Polarization imaging method used under scattered medium
Through the combination of Fourier transform and inverse transform, the Stokes spectrum amplitude and phase under scattered medium are calculated and restored, which solves the problem that the object polarization information cannot be restored in the prior art, and achieves high-quality polarization imaging.
Patent Information
- Application Number
- CN202411891647.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-20
- Publication Date
- 2025-05-23
AI Technical Summary
The prior art is difficult to restore the polarization information of an object under a scattered medium, resulting in confusion in the target feature information and degradation in the image quality.
By performing Fourier transform on the Stokes image, the amplitude and phase of the Stokes spectrum are calculated, and the polarization information is restored in combination with the inverse Fourier transform.
It realizes effective recovery of object polarization information under scattered media conditions, improves imaging quality and information integrity, and can clearly display the edge structure and details of the object.
Smart Images
Figure CN120027914A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the field of polarization imaging, and in particular to a polarization imaging method for use in a scattered medium. Background Art
[0002] Polarization imaging technology is an advanced photoelectric detection method that has attracted great attention from researchers at home and abroad in recent years. By capturing the polarization information of light, polarization imaging can obtain more details of the target scene. Compared with traditional imaging technology, polarization imaging technology can provide richer scene information, so it has significant advantages in improving target detection accuracy and is widely used in astronomical observation, target detection, biomedical imaging and other fields.
[0003] Traditional imaging methods are based on scalar imaging, which can characterize the light intensity information in the scalar imaging system, but cannot effectively characterize the imaging polarization information under scattered media. Because the polarization image of the target appears as a polarization speckle image under scattered media conditions, it is difficult for existing technologies to directly distinguish the target features from it. Therefore, there is a lack of means for characterizing polarization information in the current imaging technology methods under scattered media. There is an urgent need for a polarization imaging method suitable for scattered media conditions to effectively restore the polarization information of the object. Summary of the invention
[0004] The present invention provides a polarization imaging method for use in a scattered medium to solve the problem in the prior art that the polarization information of an object cannot be restored in a scattered medium.
[0005] In order to achieve the purpose of the present invention, the technical solution to be provided by the present invention is as follows: a polarization imaging method for a scattered medium, performing Fourier transform on the Stokes image, calculating the amplitude of the Stokes spectrum, calculating the phase of the Stokes spectrum, and finally performing inverse Fourier transform to recover the polarization information.
[0006] Furthermore, the above imaging method has the following specific steps:
[0007] Step 1: Perform Fourier transform on the Stokes image: Perform two-dimensional Fourier transform on the N images recorded by the Stokes image detector containing object information to obtain the spectrum of each channel;
[0008] Step 2: Calculate the amplitude of the Stokes spectrum in the frequency domain: Use the superposition algorithm to square the N Stokes spectrum images recorded by each channel after Fourier transformation, then sum them up, and then calculate the average value. Calculate the restored object amplitude information based on the corresponding relationship between the input and output of the imaging system;
[0009] Step 3: Calculate the phase of the Stokes spectrum in the frequency domain: Use the Stokes cross-spectrum phase unpacking algorithm to extract the Stokes cross-spectrum phase difference of the N Fourier-transformed Stokes spectrum images recorded by each Stokes channel, and recover the phase information from the Fourier spectrum point by point through the phase difference;
[0010] Step 4: Restore polarization information by inverse Fourier transform: By combining the amplitude and phase information of the calculated Stokes spectrum, an inverse Fourier transform is performed to restore the polarization information in the frequency domain to the spatial domain, thereby obtaining the complete polarization image information of the target object.
[0011] Furthermore, in the above step 1, the spectrum of each channel is expressed as:
[0012]
[0013] in, Represents the Stokes spectrum of the object, H(f x ,f y ) represents the spectrum of the optical transfer function of the polarization imaging system, represents the Stokes spectrum of the image.
[0014] Furthermore, the specific steps of the above step 2 are:
[0015] First, the amplitude of the Stokes spectrum of each channel is calculated;
[0016] Then, the N Stokes spectrum images recorded by each channel after Fourier transformation are squared and summed, and then the average value is calculated. The expression is:
[0017]
[0018] Wherein, the left subscript “k” represents the number of times, corresponding to each of the N groups of Stokes spectra.
[0019] Then calculate the average of the square of the modulus of the object's Stokes spectrum amplitude
[0020]
[0021] in, represents the transfer function of the polarization imaging system;
[0022] Finally, take the square root of formula (4) to get the final Stokes amplitude:
[0023]
[0024] in, The Stokes amplitude of the object finally calculated and restored is represented by the subscript “l” on the right. and
[0025] Furthermore, in the above step 3, the average Stokes cross spectrum of the image is expressed as:
[0026]
[0027] in, is the average cross-spectral transfer function.
[0028] The Stokes cross spectrum of an object is expressed as
[0029]
[0030] in, Indicates phase, upper right The corresponding Stokes spectrum is and From formula (9), we can know that the phase difference is
[0031] Furthermore, in the above step 4, the Stokes image of the object recovered from the scattered medium is expressed as:
[0032]
[0033] in, Represents the inverse Fourier transform operation.
[0034] Compared with the prior art, the advantages of the present invention are:
[0035] 1. The present invention proposes a polarization imaging method, which adopts different processing methods for the recovery of amplitude and phase. In this technology, by combining the amplitude and phase information of the Stokes spectrum and performing an inverse Fourier transform on it, the recovery of the polarization information of the object under the condition of a scattered medium is achieved. Among them, the amplitude is acquired by a superposition algorithm, and the phase recovery is based on the Stokes cross-spectrum phase unpacking algorithm, which ensures the integrity and accuracy of the polarization information. The phase unpacking algorithm used in the present invention has evolved from a one-dimensional operation to a polarization Stokes four-dimensional operation. For the first time, a method for extracting Stokes phase information applied to polarization image phase unpacking is proposed, which breaks through the limitation that traditional algorithms only process amplitude and phase information, and can fully describe the polarization, phase and amplitude of the light field, greatly improving the integrity and accuracy of the information. At the same time, this evolution enhances the applicability and processing capabilities of the present invention for complex light fields, expands the application field, and provides strong support for technologies such as polarization imaging.
[0036] 2. The present invention proposes a polarization imaging technology that focuses on solving imaging problems under scattered medium conditions. Unlike ordinary polarization imaging that directly obtains clear images, in a scattering environment, polarization speckle images will be generated due to the interaction between light and the medium, resulting in confusion of target feature information and degradation of image quality. By introducing amplitude and phase recovery algorithms, the present invention can effectively extract the amplitude information of the light field and reconstruct the phase information, thereby restoring the true characteristic structure of the object. This method not only breaks through the destructive effect of scattering media on the light field, but also improves the imaging quality and information integrity, making the edge structure and details of the object clearly visible. Compared with traditional methods, the present invention has stronger robustness and higher imaging accuracy, and is suitable for complex scenes such as biomedical imaging, atmospheric and underwater detection, and has broad application value and important scientific significance. BRIEF DESCRIPTION OF THE DRAWINGS
[0037] Figure 1 is a flow chart of the method of the present invention;
[0038] Figure 2 It is a schematic diagram of imaging for characterizing polarization information of the present invention. DETAILED DESCRIPTION
[0039] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.
[0040] See also Figure 1 The design idea of the present invention is: after the distorted wavefront affected by the scattered medium passes through the imaging lens, the Stokes image detector records N images with the polarization information of the target object, and the amplitude and phase information of the object are obtained respectively through the superposition algorithm and the Stokes cross-spectrum phase unpacking algorithm, and finally the inverse Fourier transform is performed to restore the polarization information.
[0041] Based on the above design ideas, the present invention provides a polarization imaging method for a scattering medium, comprising the following specific steps:
[0042] Step 1: Perform Fourier transform on the Stokes image: After the distorted wavefront containing object information affected by the scattered medium passes through the imaging lens, the Stokes image detector records N images with polarization information of the target object. For the N images recorded by the Stokes image detector containing object information, perform two-dimensional Fourier transform respectively to obtain the spectrum of each channel. The specific process is as follows:
[0043] Record the N Stokes images corresponding to each Stokes component. There is the following relationship between each image and the target object:
[0044]
[0045] The upper right subscript "Img" of "S" represents the image plane, "Obj" represents the object plane, and the lower right subscript "l" is 0, 1, 2, and 3, indicating S 0 , S 1 , S 2 , S 3 Four Stokes parameters, "*" represents convolution operation, H(x,y) represents system transfer function. Perform Fourier transform to get Stokes spectrum, that is
[0046]
[0047] in, represents the Stokes spectrum of the object, The spectrum representing the optical transfer function of the polarization imaging system, represents the Stokes spectrum of the image. Therefore, the spectrum of the image can be expressed as the product of the object spectrum and the optical transfer function of the imaging system.
[0048] Step 2: Calculate the amplitude of the Stokes spectrum in the frequency domain: Use the superposition algorithm to square and sum the N Stokes spectrum images recorded by each channel after Fourier transformation, and then calculate the average value. The restored object amplitude information is calculated based on the corresponding relationship between the input and output of the imaging system.
[0049] First, the amplitude of the Stokes spectrum of each channel is calculated. The amplitude information contains the Stokes intensity distribution of the target object at different frequencies, which can be understood as the intensity information of the polarization characteristics of the target object.
[0050] Then, the N Stokes spectrum images recorded by each channel after Fourier transformation are squared and summed, and then the average value is calculated. The expression is:
[0051]
[0052] Wherein, the left subscript “k” represents the number of times, corresponding to each of the N groups of Stokes spectra.
[0053] Then, according to formulas (2) and (3), the average square of the modulus of the object's Stokes spectrum amplitude can be calculated:
[0054]
[0055] in, represents the transfer function of the polarization imaging system.
[0056] Finally, take the square root of formula (4) to get the final Stokes amplitude:
[0057]
[0058] in, The Stokes amplitude of the object finally calculated and restored is represented by the subscript “l” on the right. and Four corresponding Stokes calculations are performed on formulas (1) to (5).
[0059] Step 3: Calculate the phase of the Stokes spectrum in the frequency domain: Use the Stokes cross-spectrum phase unpacking algorithm to extract the Stokes cross-spectrum phase difference of the N Fourier-transformed Stokes spectrum images recorded in each channel of the Stokes spectrum, and recover the phase information from the Fourier spectrum point by point through the phase difference:
[0060] First, the phase of the Stokes spectrum of each channel is extracted. The phase information reveals the Stokes phase distribution of the target object at different frequencies and reflects the polarization direction information of the target object.
[0061] Stokes cross spectrum of an image The Fourier transform of the image can be obtained by definition
[0062]
[0063] in The superscript "Img" indicates the image plane, and the subscript The corresponding Stokes spectrum is and The whole represents a set of Stokes cross spectra, symbol " * ” indicates conjugation. Substituting formula (2) into formula (6), we have
[0064]
[0065] Then, for a series of recorded Stokes images, since the object does not change, the averaging operation is only performed on The finite term average is approximated by statistical averaging, and the average Stokes cross spectrum of the image is obtained as follows:
[0066]
[0067] in, It is called the average cross-spectrum transfer function. The average cross-spectrum transfer function is a real-valued function. In this way, the average Stokes cross-spectrum phase of the image can be obtained, which is the Stokes cross-spectrum phase of the object. The phase of the object can be restored from the average Stokes cross-spectrum phase of the image.
[0068] The Stokes cross spectrum of an object is expressed as
[0069]
[0070] in, Indicates phase, upper right The corresponding Stokes spectrum is and From formula (9), we can know that the phase difference is
[0071] consider Either along v x The axis is either along v y Axis, so Either Δv x Either Δv y ,Right now or In these cases there are
[0072]
[0073] The above formula is in Δv x and Δv y If Δv is small enough, the two partial derivatives are the two orthogonal components of the gradient of the object phase spectrum. x and Δv y The phase difference can be calculated on the frequency rectangular grid according to the following formula:
[0074]
[0075] The starting point is set at the origin of the frequency plane. At this time, the object spectrum must be real and positive, which means
[0076] Finally we have the following equation, the right side of which contains only measurable quantities.
[0077]
[0078] in, The Stokes phase of the object is restored by point-by-point unpacking. The corresponding Stokes spectrum is and Four corresponding Stokes calculations are performed for formulas (6) to (12) respectively. In this way, the Fourier phase information can be extracted from the Fourier spectrum.
[0079] Step 4: Inverse Fourier transform to restore polarization information:
[0080] The amplitude and phase information of the Stokes spectrum obtained in step 2 and step 3 are combined and inverse Fourier transformed to restore the polarization information in the frequency domain to the spatial domain, thereby obtaining the complete polarization image information of the target object. This step can help us intuitively present the polarization characteristics of the target object and ultimately obtain polarization information in the spatial domain.
[0081] Assume that the amplitude and phase of the Stokes image spectrum of the object calculated by steps 2 and 3 are respectively and Then we can get the Stokes spectrum of the object, that is
[0082]
[0083] Finally, the inverse Fourier transform of formula (13) is performed to obtain the Stokes image of the object recovered from the scattered medium, as shown in the following formula:
[0084]
[0085] in, represents the inverse Fourier transform operation, and four corresponding Stokes calculations are performed on formulas (13) to (14).
[0086] See also Figure 2 The four images on the left show the polarization imaging results of the object after passing through the scattered medium, in which it is difficult to distinguish the information of the object. After being processed by the above method, the four restored images on the right are presented, in which the information of the target object is clearly distinguishable.
[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims
1. A polarization imaging method for a scattering medium, characterized in that: First, the Stokes image is Fourier transformed to calculate the amplitude of the Stokes spectrum, then the phase of the Stokes spectrum is calculated, and finally the inverse Fourier transform is performed to recover the polarization information.
2. The polarization imaging method for a scattering medium according to claim 1, characterized in that: The specific steps are as follows: Step 1: Perform Fourier transform on the Stokes image: Perform two-dimensional Fourier transform on the N images recorded by the Stokes image detector containing object information to obtain the spectrum of each channel; Step 2: Calculate the amplitude of the Stokes spectrum in the frequency domain: Use the superposition algorithm to square the N Stokes spectrum images recorded by each channel after Fourier transformation, then sum them up, and then calculate the average value. Calculate the restored object amplitude information based on the corresponding relationship between the input and output of the imaging system; Step 3: Calculate the phase of the Stokes spectrum in the frequency domain: Use the Stokes cross-spectrum phase unpacking algorithm to extract the Stokes cross-spectrum phase difference of the N Fourier-transformed Stokes spectrum images recorded by each Stokes channel, and recover the phase information from the Fourier spectrum point by point through the phase difference; Step 4: Restore polarization information by inverse Fourier transform: By combining the amplitude and phase information of the calculated Stokes spectrum, an inverse Fourier transform is performed to restore the polarization information in the frequency domain to the spatial domain, thereby obtaining the complete polarization image information of the target object.
3. The polarization imaging method for a scattering medium according to claim 2, characterized in that: In step 1, the spectrum of each channel is expressed as: in, represents the Stokes spectrum of the object, The spectrum representing the optical transfer function of the polarization imaging system, represents the Stokes spectrum of the image.
4. The polarization imaging method for a scattering medium according to claim 3, characterized in that: The specific steps of step 2 are: First, the amplitude of the Stokes spectrum of each channel is calculated; Then, the N Stokes spectrum images recorded by each channel after Fourier transformation are squared and summed, and then the average value is calculated. The expression is: Wherein, the left subscript "k" indicates the number of times, corresponding to each of the N groups of Stokes spectra; Then calculate the average of the square of the modulus of the object's Stokes spectrum amplitude in, represents the transfer function of the polarization imaging system; Finally, take the square root of formula (4) to get the final Stokes amplitude: in, Indicates the Stokes amplitude of the object finally calculated and restored. The right subscript "l" represents and 5. The polarization imaging method for a scattering medium according to claim 4, characterized in that: In step 3, the average Stokes cross spectrum of the image is expressed as: in, is the average cross-spectral transfer function; The Stokes cross spectrum of an object is expressed as in, Indicates phase, upper right The corresponding Stokes spectrum is and From formula (9), we can know that the phase difference is 6. The polarization imaging method for a scattering medium according to claim 5, characterized in that: In step 4, the Stokes image of the object recovered from the scattered medium is expressed as: in, Represents the inverse Fourier transform operation.