CN109872269B - Compton camera image fusion method based on fisheye image correction - Google Patents
Compton camera image fusion method based on fisheye image correction Download PDFInfo
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Abstract
The invention discloses a compton camera image fusion method based on fisheye image correction, which comprises the following steps: 1) placing the fisheye lens in front of the Compton camera detector to enable imaging original points of the fisheye lens and the Compton camera detector to coincide; 2) acquiring a fisheye distortion image through a fisheye lens; processing data acquired by a Compton camera detector according to a Compton scattering imaging reconstruction algorithm to obtain a gamma source reconstruction image expressed by longitude and latitude coordinates of a unit spherical coordinate system; 3) correcting the fish eye distortion image; 4) the longitude and latitude coordinates of the gamma source reconstructed image are adjusted (theta,
) The coordinate range of the fish-eye correction image is kept consistent with the coordinate range of the fish-eye correction image; 5) and overlapping the adjusted gamma source reconstruction image to the fisheye correction image to complete the image fusion of the Compton camera. The method can realize rapid and accurate image fusion, is suitable for the Compton camera equipment for acquiring optical images through the fisheye lens, and can optimize the gamma hot spot display effect of the Compton camera.
Description
Technical Field
The invention belongs to the field of nuclear radiation detection and nuclear technology application, and particularly relates to a compton camera image fusion method based on fisheye image correction.
Background
In the field of nuclear radiation detection, a gamma imaging technology for positioning and imaging gamma radiation hot spots existing in the environment is widely applied to the fields of astronomical observation, nuclear industry, nuclear emergency, nuclear security, national defense and the like. The gamma imaging technology generally gives out the reconstructed gamma radiation hot spot as a two-dimensional false color image, and fuses with an optical image of the environment to show the distribution of the gamma radiation hot spot in the environment. Compton scattering imaging is one of gamma imaging techniques, and based on the compton scattering principle of incident gamma photons, the direction of the gamma photon source is retrospectively reconstructed by measuring the positions of a scattering point and an absorption point and the deposited energy. Devices that image gamma radiation hot spots at a distance using the principles of compton scatter imaging are commonly referred to as compton cameras.
Because the Compton camera adopts the working principle of Compton scattering, a collimator is not required to be used for blocking incident gamma photons, and the visual field range can reach 2 pi or even 4 pi. Based on each scattering case, Compton scattering reconstruction forms a conical surface containing the incidence direction of gamma photons; conical surfaces corresponding to the multiple scattering cases are overlapped, and the formed overlapped densest area is the direction of the gamma radiation hot point. According to the Compton scattering imaging principle, the space coordinate system where the gamma source reconstruction image is located is a spherical coordinate system. In order to display the gamma source reconstructed image on a two-dimensional plane, a unit spherical coordinate system is generally adopted, and the vertical axis is a polar angle theta, and the horizontal axis is an azimuth angle
The longitude and latitude coordinates of (a) represent the reconstructed gamma radiation hot spot locations (theta,
) The coordinate range is 2 pi visual field theta ∈ (0, pi),
4 π field of view θ ∈ (0, π),
therefore, in a compton camera, the field of view of a common optical lens cannot meet the requirement, and at present, a fisheye lens with the field of view reaching 180 ° (pi) is generally adopted to acquire an optical image and is further fused with a gamma source reconstruction image.
The image fusion method used in the present compton camera generally directly uses the optical distortion image of the fisheye lens to superimpose the two-dimensional pseudo color image reconstructed by the gamma source on the fisheye distortion image. According to the technical scheme, because the pixel points in the fisheye distortion image contain distance information, the coordinate axis of the image is not represented by longitude and latitude coordinates under a unit spherical coordinate system, and therefore the pixel points cannot be represented by longitude and latitude coordinates under the unit spherical coordinate systemIn terms of the longitude and latitude coordinates (theta,
) The expressed gamma source reconstruction image is directly superposed on the fisheye distortion image, and the longitude and latitude coordinates (theta,
) And after projection transformation (such as planar projection (planar projection), stereoscopic projection (Stereographic projection) and the like), interpolating the gamma source reconstructed image according to the radius of the fisheye distorted image, and finally superposing the interpolated gamma source reconstructed image on the fisheye distorted image to complete image fusion.
Since the latitude and longitude coordinates (theta,
) After projection transformation, pixels projected on an imaging plane are deformed, and a sawtooth effect is generated; in order to eliminate the sawtooth effect, if the coordinate step length during the gamma source reconstruction is further subdivided or a finer interpolation method is adopted, the calculation time of the gamma source reconstruction is increased, and the rapid and real-time image reconstruction and fusion of a Compton camera are not facilitated.
Disclosure of Invention
Aiming at the problems existing in the image fusion of the Compton camera at present, the invention aims to provide a method for image fusion of the Compton camera based on fisheye image correction, and the method is applied to the rapid image registration and fusion of the Compton camera.
The method is based on the correction of fisheye distortion images, and the fisheye distortion images are mapped into a unit spherical coordinate system expressed by longitude and latitude coordinates through a corresponding imaging model; and (3) reconstructing an image of the gamma source in the same unit spherical coordinate system and with the coincident origin of coordinates, and superposing the adjusted image on the fisheye correction image to realize image fusion.
The flow chart of the method is shown in fig. 1, and the specific steps include:
1. placing a fisheye lens with a focal length of f at a position f in front of the center of the visual field of a Compton camera detector, so that the imaging origin of the fisheye lens coincides with the imaging origin of the Compton camera;
2. obtaining a fisheye distortion image with a view field range of 180 degrees (pi) through the fisheye lens; the longitude and latitude coordinates (theta,
) A representative gamma source reconstructed image;
3. the correction process for the fisheye distorted image is as follows:
3.1 determining the focal length f of the fisheye lens, the radius R of the effective area of the fisheye distorted image and the included angle theta between the incident light and the optical axis of the lens according to the fisheye lens imaging modelλThe relation between the three and the conversion method between the coordinate systems, a mapping relation F of coordinates (u, v) on the fisheye distortion image and longitude and latitude coordinates (lambda, psi) of a unit spherical coordinate system is established: (u, v) → (λ, ψ);
3.2 according to the mapping relation, filling the values of the coordinates (u, v) on the fisheye distortion image into the longitude and latitude coordinates (lambda, psi) of the corresponding unit spherical coordinate system to finish fisheye image correction;
3.3, according to the fisheye lens imaging model, extending the coordinate range of the longitude and latitude coordinates (lambda, psi) of the unit spherical coordinate system to (P (lambda), P (psi)) to obtain a fisheye correction image;
4. and for the gamma source reconstruction image, adjusting the longitude and latitude coordinates (theta,
) The coordinate range of the fish-eye correction image is kept consistent with the coordinate range of the fish-eye correction image;
5. superposing the adjusted gamma source reconstruction image on the fisheye correction image to complete the image fusion of a Compton camera; the fusion display effect is optimized by adjusting the display threshold of the gamma source reconstruction image.
Compared with the prior art, the invention has the following positive effects:
the invention avoids the need for reconstructing images from gamma sourcesThe coordinates of the weft (theta,
) Projection transformation is carried out, the information integrity of the gamma source reconstruction image is kept, and no sawtooth effect is generated; distance information of the corrected fisheye image is eliminated, and the gamma source position is positioned by a method of representing longitude and latitude coordinates under a unit spherical coordinate system; meanwhile, the origin of the coordinate system of the corrected fisheye correction image coincides with the origin of the coordinate system of the gamma source reconstruction image, and rapid and accurate image fusion can be realized. The method is suitable for the Compton camera equipment for acquiring the optical image through the fisheye lens, can optimize the gamma hot spot display effect of the Compton camera, and further enhances the market application capability of the Compton camera.
Drawings
FIG. 1 is a flow chart of a method of the present invention;
fig. 2 is a schematic diagram of the placement of the fisheye lens and the compton camera detector.
Detailed Description
The invention provides a compton camera image fusion method based on fisheye image correction, which comprises the following implementation steps:
1. placing a fisheye lens in front of the Compton camera detector to enable imaging original points of the two to coincide;
2. acquiring a fisheye distortion image through a fisheye lens; acquiring a gamma source reconstruction image expressed by longitude and latitude coordinates of a unit spherical coordinate system according to a Compton scattering imaging reconstruction algorithm through data acquired by a Compton camera detector;
3. correcting the fish eye distortion image:
3.1, according to a fisheye lens imaging model and a coordinate system conversion method, establishing a mapping relation between fisheye distortion image coordinates and longitude and latitude coordinates of a unit spherical coordinate system;
3.2 according to the mapping relation, filling the coordinate value of the fisheye distortion image into the longitude and latitude coordinates of the unit spherical coordinate system to finish fisheye image correction;
3.3 according to the fisheye lens imaging model, expanding the longitude and latitude coordinate range of the unit spherical coordinate system to obtain a fisheye correction image;
4. adjusting the coordinate range of the gamma source reconstructed image to be consistent with the coordinate range of the fisheye corrected image;
5. superposing the adjusted gamma source reconstruction image on the fisheye correction image to complete the image fusion of the Compton camera; the fusion display effect is optimized by adjusting the display threshold of the gamma source reconstruction image.
In step 1, referring to fig. 2, a method for placing a fisheye lens in front of a compton camera detector to make the imaging origins of the two coincident is as follows: and placing the fisheye lens with the focal length of f at a position f in front of the center of the visual field of the Compton camera detector, so that the imaging origin of the fisheye lens coincides with the imaging origin of the Compton camera detector.
In the step 2, the visual field range of the fisheye distortion image obtained through the fisheye lens is 180 degrees (pi); the gamma source reconstructed image obtained from the data acquired by the compton camera detector according to the compton scatter imaging reconstruction algorithm is a unit spherical coordinate system of longitude and latitude coordinates (theta,
) Expressed in the range of theta ∈ [0, pi ]]，
It should be noted that the data acquired by the compton camera detector include scattering position and deposition energy, and complete absorption position and deposition energy of the incident gamma photon in the detector, and the compton scattering reconstruction algorithm may be a Back projection algorithm (SBP), a Filtered Back projection algorithm (FBP), a Maximum likelihood Expectation Maximization (Maximum L i keliood Expectation Maximization, M L EM), and the like, which is not limited herein.
Specifically, a specific method for acquiring detector data of a compton camera and a method for obtaining a gamma source reconstruction image according to a compton scattering imaging reconstruction algorithm are known to those skilled in the art, and will not be described here again.
In step 3, the fish eye distortion image is corrected as follows:
3.1 determining the focal length f, the radius R of the effective area of the fisheye distortion image and the included angle theta between the incident ray and the optical axis of the lens according to the fisheye lens imaging modelλThe relation between the three and the conversion method between the coordinate systems, a mapping relation F of coordinates (u, v) on the fisheye distortion image and longitude and latitude coordinates (lambda, psi) of a unit spherical coordinate system is established: (u, v) → (λ, ψ);
3.2 according to the mapping relation, filling the values of the coordinates (u, v) on the fisheye distortion image into the longitude and latitude coordinates (lambda, psi) of the corresponding unit spherical coordinate system to finish fisheye image correction;
3.3, according to the fisheye lens imaging model, gradually expanding the coordinates of the longitude and latitude coordinates (lambda, psi) of the unit spherical coordinate system to (P (lambda), P (psi)) to obtain a fisheye correction image;
in step 3.1, specifically, the focal length f, the radius R of the effective area of the fisheye distorted image, and the included angle θ between the incident light and the optical axis of the lens are determined according to the fisheye lens imaging modelλThe specific method of the relationship between the three is based on thetaλR, f and the transformation between the coordinate systems to establish the mapping relationship between the coordinates on the fisheye distortion image and the longitude and latitude coordinates of the unit spherical coordinate system, which is known to those skilled in the art and will not be described herein.
In steps 3.2 and 3.3, it should be noted that the fisheye image correction process is a process of finding pixel values of corresponding coordinates in the fisheye distortion image one by one according to the mapping relationship from longitude and latitude coordinates under the unit spherical coordinate system, and filling the pixel values into the current longitude and latitude coordinates, rather than the inverse process of the process. The coordinates of the fisheye correction image obtained finally are actually the expansion (P (lambda), P (psi)) of the longitude and latitude coordinates of the unit spherical coordinate system, and the expansion relation P is determined according to the fisheye lens imaging model. As an example, when a fisheye lens employs an imaging model of equidistant projection, the extended relationship of points (P (λ, P (ψ)) on a fisheye correction image and longitude and latitude coordinates (λ, ψ) of a unit spherical coordinate system is: p (λ) ═ λ/f, and P (ψ) ═ ψ/f, where f is the focal length of the fisheye lens. This expansion process is similar to the stretching transformation of coordinates.
In step 4Adjusting the longitude and latitude coordinates (theta,
) So as to be consistent with the coordinate range of the fisheye correction image. Specifically, the method for adjusting the coordinate range is known to those skilled in the art, and will not be described herein.
In step 5, overlapping the adjusted gamma source reconstruction image to the fisheye correction image to complete the image fusion of the Compton camera; the fusion display effect is optimized by adjusting the display threshold of the gamma source reconstruction image. Specifically, the method of image superimposition and the method of adjusting the image display threshold are known to those skilled in the art, and will not be described herein again.
In summary, the above is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (8)
1. A compton camera image fusion method based on fisheye image correction comprises the following steps:
1) placing the fisheye lens in front of the Compton camera detector to enable imaging original points of the fisheye lens and the Compton camera detector to coincide;
2) acquiring a fisheye distortion image through a fisheye lens; processing data acquired by a Compton camera detector according to a Compton scattering imaging reconstruction algorithm to obtain a gamma source reconstruction image expressed by longitude and latitude coordinates of a unit spherical coordinate system;
3) correcting the fisheye distortion image to obtain a fisheye correction image; the method for correcting the fisheye distortion image comprises the following steps: a) according to a fisheye lens imaging model and a coordinate system conversion method, establishing a mapping relation between fisheye distortion image coordinates and longitude and latitude coordinates of a unit spherical coordinate system; b) according to the mapping relation, filling coordinate values on the fisheye distortion image into longitude and latitude coordinates of a unit spherical coordinate system to finish fisheye image correction; c) according to the fisheye lens imaging model, extending the longitude and latitude coordinate range of the unit spherical coordinate system to obtain a fisheye correction image;
4) adjusting longitude and latitude coordinates of the gamma source reconstruction image
To make it consistent with the coordinate range of the fisheye correction image;
5) and overlapping the adjusted gamma source reconstruction image to the fisheye correction image to complete the image fusion of the Compton camera.
2. The method of claim 1, wherein the mapping relationship is established by: firstly, determining the focal length f of a fisheye lens, the radius R of an effective area of a fisheye distortion image and the included angle theta between incident light and the optical axis of the lens according to a fisheye lens imaging modelλThe relationship between the three; then, according to the relationship and a conversion method between coordinate systems, establishing a mapping relationship F between coordinates (u, v) on the fisheye distortion image and longitude and latitude coordinates (lambda, psi) of a unit spherical coordinate system: (u, v) → (λ, ψ).
3. The method of claim 1, wherein the latitude and longitude coordinate range of the unit spherical coordinate system is extended by: according to a fisheye lens imaging model, extending the coordinate range of longitude and latitude coordinates (lambda, psi) of a unit spherical coordinate system to (P (lambda), P (psi)) to obtain a fisheye correction image; wherein, the expansion relation P () is determined according to the fisheye lens model.
4. The method of claim 1, wherein the data acquired by the compton camera detector is the scattering position and deposited energy, the fully absorbed position and deposited energy of the incident gamma photon in the detector.
5. The method of claim 1, wherein the image fusion display effect is optimized by adjusting a display threshold of the gamma source reconstructed image.
6. The method of claim 1, wherein a fisheye lens having a focal length f is placed f in front of the center of the field of view of the compton camera detector so that the imaging origin of the fisheye lens coincides with the imaging origin of the compton camera.
7. The method of claim 1, wherein the compton scatter reconstruction algorithm includes, but is not limited to, a back-projection algorithm, a filtered back-projection algorithm, a maximum likelihood expectation maximization method.
8. The method of claim 1, wherein the gamma-source reconstructed image is latitude and longitude coordinates of a unit spherical coordinate system
Expressed, its coordinate range is θ ∈ (0, π),
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| CN101783011A (en) * | 2010-01-08 | 2010-07-21 | 宁波大学 | Distortion correction method of fish eye lens |
| CN108535293A (en) * | 2018-02-26 | 2018-09-14 | 奕瑞新材料科技（太仓）有限公司 | Compton scatter imaging method |
| CN108511043A (en) * | 2018-02-27 | 2018-09-07 | 华东师范大学 | The acquisition of X-CT virtual datas and image rebuilding method based on numerical simulation and system |
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