Liquid crystal cells – elements and systems – Liquid crystal system – Projector including liquid crystal cell
Patent
1996-05-24
1998-06-02
Sikes, William L.
Liquid crystal cells, elements and systems
Liquid crystal system
Projector including liquid crystal cell
40361, G02F 11335
Patent
active
057608512
DESCRIPTION:
BRIEF SUMMARY
RELATED APPLICATIONS
This application is the U.S. National filing of PCT/EP94/03968, which was filed on Nov. 28, 1994.
FIELD OF THE INVENTION
This invention is generally related to the field of transparency viewing apparatus, and more specifically to the field of transparency viewing apparatus using a liquid crystal array display surface.
BACKGROUND OF THE INVENTION
The use of liquid crystal arrays (LCA) as the display surface for a transparency has been mooted in the past. Such systems, in order to be optimally effective, require that the portion of the array which underlies the transparency has sufficient brightness to enable viewing of the image and that the contrast ratio between the bright and dark portions of the array (namely the area outside the transparency or an image region of the transparency) be high.
The use of active matrix, passive matrix and direct drive technologies for LCAs has been described. These technologies, as they are used in the art, have substantial drawbacks when applied to a transparency viewer. Active matrix arrays have the drawback of high cost for the array because of the additional process steps required for the active elements and the difficulty in achieving large size arrays due to the limitations of semiconductor thin film technology.
Direct addressing systems have large spacings between the elements for the passage of the large number of conductors needed for this system thus reducing the contrast of the system. The large number of drivers required increases the cost of the associated electronics especially for large arrays.
Passive matrix systems suffer from much lower contrast than active matrix systems due to the scanning limitations of the multiplex drive systems which are generally required for such systems. This is especially true when a number of different areas are bright and dark in systems which have the flexibility to provide a large number of such areas. On the other hand, passive matrix systems are much more available and cheaper, both for the arrays themselves (compared to active matrix systems) and for the associated electronics (compared to direct addressing systems). However, while such systems do have smaller inactive stripes between the LCA elements than the direct addressing matrix LCAs, even these stripes can be troublesome to the viewer.
Another problem with LCA viewers is caused by the fact that the contrast of LCAs is a strong function of the angle of incidence of the light which illuminates the LCA, with maximum contrast being available for near normal incidence. Since back illumination is by its nature relatively isotropic, the contrast of the viewing surface is further degraded.
SUMMARY OF THE INVENTION
The present invention seeks, in one aspect thereof, to overcome some of the limitations of the prior art by utilizing a passive LCA and by driving the array in a novel manner which takes account of the nature and shape of the types of transparencies which are to be viewed on a transparency viewer.
The invention is especially suitable for the viewing of medical images, such as X-Ray films or films which are produced by hardcopy devices associated with digital medical imaging equipment such as computerized tomographs, gamma cameras, medical ultrasound imagers, digital subtraction angiography equipment or digital radiography equipment.
In particular, this aspect of the invention is based on the realization that, in general, at a given time, only one or two sizes of film are viewed and that this allows for both an extreme simplification of the system electronics and a large increase in the available contrast ratio (between bright and dark masked areas of the viewer surface) of the system.
Unlike most LCA systems, which require great flexibility for the placement and size of bright and dark areas, medical imaging systems require only a relatively limited number of relatively large bright regions on a dark background. Furthermore, the bright regions, even when they are not contiguous, are normally of the same height and require that the sa
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Inbar Dan
Levi Ben-zion
Wolf Hanan
Dudek James A.
Sikes William L.
SmartLight Ltd.
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