JPH06258249A - Stripe inspection method - Google Patents

Abstract

PURPOSE:To eliminate instability caused when a man evaluates a stripe, and control quality stably by processing image data of a sample to be inspected by a space filter having directionality in response to the stripe generating direction. CONSTITUTION:A sample 4 to be inspected having a periodic pattern such as a shadow mask is loaded on a stage 5, and is illuminated from below by lamps 7 through a diffusing plate 6, and an image of the transmitted light is picked up by a CCD camera 1. This image data is taken in a picture processing device 2, and picture processing is carried out. In this case, image data is processed by a space filter having directionality in response to the stripe generating direction. The space filter has such arrangement as distribution of a secondary differential value is obtained. Secondary differential image data obtained by shifting a constant picture element further in the stripe generating direction is added to secondary differential image data obtained by inter-image operation by shifting a picture element in the direction orthogonal to the stripe generating direction. When this processing is repeated, a feeble stripe can be inspected emphatically.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shadow mask used for a cathode ray tube for a color television, a color separation filter for a color image pickup tube, a color filter for a liquid crystal display, a mesh electrode used for an electron tube, a VDT filter, a photomask, a Fresnel lens. , A unit with a certain optical property and shape such as a lenticular lens (hereinafter unit pattern) is 1
Industrial products that are regularly and repeatedly arrayed in the two-dimensional or two-dimensional direction, or unit patterns are repeatedly arrayed while their optical properties, shapes, and array pitches in the one-dimensional and two-dimensional directions gradually change. The present invention relates to a method for inspecting existing industrial products or irregularities in the uniformity of paper, film, iron plate, coated surface (hereinafter referred to as streaks).

[0002]

2. Description of the Related Art Conventionally, in the case of streak inspection of industrial products such as thin steel plates and films as described above, a method of detecting streaks generated in a direction orthogonal to the scanning line direction or in a parallel direction is proposed. However, these methods have a problem that a precise inspection for a shadow mask or the like cannot be performed. Further, with these methods, it is difficult to inspect the detection of streaks that occur in an oblique direction, and it is the actual situation that humans visually judge.

[0003]

However, visual judgment requires a large amount of manpower, and further, individual differences occur due to differences in skill level, subjectivity of inspectors, etc., and even the same inspector is determined by physical condition and psychological state. There is a problem that there is no absolute level because there are variations.

The present invention is intended to solve the above problems and eliminates instability caused by human evaluation.
An object of the present invention is to provide a streak inspection method capable of performing a stable streak inspection of a sample with a high signal-to-noise ratio (S / N ratio) and quality control.

[0005]

DISCLOSURE OF THE INVENTION The present invention is a method for inspecting irregularity (streaks) in the uniformity of the optical properties of a sample to be inspected, which is performed by using image data of the sample to be inspected captured by an imaging device. It is characterized in that streaks are inspected on the basis of image data obtained by filtering with a spatial filter having directionality according to the streak generation direction. Further, the present invention is characterized in that the spatial filter is an array in which a distribution of the second derivative is obtained. Further, the present invention provides image data obtained by shifting the image data in a direction orthogonal to the streak generation direction generated on the image data of the sample to be inspected imaged using the imaging device, a direction opposite to the shift direction. Image data obtained by shifting to the original image data and the second derivative image data obtained by performing inter-image calculation on the original image data so as to obtain the second derivative distribution of the change in streaks It is characterized in that the secondary differential image data shifted by a certain pixel is added, and streaks are inspected by the image data obtained by repeating this processing. Further, according to the present invention, the processed image data is sliced on the basis of a threshold value to make a pass / fail judgment, and as the threshold value, the image data of the sample in which no streak is generated is subjected to a quadratic differential process and emphasized. It is characterized in that the standard deviation of the image data obtained is multiplied by a constant (standard deviation coefficient).

[0006]

According to the streak inspection method of the present invention, a weak streak in image data of an image of a sample to be inspected is emphasized and inspected. As a method for emphasizing streaks, a spatial filter having an array that can obtain a distribution of second-order differential values is used, or a second-order differential obtained by inter-image calculation by pixel shifting in the direction orthogonal to the streak generation direction. A method is used in which secondary differential image data obtained by further shifting the pixel by a constant pixel in the streak generation direction is added to the image data, and this process is repeated. In this way, streaks occurring in unspecified directions can be inspected with a high S / N ratio.
In addition, the image data in which streaks are emphasized is used as a threshold value by multiplying the standard deviation of the image data in which the streaks are not generated by the second derivative processing by the constant (standard deviation coefficient). It is possible to slice and select good products and defective products.

[0007]

EXAMPLES The present invention will be described in detail below based on examples. FIG. 1 is a diagram showing an apparatus configuration for carrying out an inspection method of the present invention, FIG. 2 is a diagram for explaining various filters used in filtering processing by a spatial filter,
FIG. 3 is a diagram for explaining processing of image data by calculation between image data. In the figure, 1 is a CCD camera, 2 is an image processing device, 3 is a monitor, 4 is a sample, 5 is a stage, 6 is a diffusion plate, 7 is a lamp, and 8 is a DC power supply.

In this embodiment, a CCD camera is used as the image pickup device. Cooled CCD as CCD camera 1
Use a camera or a regular CCD camera. Cooled type C
In the case of a CD camera, it is cooled by an electronic cooling method etc.
It is possible to perform long-time exposure in a dark area, the linearity of the video signal with respect to the integrated light amount is good, and it is possible to clearly project a dark area with high image quality. Also, when using a normal CCD camera, noise is reduced by adding image data of a plurality of frames. A sample 4 to be inspected having a periodic pattern such as a shadow mask is loaded on a stage 5, illuminated from below by a lamp 7 through a diffusion plate 6, and the transmitted light is detected by a CCD camera 1. .

In such a structure, the sample 4 is irradiated through the diffusion plate 6 by the lamp 7 driven by the DC power source 8, and the transmitted light is photographed by the CCD camera 1. In this case, the transmitted light image may be formed on the CCD camera 1 by a commonly used lens. At that time, the focus of the lens is defocused in order to remove moire generated between the pixel of the CCD camera 1 and the periodic pattern. It is also possible to directly take in the image data thus taken in to the image processing apparatus 2 and directly perform image processing, but there is an advantage that the transmittance image can be simultaneously measured by using the transmittance image as described below. That is, assuming that the image data captured without the sample is I ₁ , the image data captured with the sample is I, and the image data representing the dark current of the CCD camera is I ₀ , the transmittance T on the sample is T = It can be calculated as (I−I ₀ ) / (I ₁ −I ₀ ). Here, I, I ₀ , and I ₁ are image data at corresponding positions, and by performing this for each pixel, transmittance image data that is not affected by shading of the light source and long-term fluctuation can be obtained.

When transmitting transmittance image data with a normal CCD camera, a CCD camera with a built-in electronic shutter is used, and the electronic shutter is used as a method of setting the image pickup condition in which the sample is inserted and the image is taken in the CCD. Adjust the brightness of the light source so that it is close to the saturated exposure of the camera, then remove the sample, shorten the shutter time until the amount of light does not exceed, and close to the saturated exposure, and then open the shutter time T _C , Assuming that the shutter time at this time is T _O , the above formula of the transmittance is multiplied by T _C / T _O , and T = {(I−I ₀ ) / (I ₁ −I ₀ )} × (T _C /
A transmittance image can be obtained as T _O ). These calculations are performed by inter-image calculation after each image data is stored in the frame memory by the image processing device 2.

Next, a method for inspecting streaks using the spatial filter patterns shown in FIGS. 2A, 2B and 3 will be described. By producing the transmittance image data by the method described above and subjecting this image data to the second-order differential processing using the spatial filter, it is possible to emphasize the weak streak of the signal level. For example, the pattern of the second-order differential spatial filter in which pixels having coefficients of 2 and −1 shown in FIG.
The pattern of the second-order differential spatial filter in which pixels having coefficients of 2 and −1 shown in (b) are aligned in the vertical direction emphasizes stripes having directionality in the vertical direction, and d is the distance between elements. Shows. In addition, the pattern of the second-order differential spatial filter in which pixels having coefficients of 2 and -1 shown in FIG. 3 are diagonally arranged is to emphasize lines having directivity in an arbitrary direction θ ′ other than the vertical and horizontal directions. It is the pattern of the spatial filter that can do. By changing the inter-element distance d of each pattern shown above, the cycle of the streak to be extracted can be arbitrarily selected, and the S / N ratio of the streak inspection can be improved by enlarging the size of the filter in the X and Y directions. can do.

As a streak emphasizing method other than the filtering process using the spatial filter described above, FIG.
As shown in, the stripes 11 generated in the original image data 10
The images 12 and 13 shifted by N, −N pixels in the direction θ perpendicular to the generation direction θ ′ of the image and the original image 10 are secondarily differentiated by the inter-image calculation, and then, as shown in FIG. Two
The image 14 after the secondary differentiation is shifted by a constant pixel in the streak generation direction θ ′, and this is shifted to an image 15 (
As a second differential image), an image 15 is added to the image 14 after the second differential.
Is added, and the image 14 after the second derivative is further shifted by a certain pixel and the same addition process is repeated, whereby the second derivative images are integrated in the streak generation direction and the S / N ratio is increased to inspect the streak. It can be carried out.

In the inspection of streaks, a threshold value is set in advance to determine inspection data,
It is possible to easily select a good product or a defective product from the inspected sample. For this selection, for example, a second-order differential spatial filter is used, or the transmittance distribution of image data in which a sample having uniform periodicity with no stripes is emphasized by the emphasizing method described in FIG. After plotting, the standard deviation multiplied by a constant (standard deviation coefficient) was used as a threshold value, and the sample was inspected as threshold = standard deviation × standard deviation coefficient, and streaks were emphasized based on this threshold value. The image data of the sample to be inspected can be sliced, and the fluff that exceeds the threshold value can be binarized to select good products and defective products. It should be noted that both + and − slices are performed as the slices, and white stripes (large transmittance) can be detected in the + slices and black stripes (small transmittance) can be detected in the − slices.

[0014]

As described above, according to the present invention, it becomes possible to inspect delicate non-uniformity of various industrial products, and it is possible to improve reliability accuracy in quality control and inspection. The effect can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an apparatus configuration for carrying out an inspection method of the present invention.

FIG. 2 is a diagram showing a pattern of a spatial filter.

FIG. 3 is a diagram showing a pattern of a spatial filter.

FIG. 4 is a diagram for explaining image data processing by inter-image calculation.

[Explanation of symbols]

1 ... CCD camera, 2 ... Image processing device, 3 ... Monitor, 4
… Sample, 5… Stage, 6… Diffuser, 7… Lamp, 8…
DC current.

Claims (11)

[Claims] 1. A method for inspecting the irregularity (streaks) in the uniformity of the optical properties of a sample to be inspected, wherein the image data of the sample to be inspected captured by an image pickup device has a directivity corresponding to the streak generation direction. A streak inspection method characterized by inspecting a streak based on image data obtained by performing a filtering process with a spatial filter having. 2. The inspection method according to claim 1, wherein the image pickup means is a cooled CCD camera. 3. The inspection method according to claim 1, wherein the imaging means is an electronic shutter CCD camera, and the imaging conditions are set by controlling the exposure time by the electronic shutter. 4. The inspection method according to claim 3, wherein the image data is captured by adding the image data of a plurality of frames imaged by the image pickup means. 5. The inspected sample is a periodic pattern, and the imaging conditions of the imaging means are set so that moire does not occur between the inspected sample and the pixels of the imaging means. Inspection method. 6. The image data to be inspected is a transmittance distribution image data created by dividing the image data of image data obtained by placing an inspected sample on an inspection stage and image data obtained without placing the sample. The inspection method according to claim 1, wherein 7. The spatial filter is an array capable of obtaining a distribution of second derivative values.
The inspection method described. 8. Image data obtained by shifting the image data in a direction orthogonal to the streak generation direction generated on the image data of the sample to be inspected imaged by using an imaging device, and in the direction opposite to the shift direction. The image data obtained by shifting and the original image data are obtained by performing an inter-image operation on the second differential image data obtained by performing an inter-image operation so as to obtain a second differential value distribution of the change in streaks, and A streak inspection method characterized by adding secondary differential image data shifted by a certain number of pixels, and inspecting streaks by the image data obtained by repeating this process. 9. The streak inspection method according to claim 7, wherein the processed image data is sliced with a threshold value as a reference to determine quality. 10. The inspection method according to claim 9, wherein the threshold value is a constant (standard deviation coefficient) to a standard deviation of image data obtained by performing a second derivative process on image data of a sample in which no streak is generated. ) Is used for streak inspection method. 11. The inspection method according to claim 1, wherein the sample to be inspected is a shadow mask.