JPH02139827A - Focus adjusting circuit of color crt - Google Patents

Abstract

PURPOSE:To automate focus adjustment by differentiating the image pickup output, turning it binary, subjecting to Fourier's conversion, counting by a counter, and adjusting the point where the counter output maximizes as the optimum focal point. CONSTITUTION:Minute light emitting points are given on the screen of a color CRT 1, and a light emission pattern is photographed by an image pickup camera 3, and the image output 3b is differentiated by a differentiating circuit 4, and the differential output 4a is converted into digital signal 5a by a binary circuit 5. The digital signal 5a is added to the input of FF 6, and the output 6a becomes one of the inputs to an AND gate 7, while a sample signal CL is added to the other input to obtain a sampling output 7a. Then the output 7a is counted by a counter 8, and the output 8a is fed to a control circuit 9, which gives the next focus potential command 9a to a focus potential generating power supply 10 each time one counting is completed, and the focus potential 10a is given to the CRT 1. These operations are repeated, and the point where the output 8a of the counter 8 maximizes shall be adjusted as the optimum focal point.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus adjustment circuit for performing focus adjustment in the inspection and adjustment process of color cathode ray tubes.

[Conventional technology]

Conventionally, focus adjustment for color CRTs involves operating the color CRT under predetermined conditions, and adjusting the focus potential applied to the color CRT while visually observing the appearance of checkered or dotted light emitting patterns. [Problems to be Solved by the Invention] In the above-mentioned prior art, the setting values vary widely between adjusters because the adjustment is performed visually. In addition, in color cathode ray tubes used in information equipment such as computers, the screen ζ
In order to display fine patterns and letters, focus adjustment also targets fine lines and dots, which also poses problems from an occupational health perspective.

An object of the invention is to provide a focus adjustment circuit for a color cathode ray tube that can automate focus adjustment with a simple circuit.

[Means to solve the problem]

The above purpose is to provide an imaging means for imaging the light emission pattern of a color cathode ray tube, a differentiation circuit for differentiating this imaging output, a binarization circuit for binarizing this differential output, and a Fourier transform for Fourier transforming this binarized signal. A conversion means, a counter that counts Fourier transform outputs, a control circuit that outputs the next focus potential command each time the count signal is input and counting is completed, and a focus potential is applied to the color cathode ray tube using the focus potential command. This is achieved by adjusting the point where the counting output is maximum as the best focus point.

[Effect]

The light emission pattern is imaged with the color cathode ray tube in operation. This imaging output is differentiated, binarized, and then subjected to two-dimensional Fourier transform and counted by a counter.

Therefore, the control circuit outputs a focus potential command to the focus potential generation power source so that the count of the counter, that is, the 7-Que conversion output is maximized, and the focus potential generation source sequentially applies a varying focus potential to the color cathode ray tube. Based on the characteristics 711) obtained when the focus potential is sequentially changed in this way, adjustment can be made by setting the focus potential when the counting output of the counter reaches the maximum output as the best point and giving it as the focus potential of the color cathode ray tube.

By the way, the brightness of the light emitting surface of a color cathode ray tube reaches its maximum brightness when the focus state is the best because the spread of the electron beam is minimized. In addition, the electron beam shape of color cathode ray tubes generally spreads out with a Gaussian distribution, and there is also a hole in the shadow mask? Therefore, since the light is emitted in a sampled state, sufficient accuracy cannot be obtained simply by determining the maximum photoelectric conversion output. In this regard, the present invention eliminates sampling due to the holes in the shadow mask, and therefore has high accuracy by performing measurement after Fourier transforming the imaging output.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

As shown in Figures 1 and 2, a color cathode ray tube l
A minute light emitting point 2 is displayed on the screen ia. The light emitting pattern of this light emitting point 2 is imaged by an imaging camera 3. Here, the imaging range 3a of the imaging camera 3 is set to have a sufficient margin with respect to the light emitting point 2.

Incidentally, the actual light output distribution of the light emitting point 2 of the color cathode ray tube 1 has a spread as shown in FIG. 3, and the spread of the base increases or decreases as the focus potential changes. However, it is normal that it is non-uniform in the X%y direction. This light output distribution is originally an aggregation of the passing light P, which has passed through the hole in the shadow mask, into ~, as shown in Fig. 4.
If we look at an arbitrary scanning line field -1, light is emitted in sequence p, p, p, and if the focus potential is at the best point, the high frequency component to the passing light PI- will be maximum. In other words, it is sufficient to consider the integration of the differential output of the image in a two-dimensional area, and set the point where the output F of the following equation (1) is maximum as the best focus point.

...11) However, f: Camera output U two-step function Also, if the phosphor of the color cathode ray tube 1 and the scanning bright spot are both sufficiently small compared to the interval d between the horizontal scanning lines, then the image is This is the result of sampling with a delta function δ in the direction, and can be expressed by the following r21 formula.

g(x,y)=f(x,y)Σδ(y-nd)
−−−+21 However, f(x, y): Original image g(X, y): Output image n: 0.1.2... Since this is a multiplication of coordinate areas, Fourier transform G(u
, v) are as shown in equation (3).

G(u,v) =F(u,v)−x8(v)*
** (3) Spectrum S (spectrum of a delta function with an interval of v months or d, that is, a pulse of /d at frequency 2).

Since the spectrum of G (U, v) has a width, sampling 17 may be performed at intervals that satisfy equation (4) for the frequency band Bw of the imaging camera 3.

Bw(−...(4)) Therefore, the process of equation (1) is performed by the circuit shown in FIG.
, and perform the calculation of equation (1). This differential δX output 4a is converted by the binarization circuit 5 into a 1.0 digital signal 5a. This digital signal 5a is applied to the flip 7
0 input to the input of the flip-flop 6, and the flip-flop output 6a
becomes one input of the AND gate 7. and gate 7
The other input of is a sample signal CL that matches equation (4).
is added to obtain the sampling output cuff a. As a result, the [] circle of equation (11) is obtained.This sampling output cuff a
When counted by the counter 8, the output F of equation (1) is obtained. This count output 8a, ie, output F, is input to the control circuit 9. The control circuit 9 sends the next focus potential command 9a to the focus potential generation power source 10 every time one count is completed.
and a focus potential 10a is applied to the color cathode ray tube 1.

By repeating this operation, the point at which the count output 8a of the counter 8 becomes maximum is determined, the best focus point is determined, and the focus potential command 9a corresponding to this point is given to the color cathode ray tube.
Focus adjustment is completed by adding the best focus potential to .

In the above embodiment, a camera is used as a means for capturing an image of the color cathode ray tube 1, but this is not limited to Iζ. For example, a zero-dimensional photoelectric conversion element such as a photodiode is used to capture the light emitted from the color cathode ray tube Similar results can be obtained even if the surface is made to emit light in an area larger than that covering the photoelectric conversion element. In this case, a signal source, a video circuit, etc. for creating a minute light emitting point can be omitted.

〔Effect of the invention〕

According to the present invention, focus adjustment can be automated with a simple circuit. Furthermore, the adjustment accuracy can be reduced to less than IOV with respect to a focus potential of about 7 KV, for example, and the accuracy is significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a focus adjustment circuit according to an embodiment of the present invention, FIG. 2 is a front view of a color cathode ray tube screen, and FIGS. 3 and 4 are illustrations of light emitting points. 1... Color cathode ray tube, 2... Luminous point, 3...
...Image camera, 4...Differential circuit, 5...
・Binarization circuit, 6...Clip flop. 7...AND gate, 8...Counter, 9...Control circuit, 10...Focus potential generation power supply. Figure 1 Agent: Patent Attorney Katsutoshi Ogawa iAl・'-5゛'

Claims (1)

[Claims] 1. An imaging means for imaging the light emission pattern of a color cathode ray tube, a differentiation circuit for differentiating this imaging output, a binarization circuit for binarizing this differential output, and a Fourier transformation means for Fourier transforming this binarized signal. , a counter that counts the Fourier transform output, a control circuit that outputs the next focus potential command every time this count signal is input and counting is completed, and a focus potential that applies a focus potential to the color cathode ray tube based on this focus potential command. A focus adjustment circuit for a color cathode ray tube, characterized in that the circuit is equipped with a power source and adjusts the point at which the counting output is maximum as the best focus point.