CN116167930A

CN116167930A - Image enhancement method, edge line positioning method, edge inspection method and device

Info

Publication number: CN116167930A
Application number: CN202211643828.XA
Authority: CN
Inventors: 许超; 殷亚男; 张鑫
Original assignee: Suzhou Mega Technology Co Ltd
Current assignee: Suzhou Mega Technology Co Ltd
Priority date: 2022-12-20
Filing date: 2022-12-20
Publication date: 2023-05-26

Abstract

The application discloses an image enhancement method applied to positioning of a step surface or a break, comprising the following steps: and a difference value calculating step: calculating pixel value differences between each pixel of an original image of the target image and surrounding pixels of the pixel to obtain a deviation image; enhancement step: carrying out equidirectional enhancement on each pixel in the deviation map to obtain an enhancement map; the same-direction enhancement is enhancement for ensuring that the positive and negative of each pixel in the deviation graph are kept unchanged; and (3) superposition: and superposing each pixel corresponding to the original image and the enhancement image to obtain a final image. The method can not only highlight the color difference among the pixels of the target image, but also give consideration to the original pixel value attribute of each pixel, and provides a basis for positioning the step surface or the line where the break difference is located in the edge area, thereby being beneficial to follow-up edge inspection based on the step surface and the line where the break difference is located.

Description

Image enhancement method, edge line positioning method, edge inspection method and device

Technical Field

The invention relates to the technical field of inspection, in particular to an image enhancement method and device, an edge line positioning method and device, an edge inspection method and device and a storage medium.

Background

The inspection equipment is mainly used for detecting whether defects exist in the edge areas of four edges of the upper surface and the lower surface of the display panel formed by bonding the color film substrate CF and the array substrate TFT after cutting or grinding, for example, defects such as cracks, shells, fragments and burrs exist. The method aims to remove the display panel with the defect or larger defect for the subsequent process. The inspection machine device generally comprises a visual processing system, wherein the visual processing system comprises a shooting module and a processing module, the shooting module is mainly used for shooting pictures of the edge area and sending the pictures to the processing module, and the processing module is mainly used for carrying out defect identification on the pictures sent by the shooting module.

Because the CF substrate has smaller size compared with the TFT substrate, the step surface exists on one side or two sides, then the shooting module shoots a photo from the upper side of the CF substrate and sends the photo to the processing module, and the processing module needs to accurately determine a line corresponding to the step surface according to the photo and serve as an edge line of the CF, and then searches for defects nearby based on the CF edge line; in addition, due to the dicing method and the like, there is a step on each side where the CF substrate and the TFT substrate are aligned, and the step is understood as an irregular and small-sized step that should not occur, and in order to identify a defect in an edge region of each side where the CF substrate and the TFT substrate are aligned, it is necessary to identify the line where the step is located.

The visual detection system can identify target objects such as defects, edges, parts and the like of the product in the image through an image processing technology, so that whether the quality of the product is qualified or not is detected.

For example, patent application No. 201811555101.X discloses an LCD defect detection method, which obtains a first enhanced image by performing image enhancement on an acquired original image; performing texture filtering and standard mean conversion on the first enhanced image to obtain a standardized gray-scale image; calculating the gray scale range in the standardized gray scale image sliding rectangular frame to obtain a pixel value difference image, and carrying out image enhancement on the pixel value difference image to obtain a second enhanced image; and calculating a gray level histogram of the second enhanced image, calculating a segmentation threshold value by using the gray level histogram, judging the defect of the second enhanced image according to the segmentation threshold value, and marking, so that the defect and the defect category of the original image are detected.

The patent can identify the defects of the display area of the LCD panel, and mainly uses an image enhancement mode to highlight the pixel value difference between the defect area and the normal display area so as to realize defect detection. Since the overall appearance of the display area is single in color and small in noise, once the display area is defective, the difference between the defective area and the normal area is obvious. The image enhancement method of the patent and the defect detection method using the image enhancement method can complete the defect detection of the display area to a certain extent.

However, for many products, there may be relatively complex structures in the area where detection is required, and in the corresponding image, not only defects or other specific objects may exhibit color differences, but also relatively significant color differences between these different structures. In particular, the present invention relates to a scene in which the TFT substrate and the CF substrate have various structures such as circuits and board layers, and even defects may occur, and the colors of the structures or defects in the image are relatively close to those of the steps and the steps.

In this case, the prior art represented by the above patent can find only areas having color differences, and for product areas containing complex structures such as circuits, that is, the prior art scheme cannot be applied to cases where a large amount of complex information is contained in an image.

For the above problems, no effective solution has been proposed at present.

Disclosure of Invention

Based on the above problems, the application provides an image enhancement method and device, an edge line positioning method and device, an edge inspection method and device, and a storage medium.

The embodiment of the application discloses the following technical scheme:

in a first aspect, the present application provides an image enhancement method applied to positioning of a step surface or a step, the method including:

and a difference value calculating step: calculating pixel value differences between each pixel of an original image of the target image and surrounding pixels of the pixel to obtain a deviation image;

enhancement step: carrying out equidirectional enhancement on each pixel in the deviation map to obtain an enhancement map; the same-direction enhancement is enhancement for ensuring that the positive and negative of each pixel in the deviation graph are kept unchanged;

and (3) superposition: and superposing each pixel corresponding to the original image and the enhancement image to obtain a final image.

Optionally, the difference calculating step includes:

a filtering sub-step: filtering the original image to obtain a filtered image;

the calculation substep: and carrying out difference on pixel values of each pixel corresponding to each other in the original image and the filter image to obtain the deviation image.

Optionally, in the filtering substep, filtering is performed by any one of mean filtering, median filtering and weighted value filtering.

Optionally, in the enhancing step, the enhancement map is obtained by multiplying each pixel in the deviation map by a positive coefficient greater than 1 to perform homodromous enhancement.

Optionally, the method further comprises the following steps:

step surface target image acquisition: and acquiring a first preset area comprising a theoretical step line from the original image of the step surface, and taking the first preset area as the target image for positioning the step surface.

Optionally, in the step of obtaining the step surface target image, the step includes: the first preset area is finally formed by moving a first number of pixels in the original image in a first direction of the substrate based on the ideal step line and a second number of pixels in a second direction of the substrate.

Optionally, the method further comprises the following steps:

a step of obtaining a robust target image: and searching an outer edge line in the broken difference original image, and moving a third number of pixels towards a direction approaching to the broken difference original image based on the outer edge line to form the target image positioned as the broken difference.

In a second aspect, the present application further provides an edge line positioning method, including:

an image enhancement step, wherein each pixel of the target image is enhanced by adopting the enhancement method provided in the first aspect, so as to obtain an enhanced image of the target image;

a pixel determining step, namely comparing each pixel of each row of pixels in the enhanced image with a preset threshold value, and determining pixels smaller than the preset threshold value as target pixels;

and (3) a straight line fitting step: and performing straight line fitting on the target pixel in the plurality of rows of pixels to obtain a line where the step surface or the difference between the steps is located.

Optionally, in the pixel determining step, the method includes:

each column of adjacent rows of pixels in the enhanced image is subjected to mean value solving to obtain a row of mean value pixels;

searching a target column where the pixel smaller than the preset threshold value is located in the row of average value pixels;

and determining pixels corresponding to the target column in the adjacent rows of pixels, and selecting at least 1 as the target pixels.

Optionally, in the enhancing method of the image enhancing step, after the straight line fitting step, the method further includes:

step surface treatment: and merging the obtained online target image of the step surface into the original image of the step surface.

In a third aspect, the present application further provides an edge inspection method, including:

step surface and/or step positioning: by adopting the positioning method of the step surface or the offset provided in the second aspect, the step surface is positioned in the original step surface image to obtain the line of the step surface, and/or the offset is positioned in the original offset image to obtain the line of the offset;

and a defect identification step of identifying a defect located in a vicinity of a line where the step surface is located in the step surface original image and/or identifying a defect located in a vicinity of a line where the step surface is located in the step surface original image.

Optionally, identifying, in the defect identifying step, a defect located in a region near a line where the difference is located in the difference original image includes:

deleting the line where the difference exists and the image outside the line where the difference exists from the difference original image;

and identifying defects in the area near the outer edge based on the outer edge of the deleted broken difference original image.

In a fourth aspect, the present application further provides an image enhancement device applied to positioning of a step surface or a step, the image enhancement device including:

the difference value calculation module is used for calculating pixel value differences between each pixel of the original image of the target image and surrounding pixels of the pixel to obtain a deviation image;

the enhancement calculation module is used for carrying out homodromous enhancement on each pixel in the deviation graph to obtain an enhancement graph; the same-direction enhancement is enhancement for ensuring that the positive and negative of each pixel in the deviation graph are kept unchanged;

and the superposition module is used for superposing each pixel corresponding to the original image and the enhancement image to obtain a final image.

In a fifth aspect, the present application further provides a positioning device for a step surface or a step, including:

an image enhancement module, which adopts the device provided in the fourth aspect, and is configured to enhance each pixel of the target image to obtain an enhanced image of the target image;

the pixel determining module is used for comparing each pixel of each row of pixels in the enhanced image with a preset threshold value and determining pixels smaller than the preset threshold value as target pixels;

and the straight line fitting module is used for carrying out straight line fitting on the target pixels in all the rows of pixels to obtain the step surface or the line where the difference is located.

In a sixth aspect, the present application further provides an inspection apparatus, including:

a step surface and/or a difference positioning device, which is provided by the fifth aspect of the present invention, is used for positioning the step surface in the step surface original image to obtain a step surface position line, and/or positioning the difference in the difference original image to obtain a difference position line;

and the defect identification device is used for identifying the defects in the vicinity area of the line where the step surface is located in the step surface original image and/or identifying the defects in the vicinity area of the line where the step surface is located in the step surface original image.

In a seventh aspect, the present application further provides a storage medium on which program instructions are stored, the program instructions being configured, when executed, to perform the image enhancement method for step face or step difference positioning provided in the first aspect, or the step face or step difference positioning method provided in the second aspect, or the inspection method provided in the third aspect.

The application provides an image enhancement method which can not only highlight the color difference among pixels of a target image, but also give consideration to the original pixel value attribute of each pixel, so that under the condition that the image to be detected contains complex structures with a plurality of different pixel values, the method still can provide an effective basis for extracting different types of target objects in areas with different pixel values, for example, a basis for positioning step surfaces or line where the step is located in the edge area, so that the follow-up edge inspection based on the step surfaces and the line where the step is located is facilitated.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive faculty for a person skilled in the art.

Fig. 1 is a flowchart of an image enhancement method provided in an embodiment of the present application;

fig. 2 is a flowchart of step S10 in fig. 1;

fig. 3 is a top view of a CF substrate and a TFT substrate;

fig. 4 is a flowchart of an edge line positioning method according to an embodiment of the present application;

FIG. 5 is a flowchart of step S200 in FIG. 4;

FIG. 6 is a flowchart of an edge inspection method according to an embodiment of the present disclosure;

fig. 7 is a schematic block diagram of an image enhancement apparatus according to an embodiment of the present invention;

FIG. 8 is a schematic block diagram of a step surface or step height positioning device according to an embodiment of the present invention;

fig. 9 is a schematic block diagram of an inspection apparatus according to an embodiment of the present invention.

Detailed Description

In order to make the present application solution better understood by those skilled in the art, the following description will clearly and completely describe the technical solution in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are only some embodiments of the present application, not all embodiments. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are within the scope of the present disclosure.

Fig. 1 is a flowchart of an image enhancement method according to an embodiment of the present invention, as shown in fig. 1, where the method includes:

difference value calculation step S10: calculating pixel value differences between each pixel of an original image of the target image and surrounding pixels of the pixel to obtain a deviation image;

enhancement step S20: carrying out equidirectional enhancement on each pixel in the deviation map to obtain an enhancement map; the same-direction enhancement is enhancement for ensuring that the positive and negative of each pixel in the deviation graph are kept unchanged;

superposition step S30: and superposing each pixel corresponding to the original image and the enhancement image to obtain a final image.

In this embodiment, the difference calculating step, as shown in fig. 2, includes:

filtering substep S101: and filtering the original image to obtain a filtered image. More specifically, in the filtering substep S11, filtering is performed by any one of mean filtering, median filtering, and weighted value filtering. The description is in more detail: if the average filtering is adopted, summing the pixel values of other pixels around each pixel in the original image, and then obtaining the average value to be used as the filtering pixel value of the pixel, wherein the filtering pixel values of all the pixels form a filtering image.

Calculation substep S102: and carrying out difference on pixel values of each pixel corresponding to each other in the original image and the filter image to obtain the deviation image. More specifically, the pixel values of the pixels at the same position in the original image and the filtered image are subjected to difference, for example, the pixels are distributed in a mode of arranging a plurality of rows and a plurality of columns, and then the pixels at the same row and the same column correspond to the pixels at the same column, and the pixel values of the pixels at the 1 st row and the 1 st column of the original image and the pixel at the 1 st row and the 1 st column of the filtered image are subjected to difference. Still more specifically, the pixel value of the filtered image may be subtracted from the pixel value of the original image, or the pixel value of the filtered image may be subtracted from the pixel value of the original image.

In the enhancement step S20, the offset pixel value corresponding to each pixel is enhanced in the same direction, which is to ensure that the positive and negative values of the offset pixel value remain unchanged but the value becomes larger. Specifically, in the enhancement step S20, the enhancement map is obtained by multiplying each pixel in the deviation map by a positive coefficient greater than 1 to perform the same-direction enhancement, and this way belongs to the multiple enhancement. Of course, in practical application, the same direction enhancement can be performed in an odd power manner, for example, the deviation pixel value of each pixel is performed three times, so that the positive and negative values are kept unchanged and the value is increased.

By means of the steps S10-S30, color differences among pixels of the target image can be highlighted, original pixel value attributes of the pixels are considered, and therefore, under the condition that the image to be detected contains complex structures with a plurality of different pixel values, effective foundations can be provided for extracting different types of target objects in areas with different pixel values, for example, foundations are provided for locating step surfaces or line of a step position in an edge area, and edge inspection based on the step surfaces and the line of the step position is facilitated.

In this embodiment, the method further includes the steps of:

step surface target image acquisition: a first preset region (region defined by two broken lines in fig. 3) including a theoretical step line (as shown in fig. 3) is acquired in the step surface original image as a target image of step surface positioning.

More specifically, in the step face target image acquisition step, it includes: and moving a first number of pixels in the first direction of the substrate based on the ideal step line in the original image to form a first dotted line, and moving a second number of pixels in the second direction of the substrate to form a second dotted line, and finally forming the first preset area defined by the first dotted line and the second dotted line. Therefore, in the enhancement method, only the first preset area is required to be processed as a target image, and the edge area image of the whole step surface is not required to be processed as the target image, so that the operation amount is reduced and the working efficiency is improved; in addition, since there may be defects such as shells in the edge region of the CF substrate, moving the second number of pixels toward the second direction can improve the accuracy of the subsequent defect recognition work.

In this embodiment, since there is a step difference with respect to the side where the CF substrate and the TFT substrate having no step face overlap, the steps of:

a step of obtaining a robust target image: and searching an outer edge line in the broken difference original image, and moving a third number of pixels towards a direction approaching to the broken difference original image based on the outer edge line to form the target image positioned as the broken difference. Therefore, when the outer edge line moves by the third number of pixels, a new virtual outer edge line is formed, an image area between the outer edge line and the virtual outer edge line is used as a target image, and the image of the outer edge area where the whole difference is located is not required to be shot and is used as the target image to be processed, so that the operation amount can be reduced, and the working efficiency can be improved.

Fig. 4 is a schematic block diagram of an edge line positioning method according to an embodiment of the present invention, where, as shown in fig. 4, an edge line includes a line where a step surface is located and a line where a step is located, and the edge line positioning method includes:

and an image enhancement step S100, wherein each pixel of the target image is enhanced by adopting the enhancement method provided in the above embodiment, so as to obtain an enhanced image of the target image.

A pixel determining step S200, comparing each pixel of each row of pixels in the enhanced image with a preset threshold value, and determining a pixel smaller than the preset threshold value as a target pixel; since the pixel value variation of the pixels in the direction from the CF substrate to the TFT substrate in the above step surface target region is: the direction from the CF substrate to the TFT substrate is understood as the row direction, and therefore, a pixel below the preset threshold value may be a pixel where the step surface is considered to be on-line, and may be a target pixel. Similarly, in the robust target region, the pixel value change from the background to the pixels in the panel direction is also: high- →low- →high, whereas the background-to-panel direction can be understood as the row direction, and therefore, pixels below the preset threshold can be considered as the line of the offset. In practical applications, it is preferable to select 1 pixel smaller than the preset threshold as the target pixel.

Line fitting step S300: and performing straight line fitting on the target pixel in the plurality of rows of pixels to obtain a line where the step surface or the difference between the steps is located. Because each row of pixels is provided with the target pixels, the step surface or the line of the broken difference can be obtained by carrying out straight line fitting on a plurality of target pixels on a plurality of rows of pixels.

In conclusion, the edge line positioning method adopts a mode of enhancing first and then threshold segmentation to realize positioning identification of the edge line.

In the pixel determining step S200 in the present embodiment, as shown in fig. 5, it includes:

step S2001, performing an average value processing on each column of adjacent rows of pixels in the enhanced image to obtain a row of average value pixels;

step S2002, finding out a target column where the pixel smaller than the preset threshold value is located in the row of average value pixels;

step S2003, determining pixels corresponding to the target column from the adjacent rows of pixels, and selecting at least 1 pixel as the target pixel.

Since there may be a defect in the step face target image and the step difference target image, which may affect the determination of no target pixel per line of pixels of the enhanced image, the above-described steps 2001 to 2003 can be employed to solve the problem, in which the target pixel is determined by a plurality of lines of pixels.

It should be noted that, when the image enhancement step S100 adopts the enhancement method with the step-face target image acquisition step according to the above embodiment, after the straight line fitting step, the method further includes:

step surface treatment: and merging the obtained online target image of the step surface into the original image of the step surface. Thus, based on the line where the step surface is located as the CF edge line, whether defects exist around the CF edge line or not can be detected based on the original image pair later so as to carry out edge inspection.

Fig. 6 is a flowchart of an edge inspection method according to an embodiment of the present invention, please refer to fig. 6, including:

step surface and/or offset positioning step S1000: by adopting the edge line positioning method provided by the embodiment, the step surface is positioned in the step surface original image to obtain the step surface online, and/or the difference is positioned in the difference original image to obtain the difference online.

And a defect identification step S2000, wherein defects in the vicinity of the line where the step surface is located are identified in the step surface original image, and/or defects in the vicinity of the line where the step is located are identified in the step surface original image.

Further, identifying a defect located in a line vicinity area where the discontinuity is located in the discontinuity original image in the defect identification step S2000 includes:

deleting the line where the difference is located from the original image of the difference, and deleting the image outside the line where the difference is located;

based on the outer edge of the deleted robust original image, defects in the region near the outer edge are identified.

Fig. 7 is a schematic block diagram of an image enhancement device applied to step surface or offset positioning according to an embodiment of the present invention, referring to fig. 7, the image enhancement device includes:

a difference calculating module 10, configured to calculate a difference between a pixel value of each pixel of an original image of a target image and a pixel surrounding the pixel, to obtain a deviation image;

the enhancement calculation module 20 is configured to perform homodromous enhancement on each pixel in the deviation map, so as to obtain an enhancement map; the same-direction enhancement is enhancement for ensuring that the positive and negative of each pixel in the deviation graph are kept unchanged;

and the superposition module 30 is configured to superimpose each pixel corresponding to the original image and the enhancement image to obtain a final image.

Fig. 8 is a schematic block diagram of a step surface or a step difference positioning device according to an embodiment of the present invention, please refer to fig. 8, wherein the step surface and the step difference positioning device include:

the image enhancement module 100, which adopts the image enhancement device provided in the above embodiment, is configured to enhance each pixel of the target image to obtain an enhanced image of the target image;

a pixel determining module 200, configured to compare each pixel of each row of pixels in the enhanced image with a preset threshold, and determine 1 pixel as a target pixel from pixels smaller than the preset threshold;

and the straight line fitting module 300 is used for performing straight line fitting on the target pixels in all the rows of pixels to obtain the step surface or the line where the difference is located.

Fig. 9 is a schematic block diagram of an edge inspection apparatus according to an embodiment of the present invention, referring to fig. 9, the edge inspection apparatus includes:

the step surface and/or offset positioning device 1000, which is provided by the foregoing embodiment, is used for positioning the step surface in the step surface original image to obtain a step surface online, and/or positioning the offset in the offset original image to obtain an offset online;

and defect identifying means 2000 for identifying a defect located in a vicinity of a line where the step surface is located in the step surface original image, and/or identifying a defect located in a vicinity of a line where the step is located in the step surface original image.

The embodiment of the invention also provides a storage medium, on which program instructions are stored, wherein the program instructions are used for executing the image enhancement method applied to step surface or offset positioning, the step surface or offset positioning method, or the edge inspection method.

It should be noted that, in the present specification, each embodiment is described in a progressive manner, and identical and similar parts of each embodiment are all referred to each other, and each embodiment is mainly described in a different point from other embodiments. In particular, for the device embodiments, since they are substantially similar to the method embodiments, the description is relatively simple, and reference is made to the description of the method embodiments for relevant points. The apparatus embodiments described above are merely illustrative, wherein elements illustrated as separate elements may or may not be physically separate, and elements illustrated as elements may or may not be physical elements, may be located in one place, or may be distributed over a plurality of network elements. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art will understand and implement the present invention without undue burden.

The foregoing is merely one specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present application should be covered in the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. An image enhancement method applied to the positioning of a step or a step, the method comprising:

2. The method of claim 1, wherein the difference calculating step comprises:

a filtering sub-step: filtering the original image to obtain a filtered image;

3. The method of claim 2, wherein in the filtering substep, filtering is performed by any one of mean filtering, median filtering, and weighted value filtering.

4. The method of claim 1, wherein in the enhancing step, the enhancement map is obtained by performing co-directional enhancement by multiplying each pixel in the deviation map by a positive coefficient greater than 1.

5. The method of claim 1, further comprising the step of:

6. The method of claim 5, wherein in the step-face target image acquisition step, comprising: the first preset area is finally formed by moving a first number of pixels in a first direction of the substrate and a second number of pixels in a second direction of the substrate based on the ideal step line in the original image.

7. The method of claim 1, further comprising the step of:

8. An edge line locating method, comprising:

an image enhancement step of enhancing each pixel of the target image by using the enhancement method as claimed in any one of claims 1 to 7 to obtain an enhanced image of the target image;

9. The method of claim 8, wherein in the pixel determining step, comprising:

10. The method of claim 8, further comprising, after the straight line fitting step, when the image enhancing step employs the enhancing method of claim 5 or 6:

11. The edge inspection method is characterized by comprising the following steps of:

step surface and/or step positioning: positioning the step surface in the step surface original image to obtain a step surface position line, and/or positioning the difference in the difference original image to obtain a difference position line by adopting the edge line positioning method of any one of claims 8-10;

12. The inspection method according to claim 11, wherein identifying, in the defect identifying step, a defect located in a region near a line where the break is located in the broken difference original image, includes:

13. An image enhancement device is characterized by being applied to positioning of a step surface or a break; the image enhancement apparatus includes:

14. A step or step locating device comprising:

an image enhancement module, which adopts the image enhancement device of claim 13, and is used for enhancing each pixel of the target image to obtain an enhanced image of the target image;

and the linear fitting module is used for carrying out linear fitting on the target pixel in the plurality of rows of pixels to obtain the step surface or the line where the difference between the steps is located.

15. An inspection apparatus, comprising:

a step surface and/or offset positioning device, which adopts the step surface or offset positioning device of claim 14, and is used for positioning the step surface in the original step surface image to obtain the online of the step surface, and/or positioning the offset in the original offset image to obtain the online of the offset;

16. A storage medium having stored thereon program instructions for executing, when executed, the image enhancement method for step face or step difference localization as claimed in any one of claims 1 to 7, or the step face or step difference localization method as claimed in any one of claims 8 to 10, or the inspection method as claimed in claims 11 to 12.