so the display is capable of full motion animation or live 3D video. Versions with both 10 and 25 inch screen diagonal have been built. This paper describes the principles of the display, its development from an earlier monochrome version, the results of this development work, and ideas for future research. The original monochrome display, developed at Cambridge, has been in use since late 1991. It provides eight views at full VGA resolution or sixteen views at half VGA resolution. A series of views of a scene are displayed sequentially and an optical directional modulator, constructed from a liquid crystal shutting element, is synchronized with the image repetition rate to direct each image to a different zone in front of the display. The viewers eyes thus see two different images and the head can be moved from side to side to look around objects, giving an autostereoscopic display with correct movement parallax. The use of a CRT makes for a flexible system where resolution and number of views can be easily varied. Development of the color display from the monochrome version was achieved by a color sequential system using a liquid crystal color shutter. As each view direction had to be displayed three times for the three primary colors, the maximum number of view directions was decreased to six. Full color (24-bit) images have been displayed on these six view autostereoscopic displays from a number of sources: computer generated images, digitized photographs, and live color video from a multiplexed camera also designed at Cambridge.

Time-multiplexed autostereoscopic camera system

A camera system has been developed to provide live 3D video input for a time-multiplexed autostereoscopic display. The system is capable of taking video input from up to sixteen sources and multiplexing these into a single video output stream with a pixel rate an order of magnitude faster than the individual input streams. Both monochrome and color versions of the system have been built. Testing of the system with eight cameras and a Cambridge autostereo display has produced excellent live autostereoscopic video. The basic operation of the camera system is to digitize multiple input video streams, one for each view direction, and to multiplex these into a single autostereoscopic video stream. A simple circuit boards (the camera board) can digitize, process and buffer the video input from a single video source. Several of these are connected together via a backplane to another circuit board (the multiplexer board) which contains all the circuitry necessary for generating the output video and synchronization signals and for controlling the rest of the system. Alignment and synchronization were two major challenges in the design of the system. Pixel-level control of camera alignment is provided by an image processing chip on each camera board, while synchronization is provided by a number of carefully designed control mechanisms.

A time-sequential multi-projector autostereoscopic display

— We describe a new 28-view 25-in. autostereoscopic display that combines both time-sequential and multi-projector technology. It is constructed from four time-sequential subsystems, which abut behind a single ferroelectric liquid-crystal shutter. The display has a resolution of 512 × 384 pixels in 24-bit color. It allows multiple viewers to simultaneously view stereoscopic images without the need for special glasses or headgear.

Time-multiplexed three-dimensional video display

A true 3D image is synthesised from many 2D views of the original. The views are presented in rapid succession on a CRT whose field of view is restricted to a different zone for each view. This restriction is achieved by using optical fourier transforms which result in a 3D image that is especially sharp and clear. The display is bulky but inherently robust and flexible. It is therefore well adapted for the design of novel 3D systems.

A 50 time-multiplexed autostereoscopic display

We describe the development and construction of a large screen version of the Cambridge time-multiplexed autostereo display. The new device uses a 50 inch diagonal spherical mirror in place of the 10 inch Fresnel lens of the original Cambridge color display. A fivefold increase in image luminance has been achieved by the replacement of sequential color on a single CRT with separate red, green, and blue CRTs. Fifteen views are displayed at 640 X 480 (VGA) resolution with about 250 cd/m2 luminance and 30 Hz interlaced refresh rate. A 22 mm interview separation provides three views between a typical viewers eyes, giving a smooth stereoscopic effect over a 330 mm wide eye box. Two identical optical systems have been built, allowing simultaneous use of the device by two viewers. The two system are off-axis with respect to the main mirror, requiring geometric compensation on the CRTs in addition to the normal color convergence. The prototype produces two independent full color, large 3D images which can be viewed under normal lighting conditions.

A 2nd generation autostereoscopic 3-D display

A useful and practical autostereoscopic 3-D display has been developed from an earlier experimental design which was demonstrated in 1990 [8]. The concept of the new autostereo display is unchanged from the earlier one. The use of commercially available components and purpose designed electronics, however, has meant we now have a practical and reliable autostereoscopic display to work with. We are manufacturing a small number of the autostereoscopic displays for research workers investigating applications of autostereoscopy. Various new applications are being developed here in Cambridge using these autostereo displays, transforming autostereo from a novelty item into a useful tool. In turn the displays requirements are beginning to drive other computer and network system design issues. This paper gives a brief primer of technologies of autostereopsis, discusses the hardware architecture of the display and its associated computer, describes the software controlling the display and lists some applications. Other state-of-the-art papers [7] [5] [6] consider some of the computer and network system design issues and broader opportunities being opened up by this new display technology.

A new light pen tracking method

The method is based on a simple prediction and correction sequence applied to the position of a tracking box, according to which arm or side of the box has received a light pen hit. The box pattern and method has a number of advantages. When the pen is stationary above the box, which is square and marginally larger than the field of view of the pen, then the light pen interrupt rate is minimal the converse is true of a tracking cross pattern; also no preqise position of the light pen interrupt on a box side is required rather just which side was hit; the pattern can also be expanded and directly used in a pen search sequence.