A vignetting correction method for image-based photometer

Abstract

The present invention relates to a vignetting correction method for an image-based photometer. After the vignetting correction formula is obtained by calculation, the actual light source brightness is realized by a movable standard light source installed on a workbench. The present invention can improve the accuracy of brightness and effectively improve the measurement accuracy for later tests.

Description

Technical Field

[0001] The invention belongs to the field of graphics processing technology, and in particular relates to a dark corner correction method of an image-based photometer. Background Art

[0002] With the development of science and technology and the improvement of living standards, people have higher and higher requirements for product quality, and the industrial requirements for product quality inspection are also getting higher and higher, such as the uniformity of screen brightness, the uniformity of keyboard lighting, etc. The application of machine vision with industrial cameras as core components is becoming more and more extensive.

[0003] Generally, image acquisition devices use photosensitive elements such as charge-coupled devices (CCD) or complementary metal-oxide semiconductors (CMOS) to capture light that enters the camera body through the lens. When light passes through the lens group, it will be refracted and the image will be presented on the photosensitive element. However, since the refraction of light will cause energy attenuation, and the refraction angle of light passing through the edge of the lens will be larger than the refraction angle of light passing through the center of the lens, the edge area of ​​the image will be darker and the center area will be brighter. This phenomenon is called "shading" or "vignetting" in the field of photography and optics. If the image method is used to detect brightness, the vignetting effect will seriously affect the measurement accuracy. Summary of the invention

[0004] In order to solve the above technical problems, an object of the present invention is to provide a vignetting correction method for an image-based photometer.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A method for correcting vignetting of an image-based photometer, characterized in that it comprises the following calibration steps:

[0007] Step 1: A standard light source is set in the workbench. There are N narrow-band filters on the standard light source. The main wavelength corresponding to each filter is evenly distributed in the band of 380-750. The standard light source moves in a rectangular array in the workbench. There are M shooting points on the workbench, and the camera is always in the same position during the entire calibration process;

[0008] Step 2: Move the standard light source to the shooting point i, and the camera takes a picture of the position with the standard light source on the working platform;

[0009] Step 3: Measure the brightness of the filter corresponding to the i-th shooting point in step 2, that is, V 1i 、V2i 、V 3i 、V 4i …V Ni ;

[0010] Step 4: Repeat steps 2 and 3 until M points are photographed;

[0011] Step 5: According to V i1 , V i2 , …, V iM Calculate the vignetting correction coefficient K corresponding to the i-th filter i0, K i1 ,…,K in , 1<=i<=N

[0012] Step 6: Obtain spectral data of the target light source;

[0013] Step 7: Based on the spectral data, calculate the spectral intensity V1, V2, V3, V4…V at the corresponding wavelength position of the filter N , and then normalize: V1 / (V1+V2+V3+V4…V N )=R1, and the normalized ratios of N wavelengths are calculated respectively: R1, R2, R3, R4…R N ;

[0014] Step 8: The camera shoots the product on the work platform to obtain the brightness Y' at any point. The brightness Y' at each point is used to obtain the brightest Y at any point using the vignetting correction formula. The vignetting correction formula is as follows:

[0015]

[0016] in

[0017] R is the normalized ratio;

[0018] Y is the final brightness at a certain location;

[0019] k is the coefficient;

[0020] Y' is the brightness at any point;

[0021] r is the radius away from the brightest point.

[0022] Preferably, in the vignetting correction method of an image-based photometer, the standard light source is a broad-spectrum light source.

[0023] Preferably, in the vignetting correction method of the image-based photometer, the moving range of the standard light source is within the range captured by the camera lens.

[0024] Preferably, in the vignetting correction method of an image-based photometer, the filter on the standard light source can divide the light source into a plurality of matrices with different spectra.

[0025] By means of the above scheme, the present invention has at least the following advantages:

[0026] The present invention adds a spectral light source with a filter to the light source of the working platform, so that a stable light source for the working platform can be calculated, thereby effectively improving the accuracy of subsequent products.

[0027] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail as follows. DETAILED DESCRIPTION

[0028] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] Example

[0030] A vignetting correction method for an image-based photometer includes the following calibration steps:

[0031] Step 1: A standard light source is set in the workbench. There are N narrow-band filters on the standard light source. The main wavelength corresponding to each filter is evenly distributed in the band of 380-750. The standard light source moves in a rectangular array in the workbench. There are M shooting points on the workbench, and the camera is always in the same position during the entire calibration process;

[0032] Step 2: Move the standard light source to the shooting point i, and the camera takes a picture of the position with the standard light source on the working platform;

[0033] Step 3: Measure the brightness of the filter corresponding to the i-th shooting point in step 2, that is, V 1i 、V 2i 、V 3i 、V 4i …V Ni ;

[0034] Step 4: Repeat steps 2 and 3 until M points are photographed;

[0035] Step 5: According to V i1 , V i2 , …, V iM Calculate the vignetting correction coefficient K corresponding to the i-th filter i0, Ki1 ,…,K in , 1<=i<=N

[0036] Step 6: Obtain spectral data of the target light source;

[0037] Step 7: Based on the spectral data, calculate the spectral intensity V1, V2, V3, V4…V at the corresponding wavelength position of the filter N , and then normalize: V1 / (V1+V2+V3+V4…V N )=R1, and the normalized ratios of N wavelengths are calculated respectively: R1, R2, R3, R4…R N ;

[0038] Step 8: The camera shoots the product on the work platform to obtain the brightness Y' at any point. The brightness Y' at each point is used to obtain the brightest Y at any point using the vignetting correction formula. The vignetting correction formula is as follows:

[0039]

[0040] in

[0041] R is the normalized ratio;

[0042] Y is the final brightness at a certain location;

[0043] k is the coefficient;

[0044] Y' is the brightness at any point;

[0045] r is the radius away from the brightest point.

[0046] The standard light source in the present invention is a broad-spectrum light source, and the broad-spectrum light source is covered with filters, wherein the filters are covered on the spectrum light source in an M*N rectangular array.

[0047] The moving range of the standard light source in the present invention is within the range captured by the camera lens.

[0048] The filter on the standard light source described in the present invention can divide the light source into a plurality of matrices with different spectra.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A vignetting correction method for an image-based photometer, characterized in that: The calibration steps include the following: Step 1: A standard light source is set in the workbench. There are N narrow-band filters on the standard light source. The main wavelength corresponding to each filter is evenly distributed in the band of 380-750. The standard light source moves in a rectangular array in the workbench. There are M shooting points on the workbench, and the camera is always in the same position during the entire calibration process; Step 2: Move the standard light source to the shooting point i, and the camera takes a picture of the position with the standard light source on the working platform; Step 3: Measure the brightness of the filter corresponding to the i-th shooting point in step 2, that is, ; Step 4: Repeat steps 2 and 3 until M points are photographed; Step 5: According to Calculate the vignetting correction coefficient corresponding to the i-th filter , 1<=i<=N; Step 6: Obtain the spectrum data of the target light source; Step 7: Based on the spectral data, calculate the spectral intensity V1, V2, V3, V4…V at the corresponding wavelength position of the filter N , and then normalize: V1 / (V1+V2+V3+V4…V N ) = R1, and the normalized ratios of N wavelengths are calculated respectively: R1, R2, R3, R4…R N ; Step 8: The camera shoots the product on the work platform to obtain the brightness Y' at any point. The brightness Y' at each point is used to obtain the brightest Y at any point using the vignetting correction formula. The vignetting correction formula is as follows: ； in, R i is the normalized ratio; Y is the final brightness at a certain location; k ij is the coefficient; Y' is the brightness at any point; r j is the radius away from the brightest point.

2. The vignetting correction method of the image-based photometer according to claim 1, characterized in that: The standard light source is a broad-spectrum light source.

3. A vignetting correction method for an image-based photometer according to claim 1 or 2, characterized in that: The moving range of the standard light source is within the range captured by the camera lens.

4. The vignetting correction method of an image-based photometer according to claim 1, characterized in that: The filter on the standard light source can divide the light source into several matrices with different spectra.

Images