Cathode ray tube and intensity controlling method

Details Cathode ray tube and intensity controlling method Cathode ray tube and intensity controlling method

2001-09-13

2003-06-17

Philogene, Haissa (Department: 2821)

Electric lamp and discharge devices: systems

Cathode ray tube circuits

Cathode-ray deflections circuits

C315S368120, C315S368130, C315S370000, C315S371000

Reexamination Certificate

active

06580233

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cathode ray tube for displaying an image by forming a single picture plane by joining a plurality of split picture planes, and an intensity controlling method.
2. Description of the Related Art
At present, a cathode ray tube (CRT) is widely used in an image display apparatus (such as a television receiver, various monitors, and the like). In the CRT, an electron beam is emitted from an electron gun provided in the tube toward a phosphor screen and is electromagnetically deflected by a deflection yoke or the like, thereby forming a scan image according to the scan with the electron beam on the tube screen.
Generally, a CRT has a single electron gun. In recent years, a CRT having a plurality of electron guns is also being developed. For example, a gun type having two of electron guns for emitting three electron beams of red (R), green (G), and blue (B) has been developed (in-line electron gun type). In the CRT of the in-line electron gun type, a plurality of split picture planes are formed by a plurality of electron beams emitted from the plurality of electron guns and are joined, thereby displaying a single image. For example, the techniques related to the CRT of the in-line electron gun type are disclosed in Japanese Patent Laid-open No. Sho 50-17167, and the like. Such a CRT having a plurality of electron guns has an advantage that a larger screen can be achieved while reducing the depth as compared with a CRT using a single electron gun.
Methods of joining split picture planes in a CRT of the in-line electron gun type or the like includes a method of obtaining a single picture plane by linearly joining end portions of the split picture planes and a method of obtaining a single picture plane by partially overlapping neighboring split picture planes.
FIGS. 1A and 1B
show an example of obtaining a single picture plane by overlapping neighboring end portions of two split picture planes SR and SL as an example of forming a picture plane. In the example, the central portion of the picture plane is an overlapped area OL of the two split picture planes SR and SL.
In the CRT of the in-line electron gun type and the like, when a single picture plane is displayed by joining a plurality of split picture planes, it is desirable to make the joint of the split picture planes inconspicuous. Conventionally, however, the technique of making the joint inconspicuous has been insufficiently developed. For example, when the intensity at the joint portion is not properly adjusted, what is called intensity unevenness such that variation occurs in magnitude of intensity in the neighboring split picture planes. Conventionally, the technique of reducing the intensity unevenness has been insufficiently developed. In the case of obtaining a single picture plane by partially overlapping the neighboring split picture planes SR and SL as shown in
FIGS. 1A and 1B
, such intensity unevenness becomes a problem in the overlapped area OL of the neighboring split picture planes.
A method of reducing the intensity unevenness as described above is disclosed in, for example, the literature of SID digest, pp 351-354, 23.4: “The Camel CRT”. The technique disclosed in the literature will be described by referring to
FIGS. 1A and 1B
. In the technique, a video signal corresponding to the overlapped area OL of the picture planes in a CRT is multiplied by a predetermined factor for correction in accordance with the position in the horizontal direction of a pixel (direction of overlapping the picture planes, that is, the X direction in FIG.
1
B), that is, the signal level of an input signal is changed according to the direction of overlapping the picture planes and the resultant is output. In the method, for example, the level of the input signal for each of the picture planes corresponding to the overlapped area OL is corrected to have a sine function shape so that a value obtained by adding the intensity levels of input signals in the same pixel positions Pi.j (Pi.j
1
, Pi.j
2
) of the overlapped picture planes SL and SR is equal to the intensity in the same pixel position in an original image. However, such method has difficulty in improving the intensity in the entire intensity area, although the intensity can be improved in a part of an intensity area.
The problem in the conventional method of reducing the intensity unevenness will be described further in detail hereinbelow. Generally, the intensity Y of the screen in a CRT or the like is expressed by the following equation (1) when the level of an input signal is D and a characteristic value (gamma value) indicative of so-called gamma characteristic is &ggr;. C is generally called perveance which is a coefficient determined according to the structure of the electronic gun or the like.
Y=C×D&ggr;
  (1)
The intensity distribution in the case where a single picture plane is formed by partially overlapping the two split picture planes like the example of
FIGS. 1A and 1B
will be considered. When gamma values in the two split picture planes SL and SR are &ggr;1 and &ggr;2, respectively, intensity Y′1 and Y′2 in the two split picture planes SL and SR in the overlapped area OL can be expressed by the following equations (2) and (3) similar to the above equation (1). In the equations (2) and (3), k1 and k2 are factors for correction by which the input signal D corresponding to the overlapped area OL in the picture plane is multiplied in accordance with the pixel position Pi.j. C1 and C2 denote predetermined coefficients corresponding to the coefficient C in the equation (1).
Y′
1
=C
1×(
k
1
×D
)&ggr;
1
  (2)
Y′
2
=C
2×(
k
2
×D
)&ggr;
2
  (3)
When the intensity in the two split picture planes SL and SR except for the overlapped area are Y1 and Y2, respectively, if the level of the input signal is the same in the entire area of the picture plane, the intensity is expected to be constant in the entire area of the picture plane. The condition under which the intensity unevenness does not occur can be expressed by the following equation (4). Y′1+Y′2 is a value obtained by adding the intensity values in the two split picture planes SL and SR in the overlapped area OL. When the equation (4) is solved, the following relational expression (5) is derived.
Y
1
=Y
2
=Y′
1
+Y′
2  (4)
k
1&ggr;
1
+k
2&ggr;
2
=1  (5)
In the relational expression (5), when the gamma values &ggr;1 and &ggr;2 are fixed values, the factors k1 and k2 for correction can be unconditionally determined irrespective of the level of the input signal. In practice, however, as shown in
FIG. 2
, the gamma value depends on the level of the input signal and the intensity of the picture plane and is not constant.
The characteristic graph of
FIG. 2
shows the relation between the level of an input signal (lateral axis) and the magnitude of intensity (cd/m
2
) actually measured on the screen (vertical axis). The graph is obtained by locally linearly connecting actual measurement points (indicated by painted dots • in the graph) each indicative of the value of the input signal and the value of intensity. In
FIG. 2
, the value of the input signal and the value of intensity are expressed as logarithm values. The gamma value &ggr; corresponds to the gradient of the graph (straight line). When the gradient of the graph is constant irrespective of the level of the input signal, the gamma value &ggr; is constant irrespective of the level of the input signal. In practice, however, the gradient of the graph varies according to the level of the input signal. It is therefore understood that the gamma value &ggr; varies according to the level of the input signal. Consequently, in order to satisfy the condition of the equation (5), a plurality of factors k1 and k2 for correction according to the level of an input signal are inherently necessary.
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