Television – Video display – Cathode-ray tube
Reexamination Certificate
1999-08-27
2002-11-12
Lee, Michael H. (Department: 2714)
Television
Video display
Cathode-ray tube
C315S368110
Reexamination Certificate
active
06480242
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image display correcting system and image display correcting apparatus and method for correcting a display state such as distortion of a displayed image, and image display apparatus and method for displaying the corrected image.
2. Description of the Related Art
In an image display apparatus such as a television receiver or a monitor apparatus for a computer, a CRT (cathode ray tube) is widely used. In the CRT, an electron beam is emitted from an electron gun and the electron beam is deflected by a magnetic field or an electric field for deflection applied from the outside, thereby displaying an image.
FIG. 1
is a diagram showing a display screen of an image display apparatus using the CRT. In the CRT, an electron beam emitted from an electron gun is deflected both in the vertical and in the horizontal directions by a deflector using a deflecting coil and a scanned image called a raster is displayed on a display surface S (screen). The electron beam is deflected by scan signals having sawtooth waveforms. Denote the deflection center point of the electron beam by O, and the center point of the screen by O
S
. Then, the distance l from the deflection center point O to a scan position of the electron beam on the display surface S can be given by r·tan&thgr; in which r is the distance from the deflection center point O to the display face S (distance from the deflection center point O to the screen center point O
S
) and &thgr;, is the deflection angle of the electron beam. The distance lv from the center point O
S
of the screen to an end of the screen in the vertical direction is given by r·tan&thgr;v, in which &thgr;v is the maximum deflection angle in the vertical direction of the screen. Therefore, the size Lv in the vertical direction of the screen can be given by 2lv=2r·tan&thgr;v.
FIGS. 2A and 2B
and
FIGS. 3A and 3B
are diagrams for describing an image displayed on the CRT more specifically. Since the screen of the CRT has generally a rectangular shape, the emission length of the electron beam reaching each of the four corners of the screen of the CRT is the longest. Consequently, an image displayed on the screen usually looks distorted in a bobbin shape. The distortion of the image (hereinafter, called an “image distortion”) can be expressed as a difference between an image inputted as an image signal (image to be displayed) and an image actually displayed on the screen of the CRT.
FIG. 2A
shows an image to be displayed and
FIG. 2B
illustrates a distorted image actually displayed on the screen (part shown by solid lines). In
FIG. 2B
, the part shown by broken lines denotes an image to be displayed.
In case of displaying a color image, electron beams for three colors (for example, R (red), G (green), and B (blue)) as the base of the color display are used. There is a case in which the electron beam for each color is influenced by a magnetic field which is different according to color and the electron beams for respective colors do not converge on the same spot. In order to reproduce input signals on the screen of the CRT, however, the electron beams for respective colors have to converge on the same point on the screen. A phenomenon in which the positions of the electron beams for the three colors on the screen are deviated when the electron beams are deflected by a deflecting yoke is called misconvergence.
FIG. 3A
shows an image to be displayed and
FIG. 3B
shows an image accompanied by misconvergence which is actually displayed on the screen.
FIGS. 3A and 3B
illustrate a case of the misconvergence when a cross hatch signal of white is displayed on the CRT. In
FIG. 3B
, parts shown by reference numerals
100
R,
100
G, and
100
B represent images of the colors of R, G, and B, respectively. There is a case in which a distortion of the electron beam such as image distortion and misconvergence influenced by the magnetic field is, although not much, influenced by earth magnetism and arrangement of components in the apparatus.
The occurrence of the image distortion is conventionally minimized by optimizing the deflecting magnetic field generated by the deflecting yoke. In recent years, however, in association with the wider angle of the screen of a video display apparatus, a flat screen of the CRT, changes in the permissible level of the image distortion demanded by the market, the image distortion cannot be corrected with sufficient performance only by optimizing the deflecting magnetic field generated by the deflecting yoke. There are several methods of correcting the image distortion of an amount which has not been corrected by the deflecting magnetic field: one is to modulate a deflecting current passed to the deflecting yoke, and another is to modulate a signal supplied to the cathode of the electron gun. The method of modulating the deflecting current, however, requires an additional circuit for the modulation and this causes a problem of cost increase. Although a cheap circuit may be used in order to reduce the cost, there is another problem that it is difficult to perform accurate correction with a cheap circuit. With the method of modulating the signal supplied to the cathode of the electron gun, the image distortion in the same scan line, that is, in the lateral direction can be corrected, however, it is difficult to correct the image distortion in the vertical direction.
As for the correction of the misconvergence as well, basically in a manner similar to the correction of the image distortion, the electron beams of the three colors are designed to converge to the same spot with respect to the whole screen on the basis of a distribution of deflecting magnetic fields generated by the deflecting yoke. In a manner similar to the correction of the image distortion, it is difficult to perfectly correct the misconvergence by using only the distribution of the magnetic fields of the deflecting yoke. A method adopted in the related art in order to correct the misconvergence of an amount which has not been corrected in the above-mentioned manner is to converge the electron beams accurately by adding a subyoke for correction independent of the originally used deflecting yoke, and to move the electron beams for the respective colors color by color. This method, however, requires a circuit for driving the subyoke as well as the subyoke itself thus increase in resulting in the manufacturing cost.
As described above, the method of correcting the image distortion and the misconvergence by optimizing the deflecting magnetic field has been generally used in the related art. Since it is necessary to repeatedly spread the image to the whole screen in each of the horizontal and vertical directions in order to adjust the correction by the deflecting magnetic field, there are problems of the low efficiency of the work and the variation according to the adjusting persons. Therefore it is not always possible to perform optimum adjustment of the image distortion. Additional components such as a complicated deflecting coil and an adjusting mechanism make the cost of the apparatus even higher.
When image distortion and misconvergence are reduced by using the deflecting yoke, it is necessary to forcibly distort the deflecting magnetic field, so that the magnetic fields become non-uniform. In the related art, there is a problem that focusing characteristics (spot size and the like) of the electron beam deteriorate due to the distorted magnetic field, thus causing deterioration in resolution. Further, in order to correct the image distortion and the misconvergence by the deflecting yoke, a period of developing and designing the deflecting yoke is necessary. This also causes a cost increase.
In the method of adjusting the image distortion and the misconvergence, which is performed when a television receiver of a related art is manufactured, the correction amount is not so large. Therefore it is necessary to suppress variations in the assembly of the CRT and the deflecting yoke in order
Hosokawa Hiromu
Inoue Takahiro
Kato Yasunobu
Okada Masamichi
Takayanagi Yoshio
Kananen, Esq. Ronald P.
Lee Michael H.
Rader & Fishman & Grauer, PLLC
Sony Corporation
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