Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1997-10-07
2001-02-06
Nguyen, Chanh (Department: 2775)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S077000
Reexamination Certificate
active
06184850
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image display apparatus comprising a light source and a transmission type optical modulation panel and a method of driving the same.
2. Related Background Art
Image display apparatuses comprising a transmission type optical modulation panel such as a liquid crystal display panel to be illuminated from behind to show images are known. Such display apparatuses are normally classified into a direct viewing type comprising an image carrying panel to be directly viewed and a projection type comprising a screen for showing projected images.
As a matter of course, such image displays are required to show satisfactorily bright images without uneven distribution of illumination.
FIG. 37
of the accompanying drawings schematically shows a conventional direct viewing type image display apparatus. Referring to
FIG. 37
, the apparatus comprises a fluorescent lamp
641
, a reflector
642
having a concave cross section, a diffusing panel
643
and a liquid crystal display panel
644
. Rays of light emitted from the fluorescent lamp
641
are partly made to hit the diffusing panel
643
directly and partly reflected by the reflector
642
before they get to the diffusing panel
643
. The liquid crystal display panel
644
is illuminated from behind by the rays of light that have been diffused by the diffusing panel
643
.
However, it is a known fact that it is practically impossible for an image display apparatus having a configuration as described above to show satisfactorily bright images without uneven distribution of illumination, even if the fluorescent lamp
641
and the reflector
642
are designed optimally in terms of brightness and distribution of illumination. A net result is then an unevenly illuminated display panel.
On the other hand, it is desired for a projection type image display apparatus to have its transmission type optical modulation panel illuminated brighter than that of a direct viewing type apparatus with an enhanced level of even distribution of illumination. According to a known method developed to achieve this objective, a highly bright luminous tube such as a metal halide lamp and a concave mirror are combined to produce a light source for illuminating a liquid crystal display panel. With such an arrangement, however, the metal halide lamp itself intercepts some of the rays of light reflected by the concave mirror to project its shadow on the panel and hence hinders the attempt of evenly illuminating the panel.
Another known illumination method involves the use of a cathode luminescence light source.
FIG. 38
of the accompanying drawings schematically shows a display apparatus using such a light source. Referring to
FIG. 38
, the apparatus comprises a glass vacuum container
701
, a phosphor layer
702
, a metal backing layer
703
and an electron gun having a thermionic cathode as an electron source. Again, however, it is practically impossible for such a light source to irradiate the phosphor layer with evenly distributed electron beams, even if its electronic optical lens and electron gun are designed optimally in terms of brightness and distribution of illumination. A net result is also an uneven illumination.
There has also been proposed a cathode luminescence light source for a display apparatus as schematically illustrated in
FIG. 39
of the accompanying drawings in an attempt to achieve an evenly distributed illumination. In
FIG. 39
, reference numerals
701
through
703
denote, respectively, the same components as those of
FIG. 38
, although a plurality of wire cathodes (linear thermionic cathodes)
805
are arranged in parallel to replace the electron gun
704
of FIG.
38
. Additionally, a grid electrode
806
is provided to improve the even distribution of electron beams irradiating the phosphor layer
702
. However, the display panel of this apparatus is accompanied by regularly distributed variations in the intensity of illumination attributable to the arrangement of wire cathodes
805
and variations in the temperature of the wire cathodes
805
(mainly attributable to the heat loss that takes place at the wire cathode supporting sections) and it is extremely difficult, if not totally impossible, to completely eliminate these variations. Since each of the light valves of a liquid crystal display panel is very small in its effect when compared with the wire cathodes
805
, the regularly distributed variations in the intensity of illumination of the panel are directly reflected on the brightness of the images projected on the panel.
SUMMARY OF THE INVENTION
In view of the above identified problems of the existing transmission type optical modulation panels, it is therefore an object of the invention to provide a display apparatus comprising a panel of the type under consideration showing an extremely even distribution of brightness as well as a method of driving such an apparatus.
According to the invention, the above object is achieved by providing an image display apparatus comprising a panel type light source including a plurality of cold-cathode devices arranged two-dimensionally on a substrate and a phosphor member contained in a same vacuum container for emitting visible light upon irradiation of electron beams by the cold-cathode devices, and a transmission type optical modulation panel using the panel type light source as a back light source.
According to the invention, there is also provided a method of driving an image display apparatus comprising a panel type light source including a plurality of cold-cathode devices arranged two-dimensionally on a substrate and a phosphor member contained in a same vacuum container for emitting visible light upon irradiation of electron beams by the cold-cathode devices and a transmission type optical modulation panel, said method comprising steps of applying a voltage to the plurality of cold-cathode devices arranged two-dimensionally on a substrate to force them to emit electron beams, irradiating the phosphor member with electron beams emitted by said plurality of cold-cathode devices to cause it to emit visible light, illuminating the transmission type optical modulation panel from the back and driving the transmission type optical modulation panel according to picture signals.
According to the invention, there is further provided a method of driving an image display apparatus comprising a panel type light source including a plurality of cold-cathode devices arranged two-dimensionally on a substrate and a phosphor layer contained in a same vacuum container for emitting visible light upon irradiation of electron beams by the cold-cathode devices and a transmission type optical modulation panel, wherein said plurality of cold-cathode devices are arranged in rows in parallel with an X-axis and stripe-shaped light valves are arranged in parallel with a Y-axis rectangularly intersecting said X-axis, said X- and Y-axes being defined by a coordinate system, said method comprising steps of sequentially scanning the light emitting areas of the panel type light source according to incoming picture signals and applying a modulation signal to the light valves of the transmission type optical modulation panel in synchronism with the scanning operation.
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Kaneko Tetsuya
Nakamura Naoto
Nomura Ichiro
Suzuki Hidetoshi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Nguyen Chanh
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