JPH0937310A - Method for inspecting luminance uneveness of color cathod-ray tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly accurately detect and evaluate fine uneven stripes generated at the time of exposing and forming phosphor dots on a color cathod-ray tube(CRT) independently of luminance grading. SOLUTION: A panel 5 to be inspected is illuminated by an illumination board and photographed by a telecamera 7. The picked-up image is converted into one-dimensional data by projection processing and then a secondary differential value is obtained. Detection and evaluation are executed based upon the secondary differential value and the contrast calculated from the secondary differential value. Since fine uneven stripes can be detected by this processing independently of luminance grading, the quality of a product can be improved and stabilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting brightness unevenness of a color cathode ray tube, and more particularly to a method for quantitatively evaluating "streak unevenness" that occurs when fluorescent dots are formed by exposure.

[0002]

2. Description of the Related Art In many cases, the brightness unevenness inspection of a color cathode ray tube is performed by visual inspection. An example of automatic inspection is for a liquid crystal display, but it is disclosed in Japanese Patent Laid-Open No. 193271/1990. And the captured image,
There is a method in which unevenness is detected based on a difference in brightness from an image obtained by shifting the image in a predetermined direction. However, unlike a liquid crystal display, the color cathode-ray tube has a brightness value at the four corners of about 50 to 80% of the middle history, a large brightness grading, and when the image is shifted, a difference in the brightness value appears even in the normal part. It becomes difficult to detect uneven defects.

[0003]

A typical unevenness in brightness of a color cathode ray tube is "streak unevenness" that occurs when red, green, and blue phosphor dots are formed by exposure. In the exposure, a light source is placed on a portion corresponding to an electron gun on an exposure table, a shadow mask is placed near a panel forming a phosphor, and a continuous lens and a discontinuous lens are called between the light source and the shadow mask. Put the corrective lens of the seed. Exposure is performed by refracting the light rays by these two types of lenses to approximate the actual electron beam trajectory. However, since the discontinuous lens is divided by a plurality of blocks, the grid-like dark line pattern of the discontinuous boundary surface may be exposed on the photosensitive film, resulting in "streaking". The streak is generated in the vertical or horizontal direction of the display screen, and the direction is fixed, but it is weak and difficult to detect. In particular, the color cathode ray tube has 50 to 80% of the center of the screen at the four corners of the screen, which is called brightness grading.
It is about the brightness, and if you simply differentiate it,
The differential output due to luminance grading is larger than the differential output of the streak, and the streak cannot be detected. In addition, since there are various thicknesses of streaks, it is necessary to have a detection / evaluation method capable of coping with this.

[0004]

[Means for Solving the Problems] Tube brightness data captured by a television camera or the like is added in the horizontal and vertical directions,
A so-called projection process is performed. As a result, random noise is reduced, and faint unevenness can be emphasized. The result of this projection processing includes luminance grading, but in the streak area, the slope of increase or decrease is different.
It can be detected accurately. That is, even if the projection value increases monotonically, if the rate of increase is locally low,
That part appears "dark" to the human eye and is recognized as a streak. Therefore, not the first derivative but the second derivative value is in good agreement with the visual evaluation result.

Since there are various widths of the streak,
Plural kinds of section widths are prepared when obtaining the secondary differential value.

[0006]

FIG. 1 shows the streak unevenness and the processing principle. The image pickup screen 4 is an image of a part of the tube surface of the inspected cathode ray tube taken by a television camera, and is an example in which three streak lines 1 are present. In this example, the projection value 2 including the brightness grading can be obtained by performing the projection process in the vertical direction. Where the projection value is 2 and the rate of increase is lower than that of the surrounding area, it is the streak portion, and the second derivative processing result 3 is obtained, and the streak portion can be detected and evaluated.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the objects to be inspected are the state of a panel that has been coated with a phosphor and exposed, and the state of a finished product that has been attached with an electron gun and exhausted. When finished, a white raster is displayed on the screen for inspection. Hereinafter, in this embodiment, the inspection in the state of the panel will be described, but the processing method is exactly the same for both inspection targets.

FIG. 2 shows the entire structure of the panel in the inspection. The exposed panel 5 to be inspected is set on the illumination table 6. Inside the lighting stand 6, there is a fluorescent lamp,
The panel 5 to be inspected is displayed in white.

The television camera 7 picks up an image of the panel 5 to be inspected, and the output signal thereof is digitized by the AD converter 8 and stored in the image memory 9. The content of the image memory 9 is analyzed by the computer 10 to detect and evaluate streaks.

FIG. 3 shows the overall configuration of processing in the computer 10. The image obtained by the television camera 7 is converted into one-dimensional data by performing the projection process 11. Next, the second-order differential processing 12 is performed on the one-dimensional data to detect the streak uneven part. The contrast calculation 13 for unevenness is performed, and the quality determination 14 is performed by comparing with the standard value.

The details of the processing will be described below with reference to FIG. There is a streak 1 in the imaged screen 4. The number of pixels in the vertical direction of the imaging screen 4 is 1, and the projection process 11 in the vertical direction is performed. At this time, P (x) where the projection value is 2 is (Equation 1) when the luminance image data is expressed as f (x, y).

[0012]

[Equation 1]

Next, for the projection value 2, the secondary differential value ΔP is calculated by the following equation.

[0014]

[Equation 2]

In (Equation 2), the section width d determines an appropriate value depending on the thickness of the line to be detected.

Next, the contrast C (x) is calculated by the following equation.

[0017]

(Equation 3)

The contrast C (x) enables quantitative evaluation of the strength of streaking. Next, by comparing with the standard value Co, C
If it is larger than o, it is determined to be defective.

FIG. 5 shows an example in which there are various thicknesses of the streak. In this example, three types of section widths d are prepared, the secondary differential value is obtained for each section width, and the quality judgment is performed.
In FIG. 5, for example, when d = d ₁ , the thinnest streak can be detected, when d = d ₂ , an intermediate thickness can be detected, and when d = d ₃ , the thickest streak can be detected. The final judgment is these d _{1 to} d _3.
Integrate the results in.

In this embodiment, the vertical streak is described as an example, but since streaking may occur in the horizontal direction, the above method is also performed in the horizontal direction.

[0021]

According to the present invention, it has been difficult until now,
Even in the presence of brightness grading, weak streaks can be detected and evaluated, which has the effect of improving product performance and stabilizing quality.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of a streak unevenness detecting method.

FIG. 2 is a block diagram of the entire apparatus according to the present invention.

FIG. 3 is a processing flowchart of streak unevenness detection / evaluation.

FIG. 4 is a diagram illustrating a method of obtaining a secondary differential value of a projection value.

FIG. 5 is a diagram illustrating a method of detecting streak unevenness of various thicknesses.

[Explanation of symbols]

1 ... Streaks, 2 ... Projection value, 3 ... Second derivative value 4 ... Imaging screen, 5 ... Inspected panel, 6 ... Illumination stand, 7 ... Television camera, 10 ... Computer

Front Page Continuation (72) Inventor Takashi Nishiguchi 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Stock Engineering Co., Ltd.

Claims (2)

[Claims] 1. In a picture quality inspection of a color cathode ray tube, a light emitting surface is imaged by a television camera, and a second-order differential value of a luminance value is obtained with respect to a result of projection processing of the luminance in the direction of the streak defect. By evaluating the strength of the lines,
A brightness unevenness inspection method that enables quantitative evaluation of streak unevenness that matches visual evaluation. 2. When the second derivative is performed in claim 1,
Luminance unevenness inspection method that enables quantitative evaluation of streak strength regardless of the streak thickness by using multiple types of section widths for differential operations.