Television – Modular image display system
Reexamination Certificate
2000-06-05
2003-04-08
Miller, John (Department: 2614)
Television
Modular image display system
C348S778000, C348S687000
Reexamination Certificate
active
06545718
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cathode ray tube, which forms a single screen by joining a plurality of divided screens for image display and an apparatus and a method of controlling brightness of an image displayed on an image display device such as a cathode ray tube.
2. Description of the Related Art
In an image display device such as a television receiver or a monitor device for a computer, a cathode ray tube (CRT), for example, is widely used. A cathode ray tube forms a scan screen according to scanning of an electron beam by irradiating an electron beam toward a phosphor surface from an electron gun provided inside of the cathode ray tube (simply called inside of the tube below). A cathode ray tube comprising a single electron gun is common. However, in recent years, a cathode ray tube with multiple electron guns has been developed.
In this type of cathode ray tube, a plurality of divided screens are formed by a plurality of electron beams emitted from a plurality of electron guns, and image display is performed by forming a single screen by joining the plurality of divided screens. A technology relating to the cathode ray tube comprising the plurality of electron guns is disclosed in, for example, Japanese Examined Utility Model Publication No. Sho 39-25641, Japanese Examined Patent Publication No. Sho 42-4928 and Japanese Unexamined Patent Publication No. Sho 50-17167. The cathode ray tube comprising the plurality of electron guns has such advantages that the depth can be shortened while the screen is enlarged compared to a cathode ray tube with a single electron gun. In order to join the plurality of divided screens, one screen may be obtained simply by joining an end portion of each divided screen linearly, or one screen may be obtained by partially overlapping adjacent divided screens. In
FIGS. 23A and 23B
, one example of a method for forming a screen is shown where one screen is obtained by overlapping adjacent end portions of two divided screens SL, SR. In this example, the center part of the screen is an overlapped region OL of the two divided screens SL, SR.
In addition to the cathode ray tube, one for forming a single screen by joining a plurality of divided screens for image display also has been developed as a projection type image display apparatus, for example. The projection type image display apparatus enlarges and projects an image displayed in a cathode ray tube or the like on a screen through a projection optical system. A technology related to such a projection type image display apparatus is disclosed in Japanese Examined Patent Publication No. Sho. 54-23762 and Japanese Unexamined Patent Publication No. Hei 5-300452, for example.
In the above-mentioned cathode ray tube with multiple electron guns, it is preferable that the joint area of the divided screens is as inconspicuous as possible when displaying a single screen in which the plurality of divided screens are jointed. However, in the related art, the technique for making the joint area of the divided screens inconspicuous is insufficient. For example, if the brightness is not adjusted properly in the joint area, differences in brightness are caused between adjacent divided screens, which is so called “brightness inconsistencies.” In the related art, the technique for improving the brightness inconsistencies is insufficient. The brightness inconsistencies become a big problem in the overlapped region OL between the adjacent divided screens when a single screen is obtained by overlapping the adjacent divided screens SL, SR partially, as the example shown in
FIGS. 23A and 23B
.
A method for improving the brightness inconsistencies as mentioned above is described in a literature called “SID digest p351-354 23.4: ‘The Camel CRT’,” for example. The technology described in the literature will be explained with reference to
FIGS. 23A and 23B
. In this technology, a method is proposed where a video signal corresponding to the overlapped region OL on the screen is multiplied by a predetermined coefficient for correction depending on a position of a pixel in a horizontal direction (the direction of overlapping the screen, X direction in FIG.
23
B), that is, a signal level of an inputted signal is changed depending on the position in the direction of overlapping screens for outputting. In this method, the level of the inputted signal for each screen corresponding to the overlapped region OL is corrected to a sine function, for example, such that a values in which brightness levels of the inputted signals at the same pixel positions P
i,j
(P
i,j
1
, P
i,j
2
) on each of SL, SR screens overlapped is equal to brightness of an original image at the same pixel position, for example. However, while this method enables to improve the brightness of a part of the brightness area, it is difficult to improve the brightness all over the brightness area, as described in detail below.
Problems in the method of the related art for improving the brightness inconsistencies will be explained in more detail below. Generally, a brightness Y of a screen in a cathode ray tube or the like is expressed in a equation (1) below where a level of an inputted signal is D and a characteristic value for indicating a so-called gamma characteristic, gamma value, is &ggr;. C is generally called perveance, which is a coefficient determined by a structure of an electron gun, for example.
Y=C×D
&ggr;
(1)
The brightness distribution will be considered here, where two divided screens SL, SR are partially overlapped to form one single screen as the example shown in
FIGS. 23A and 23B
. Each brightness, Y′
1
and Y′
2
, of the two divided screens SL, SR in the overlapped region OL can be expressed equations (2) and (3), respectively, similarly to the equation (1) above, where gamma values of the two divided screens SL, SR are &ggr;
1
, &ggr;
2
, respectively. In these equations (2), (3), k
1
and k
2
are coefficients for correction, to be multiplied to an inputted signal D corresponding to an overlapped region OL of a screen, depending on a pixel position P
i,j
. Each of C
1
and C
2
is a predetermined coefficient corresponding to the coefficient C in the equation (1) above.
Y′
1
=
C
1
×(
k
1
×
D
)
&ggr;1
(2)
Y′
2
=
C
2
×(
k
2
×
D
)
&ggr;2
(3)
Next, if a level of an inputted signal keeps the same value in the whole area of the screen, the brightness should be constant in the whole area, where degrees of brightness of the two divided screens SL, SR in the non-overlapped region are Y
1
and Y
2
, respectively. Here, a condition for not causing the brightness inconsistencies described above can be expressed in an equation (4) below. Y′
1
+Y′
2
is a value in which the degrees of brightness of the two divided screens SL, SR in the overlapped region OL are combined. When the equation (4) is solved, a relationship equation (5) below is derived.
Y
1
=
Y
2
=
Y′
1
+
Y′
2
(4)
k
1
&ggr;1
+k
2
&ggr;2
=1 (5)
Here, in the relationship equation (5) above, when the gamma values &ggr;
1
, &ggr;
2
are constant values, the coefficients k
1
and k
2
for correction can be determined uniquely irrespective of a level of an inputted signal. However, in practice, since the gamma values depend on a level of an inputted signal and a degree of brightness of the screen, as shown in
FIG. 24
, they are not constant values.
A characteristic graph shown in
FIG. 24
indicates a relationship between a level of an inputted signal (horizontal axis) and a degree of brightness (cd/m
2
) (vertical axis) actually observed on the screen. The graph was obtained by locally connecting measured points (·in
FIG. 24
) indicating values of inputted signals and values of the brightness with straight lines. In
FIG. 24
, the values of the inputted signals and the values of the brightness are indicated in logarithm (log). A gamma
Kato Yasunobu
Nakanishi Satoru
Okada Masamichi
Frommer William S.
Miller John
Tran Trang U.
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