CN112284983A - Method for measuring contact angle by image processing - Google Patents
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- CN112284983A CN112284983A CN202011107946.XA CN202011107946A CN112284983A CN 112284983 A CN112284983 A CN 112284983A CN 202011107946 A CN202011107946 A CN 202011107946A CN 112284983 A CN112284983 A CN 112284983A
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- 238000000034 method Methods 0.000 title claims abstract description 31
- 238000012545 processing Methods 0.000 title claims abstract description 17
- 239000007788 liquid Substances 0.000 claims abstract description 34
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 30
- 238000004422 calculation algorithm Methods 0.000 claims abstract description 17
- 238000007781 pre-processing Methods 0.000 claims abstract description 13
- 230000011218 segmentation Effects 0.000 claims abstract description 6
- 230000005484 gravity Effects 0.000 claims abstract description 5
- 238000005520 cutting process Methods 0.000 claims abstract description 4
- 238000004364 calculation method Methods 0.000 claims description 7
- 239000004973 liquid crystal related substance Substances 0.000 claims description 5
- 238000009736 wetting Methods 0.000 claims description 5
- 239000005304 optical glass Substances 0.000 claims description 3
- 238000005259 measurement Methods 0.000 abstract description 7
- 238000005070 sampling Methods 0.000 description 4
- 230000003749 cleanliness Effects 0.000 description 3
- 238000013461 design Methods 0.000 description 3
- 239000005357 flat glass Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012544 monitoring process Methods 0.000 description 2
- 238000009795 derivation Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 238000010191 image analysis Methods 0.000 description 1
- 238000003703 image analysis method Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 238000002310 reflectometry Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 230000003746 surface roughness Effects 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 238000012795 verification Methods 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N13/00—Investigating surface or boundary effects, e.g. wetting power; Investigating diffusion effects; Analysing materials by determining surface, boundary, or diffusion effects
- G01N13/02—Investigating surface tension of liquids
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N13/00—Investigating surface or boundary effects, e.g. wetting power; Investigating diffusion effects; Analysing materials by determining surface, boundary, or diffusion effects
- G01N13/02—Investigating surface tension of liquids
- G01N2013/0208—Investigating surface tension of liquids by measuring contact angle
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Abstract
The invention discloses a method for measuring a contact angle through image processing, which comprises the following steps: collecting image information by using a CCD (charge coupled device), cutting and amplifying, increasing the contrast ratio of a background and liquid drops by self-adaptive gray scale stretching in the preprocessing process, carrying out threshold segmentation, tracking the gravity center of the liquid drops to determine a range, and capturing an effective picture to remove an interference curve and extract a liquid drop contour curve; after image preprocessing is finished, extracting the outline of the water drop, namely the circular arc part, and fitting the circle where the circular arc is located to obtain the circle center and the radius of the circular arc; then calculating the tangent angle of the water drop profile according to the height and the radius of the arc, namely the contact angle; compared with the traditional method of drawing a tangent line at the end point of a curve and the like, the reliability of the algorithm is verified by manually measuring the included angle between the tangent line and a straight line, namely the contact angle, by using MB-ruler angle measurement software and directly comparing the contact angle with the contact angle obtained by the algorithm. The method has the advantages of high intelligence, simple and easily mastered operation, small measurement error, high accuracy and more perfect functions.
Description
Technical Field
The invention relates to a method for measuring a contact angle by image processing.
Background
In the research and production of electronic devices, it is necessary to evaluate information on cleanliness of the device surface and the like. For example, the surface cleanliness of the liquid crystal display screen is measured, and the surface roughness of the formed cover plate glass is required to be measured to judge the wear resistance of the cover plate glass when the capacitive touch screen is manufactured. The contact angle is an important parameter for representing the wetting degree of liquid to solid, and is often used for measuring related information of the surfaces of equipment such as liquid crystal screens and the like. For the surface of the same material, the corresponding degree of cleanness can be known by comparing the contact angle of the surface of the same material. The larger the diameter of the water drop spread on the surface, the higher the surface cleanliness.
The existing measuring methods for contact angle are generally two types: one is a shape image analysis method; the second method is a weighing method. The most direct and accurate of which is the shape image analysis. After extracting the droplet profile, the current common method is to perform curve fitting on the droplet profile near the contact point of the droplet and the measured surface, commonly use a polynomial fitting function, and then calculate the slope of the tangent line at the contact point of the droplet profile and the measured surface, i.e. to obtain the contact angle value by derivation. However, the selection of the boundary points in the method will affect the result of the final tangent slope, and the slope of the curve fitted by selecting different fitting sampling points is also different.
Disclosure of Invention
The invention aims to provide a method for measuring a contact angle through image processing, which has the advantages of high intelligence, simple and easily mastered operation, small measurement error, high accuracy and more complete functions.
In order to achieve the above object, the present invention provides a method of measuring a contact angle by image processing, comprising:
collecting image information by using a CCD (charge coupled device), cutting and amplifying, increasing the contrast ratio of a background and liquid drops by self-adaptive gray stretching in a preprocessing process, carrying out threshold segmentation, tracking the gravity center of the liquid drops to determine a range, and capturing an effective picture to remove an interference curve and extract a liquid drop contour curve;
after image preprocessing is finished, extracting the outline of the water drop, namely the circular arc part, and fitting the circle where the circular arc is located to obtain the circle center and the radius of the circular arc; then calculating the tangent angle of the water drop profile according to the height and the radius of the arc;
the reliability of the algorithm is verified by manually measuring the included angle between the tangent and the straight line, namely the contact angle, by using MB-ruler angle measurement software, and directly comparing the included angle with the contact angle obtained by the algorithm.
Preferably, the circle where the arc is fitted needs to find the boundary line between the water drop and the desktop, the water drop is subjected to mirror reflection on the surface of the equipment, and the boundary between the water drop and the desktop can be found by calculating the position of the contour symmetry line.
Preferably, the contour average curve is extracted according to the contour pixel points.
Preferably, a circle is fitted according to the semicircular arc part on the symmetry line, and the circle center position and the radius are obtained.
Preferably, an included angle theta between the liquid drop and the surface of the equipment is calculated according to the distance H from the circle center to the symmetry line and the radius R; because the calculation mode is different when theta is larger than 90 degrees and smaller than 90 degrees, the algorithm needs to judge whether the height X of the upper half arc is larger than the radius R before calculation; wherein when X > R, the droplet is in a non-wetting state:
when X is less than or equal to R, the liquid drop is in a wet state, and the position from the circle center to the symmetry line is also H-R-X:
preferably, an image processing program for measuring the contact angle of the surface of the device is designed based on MATLAB and GUI, so as to quickly and reliably calculate the contact angle of a water drop on the surface of a liquid crystal screen and optical glass.
Preferably, the program further includes non-specular processing in the case where the droplets are not specularly reflected: scanning line by line from bottom to top from the lower part of the picture, searching the edge part of the water drop, taking the edge part as the junction of the water drop and the desktop, and calculating the tangent angle of the intersection point of the fitting circle and the boundary line.
According to the technical scheme, the contact angle testing equipment based on digital image processing is independently built according to the characteristics of the liquid drop image on the surface of the equipment, the CCD camera is used for collecting the image, and the image processing program based on MATLAB and GUI design is compiled.
Additional features and advantages of the invention will be set forth in the detailed description which follows.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:
FIG. 1 is a GUI interface for contact angle measurement;
FIG. 2 shows the state of the droplet when the height X of the upper half arc is different, where a is when X is smaller than or equal to the radius R, and b is when X is larger than the radius R;
FIG. 3 is a GUI interface in the non-specular case;
FIG. 4 is a manual measurement of the contact angle of MB-ruler;
fig. 5 is a measurement interface for measuring contact angle by image processing.
Detailed Description
The following detailed description of embodiments of the invention refers to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.
In the present invention, unless otherwise specified, the directional words "upper, lower" and the like included in the terms merely represent the orientation of the terms in the conventional use state or are colloquially known by those skilled in the art, and should not be construed as limiting the terms.
The invention provides a method for measuring a contact angle through image processing, which comprises the following steps:
collecting image information by using a CCD (charge coupled device), cutting and amplifying, increasing the contrast ratio of a background and liquid drops by self-adaptive gray stretching in a preprocessing process, carrying out threshold segmentation, tracking the gravity center of the liquid drops to determine a range, and capturing an effective picture to remove an interference curve and extract a liquid drop contour curve;
after image preprocessing is finished, extracting the outline of the water drop, namely the circular arc part, and fitting the circle where the circular arc is located to obtain the circle center and the radius of the circular arc; then calculating the tangent angle of the water drop profile according to the height and the radius of the arc;
the reliability of the algorithm is verified by manually measuring the included angle between the tangent and the straight line, namely the contact angle, by using MB-ruler angle measurement software, and directly comparing the included angle with the contact angle obtained by the algorithm.
The invention also designs an image processing program for measuring the contact angle of the surface of the equipment based on MATLAB and GUI, and can quickly and reliably calculate the contact angle of water drops on the surfaces of equipment such as liquid crystal screens, optical glass and the like. The GUI user interface is shown in figure 1, a CCD real-time monitoring picture (1-1), a picture (1-2) after image preprocessing, a contact angle picture (1-3) is calculated, the outline of a liquid drop, a fitting circle and other parts are displayed, a shooting start button (1-4) starts to be called after clicking, a camera real-time monitoring picture is called after clicking, a shooting end button (1-5), a screenshot button (1-6) performs image preprocessing after clicking, the position of the liquid drop is positioned, an algorithm calculates the contact angle through preprocessed data after clicking the image processing button (1-7), a non-mirror check box (1-8) realizes calculation of the contact angle under the non-mirror condition, and a static text box (1-9) displays the calculated contact angle value.
The key point of the design of the measuring device surface contact angle image processing program is to improve the stability and accuracy of the algorithm. Actually, when measuring the contact angle, the requirement on the background light of a picture is high, a polynomial fitting function is often adopted when the contact angle is calculated, and then the curve is derived at the contact point, so that the accuracy of the contact angle measurement is influenced by different fitting sampling points and inaccuracy of sampling points at two ends.
Therefore, the contrast ratio of the background and the liquid drops is increased through self-adaptive gray scale stretching in the preprocessing process, then threshold segmentation is carried out, and then effective pictures are captured by tracking the gravity center of the liquid drops and determining the range, so that an interference curve is removed, a liquid drop contour curve is better extracted, and the problems that the contrast ratio of the background and the liquid drops is low and the information of the extracted liquid drops cannot be obtained are solved.
After image preprocessing is finished, the outline of the water drop, namely the circular arc part, is extracted, and the circle where the circular arc is located is fitted to obtain the parameters of the circle center, the radius and the like. And calculating the tangent angle of the water drop profile according to the parameters such as the height and the radius of the arc. To fit the circle where the arc is located, the boundary line between the water drop and the desktop needs to be found, for most cases, the water drop can be subjected to mirror reflection on the surface of the equipment, and the boundary between the water drop and the desktop can be found by calculating the position of the contour symmetry line.
Because the picture contour is synthesized by a plurality of pixel points, a contour average curve is extracted according to the contour pixel points. And fitting a circle according to the semicircular arc part on the symmetry line to obtain the position and the radius of the circle center. As shown in fig. 2, the included angle θ between the droplet and the surface of the device can be calculated according to the distance H from the center of the circle to the symmetry line and the radius R. Since the calculation mode is different when theta is larger than 90 degrees and smaller than 90 degrees, the algorithm judges whether the height X of the upper half circular arc is larger than the radius R before calculation. When X > R, the droplet is in a non-wetting state:
when X is less than or equal to R, the liquid drop is in a wet state, and the position from the circle center to the symmetry line is also H-R-X:
considering that not all devices can cause the droplets to be specularly reflected, a non-specular check box is added to the GUI interface, as shown in fig. 3, and the check box is checked in case the droplets are not specularly reflected, and when the process image button is clicked, the algorithm will not calculate the contour symmetry line position, but will go into the non-specular case: scanning line by line from bottom to top from the lower part of the picture, searching the edge part of the water drop, taking the edge part as the junction of the water drop and the desktop, and calculating the tangent angle of the intersection point of the fitting circle and the boundary line.
The reliability of the algorithm is verified by manually measuring the included angle between the tangent and the straight line, namely the contact angle, by using MB-ruler angle measurement software, and directly comparing the included angle with the contact angle obtained by the algorithm.
In actual use, as shown in fig. 4 and 5, the same image was measured, the manually measured angle of MB-roller was 53.39 °, and the contact angle detected by image processing was 53.9723 °. After multiple times of verification, the use requirement can be met through the image processing detection method, and the precision is high.
Therefore, according to the characteristics of the liquid drop image on the surface of the equipment, the MATLAB is used for calling the camera to acquire the liquid drop image, the GUI interface is established for image processing, operations including gray level stretching, threshold segmentation, median filtering, barycentric coordinate obtaining and the like are adopted in image preprocessing, the influence of background noise is eliminated, the position of the water drop is accurately detected through an algorithm, and liquid drop information is extracted. And then extracting the outline of the liquid drop, calculating the boundary line between the liquid drop and the equipment, fitting the circle where the circular arc of the liquid drop is positioned, obtaining the parameters of the radius and the like of the circle, and calculating the contact angle by a chordal height method. And additionally considers the condition of equipment with low measured reflectivity, and adds a non-mirror check box in the GUI interface.
The method reduces the influence of background light by positioning the liquid drop, and compared with a tangent method, the method avoids the measurement error caused by insufficient fitting sampling points, inaccurate end points on two sides of the liquid drop and the like, and has more perfect functions.
The preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications can be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.
It should be noted that the various technical features described in the above embodiments can be combined in any suitable manner without contradiction, and the invention is not described in any way for the possible combinations in order to avoid unnecessary repetition.
In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.
Claims (7)
1. A method of measuring contact angles by image processing, comprising:
collecting image information by using a CCD (charge coupled device), cutting and amplifying, increasing the contrast ratio of a background and liquid drops by self-adaptive gray scale stretching in the preprocessing process, carrying out threshold segmentation, tracking the gravity center of the liquid drops to determine a range, and capturing an effective picture to remove an interference curve and extract a liquid drop contour curve;
after image preprocessing is finished, extracting the outline of the water drop, namely the circular arc part, and fitting the circle where the circular arc is located to obtain the circle center and the radius of the circular arc; then calculating the tangent angle of the water drop profile according to the height and the radius of the arc;
the reliability of the algorithm is verified by manually measuring the included angle between the tangent and the straight line, namely the contact angle, by using MB-ruler angle measurement software, and directly comparing the included angle with the contact angle obtained by the algorithm.
2. The method of claim 1, wherein fitting the circle to the arc requires finding the boundary between the water drop and the table top, and the water drop is specularly reflected on the surface of the device, and the boundary between the water drop and the table top can be found by calculating the position of the symmetry line of the profile.
3. The method of claim 1, wherein the average profile curve is extracted from the profile pixels.
4. The method of claim 1, wherein the circle center position and the radius are obtained by fitting a circle to the semicircular arc portion on the symmetry line.
5. The method of claim 4, wherein an angle θ between the droplet and the surface of the device is calculated according to the distance H from the center of the circle to the symmetry line and the radius R; because the calculation mode is different when theta is larger than 90 degrees and smaller than 90 degrees, the algorithm needs to judge whether the height X of the upper half arc is larger than the radius R before calculation; wherein when X > R, the droplet is in a non-wetting state:
when X is less than or equal to R, the liquid drop is in a wetting state:
6. the method of claim 1, wherein an image processing program for measuring the contact angle of the device surface is designed based on MATLAB and GUI to quickly and reliably calculate the contact angle of a water drop on the surface of a liquid crystal screen or an optical glass.
7. The method of claim 1, wherein the program further comprises a non-specular processing when the liquid droplet is not specularly reflected, wherein the non-specular processing comprises: scanning line by line from bottom to top from the lower part of the picture, searching the edge part of the water drop, taking the edge part as the junction of the water drop and the desktop, and calculating the tangent angle of the intersection point of the fitting circle and the boundary line.
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Cited By (2)
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| CN114894125A (en) * | 2022-03-31 | 2022-08-12 | 人本股份有限公司 | Radial ball bearing raceway line quantitative detection method |
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