JPH01195351A - Measuring method for crack on surface of concrete - Google Patents

Abstract

PURPOSE:To execute the measurement in a short time and exactly by calculating a suitable threshold level from an image of concrete to be measured, making a binary image consisting of white and black picture elements by setting said level as a boundary, eliminating a contaminated image and measuring a coordinate and a number of the black picture element. CONSTITUTION:A surface image of concrete 1 to be measured is stored in a computer 4 as a gradation value D by a high resolution line sensor 3. Subsequently, a suitable threshold level T is calculated as a reference for discriminating a crack and others, and a binary image consisting of a white picture element in which the value D is above the value T and a black picture element in which the value D is under the value T is formed. Next, from this image, a black part in which the number of black picture elements is small and a black part whose length and breadth are small and hot linear are eliminated. Thereafter, by a coordinate and a number of the black picture element, width and length of a crack measured. In such a way, a measurement of the crack is executed in a short time and exactly, and also, the accuracy of the measurement is raised and time aging can be caught surely.

Description

[Detailed Description of the Invention] 1) The present invention relates to a method for measuring cracks on a concrete surface.
In particular, it relates to a method for measuring the pattern, width, and length of cracks on concrete surfaces using image processing technology.

Measuring cracks on concrete surfaces is necessary for investigating and diagnosing concrete structures. Investigation items regarding cracks on the concrete surface include crack patterns, widths, lengths, and changes in these over time. Crack pattern investigation involves visually observing and recording the form of cracks on the concrete surface, and serves as data for analysis such as when they occur, whether they are regular, and the cause of the cracks.

Crack width is the dimension measured perpendicular to the length direction of the crack on the concrete surface using a crack scale, loupe, etc., and investigating the crack width is used to estimate the cause of the crack,
According to the Japan Concrete Institute's "Guidelines for Concrete Crack Investigation, Repair and Reinforcement," which serve as materials for determining whether repair/reinforcement is necessary and selecting repair/reinforcement methods, the crack width limit is 0 in terms of durability
．． 1) 0.05 ffIm is proposed in terms of waterproofness.

Crack length surveys are primarily used to determine the scale (range, etc.) of repairs and reinforcement and to provide information for calculating construction costs.

Investigation of changes in crack width over time, that is, changes in crack width, is important data for estimating the cause of cracks and selecting repair/reinforcement methods.

The conventional method for measuring cracks on concrete surfaces involves making sketches by visual observation or photographs, and measuring with a regular scale, a crack scale, a magnifying glass, etc.;
) It requires a lot of manpower and time, and (b) it is difficult to accurately measure the L pattern, width, and length.

One object of the present invention is to provide a method for measuring concrete surface cracks by computer-based image processing technology, thereby solving the above-mentioned problems of the prior art.

1-III+87 1- Referring to FIGS. 1 and 2, according to the method for measuring concrete surface cracks of the present invention, the concrete surface to be measured)
An image of the surface of the pixel 1 is stored in the computer 4 by a high-resolution line sensor 3 or the like as a gradation value D (FIG. 3) proportional to the brightness of the pixel.

Preferably, the concrete to be measured 1 is a photograph of the concrete surface to be measured 411. More preferably, the concrete to be covered 411 is illuminated by a suitable light source 2.

FIG. 3 shows, as an example of the gradation value, 25 of 0-255, which is generated by the high-resolution line sensor 3 in proportion to the brightness of the pixel.
A gray value signal having six gradations is shown.

As is clear from FIGS. 3 and 4, the gradation values of the surface image of the concrete to be measured 1 include values representing things other than cracks 1O. According to the invention, crack l
As a standard for distinguishing the r&'JL value of O from the shading value representing something other than crack 10, an appropriate threshold T is calculated for the shading value of the above pixel. A binary image is created from the image, consisting of white pixels whose gradation value is equal to or greater than a threshold value T and black pixels whose gradation value is less than a threshold value 1. Furthermore, the non-linear black pixel portion is defined by the fact that the number of black pixels corresponding to the area is very small, or the vertical and horizontal length I
Eliminated on the basis that IX, Qy (Figure 6) are very short. Finally, the width and length of the crack are measured using the coordinates and number of black pixels.

1'' The operation of the method for measuring concrete surface cracks of the present invention will be explained with reference to the case of measuring cracks 10 in FIG. The gray scale image of FIG. 4 showing the concrete surface contains many things that show things other than cracks 1O. As a result of various experimental studies, the present inventor selected an appropriate threshold T (=f(D)) based on the distribution of gradation values in the image,
It has been found that if the gradation values are binarized using the threshold value T, it is possible to separate the crack lO and an image close to the crack. In the case of the concrete surface image shown in FIG. 4 based on the 256-gradation scale described above, an appropriate threshold value T can be determined using the following equation.

T=f(D)=A−N −−” (1
) Here, A is the average value of the grayscale values in the image, and N is a constant between 5 and 1O. In the example shown in FIG. 3, good results were obtained by setting T=leO. In order to extract even the smallest cracks, it is necessary to choose a large 24rti T.

If we change the image in Figure 4 to an image consisting of white pixels whose gray level is less than the threshold T - L in equation (1) and black pixels whose gray level is less than the dark value 1, we get the image shown in Figure 5. Cracks like +, l 10
It is possible to create a binary image in which dirt and stains similar to those are extracted.

In order to separate dirt from the binary image in Figure 5, crack 1
Consider G as "a linear black part with a length close to one side of the image" and remove the following:

i) A black area with a very small area, that is, a very small number of black pixels; ii) A black area with a very small number of black pixels; ii) Even if the area is large, the vertical and horizontal dimensions are small (non-linear, i.e., Q!) as shown in Figure 6. and 1! A black portion where y is very small. An image after this processing is shown in FIG.

If the concrete surface is only slightly soiled, only the crack image remains at a stage corresponding to FIG. 7, so the width and length of the crack can be measured by the coordinates and number of black pixels.

A dirt separation method based on changes in shading will be explained below. When the binarized image of FIG. 7 is subjected to line thinning processing that leaves only the center of the width of the black portion, the result is as shown in FIG. 8. In FIG. 8, if a branch J where three or more thin lines intersect is removed, the image becomes a collection of individual point portions S having one starting point and one ending point, as shown in FIG. 9. As shown in Figure 10, each individual point part S
Identify each one by assigning a number to it.

The inventor of the present invention discovered the fact that the variation range ΔD of the gradation value in the crack 10 is within a certain range through experiments, that is, 2 of L.
It has been found that in the case of a gradation value having 56 gradations, the variation width ΔD is within the range of 5-10. For each individual point portion S, it is inspected whether the L change width ΔD in the C light value image recorded first is within the range of that of the crack 10, and individual point portions S outside the range are removed. It will look like the figure. If the branch parts J removed earlier from Fig. 8 that fit into the remaining point parts S in Fig. 11 are restored, the result will be as shown in Fig. 12. When the black pixels other than the center removed from FIG. 7 are restored for the branch J, the result is as shown in FIG. 13. In this way, it is possible to remove stains with a large variation range ΔD in the gradation value.

Once the processing up to FIG. 13 is completed, it is possible to output a hard copy of the crack pattern from the computer 4 using, for example, a plotter 5 at any time, and furthermore, the measurement results of the width and length of the crack can be outputted from the computer 4 using, for example, a printer 6.
It can be output as a histogram as shown in Figure 4.

In the examples shown in FIGS. 3 to 14, a 2000×3000 pixel high-resolution line sensor 3 in FIG. 2 was used. Further, as the concrete to be measured 1, a photograph of a concrete surface taken at a size such that an actual crack with a width of about 0.1 +u+ could be identified by the high-resolution line sensor 3 was used.

If a wide area of the concrete surface is photographed on a small film, it will be difficult to identify cracks that actually exist on the film image even with the resolution of the high-resolution line sensor 3. Although cracks can be easily identified by photographing them, the amount of film required and the effort involved in photographing them increase.

The computer 4 has an image memory that can store 8 screens of 1024 x 1024 pixels and a main memory of 4M.
A mini-computer with Byte was used. Furthermore, a magnetic disk Et8MB x 2 was used as an external memory.

As explained above, the method for measuring concrete surface cracks according to the present invention uses computer image processing technology to calculate 7-values consisting of white pixels and black pixels with an appropriate threshold value as the boundary based on the gray value image of the concrete surface to be measured. An image is created, images of dirt other than cracks are removed as necessary, and the width and length of the crack are measured based on the coordinates and number of black pixels, so the first-order effect is achieved.

(a) Cracks can be measured easily within a short time.

(b) The accuracy of crack measurement can be improved.

(c) Changes in the crack t1 over time can be reliably captured.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the procedure of the method of the present invention, Fig. 2 is an explanatory diagram of the apparatus used in the method of the present invention, Fig. 3 is a grayscale signal showing the gray level signal and its darkness value, and Figs. 4 to 14 The foregoing are explanatory diagrams of one embodiment. 1. Concrete to be measured, 2. Light source,
3...High resolution line sensor, 4...Computer, 5...Plotter, 6...Printer,
10...Crack, J...Branch, S...
・Individual point part. 1 = :l> 2 I C1→3 1 This, τ4 Figure Figure 5 60 -1×→ Figure 7 - (Figure 8 Figure 9 Figure 10 Figure 11 Figure 12

Claims (2)

[Claims] (1) Storing an image of the concrete surface to be measured as a gradation value (D) proportional to the brightness of the pixel, calculating an appropriate threshold value (T) for the gradation value (D) of the pixel, and calculating the gradation value from the above image. White pixels whose (D) is above the threshold (T) and the gray value (D)
Concrete processing consists of creating a binary image with black pixels whose values are less than a threshold (T), removing non-linear black pixel parts, and measuring the width and length of cracks based on the coordinates and number of black pixels. How to measure surface cracks. (2) In the measuring method according to claim 1,
After removing the non-linear black pixel portion, forming a plurality of individual black portions excluding branch portions in the image of the black pixel;
Width of change (ΔD) in gray value (D) of pixels within each individual black area
A method for measuring cracks in concrete, which includes calculating the width of change (ΔD) and excluding individual black portions where the width of change (ΔD) is greater than a predetermined value.