CN114494129B - Contrast enhancement method for surface slight deformation defect - Google Patents

Abstract

The invention discloses a contrast enhancement method for a surface slight deformation defect, which comprises the following steps: set up the slight deformation defect contrast enhancement device in surface to illumination source is to examining the surface irradiation, and move gradually to a direction illumination source, in order to ensure illumination source's marginal light covers wholly examine the surface, gather the removal in-process examine many reflection light line graphs on surface, get rid of bright background in many reflection light line graphs obtains many no stripe interference images, will many no stripe interference images carry out image synthesis, obtain the synthetic image of target, have realized the contrast enhancement to the slight deformation defect in surface, through contrast enhancement can be better acquire image information, detect the defect.

Description

A Contrast Enhancement Method for Slightly Deformed Surface Defects

related application

This application claims the rights and priority of the Chinese patent application entitled "A Method, Device and Storage Medium for Surface Defect Detection of Workpieces" filed on December 14, 2021, with application number 202111527576.X, which is hereby incorporated by reference in its entirety incorporated into this article.

technical field

The invention relates to the technical fields of machine vision and digital image processing, in particular to a contrast enhancement method for slight surface deformation defects.

Background technique

The quality control of products in industrial production is becoming increasingly strict, and the demand for a powerful surface defect detection system is becoming more and more urgent. At present, a large number of enterprises still use the traditional manual visual inspection method, and the surface inspection is carried out by experienced workers observing the product surface one by one. The subjective influence is large. In view of the many insurmountable disadvantages of manual inspection, automatic surface defect inspection dominated by machine vision is becoming the current mainstream inspection method because it can reduce costs in all aspects, improve the efficiency and accuracy of inspection, and improve the quality of product exports. More and more industries of all ages.

At this stage, surface defect detection based on machine vision mainly collects images of the surface of the object to be tested through industrial cameras, and analyzes the grayscale, texture, color and other information of the surface of the object to be tested through image processing technology to determine whether there are defects. Existing surface detection technology has been well applied to obvious defects in industrial online detection; for small deformation defects on the surface, such as slight dents on steel plates, structured light is currently used as the light source, and by analyzing the stripe light However, this method cannot completely obtain defect information, which affects the subsequent analysis of defects, and pit defects have little effect on the bending of stripes, so the detection effect is not ideal.

Slightly deformed defects on the surface have low contrast and no obvious edges under uniform light, and the imaging effect is low, and the defect information cannot be completely obtained under striped light. Therefore, how to collect complete and clear images of such defects in industrial inspection is a difficult point .

From the above, it can be seen that how to provide a method that can enhance the contrast of slightly deformed defects on the surface is a problem to be solved at present.

Contents of the invention

Therefore, the object of the present invention is to provide a method for enhancing the contrast of slightly deformed defects on the surface, so as to solve the problem that the prior art cannot obtain complete defect information and is not ideal for slightly deformed detection. In order to solve the above-mentioned technical problems, the present invention provides a method for enhancing the contrast of slightly deformed defects on the surface, including: setting a device for enhancing the contrast of slightly deformed defects on the surface;

Provide an illumination source, the illumination source is a movable combination light source including bright and dark areas, wherein the edge area of the bright area close to the dark area constitutes the edge light of the combined light source;

irradiating the surface to be inspected with the illumination source, and gradually moving the illumination source in one direction to ensure that the edge light of the illumination source covers the entire surface to be inspected;

Collecting multiple reflected light images of the surface to be inspected during the movement;

Remove the bright background from the multiple reflected light images and perform image synthesis to obtain a target composite image. Preferably, the illumination light source is stripe light.

Preferably, the edge light adopts 14% to 75% of the maximum brightness of the streak light, that is, the area where the width of the dark area near the bright-dark boundary of the inspected surface is W _edge , and the selection of the width W _edge can be based on different positions of the inspected surface It can also be calculated according to the actual imaging effect of the defect.

Preferably, the plurality of reflected ray images of the surface to be inspected during the collection movement include:

Collecting k pieces of reflected light diagrams of the surface to be inspected during the movement of the illumination source with a step size of W _edge ;

The selection of k is determined according to the following formula:

k＝max(W _dark /W _edge -2,W _bright /W _edge )+1

W _dark is the width of dark stripes, and W _bright is the width of bright stripes. The selection of W _edge can be calculated according to the gray value ratio of different positions on the surface to be inspected, or can be judged according to the actual imaging effect of the defect. The dark stripe width When W _dark = 2*W _edge , the dark fringe area is the edge light detection area, k=W _bright /W _edge +1, then select the minimum scanning period according to the bright fringe width W _bright to ensure that the detected area can be covered .

Preferably, removing the bright background from the multiple reflected light images and performing image synthesis to obtain the target composite image includes:

Converting the multiple reflected light maps into multiple image signals and sending them to the computer;

Using the local maximum difference method to perform dilation and corrosion operations on multiple image signals of the multiple input reflected light maps to determine the maximum value and minimum value near the specified neighborhood, and obtain multiple dilation and corrosion images;

Linearly combining the multiple expansion and erosion images to obtain the multiple streak-free images;

Taking the average value of the grayscale of corresponding positions in the image information of the plurality of streak-free images as the grayscale value of the target composite image;

The gray scale value of the target composite image is proportionally adjusted to obtain the target composite image.

A method for enhancing the contrast of slight surface deformation defects provided by the present invention includes: setting up a device for enhancing the contrast of slight surface deformation defects, and providing an illumination source. The illumination source is a movable combined light source including bright and dark areas. The edge area of the bright area constitutes the edge light of the combined light source, irradiates the surface to be inspected with the illumination light source, and gradually moves the illumination light source in one direction to ensure that the edge light of the illumination light source covers the entire described object to be inspected If there is no defect on the surface to be inspected, the light will be specularly reflected on the surface. If there is a defect on the surface to be inspected, part of the light will diverge. Since the light entering the defect accounts for a large proportion of the total light, the surrounding light will have a large impact on the defect. The interference of imaging is small, and the contrast of the slight deformation defect on the surface to be inspected is enhanced; the bright background is removed from the multiple reflected light images and image synthesis is performed to obtain the target composite image, which further enhances the slight deformation of the surface from the algorithm The contrast of defects. The method for enhancing the contrast of a slightly deformed surface defect provided by the present invention utilizes the marginal light of the illumination source to irradiate the surface to be inspected to enhance the contrast of the slightly deformed surface, and removes the bright background from the collected light pictures and synthesizes them to further enhance the The contrast of the slightly deformed surface can better obtain image information and detect defects through contrast enhancement.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the following will briefly introduce the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only For some embodiments of the present invention, those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is a flow chart of a specific embodiment of the method for enhancing the contrast of slightly deformed defects on the surface provided by the present invention;

Figure 2 is a schematic diagram of edge light;

Figure 3 is a schematic diagram of a striped light source;

Figure 4 is a schematic diagram of bright stripe edge defect imaging;

Figure 5 is a schematic diagram of the principle of a slight deformation defect on the surface;

Figure 6 is a schematic diagram of the defect detection device provided in the implementation case;

Fig. 7 is a schematic diagram of stripe light movement;

Figure 8 is a schematic diagram of imaging of slight dents on the surface of the steel plate;

Figure 9 is a schematic diagram of imaging of slight surface defects under streaked light;

Figure 10 is a schematic diagram of a synthetic image;

Fig. 11 is a structural block diagram of a device for enhancing the contrast of a slight surface deformation defect provided by an embodiment of the present invention.

Detailed ways

The core of the invention is to provide a method for enhancing the contrast of slightly deformed defects on the surface, which enhances the contrast of slightly deformed defects on the surface.

In order to enable those skilled in the art to better understand the solution of the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. Apparently, the described embodiments are only some of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Please refer to Fig. 1, Fig. 1 is a flow chart of a specific embodiment of the contrast enhancement method for surface slight deformation defects provided by the present invention; the specific operation steps are as follows:

Step S101: setting a contrast enhancement device for slight surface deformation defects;

Step S102: illuminating the surface to be inspected with an illumination source, and gradually moving the illumination source in one direction to ensure that the edge light of the illumination source covers the entire surface to be inspected;

Step S103: collecting multiple reflected light images of the surface to be inspected during the movement;

Step S104: Remove the bright background from the multiple reflected light images and perform image synthesis to obtain a target composite image.

A method for enhancing the contrast of slight surface deformation defects provided by the present invention includes: setting up a device for enhancing the contrast of slight surface deformation defects, and providing an illumination source. The illumination source is a movable combined light source including bright and dark areas. The edge area of the bright area constitutes the edge light of the combined light source, irradiates the surface to be inspected with the illumination light source, and gradually moves the illumination light source in one direction to ensure that the edge light of the illumination light source covers the entire described object to be inspected If there is no defect on the surface to be inspected, the light will be specularly reflected on the surface. If there is a defect on the surface to be inspected, part of the light will diverge. Since the light entering the defect accounts for a large proportion of the total light, the surrounding light will have a large impact on the defect. The interference of imaging is small, and the contrast of the slight deformation defect on the surface to be inspected is enhanced; the bright background is removed from the multiple reflected light images and image synthesis is performed to obtain the target composite image, which further enhances the slight deformation of the surface from the algorithm The contrast of defects. The method for enhancing the contrast of a slightly deformed surface defect provided by the present invention utilizes the marginal light of the illumination source to irradiate the surface to be inspected to enhance the contrast of the slightly deformed surface, and removes the bright background from the collected light pictures and synthesizes them to further enhance the Contrast of slightly deformed surfaces.

Based on the above-mentioned embodiment, this embodiment takes the steel plate as the surface to be inspected to further illustrate the above process, and the specific steps are as follows:

Step S201: setting a contrast enhancement device for slight surface deformation defects;

Step S202: illuminating the surface to be inspected with an illumination source, and gradually moving the illumination source in one direction to ensure that the edge light of the illumination source covers the entire surface to be inspected;

The illumination source is a movable combined light source including bright and dark areas, wherein the edge area of the bright area close to the dark area constitutes the edge light of the combined light source, and the edge light adopts 14% to 75% of the maximum brightness of the stripe light, That is, the area where the width of the dark area near the bright-dark boundary of the inspected surface is W _edge , the selection of the width W _edge can be calculated based on the gray value ratio of different positions on the inspected surface, or can be judged according to the actual imaging effect of the defect, please refer to Figure 2, Figure 2 is a schematic diagram of edge light;

The lighting source can be striped light, which is made by sticking reflective or non-reflective stickers on a specific surface light source. The area with the sticker is a dark area, and the light-emitting area without the sticker is a bright area, as shown in the figure 3. Set the illumination light source to overexposure, gradually move the dent on the surface to be inspected and collect images, as shown in Figure 4, Figure 4(a) is far away from the bright stripes, and the imaging effect of the defect is not obvious, Figure 4(b) and Figure 4(c) are respectively the farthest positions on both sides of the bright stripes that can enhance the contrast of slight deformation defects on the surface. Through actual measurement, it is found that when the light source is overexposed, the boundary line between bright and dark areas is within 5mm of the dark area. The contrast ratio is the largest, that is, the W _edge is 5mm, so in this implementation case, the bright and dark stripes on the surface to be inspected can be set to have a width of 10mm, and through the mutual movement between the illumination source, the surface to be inspected, and the image acquisition device Realize switching between bright and dark areas to be checked.

Please refer to Figure 5, which is a schematic diagram of the principle of a slight deformation defect on the surface;

In this embodiment, the illumination light source is an important part of image input, which directly affects the quality of the acquired image information. Since there are many kinds of surface defects to be detected, with different positions and sizes, it is necessary to select Appropriate light source for best results. In this embodiment, the light and dark boundary of the stripe is used as the light source near the dark area, and its schematic diagram refers to Fig. 5 (a). will change, and the light detected by the image acquisition device is also uniform; with reference to Fig. The received light also changes accordingly. Since the light entering the defect accounts for a larger proportion of the total light under the streak light, the surrounding light has less interference with the defect imaging, and the contrast of the slightly deformed defect on the surface is enhanced.

Since the structure of the defect detection device has a great influence on the quality of the entire acquisition scheme, its structural layout directly affects the uniformity of illumination. Therefore, the structure of the defect detection device in this embodiment is shown in FIG. 6 .

Step S203: collecting multiple reflected light images of the surface to be inspected during the moving process;

The image acquisition device observes the image of the reflected light source through the surface to be inspected, wherein the image acquisition device selects an industrial camera, and the industrial camera is provided with an image acquisition card. The image acquisition device used in this embodiment is a CMOS Camera, after the light is incident on the surface to be inspected, when there is no defect in the surface to be inspected, the direction of emission will not change, and the light detected by the target surface of the CMOS camera is also uniform; when the surface to be inspected When there is a slight concave-convex defect, the emitted light will change, and the light detected by the target surface of the CMOS camera will also change accordingly.

Collecting k pieces of reflected light diagrams of the surface to be inspected during the movement of the illumination source with a step size of W _edge ;

The selection of k is determined according to the following formula:

k＝max(W _dark /W _edge -2,W _bright /W _edge )+1

W _dark is the width of dark stripes, and W _bright is the width of bright stripes. The selection of W _edge can be calculated according to the gray value ratio of different positions on the surface to be inspected, or can be judged according to the actual imaging effect of the defect. The dark stripe width When W _dark = 2*W _edge , the dark fringe area is the edge light detection area, k=W _bright /W _edge +1, then select the minimum scanning period according to the bright fringe width W _bright , when W _edge is W _edge ~ When between 3*W _edge , the full coverage detection of the surface to be inspected can be completed by scanning the surface to be inspected in 2-4 steps;

According to the above formula, in order to ensure the detection of slight defects, the present invention sets the width of bright and dark stripes to 2*W _edge , and the step length is W _edge , and collects 4 images in total to realize the full coverage of the surface to be inspected;

Move the illuminating light source in one direction step by step W _edge and collect images, and move four times in total to obtain 4 light images of the surface to be inspected. Please refer to FIG. 7 , which is a schematic diagram of stripe light movement.

Step S204: removing the bright backgrounds in the multiple reflected light images to obtain multiple streak-free images;

The computer is connected to the industrial camera to read the image information. The computer is equipped with an image processing system, which transmits the acquired multiple reflected light images to the computer. First, the collected light images are Preprocessing is carried out to eliminate the black and white stripe background and highlight the detection defects through local maximum difference filtering. The input black and white stripe images are respectively expanded and corroded, and the maximum value and minimum value near the specified neighborhood are determined by dilation and corrosion. value, and then linearly combine the dilated and eroded images to obtain an image without fringe interference.

Step S205: performing image synthesis on the multiple stripe-free images to obtain a target composite image;

Synthesize all the preprocessed images, and the synthesis algorithm uses the average value of the gray values of the corresponding positions in each image as the most important reference gray value. The target composite image;

The new composite image obtained by the algorithm not only covers the surface to be inspected, but also further enhances the contrast of the slightly deformed defect on the surface.

Step S206: performing defect feature extraction on the target composite image to obtain a surface defect feature map to be inspected;

The present invention enhances the contrast of slightly deformed defects on the surface by illuminating the edge area of the bright area with striped light, and selects the appropriate width of bright and dark stripes, the moving step length and the number of times of the lighting source according to the width of the edge light area, and moves the The illumination source shoots multiple light images to ensure that the collected light images can cover the surface to be inspected; after the black and white background is removed by the local maximum difference method, the image without stripe interference is synthesized, The newly synthesized image both removes the noise of the black and white background and enhances the contrast of slightly deformed defects on the surface.

Based on the above embodiments, the operation process of using this method to enhance the defect contrast: take the steel plate as an example to describe the specific implementation mode, and the main confirmation content is dents and pits. The specific steps are as follows:

Firstly, the steel plate to be tested is placed on the storage table, which is a fixed device and cannot be moved. The image of the object under test collected without adopting the scheme of the present invention, as shown in FIG. 8( a ), is not effective in detecting slight deformation defects on the surface by ordinary lighting.

In this case, the striped light is used as the lighting source, and the lighting source is controlled to display bright stripes of a certain width and move in one direction 4 times, and the image acquisition device collects and saves images corresponding to each movement, as shown in Figure 9 As shown, Fig. 9 is a schematic diagram of imaging of surface slight defects under striped light.

After the acquisition is completed, image processing can be carried out. First, all the collected images are preprocessed, and the purpose of eliminating black and white stripe background and highlighting detection defects is achieved through local maximum difference filtering. Then, multiple images are synthesized. The average value of the gray value of the corresponding position in the image is taken, and after the ratio is adjusted, a new composite image is obtained. After calculating and processing all the pictures, the image in Figure 10 can be obtained, and Figure 10 further enhances the defect contrast in the algorithm.

After the image in Figure 10 is obtained, preprocessing is performed sequentially according to the general visual processing algorithm, image feature extraction, and based on the circularity value and length-width comparison value of the steel plate defect, the dent in the defect is distinguished from the concave-convex point .

A method for enhancing the contrast of slight surface deformation defects provided by the present invention includes: setting up a device for enhancing the contrast of slight surface deformation defects, and providing an illumination source. The illumination source is a movable combined light source including bright and dark areas. The edge area of the bright area constitutes the edge light of the combined light source, irradiates the surface to be inspected with the illumination light source, and gradually moves the illumination light source in one direction to ensure that the edge light of the illumination light source covers the entire described object to be inspected If there is no defect on the surface to be inspected, the light will be specularly reflected on the surface. If there is a defect on the surface to be inspected, part of the light will diverge. Since the light entering the defect accounts for a large proportion of the total light, the surrounding light will have a large impact on the defect. The imaging interference is small, and the contrast enhancement of the slight deformation defect on the surface to be inspected is realized; the bright background in the multiple reflected light images is removed to obtain multiple streak-free interference images, and the multiple streak-free interference images are Image synthesis is carried out to obtain the target composite image, which further enhances the contrast of the slight deformation defect on the surface from the algorithm.

The contrast enhancement device for slight surface deformation defects provided by the present invention ensures the uniformity of the illumination light source structurally, and is easy to operate; the contrast enhancement method for slight surface deformation defects provided by the present invention, through the edge of the bright area of the striped light Area lighting, which enhances the contrast of slight deformation defects on the surface, and selects the appropriate width of bright and dark stripes, the moving step size and times of the lighting source according to the width of the edge light area, and moves the lighting source to take multiple photos of the Light image, to ensure that the collected light image can cover the surface to be inspected, by removing the background and synthesizing the light image, the interference of the bright background is removed, and the contrast of the slight deformation defect on the surface is further enhanced; The invention provides a method for enhancing the contrast of slight surface deformation defects, which enhances the contrast of defects such as small concave and convex points on the surface to be inspected, and solves the problem of low contrast and no obvious edges of surface slight deformation defects in the past under uniform light, and the imaging effect is low. , by analyzing the technical problem that the fringe bending is not ideal for micro-deformation detection, image information can be better obtained and defects can be detected through contrast enhancement.

Please refer to Fig. 11. Fig. 11 is a structural block diagram of a contrast enhancement device for slight surface deformation defects provided by an embodiment of the present invention. The specific device may include:

The illuminating light source module 100 is used to detect the surface defect to be inspected, illuminate the surface to be inspected with the illuminating light source, and gradually move the illuminating light source in one direction to ensure that the edge light of the illuminating light source covers the entire the surface to be inspected;

An image acquisition module 200, configured to acquire multiple reflected light diagrams of the surface to be inspected during the movement process;

The image synthesis module 300 is configured to remove the bright background from the multiple reflected light images and perform image synthesis to obtain a target composite image.

The device for enhancing the contrast of slightly deformed surface defects in this embodiment is used to implement the aforementioned method for enhancing the contrast of slightly deformed defects on the surface. Therefore, the specific implementation of the method for enhancing the contrast of slightly deformed defects on the surface can be seen in the previous part of the embodiment of the method for enhancing the contrast of slightly deformed defects on the surface. For example, the illumination light source module 100, the image acquisition module 200, and the image synthesis module 300 are respectively used to realize the steps S101, S102 and S103 in the method of the above-mentioned slight deformation defect contrast enhancement device on the surface, so the specific implementation methods can refer to the corresponding parts The description of the embodiment will not be repeated here.

Each embodiment in this specification is described in a progressive manner, each embodiment focuses on the difference from other embodiments, and the same or similar parts of each embodiment can be referred to each other. As for the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and for the related information, please refer to the description of the method part.

The method and device for enhancing the contrast of slight surface deformation defects provided by the present invention have been described in detail above. In this paper, specific examples are used to illustrate the principle and implementation of the present invention, and the descriptions of the above embodiments are only used to help understand the method and core idea of the present invention. It should be pointed out that for those skilled in the art, without departing from the principle of the present invention, some improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims (2)

1. A method for enhancing the contrast of slightly deformed defects on the surface, comprising: Set up a contrast enhancement device for slight surface deformation defects; Provide an illuminating light source, the illuminating light source is a movable combined light source including bright and dark areas, and is a striped light, wherein the edge area of the bright area close to the dark area constitutes the edge light of the combined light source, and the edge light adopts the maximum brightness of the striped light 14% to 75 _{% of the inspected surface, that is, the area where the width of the dark area near the bright-dark boundary of the inspected surface is W edge .} The actual imaging effect judgment; irradiating the surface to be inspected with the illumination source, and gradually moving the illumination source in one direction to ensure that the edge light of the illumination source covers the entire surface to be inspected; Collect multiple reflected ray maps of the surface to be inspected during the movement: Collecting k pieces of reflected light diagrams of the surface to be inspected during the movement of the illumination source with a step size of W _edge ; The selection of k is determined according to the following formula: k＝max(W _dark /W _edge -2,W _bright /W _edge )+1 W _dark is the width of the dark stripes, and W _bright is the width of the bright stripes. When the dark stripe width W _dark = 2*W _edge , the dark stripe areas are all edge light detection areas, and k=W _bright /W _edge +1, then according to The bright stripe width W _bright selects the minimum scanning period to ensure that the inspected area can be covered; Remove the bright background from the multiple reflected light images and perform image synthesis to obtain a target composite image. 2. The method for enhancing the contrast of slightly deformed defects on the surface according to claim 1, wherein the step of removing the bright background from the multiple reflected light images and performing image synthesis to obtain the target composite image includes: Converting the multiple reflected light maps into multiple image signals and sending them to the computer; Using the local maximum difference method to perform dilation and corrosion operations on multiple image signals of the multiple input reflected light maps to determine the maximum value and minimum value near the specified neighborhood, and obtain multiple dilation and corrosion images; Linearly combining the multiple expansion and erosion images to obtain the multiple streak-free images; Taking the average value of the grayscale of corresponding positions in the image information of the plurality of streak-free images as the grayscale value of the target composite image; The gray scale value of the target composite image is proportionally adjusted to obtain the target composite image.

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