JPH08247954A - Measuring method of optical distortion - Google Patents

Abstract

PURPOSE: To enable measurement of a dynamic distortion conforming to human sensitivity by changing the position of a subject to a light source and an image sensor relatively to use images before and after passing through a boundary edge part between a diffused light part and a light shielding part. CONSTITUTION: An object 2 to be measured is moved in the direction A and images on two screens before and after a distortion of an object 2 to be measured passes through a boundary edge 20 between a diffused light part 1a and a light shielding part 1b of a light source 1 are taken by an image sensor 3. Image signals obtained by the element 3 are processed and computed by an image processor 4. In other words, an absolute value of a difference is determined between image information on the two screens before and after the passage. Here, when no distortion exists, the level of the quantity of light is constant and when a distortion exists, a signal change P is presented for the distortion. The features such as size, shape of the change P are utilized and combined to evaluate a dynamic distortion quantitatively. This enables measuring and evaluating of an optical distortion quantitatively using an index closer to human sensitivity handily.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical strain measuring method for inspecting and evaluating the strain of a glass plate or the like.

[0002]

2. Description of the Related Art Conventionally, in the case of measuring optical strain, a sensory test by an inspector or a deformation amount of a lattice pattern (Japanese Patent Laid-Open No. Hei 3)
-199946) and the degree of pattern blurring (Japanese Patent Laid-Open No. 7-20059).

[0003]

However, in the sensory test by the inspector, it is difficult to obtain an objective index due to individual differences. Further, in the examples of the two methods described in the above-mentioned publication, the strain is measured in a static state where the positions of the glass, the pattern, the imaging device, etc. are fixed. On the other hand, people feel distortion more strongly with moving objects. Since the measurement by these methods is static, there is a possibility that the human sensory amount does not match the measurement value of these methods. Further, even when the static strain measuring method is used, it is necessary to confirm the correlation with the dynamic strain measuring method which is more likely to match the human sensory amount.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a method for measuring optical strain which enables dynamic strain measurement in conformity with human sensory quantities.

[0005]

To achieve the above object, in the present invention, light from a surface light source consisting of a light-shielding portion and a diffused light portion is transmitted through an object to be measured or reflected by the object to be measured. In an optical distortion measuring method for imaging with an image sensor, an image before a measured part passes through an edge part of a boundary between a diffused light part and a light shielding part while changing a position of a measured object relative to a light source and an image sensor. Disclosed is a method for measuring optical strain, which comprises measuring the strain using the image and a subsequent image.

In a preferred embodiment, the distortion is measured by using the difference between the image information before passing through the edge portion and the image information after passing through the edge portion or the absolute value of the difference.

A further preferred embodiment is characterized in that a wide range of measurement can be performed at the same time by using a light source in which the edge portion is spread and distributed in the surface of the surface light source.

In still another preferred embodiment, the light source in which the light shielding portion and the diffused light portion are alternately continuous in a stripe shape is used, and the measurement is performed while the object to be measured is relatively moved in the direction crossing the stripe. It is characterized by that.

In yet another preferred embodiment, the distortion is measured by using the addition result of the image information before passing through the edge portion and the image information after passing through the edge portion.

In another preferred embodiment, the distortion is measured by utilizing the blur of the edge portion in the addition result.

In still another preferred embodiment, in the optical distortion measuring method, the addition result image is differentiated and the differential image of the addition result image in the portion where the distortion is to be measured is used as a method for evaluating the blur of the edge portion. It is characterized in that the optical distortion is measured and evaluated by comparing with the differential image of the addition result image in the normal portion without distortion.

In still another preferred embodiment, in the differential result of the addition result image, the optical distortion is measured and evaluated by the reduction amount of the differential value of the boundary edge of the distorted portion with respect to the normal portion. .

In still another preferred embodiment, the amount of movement of the edge when the assumed distortion passes or the exposure time of the image pickup element according to the moving object to be inspected and the black and white stripes of the light source. It is characterized by measuring the strength of distortion by adjusting the pitch and decreasing the contrast of black and white.

[0014]

In the present invention, when the optical strain is measured,
In a method for measuring optical distortion, in which light from a surface light source having a light-shielding portion and a diffused light portion is transmitted through a measurement object or reflected by the measurement object and is imaged by an image sensor, an object to be measured for the light source and the image sensor is measured. The relative position is changed, and the optical distortion is measured by using the absolute value of the difference between the image information before and after the image information passes through the edge portion of the boundary between the diffused light portion and the light shielding portion. ing. Therefore, the sensitivity is high in a dynamic situation, which is close to the human sense of the strain, and the measurement can be performed using the dynamic change of the pattern due to the strain as an index.
Further, by using a patterned light source such as a stripe or a checker pattern in which the edge portion of the boundary between the diffused light portion and the light shielding portion spreads in the light source surface, it is possible to simultaneously measure the optical distortion in a wide range.

The evaluation based on the addition result corresponds to the measurement of the blur of the pattern due to the object to be measured. Further, although the description has been made of the addition of images, the present invention can also be realized by continuous imaging by long-time exposure while the distortion passes through the edge portion.

As a method of relatively moving the object to be inspected (object to be measured), it is possible to realize it by moving the object to be inspected, or by moving the image sensor and the light source at the same time, using a combination of mirrors, or the like. The same effect can be expected.

According to the present invention, it is possible to measure a dynamic strain that matches a human functional amount, and the measurement result is measured by the method of the present invention even for other simple static strain measuring methods. By comparing the results with the results, it is possible to prove the usefulness of the measuring method. Further, the measuring method of the present invention also enables the measurement of the shape of the object to be measured.

[0018]

EXAMPLE An example of the present invention will be described below. FIG. 1 is a structural explanatory view of an optical distortion measuring apparatus according to the present invention, in which 1 is a light source having a diffused light portion 1a and a light shielding portion 1b,
Reference numeral 2 is an object to be measured such as a glass plate, 3 is an image pickup device such as a camera, and 4 is an image processing device for processing and calculating a signal obtained from the image pickup device 3. In this state, the DUT 2 is moved in the direction of the arrow A, and the edge 20 of the boundary between the diffused light portion 1a and the light shielding portion 1b of the light source 1 is distorted (not shown) in the DUT 2.
Detects images on two screens before and after passing.

FIG. 2 is an explanatory diagram of an image example obtained in the embodiment of the present invention. The figure (A) shows the case where the DUT 2 is not distorted, and images 5 and 6 are images before and after an arbitrary position of the DUT 2 passes through the edge of the light source. The images 5 and 6 are bright portions 5a and 6a and dark portions 5b corresponding to the diffused light portion 1a and the light shielding portion 1b of the light source 1, respectively.
6b respectively. (B) shows the case where the DUT 2 has a point distortion, and the image 7 is an image before the point distortion passes through the edge 20 of the boundary between the diffused light portion 1a and the light shielding portion 1b, Image 8 is the image after passing. The bright portions 7a and 8a and the dark portions 7b and 8b of the images 7 and 8 correspond to the diffused light portion 1a and the light shielding portion 1b of the light source 1, respectively.

The absolute value of the difference between the image information of two images using these is shown in FIG. In this example, the brightness of the image is taken as a signal as the image information, and the difference between the signals is used. Image 9 is a processed image of images 5 and 6 when the object to be measured has no distortion, and image 10 is a processed image of images 7 and 8 when there is point-like distortion.

As shown in FIG. 3B, when there is a point distortion, a bright portion 10a appears in the processed image 10 corresponding to the distortion. That is, when there is no distortion, the signal level of the image 6 is subtracted from the signal level of the image 5 of FIG. 2A to obtain the difference, and the difference between the bright portions 5a and 6a and the dark portions 5b and 6b in the image is calculated. 3A and FIG.
As shown in (A), an image of a signal having a constant level is obtained.

On the other hand, if there is distortion, the difference between the signal level of the image 7 and the signal level of the image 8 of FIG. On the other hand, in the central portion corresponding to the distortion, one is a bright portion and the other is a dark portion, so that the signal difference (or its absolute value) is larger than that of the surrounding portion. Therefore, a change in the signal level corresponding to the distortion is detected as indicated by the bright portion 10a in FIG. 3B and the signal change P in FIG. 4B.

FIG. 3C is a diagram of a processed image when the DUT 2 has a linear distortion parallel to the boundary edge 20 of the light source. In this case, the position of the edge shifts left and right on the image before and after the linear distortion passes through the boundary edge. An image 11 as shown in FIG. 7C is obtained by performing image processing based on the absolute value of the difference between these shifted image signals.

4 (A) and 4 (B) are respectively shown in FIG.
The amounts of light on the lines AA ′ and BB ′ of (A) and (B) are shown.

As shown in the figure, when there is no distortion shown in (A), the light intensity level is constant, whereas when there is distortion shown in (B), the signal changes corresponding to this distortion. P appears.

Using the characteristics such as the size and shape of the signal change P due to this distortion, the dynamic distortion is quantitatively evaluated in combination.

FIG. 5 shows another embodiment of the present invention, 15
Is a light source that has a diffused light portion 15a and a light shielding portion 15b alternately in stripes, 2 is an object to be inspected, 3 is an image sensor such as a camera, and 4 is an image processing device that processes and calculates a signal obtained from the image sensor 3. Is. In this state, the inspection object 2 is moved in the direction of arrow A in the figure for measurement. In the embodiment using this stripe pattern light source, the edge 20 between the diffused light portion 15a and the light shielding portion 15b of the light source 15 is spread and distributed in the plane, so that a wide range of the object to be measured can be measured at the same time. It is possible to

The light source 15 does not have to be a stripe pattern, but any light source such as a checker pattern having a wide distribution in the light source surface and having a boundary edge between a large number of diffused light portions and light shielding portions can be used. A light source having a different pattern may be used.

In practice, using the structure shown in FIG. 5, a checker pattern light source is used and a CCD camera is used as an image pickup element.
The measurement was carried out on a glass containing streaky perspective distortion as an object to be measured. The f55 lens is used as the optical system, 400 mm from the lens to the glass, and 5 from the lens to the light source.
An arrangement of 50 mm was used. The pitch of the checkered pattern is 4.5 mm, and the gradation value based on the brightness of the light source part is 20
0, the gradation value of the light-shielded portion is 30. At this time, when the absolute value of the difference between the two images obtained before and after moving the glass by about one pitch is calculated, the most distorted part has a gradation value of 180, and the undistorted part has a gradation value of The maximum value was 11, and it was possible to evaluate the strength of dynamic strain by this value.

FIG. 6 shows an embodiment in which the present invention is applied to the distortion measurement of a reflection image. Also in this case, the optical strain can be measured by moving the DUT 2 in the direction of arrow A and performing the same process. Further, the light source 1 can also be realized by a stripe pattern, a checker pattern, or the like, as in the case of measuring the perspective distortion.

Next, another embodiment of the present invention will be described. In this embodiment, the inspected object 2 is moved in the direction of the arrow A by using the apparatus shown in FIG. 1 to perform continuous imaging while the distortion passes, and the image information is added or averaged. In this case, the image screens may be simply combined, the brightness of the image may be taken as a signal, and both may be added.
Further, image information before and after passing may be added by performing long-time exposure before and after passing. Also,
As the front and back information, one image may be captured for each, or a plurality of images may be captured for each. By dividing by the number of times of imaging in this way, the average of image information can be obtained.

FIG. 7 is an explanatory view of an example of an image obtained in this embodiment. As in FIG. 2, images 5'and 6'are when the object 2 is not distorted, and image 7'is a dot-like image. Distortion is light source 1
Before passing through the edge 20 of the image 8 ′ is an image after passing. FIG. 8 shows the results obtained by adding these images or continuously picking up and processing the images between them. An image 9 ′ of FIG. 8A is a processed image of the object 2 under measurement without distortion (images 5 ′ and 6 ′ of FIG. 7), and an image 10 ′ of FIG. 8B. Is a processed image (images 7 ′ and 8 ′ in FIG. 7) in the case of dot distortion.

An image 11 'in FIG. 8C is a processed image when the object 2 to be measured has a linear distortion parallel to the boundary edge 20 of the light source, as in FIG. 3C.

FIGS. 9 (A) and 9 (B) show the amounts of light in the cross sections taken along the lines AA 'and BB' of the images 9'and 10 'in FIG. 8, respectively. (A) is the light quantity when there is no distortion, and the light quantity when there is distortion in (B) is such that the gradient of Q corresponding to the edge becomes gentle and a flat portion is generated. There are also things. Quantitative evaluation of the dynamic strain intensity is performed based on the degree of change in the edge gradient. As those specific methods, the image 9'of FIG.
Images 15 and 16 in FIG. 10 are obtained by spatially differentiating the added image corresponding to 10 ′. The graph of FIG. 11A shows the CC ′ cross section of the image 15, and the graph of FIG. 11A shows the DD ′ cross section of the image 16.
It is a graph of (B). When there is no distortion, Fig. 11 (A)
A portion having a high calculation result corresponding to the edge indicated by R appears. This is the white part 15 in the center of the image 15 in FIG.
Corresponding to the thinning of a, the differential value is shown in FIG.
The value corresponding to R of 1 (A) is also high. On the other hand, in the image 16 in the case where there is a point-like distortion, the area having a high value corresponding to the distorted portion is wider than the area in the case where there is no distortion, and as shown by S in FIG. The value is low and the central part is dented. The dynamic strain intensity can be quantitatively evaluated by the degree of decrease of the differential value of the measured object with respect to the differential value of the normal part.

That is, when there is no distortion, when the signals of the images 5'and 6'in FIG. 7 (A) are added, the bright and dark portions are added together, and the level difference becomes large, resulting in the level difference in FIG. 8 (A). As shown in the image 9 ′ and FIG. 9 (A), a difference between the bright portion and the dark portion occurs.

If there is distortion, the image 7'of FIG.
By adding 8'and 8 ', the level difference similar to the case where there is no distortion occurs in the part other than the part corresponding to the distortion in the central part, whereas in the central part corresponding to the distortion, one is a bright part and one is a dark part. Therefore, the added level is low. Therefore, FIG.
As shown in (B), the smooth portion Q of the signal level change
Occurs.

Actually, using the configuration shown in FIG. 1, a CCD camera was used as an image pickup device, and a glass containing streaky perspective distortion was measured as an object to be measured. F55 as an optical system
250mm from the lens to the glass,
An arrangement of 400 mm from the lens to the light source was used. The gradation value corresponding to the light amount of the light source portion is 200, and the gradation value of the light shielding portion is 30. At this time, when the glass is moved to such an extent that distortion passes through the edge of the boundary between the diffused light portion and the light shielding portion, and the average of eight images obtained continuously during that time is used as the original image to perform the differential operation, it is equivalent to the edge. There was a decrease in the value due to the distortion in the part with a high calculation result. The value was 98 for the strained portion and 122 for the unstrained portion, and it was possible to evaluate the dynamic strain strength by this value.

Also in this embodiment, similarly to the above-mentioned embodiments, it is possible to use the stripe light source or the checker pattern light source of FIG. 5 or the reflection type measuring method of FIG.

[0039]

By carrying out the present invention, it is possible to quantitatively measure and evaluate optical strain easily by using an index close to human sensitivity in a short time, and it is possible to perform a large amount of evaluation and in-process inspection. .

[Brief description of drawings]

FIG. 1 is a structural explanatory view of an apparatus for carrying out a method for measuring a perspective distortion of a translucent object according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an image example obtained in the embodiment of the present invention.

FIG. 3 is an explanatory diagram related to processing of an image obtained in an example of the present invention.

FIG. 4 is a graph relating to processing of an image obtained in an example of the present invention.

FIG. 5 is a structural explanatory view of an apparatus for carrying out the method for measuring the perspective distortion of a transparent object according to another embodiment of the present invention.

FIG. 6 is a structural explanatory view for carrying out a reflection type strain measuring method according to still another embodiment of the present invention.

FIG. 7 is an image example diagram for explaining another embodiment of the present invention.

FIG. 8 is an explanatory diagram related to processing of an image obtained in another embodiment of the present invention.

FIG. 9 is a graph relating to processing of an image obtained in another example of the present invention.

FIG. 10 is an explanatory diagram related to processing of an image obtained in another embodiment of the present invention.

FIG. 11 is a graph relating to processing of an image obtained in another example of the present invention.

[Explanation of symbols]

1: Light source 1a: Diffused light part 1b: Light-shielding part 2: Object to be measured 3: Image sensor 4: Image processing device 5, 6, 5 ', 6': Detection image when the object to be measured has no optical distortion 7, 8, 7 ', 8': Detected image when the object to be measured has point-like optical distortion 9, 9 ': Processing result when there is no optical distortion 10, 10': Processing when there is point-like optical distortion Result 11, 11 ': Processing result when linear optical distortion is present 20: Edge

Claims (9)

[Claims] 1. A method for measuring optical distortion, wherein light from a surface light source composed of a light shielding part and a diffused light part is transmitted through a measurement object or reflected by the measurement object and imaged by an image sensor,
The distortion is measured using an image before and after the measured portion passes through the edge portion of the boundary between the diffused light portion and the light shielding portion while changing the position of the measured object relative to the light source and the image sensor. A method for measuring optical distortion, which is characterized in that 2. The optical distortion according to claim 1, wherein the distortion is measured using the difference between the image information before passing through the edge portion and the image information after passing through the edge portion or the absolute value of the difference. Measuring method. 3. The method for measuring optical strain according to claim 1, wherein a light source in which the edge portion is distributed in a plane of a surface light source is used to simultaneously measure a wide range. 4. The measurement is performed by using a light source in which the light-shielding portion and the diffused light portion are alternately continuous in a stripe shape, while the object to be measured is relatively moved in a direction crossing the stripe. 3. The method for measuring optical strain according to item 3. 5. The optical distortion measuring method according to claim 1, wherein distortion is measured by using a result of addition of image information before passing through the edge portion and image information after passing through the edge portion. 6. The optical distortion measuring method according to claim 5, wherein the distortion is measured by utilizing the blur of the edge portion in the addition result. 7. In the optical distortion measuring method, as an edge blurring evaluation method, an addition result image is differentiated, and a differential image of an addition result image in a portion where distortion is desired to be measured is added in a normal portion without distortion. The optical distortion measuring method according to claim 6, wherein the optical distortion is measured and evaluated by comparing the resultant image with a differential image. 8. The optical distortion is measured and evaluated by the amount of decrease in the differential value of the boundary edge of the distorted portion with respect to the normal portion in the differential result of the addition result image.
The method for measuring optical strain according to. 9. A black-and-white image is obtained by adjusting the amount of edge movement when an assumed distortion passes or the exposure time of an image pickup element according to the moving object to be inspected and the pitch of a black-and-white stripe of a light source. The method for measuring optical strain according to claim 4, wherein the intensity of the strain is measured by decreasing the contrast.