1. Field of the Invention
This invention relates to projection display systems and more particularly to a projection display system that provides projection of distortion free analog and digital information and images on direct view displays without electromagnetic cross-talk interference between adjacent displays.
2. Description of Related Art
Conventional cathode-ray tube (CRT) monitors are presently utilized for projection of analog images for direct viewing. In many applications, including WAC window simulation environments, the direct view CRT monitors must be placed adjacent one another to provide a realistic view of the simulation environment or the desired projected image.
Conventional CRT displays and monitors are known in the art and generally utilize one or more electron beam generating guns, a focusing system, and a deflection system to project, focus, and steer a beam of electrons onto a display screen that is illuminated under electron bombardment. Typically, the CRT tube is somewhat funnel shaped and has a phosphor image surface or screen at the large end. The tube, sometimes referred to as the envelope, serves as a vacuum enclosure, and must provide for entry and deflection of the beam of electrons. Illumination resulting in color displays is well known and will not be described herein.
In many applications, multiple CRT displays are placed adjacent each other to create a larger projection image than can be projected by one display monitor alone with reasonable size and picture quality, or to project an image of shape that cannot reasonably be obtained by a single display monitor.
Many CRT monitors utilize magnetic deflection systems to steer the electron beam. When CRTs are placed adjacent each other the magnetic deflection systems as well as other electromagnetic emissions can cause interference between the adjacent CRTs, sometimes known as cross-talk, causing noise to appear in the display images.
CRTs tend to be large and heavy, partially because of the vacuum enclosure required, thereby creating an additional problem when placed adjacent each other. To create a large display made of individual CRTs, a sturdy framework must be constructed to hold the CRTs in place.
A further problem exists in that each CRT normally includes a framework to contain the tube and electronics. Therefore, CRTs can only be placed as close as the framework will allow. Even if a custom framework is designed to hold multiple CRTs as close as possible to each other, each CRT itself includes an outer area at the perimeter of the screen or front display area that is part of the thick vacuum container and does not illuminate. Therefore, there is a space between each adjacent CRT that cannot project an image and presents a series of gaps in the overall image as viewed on a combination of CRTs.
In many simulation applications, the operator views a series of CRT screens linked together visually to provide a 360 degree panoramic simulated view of the world surrounding the operator. One CRT is not large enough or physically configurable to provide such a view. For example, in a certain position, a military tank operator can view the terrain around the tank through a 360 degree, 6 inch high viewport in a portion of the tank. To simulate this 6 inch high view of the world, the simulation system must provide a series of CRTs, mounted side-by-side, 360 degrees, around the tank opening simulator. This requires a very sturdy framework, and as described above, will include a series of visual gaps between each adjacent display.
CRTs are analog devices and cannot display digital information directly. Computer generated images and other digital information must be converted to analog signals before being displayed on a CRT screen. In many systems, especially those systems operated by computer, all of the data is in digital form, and the conversion process from digital to analog signals occurring before display on a CRT screen can introduce noise to the original digital image, resulting in poor picture or display quality.