Synthetic aperture imaging method and system based on coded fourier lenticular technology

Abstract

The application belongs to the field of synthetic aperture imaging, and discloses a synthetic aperture imaging method and system based on encoding Fourier superposition technology. A plurality of images are collected by an imaging system, and a target image is reconstructed by using Fourier superposition imaging technology. The imaging system sequentially includes a laser, a beam expander, a diaphragm and a movable camera along an optical path. The movable camera includes an electric displacement platform and an encoding camera. The encoding camera includes an image sensor and an imaging lens located in front of the image sensor. A surface of the image sensor is provided with an encoding layer composed of scattering particles. When the plurality of images are collected by the imaging system, a target is placed between the diaphragm and the imaging lens, the encoding camera is driven to move in an x-y plane by the electric displacement platform, and the target is simultaneously subjected to image collection. The application realizes accurate reconstruction of slowly-varying low-frequency phase information under long-distance imaging conditions, and simultaneously improves imaging quality.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of synthetic aperture imaging, and particularly relates to a synthetic aperture imaging method and system based on an encoding Fourier lamination technology. BACKGROUND

[0002] Due to the existence of the optical diffraction limit, the resolution is directly related to the aperture of the optical system, and thus increasing the aperture of the imaging system is an effective means to directly improve the resolution of the optical imaging system for the traditional optical imaging system. However, with the continuous increase of the aperture of the optical system, the quality, volume and design cost of the optical imaging system are continuously improved, which is an important factor limiting the further increase of the aperture of the optical system.

[0003] The method of increasing the equivalent aperture of the optical system by using the optical synthetic aperture technology improves the spatial resolution of the optical system while ensuring the light weight of the system. However, the technology requires that each small aperture satisfies the equal optical path geometric imaging and that the strict phase coincidence is met between each sub-aperture. Since the optical synthetic aperture has high design requirements for the surface accuracy and control accuracy, and the phase control accuracy is in the order of magnitude of one-tenth of the wavelength, the technology puts high requirements on the machining and control accuracy and the stability of the platform.

[0004] In the related art, Zheng et al. of California Institute of Technology proposed the concept of Fourier ptychographic microscopy (FPM). Unlike traditional ptychographic imaging, the "stacking" in FPM imaging does not occur in the spatial domain, but in the frequency domain. A typical FPM imaging system places the sample at the object plane, the aperture stop at the Fourier plane, and the detector at the image plane. A programmable LED array is used to control the illumination beams at different angles to scan the sample, and the objective lens performs Fourier transform to convert the outgoing wave of the object from the spatial domain to the frequency domain, and the tube lens performs a second Fourier transform to convert the light wave back to the spatial domain to form a low-resolution original image. FPM uses a traditional lens imaging system to convert the spatially limited illumination aperture constraint in the previous ptychographic imaging technology into a frequency domain limited aperture pupil constraint. Both have the same need to collect a redundant data set overlapping between adjacent apertures to ensure the robustness of the phase recovery process. FPM combines the ideas of ptychographic imaging technology, synthetic aperture, and phase recovery technology, and overcomes the contradiction between the field of view and the resolution of the traditional microscope system. FPM does not need to mechanically scan the sample, only needs to add a programmable LED illumination light source to the traditional microscope system, the system is simple, the cost is low, and the compatibility is strong. The spatial bandwidth product of the traditional microscope system is improved from the order of magnitude of ten million pixels to the order of magnitude of one billion pixels. The FPM reconstruction process uses an iterative phase recovery algorithm to use a series of low-resolution intensity images obtained by the detector to realize the amplitude-constrained reconstruction of the complex amplitude information of the high-resolution target.

[0005] However, in the traditional Fourier ptychographic imaging image acquisition process, the slowly varying low-frequency phase information is lost, so the slowly varying phase object cannot be reconstructed by the phase recovery process, resulting in a poor quality of the reconstructed target image and a low signal-to-noise ratio, which cannot meet the high-quality imaging requirements. SUMMARY

[0006] In order to solve the above problems existing in the prior art, the present application provides a synthetic aperture imaging method and system based on coded Fourier ptychographic technology.

[0007] The technical problem to be solved by the present application is solved by the following technical scheme:

[0008] A synthetic aperture imaging method based on coded Fourier ptychographic technology, comprising:

[0009] acquiring a plurality of images; the plurality of images are obtained by a pre-built imaging system;

[0010] reconstructing a target image using Fourier ptychographic imaging technology according to the plurality of images;

[0011] The imaging system sequentially comprises, along an optical path: a laser, a beam expander, an aperture, and a movable camera; the movable camera comprises a motorized displacement platform and a coded camera; the motorized displacement platform carries the coded camera to move in an x-y plane; the optical path coincides with a z axis; the coded camera comprises an image sensor and an imaging lens in front of the image sensor; a surface of the image sensor is provided with a coded layer composed of scattering particles;

[0012] When the plurality of images are acquired by the imaging system, a target is placed between the aperture and the imaging lens, the coded camera is driven by the motorized displacement platform to move in the x-y plane, and the target is imaged to obtain the plurality of images.

[0013] Optionally, according to the plurality of images, a target image is reconstructed by using a Fourier ptychographic imaging technology, comprising:

[0014] Step 1: initializing a pupil function according to a numerical aperture of the imaging system, and initializing a target spectrum according to the plurality of images;

[0015] Step 2: extracting a local spectrum of a different sub-region from the current target spectrum according to a camera position corresponding to each image, and performing low-pass filtering on the local spectrum by using the current pupil function to obtain a filtered spectrum;

[0016] Step 3: inversely propagating the filtered spectrum to the coded layer and performing inverse Fourier transform to obtain a first exit wave front of the light wave reaching the coded layer, multiplying the first exit wave front with a complex amplitude of the coded layer point by point to obtain a second exit wave front of the light wave leaving the coded layer;

[0017] Step 4: after the second exit wave front is propagated to the image sensor, updating amplitude information and keeping phase unchanged to obtain a target complex amplitude;

[0018] Step 5: inversely propagating the target complex amplitude to leave the coded layer to obtain an updated second exit wave front;

[0019] Step 6: updating the first exit wave front by using an rPIE algorithm according to the updated and un-updated second exit wave fronts and the complex amplitude of the coded layer;

[0020] Step 7: propagating the updated first exit wave front back to the image sensor and performing Fourier transform to obtain an updated filtered spectrum;

[0021] Step 8: Based on the filtered spectrum before and after the update, reconstruct the local spectrum of the target and update the pupil function using the rPIE (Regularized Ptychographic Iterative Engine) algorithm;

[0022] Step 9: Update the target spectrum based on the reconstructed local spectrum and determine whether the convergence condition is met; if it is met, perform target imaging based on the current target spectrum; if it is not met, return to step 2.

[0023] Optionally, in step 1, initializing the pupil function according to the numerical aperture of the imaging system includes:

[0024] ;

[0025] in, Represents the pupil function. For two-dimensional coordinates in the frequency domain, Numerical aperture of the imaging system Indicates the wavelength of light. It is a circular domain function.

[0026] Optionally, in step 1, initializing the target spectrum based on the multiple images includes:

[0027] ,

[0028] ;

[0029] in, Indicates the first Zhang Image For two-dimensional coordinates in the spatial domain, Indicates the total number of images. Indicates according to Target imaging initialized from a single image. Indicates upsampling operation. Indicates Fourier transform, For the initial target spectrum, These are two-dimensional coordinates in the frequency domain.

[0030] Optionally, in step 3, the filtered spectrum is backpropagated to the coding layer and an inverse Fourier transform is performed to obtain the first outgoing wavefront of the light wave reaching the coding layer, including:

[0031] ;

[0032] in, Represents the filtered spectrum. Number the images. For two-dimensional coordinates in the frequency domain, represents a convolution kernel of the light wave propagating in free space, and its Fourier transform is an optical transfer function of the light wave propagating in free space, represents a distance of back propagation in a spatial domain represents an inverse Fourier transform, represents a convolution operation, represents a first exit wave front.

[0033] Optionally, in step 4, after the second exit wave front is propagated to the image sensor, the amplitude information of the second exit wave front is updated and the phase is kept unchanged to obtain a target complex amplitude, including:

[0034]

[0035]

[0036] wherein, represents a second exit wave front, is an image number, represents a convolution kernel of the light wave propagating in free space, and its Fourier transform is an optical transfer function of the light wave propagating in free space, represents a distance of propagation in a spatial domain, represents a convolution operation, represents a first exit wave front. represents a first exit wave front. represents a spatial domain two-dimensional coordinate, is a target complex amplitude obtained in step 4, is a target complex amplitude before the amplitude information is updated, represents a modulo operation.

[0037] Optionally, in step 6, according to the second exit wave front before and after the update and the complex amplitude of the encoding layer, the first exit wave front is updated by using an rPIE algorithm, including:

[0038]

[0039] wherein, is a complex amplitude of the encoding layer, represents an updated second exit wave front, represents a second exit wave front before the update, is an image number, represents a conjugate of a complex number, is a constant parameter of the rPIE algorithm, represents a maximum value in different spatial domain two-dimensional coordinates corresponding to represents a modulo operation, ​​​​​represents the first exit wavefront before update, represents the first exit wavefront after update.

[0040] Optionally, according to the filtered spectrum before and after update, the local spectrum of the target is reconstructed by using the rPIE algorithm, and the pupil function is updated, comprising:

[0041]

[0042]

[0043] wherein, represents the filtered spectrum before update, is an image number, represents the filtered spectrum after update, is the pupil function before update, α O and α P are common parameters of the rPIE algorithm, is the local spectrum before reconstruction, is the local spectrum after reconstruction, conj represents the conjugate of a complex number, represents the maximum value in the corresponding of different frequency domain two-dimensional coordinates , represents the maximum value in the corresponding of different frequency domain two-dimensional coordinates , represents a modulus operation, is the pupil function after update.

[0044] The application further provides a synthetic aperture imaging system based on an encoding Fourier layer technology, which comprises, in sequence along an optical path, a laser, a beam expander, an aperture, a movable camera and an imaging processing module.

[0045] The movable camera comprises a motorized displacement platform and an encoding camera; the motorized displacement platform carries the encoding camera to move in an x-y plane; the optical path is coincident with a z axis; the encoding camera comprises an image sensor and an imaging lens in front of the image sensor; a surface of the image sensor is provided with an encoding layer composed of scattering particles;

[0046] The imaging processing module is used for:

[0047] acquiring a plurality of images; the plurality of images are acquired by the following manner: placing a target between the aperture and the imaging lens, moving the encoding camera in the x-y plane by the motorized displacement platform, and simultaneously collecting images of the target to obtain the plurality of images;​​

[0048] reconstruct the target image according to the multiple images by using a Fourier ptychographic imaging technique.

[0049] Optionally, the imaging processing module, in the process of reconstructing the target image according to the multiple images by using the Fourier ptychographic imaging technique, comprises:

[0050] Step 1, initializing a pupil function according to a numerical aperture of the imaging system, and initializing a target spectrum according to the multiple images;

[0051] Step 2, extracting a local spectrum of a different sub-region from the current target spectrum according to a camera position corresponding to each image, and performing low-pass filtering on the local spectrum by using the current pupil function to obtain a filtered spectrum;

[0052] Step 3, inversely propagating the filtered spectrum to the encoding layer and performing inverse Fourier transform to obtain a first exit wave front of the light wave reaching the encoding layer, multiplying the first exit wave front with a complex amplitude of the encoding layer point by point to obtain a second exit wave front of the light wave leaving the encoding layer;

[0053] Step 4, after propagating the second exit wave front to the image sensor, updating amplitude information and keeping the phase unchanged to obtain a target complex amplitude;

[0054] Step 5, inversely propagating the target complex amplitude to leave the encoding layer to obtain an updated second exit wave front;

[0055] Step 6, updating the first exit wave front by using an rPIE algorithm according to the updated and un-updated second exit wave fronts and the complex amplitude of the encoding layer;

[0056] Step 7, propagating the updated first exit wave front back to the image sensor and performing Fourier transform to obtain an updated filtered spectrum;

[0057] Step 8, reconstructing a local spectrum of the target and updating the pupil function by using the rPIE algorithm according to the updated and un-updated filtered spectra;

[0058] Step 9, updating the target spectrum according to the reconstructed local spectrum, and judging whether a convergence condition is met; if yes, performing target imaging according to the updated target spectrum; if no, returning to Step 2.

[0059] The application provides a synthetic aperture imaging method and system based on coded Fourier superposition technology.

[0060] The application will be further described in detail below with reference to the drawings and the application. BRIEF DESCRIPTION OF DRAWINGS

[0061] Figure 1 is a flowchart of a synthetic aperture imaging method based on coded Fourier superposition technology provided by the application;

[0062] Figure 2 is a flowchart of a method for reconstructing a target image by using Fourier superposition imaging technology in the method shown in Figure 1

[0063] Figure 3 is a structural diagram of a synthetic aperture imaging system based on coded Fourier superposition technology provided by the application;

[0064] Figure 4 is a group of simulation experiment results provided by the application. DETAILED DESCRIPTION

[0065] The application will be further described in detail below with reference to the drawings and the application.

[0066] In order to realize accurate reconstruction of slowly-varying low-frequency phase information and improve imaging quality under long-distance imaging conditions, the application provides a synthetic aperture imaging method based on coded Fourier superposition technology, which is shown in Figure 1 The method comprises the following steps.

[0067] S10, a plurality of images are acquired, which are acquired by a synthetic aperture imaging system based on coded Fourier superposition technology that is pre-built.

[0068] Specifically, as shown in Figure 3 The imaging system comprises, along an optical path, a laser, a beam expander, a diaphragm and a movable camera in sequence; the movable camera comprises an electric displacement platform (DMD) and a camera. Figure 3 ​and an encoding camera; an electric displacement platform carries the encoding camera to move in an x-y plane; an optical path is coincident with a z axis; the encoding camera comprises a conventional image sensor and an imaging lens in front of the image sensor; a surface of the image sensor is provided with an encoding layer composed of scattering particles, and the encoding layer has three functions including:

[0069] (1) the encoding layer is composed of thin scattering particles, and when light waves interact with the thin scattering layer, the scattering effect has the effect of increasing the effective numerical aperture of the detector;

[0070] (2) the modulation effect of the encoding layer can enhance the detection ability of the detector to low-frequency slowly-varying phase information;

[0071] (3) through a calibration experiment, the complex amplitude of the encoding layer can be reconstructed in advance. Then, the complex amplitude of the encoding layer is taken as a fixed known mask to increase the effective constraint, thereby helping to improve the image quality of the reconstructed image.

[0072] In the imaging system shown in Figure 3 When a plurality of images are collected, the target is placed between the stop and the imaging lens, the encoding camera is driven by the electric displacement platform to move in the x-y plane, and the target is imaged to obtain a plurality of images.

[0073] S20, according to the collected plurality of images, the target image is reconstructed by using the Fourier piling imaging technology.

[0074] The Fourier piling imaging technology can realize the spatial resolution of an equivalent large-aperture optical system by using a small-aperture optical system, without co-phasing, and has a lower requirement for phase control accuracy. At the same time, accurate quantitative phase information and additional optical system aberration information can be reconstructed based on the phase recovery technology, which has important significance for the further development of the field of large-field high-resolution imaging.

[0075] Specifically, referring to Figure 2 According to the collected plurality of images, the target image is reconstructed by using the Fourier piling imaging technology in the present application, which comprises steps 1-9 as shown below, wherein steps 2-9 involve a repeated iterative process, and the specific description is as follows:

[0076] Step 1, initializing a pupil function according to the numerical aperture of the imaging system, and initializing a target spectrum according to the collected plurality of images.

[0077] Specifically, in step 1, the pupil function is initialized according to the numerical aperture of the imaging system, which is realized by the following formula:

[0078] ;

[0079] Wherein, represents the pupil function, For two-dimensional coordinates in the frequency domain, Numerical aperture of the imaging system Indicates the wavelength of light. It is a circular domain function.

[0080] In step 1, the target spectrum is initialized based on the acquired multiple images, achieved using the following formula:

[0081] ,

[0082] ;

[0083] in, For the identification of the acquired images, Indicates the number of collected data. Zhang Image For two-dimensional coordinates in the spatial domain, This indicates the total number of images acquired. Indicates according to Initial target imaging of the acquired image, Indicates upsampling operation. Indicates Fourier transform, The target spectrum for initialization is a two-dimensional image.

[0084] Step 2: Based on the camera position corresponding to each image, extract the local spectrum of different sub-regions from the current target spectrum, and use the current pupil function to perform low-pass filtering on the local spectrum to obtain the filtered spectrum.

[0085] For details, see Figure 3 When capturing each image, the position of the encoding camera in the xy-plane varies, resulting in different angles at which the light emitted from the target enters the encoding camera. Specifically, when the displacement platform coincides with the z-axis, the center point of the target coincides with the imaging center of the encoding camera. Each time the displacement platform moves to a new position, it undergoes a deflection angle relative to the z-axis. Based on this deflection angle, the distance between the target and the xy-plane, and the distance between the encoding camera and the z-axis, the spatial geometric relationships between these factors allow calculation of the coordinates of the target's center at each position where the displacement platform stops, relative to the imaging center of the encoding camera. This allows extraction of a local spectrum within a sub-region of the current target spectrum, centered on these coordinates. This local spectrum can be understood as a sub-map in the frequency domain.

[0086] Then, the local spectrum is low-pass filtered using the current pupil function to obtain the filtered spectrum, which is represented as follows:

[0087] ;

[0088] in, for the extracted local spectrum, denotes the filtered spectrum, note that in using , , the frequency domain two-dimensional coordinates in the center coordinates of .

[0089] Step 3, the filtered spectrum is back-propagated to the encoding layer and inverse Fourier transformed to obtain a first exit wave front of the light wave reaching the encoding layer, and the first exit wave front is multiplied point by point with the complex amplitude of the encoding layer to obtain a second exit wave front of the light wave leaving the encoding layer.

[0090] Specifically, in this step 3, the filtered spectrum is back-propagated to the encoding layer and inverse Fourier transformed to obtain a first exit wave front of the light wave reaching the encoding layer, which is realized by the following formula:

[0091] ;

[0092] wherein, denotes the convolution kernel of the free-space propagation of the light wave, and its Fourier transform is the optical transfer function of the free-space propagation of the light wave, denotes the back-propagation distance in the spatial domain , denotes the inverse Fourier transform, denotes the convolution operation, denotes the first exit wave front.

[0093] Then, the first exit wave front is multiplied point by point with the complex amplitude of the encoding layer to obtain a second exit wave front of the light wave leaving the encoding layer :

[0094] .

[0095] Step 4, after the second exit wave front is forward-propagated to the image sensor, the amplitude information thereof is updated and the phase is kept unchanged to obtain a target complex amplitude.

[0096] Specifically, in this step 4, after the second exit wave front is forward-propagated to the image sensor, the amplitude information thereof is updated and the phase is kept unchanged to obtain a target complex amplitude, which is realized by the following formula:

[0097] ,

[0098] ;

[0099] wherein, is the target complex amplitude obtained in this step 4, the target complex amplitude before the amplitude information is updated, represents a modulo operation.

[0100] Step 5, back-propagating the target complex amplitude to the exit encoding layer to obtain an updated second exit wavefront.

[0101] Specifically, the operation of back-propagating the target complex amplitude to the exit encoding layer to obtain an updated second exit wavefront is as follows:

[0102] ;

[0103] Here, represents the updated second exit wavefront.

[0104] Step 6, updating the first exit wavefront using the rPIE algorithm according to the second exit wavefront before and after the update and the complex amplitude of the encoding layer.

[0105] Specifically, updating the first exit wavefront using the rPIE algorithm according to the second exit wavefront before and after the update and the complex amplitude of the encoding layer is achieved by the following formula:

[0106] ;

[0107] wherein, represents the conjugate of a complex number, is a constant parameter of the rPIE algorithm, generally with a size of 1, represents the maximum value of different spatial domain two-dimensional coordinates corresponding to in the second exit wavefront before the update, represents the first exit wavefront before the update, represents the first exit wavefront after the update.

[0108] Step 7, back-propagating the updated first exit wavefront to the image sensor and performing Fourier transform to obtain an updated filter spectrum.

[0109] Specifically, the specific operation of back-propagating the updated first exit wavefront to the image sensor and performing Fourier transform to obtain an updated filter spectrum is as follows:

[0110] ;

[0111] Here, represents the updated filter spectrum.

[0112] Step 8, reconstructing the local spectrum of the target and updating the pupil function using the rPIE algorithm according to the filter spectrum before and after the update.

[0113] Specifically, according to the filtered spectrum before and after the update, the local spectrum of the target is reconstructed by using the rPIE algorithm and the pupil function is updated, which is realized by the following formula:

[0114] ;

[0115] ;

[0116] wherein, represents the filtered spectrum before the update, represents the filtered spectrum after the update, is the pupil function before the update, α O and α P are the constant parameters of the rPIE algorithm, and the size is generally 1, is the local spectrum before the reconstruction, is the local spectrum after the reconstruction, conj represents the conjugate of a complex number, represents the maximum value in the corresponding of different frequency domain two-dimensional coordinates . represents the maximum value in the corresponding of different frequency domain two-dimensional coordinates . is the pupil function after the update.

[0117] Step 9, updating the target spectrum according to the reconstructed local spectrum, and judging whether the convergence condition is met; if met, performing target imaging according to the current target spectrum; if not met, returning to step 2.

[0118] wherein, the target spectrum is updated according to the reconstructed local spectrum, which can be specifically that according to the center coordinates of each local spectrum, each local spectrum is fused into an integral spectrum (target spectrum), and for the pixels with the same coordinates, the fusion can be realized by taking the average value of the pixels, of course, it is not limited to this. Then, judging whether the convergence condition is met, which can be realized by judging whether the imaging quality meets the expected way. Or, it can also be realized by the way of pre-setting the maximum number of iterations, once the iteration reaches the maximum number, the quality of target imaging has generally converged at this time. It can be understood that each execution of the process of steps 2-9 is one iteration.

[0119] When it is determined that the convergence condition is met, the target is imaged according to the updated target spectrum, and the specific operation is as follows:

[0120] ;

[0121] wherein, This represents the target spectrum when the convergence condition is met. This represents the final target image. It's understandable that if the convergence condition is determined by assessing image quality, then target imaging based on the updated target spectrum can also be achieved using the formula above.

[0122] The invention will be further illustrated below through simulation experiments:

[0123] (1) Experimental parameters: The pixel size of the image sensor was set to 2.25. μm (Image size: 1024×1024), the laser wavelength is 532 nm. nm The numerical aperture of the system NA The value is 0.02, which represents the distance between the target's position and the imaging lens. z 550 mm The distance between the coding layer and the image sensor d 840 μm The number of images acquired is 15×15. Here, the amplitude and phase of the original acquired images are loaded to simulate the electric displacement platform driving the coded camera to acquire original low-resolution images at different spatial scanning positions. The scanning path of the displacement platform during movement is spiral.

[0124] (2) Image reconstruction: The method of this invention is used to recover the distorted original low-resolution image, thereby imaging the target. Experimental results are shown in [reference]. Figure 4 In the figures, (a) and (d) show the true intensity and phase of the original image. (b) and (c) show the image intensity information recovered using the conventional Fourier layering technique and the coded Fourier layering technique of the present invention, respectively. (e) and (f) show the phase information recovered using the conventional Fourier layering technique and the coded Fourier layering technique of the present invention, respectively. The comparison shows that the image recovered using the method proposed in this invention has clearer intensity information, but the difference in image intensity information between the result and the image recovered using the conventional Fourier layering technique is not significant. However, the present invention has a significant advantage over the conventional Fourier layering technique in recovering the phase information of the image, demonstrating that the present invention has the ability to more accurately acquire the target phase information and improve imaging quality.

[0125] The application provides a synthetic aperture imaging method based on a coded Fourier superposition technology, which is based on a long-distance synthetic aperture imaging method of coded Fourier superposition imaging and can reconstruct a slowly-varying phase image which cannot be reconstructed under long-distance imaging conditions by existing methods, accurately reconstruct slowly-varying low-frequency phase information, quickly and accurately obtain a target image phase, effectively improve the quality of a reconstructed image, overcome the problem that the quality of a target image phase reconstructed by a traditional Fourier superposition imaging is poor and image quality evaluation parameters such as signal-to-noise ratio cannot meet the demand of high-quality imaging, and realize high-precision reconstruction of a target.

[0126] Based on the same inventive concept, the application further provides a synthetic aperture imaging system based on a coded Fourier superposition technology, which comprises, in sequence along an optical path, a laser, a beam expander, an aperture, a movable camera and an imaging processing module. Figure 3 The imaging processing module is not shown in the application. Figure 3

[0127] The movable camera comprises an electric displacement platform and a coded camera; the electric displacement platform carries the coded camera to move in an x-y plane; the optical path is coincident with a z axis; the coded camera comprises an image sensor and an imaging lens in front of the image sensor; the surface of the image sensor is provided with a coded layer composed of scattering particles;

[0128] The imaging processing module is configured to:

[0129] acquire a plurality of images; the plurality of images are acquired by placing a target between the aperture and the imaging lens, moving the coded camera in the x-y plane by the electric displacement platform, and simultaneously collecting images of the target to obtain the plurality of images;

[0130] reconstruct a target image by using a Fourier superposition imaging technology according to the plurality of images.

[0131] Optionally, the imaging processing module reconstructs the target image by using the Fourier superposition imaging technology according to the plurality of images, and the process comprises the following steps:

[0132] Step 1: initializing a pupil function according to a numerical aperture of the imaging system, and initializing a target spectrum according to the plurality of images;

[0133] Step 2: extracting a local spectrum of a different sub-region from the current target spectrum according to a camera position corresponding to each image, and performing low-pass filtering on the local spectrum by using the current pupil function to obtain a filtered spectrum;

[0134] ​Step 3, the filtered spectrum is reversely propagated to the encoding layer and inverse Fourier transform is performed to obtain a first emergent wave front of the light wave reaching the encoding layer, and the first emergent wave front is multiplied point by point with the complex amplitude of the encoding layer to obtain a second emergent wave front of the light wave leaving the encoding layer;

[0135] Step 4, after the second emergent wave front is propagated to the image sensor, the amplitude information is updated and the phase is kept unchanged to obtain the target complex amplitude;

[0136] Step 5, the target complex amplitude is reversely propagated to leave the encoding layer to obtain an updated second emergent wave front;

[0137] Step 6, according to the updated and un-updated second emergent wave fronts and the complex amplitude of the encoding layer, the rPIE algorithm is used to update the first emergent wave front;

[0138] Step 7, the updated first emergent wave front is propagated back to the image sensor and Fourier transform is performed to obtain an updated filtered spectrum;

[0139] Step 8, according to the updated and un-updated filtered spectra, the rPIE algorithm is used to reconstruct the local spectrum of the target and update the pupil function;

[0140] Step 9, according to the reconstructed local spectrum, the target spectrum is updated, and it is judged whether the convergence condition is met; if yes, target imaging is performed according to the updated target spectrum; if not, the step 2 is returned.

[0141] In practice, the imaging processing module can be a computer, of course, but is not limited thereto.

[0142] Here, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the related parts can be referred to the part of the method embodiment.

[0143] The synthetic aperture imaging system based on the encoding Fourier stack technology provided by the application can effectively improve the quality of the reconstructed image, overcome the problem that the quality of the target image phase reconstructed by the traditional Fourier stack imaging is poor, and the image quality evaluation parameters such as signal-to-noise ratio cannot meet the high-quality imaging requirement, and realize high-precision reconstruction of the target.

[0144] In the description of the specification, the terms "first", "second", and so on are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the application described herein can be implemented in an order other than those illustrated or described herein. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the present application. The description of the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" and the like means that the specific features or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the description, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in the specification.

[0145] Although the present application is described herein in conjunction with various embodiments, those skilled in the art, with reference to the drawings and the disclosure, can understand and implement other variations of the disclosed embodiments in implementing the claimed application. In the description of the present application, the word "comprising" does not exclude other components or steps, "a" or "one" does not exclude a plurality, and "plurality" means two or more, unless otherwise explicitly specified. In addition, some measures are described in different embodiments, but this does not mean that these measures cannot be combined to produce good results.

[0146] The above is a further detailed description of the present application in conjunction with specific preferred embodiments, and cannot be considered as limiting the specific implementation of the present application to these descriptions. For those skilled in the art to which the present application belongs, without departing from the concept of the present application, a number of simple deductions or substitutions can be made, which should be considered as falling within the scope of protection of the present application.

Claims

1. A synthetic aperture imaging method based on coded Fourier lamination technique, characterized in that, The application relates to a method for reconstructing a target image by using a Fourier ptychographic imaging technology. The method comprises the following steps: a plurality of images are acquired by using a pre-built imaging system; the target image is reconstructed by using the Fourier ptychographic imaging technology according to the plurality of images; wherein the imaging system comprises, along an optical path, a laser, a beam expander, an aperture and a movable camera; the movable camera comprises an electric displacement platform and a coded camera; the electric displacement platform carries the coded camera to move in an x-y plane; the optical path is coincident with a z-axis; the coded camera comprises an image sensor and an imaging lens located in front of the image sensor; a surface of the image sensor is provided with a coded layer composed of scattering particles; when the plurality of images are acquired by using the imaging system, a target is placed between the aperture and the imaging lens, the coded camera is driven by the electric displacement platform to move in the x-y plane, and the target is imaged to obtain the plurality of images; wherein the target image is reconstructed by using the Fourier ptychographic imaging technology according to the plurality of images, which comprises the following steps: step 1: initializing a pupil function according to a numerical aperture of the imaging system, and initializing a target spectrum according to the plurality of images; step 2: extracting local spectra of different sub-regions from the current target spectrum according to the camera positions corresponding to the images, and performing low-pass filtering on the local spectra by using the current pupil function to obtain filtered spectra; step 3: inversely propagating the filtered spectra to the coded layer and performing inverse Fourier transform to obtain a first emergent wave front of light waves reaching the coded layer, and multiplying the first emergent wave front with the complex amplitude of the coded layer point by point to obtain a second emergent wave front of light waves leaving the coded layer; step 4: after the second emergent wave front is propagated to the image sensor, the amplitude information is updated and the phase is kept unchanged to obtain a target complex amplitude; step 5: inversely propagating the target complex amplitude to the coded layer to obtain an updated second emergent wave front; step 6: updating the first emergent wave front by using an rPIE algorithm according to the updated and un-updated second emergent wave fronts and the complex amplitude of the coded layer; step 7: propagating the updated first emergent wave front back to the image sensor and performing Fourier transform to obtain an updated filtered spectrum; step 8: reconstructing the local spectrum of the target and updating the pupil function by using the rPIE algorithm according to the updated and un-updated filtered spectra; 2. The coded Fourier on-lay technique based synthetic aperture imaging method of claim 1, wherein, step 9: updating the target spectrum according to the reconstructed local spectrum, and judging whether a convergence condition is met; if the convergence condition is met, target imaging is performed according to the current target spectrum; if the convergence condition is not met, returning to step 2. ； wherein represents a pupil function, is a two-dimensional coordinate in the frequency domain, represents a numerical aperture of the imaging system, represents a light wavelength, is a circular domain function.

3. The coded Fourier on-lay technique based synthetic aperture imaging method of claim 1, wherein, In step 1, the pupil function is initialized according to the numerical aperture of the imaging system, which comprises the following steps: ， ； wherein, represents the represents the represents the spatial domain two-dimensional coordinate, represents the total number of images, represents the target imaging initialized according to represents the target imaging initialized according to represents the up-sampling operation, represents the Fourier transform, represents the initialized target spectrum, represents the frequency domain two-dimensional coordinate.

4. The coded Fourier on-lay technique based synthetic aperture imaging method of claim 1, wherein, In step 1, the target spectrum is initialized according to the plurality of images, which comprises the following steps: ； wherein, represents a filtered spectrum, is an image number, is a frequency domain two-dimensional coordinate, represents a convolution kernel of the propagation of the light wave in free space, and the Fourier transform thereof is an optical transfer function of the propagation of the light wave in free space, represents a back propagation distance in the spatial domain , represents an inverse Fourier transform, represents a convolution operation, represents a first exit wavefront.

5. The coded Fourier on-lay technique based synthetic aperture imaging method of claim 1, wherein, In step 3, the filtered spectrum is inversely propagated to the coded layer and inverse Fourier transformed to obtain the first emergent wave front of light waves reaching the coded layer, which comprises the following steps: In step 4, after the second emergent wave front is propagated to the image sensor, the amplitude information is updated and the phase is kept unchanged to obtain the target complex amplitude, which comprises the following steps: ， ； wherein, represents the second exit wave front, is an image number, represents a convolution kernel of the free-space propagation of the light wave, whose Fourier transform is the optical transfer function of the free-space propagation of the light wave, represents a distance of propagation in the spatial domain, represents a convolution operation, represents the first exit wave front, is a map image, is a spatial domain two-dimensional coordinate, is the target complex amplitude obtained in step 4, is the target complex amplitude before the amplitude information is updated, represents a modulo operation.

6. The coded Fourier on-lay technique based synthetic aperture imaging method of claim 1, wherein, In step 6, the first exit wave front is updated by using the rPIE algorithm according to the second exit wave front before and after the update and the complex amplitude of the encoding layer, including: ； wherein, is the complex amplitude of the encoding layer, denotes the updated second exit wavefront, denotes the non-updated second exit wavefront, is the image number, denotes the conjugate of a complex number, is a constant parameter of the rPIE algorithm, denotes the different spatial domain two-dimensional coordinates corresponding to the maximum value in, denotes the modulo operation, denotes the non-updated first exit wavefront, denotes the updated first exit wavefront.

7. The coded Fourier on-lay technique based synthetic aperture imaging method of claim 1, wherein, In step 8, the local spectrum of the target is reconstructed by using the rPIE algorithm according to the filtered spectrum before and after the update, and the pupil function is updated, including: ； ； wherein, represents the filtered spectrum before update, is the image number, represents the filtered spectrum after update, is the pupil function before update, α O and α P are the constant parameters of the rPIE algorithm, is the local spectrum before reconstruction, is the local spectrum after reconstruction, conj represents the conjugate of a complex number, represents the maximum value in the corresponding represents the maximum value in the corresponding represents the modulo operation, is the pupil function after update.​​​​ 8. A synthetic aperture imaging system based on coded Fourier lamination, characterized by The system sequentially comprises, along an optical path, a laser, a beam expander, an aperture, a movable camera and an imaging processing module; The movable camera comprises a motorized displacement platform and an encoding camera; the motorized displacement platform carries the encoding camera to move in an x-y plane; the optical path coincides with a z axis; the encoding camera comprises an image sensor and an imaging lens located in front of the image sensor; a surface of the image sensor is provided with an encoding layer composed of scattering particles; The imaging processing module is used for: Obtaining a plurality of images; the plurality of images are obtained by the following manner: placing a target between the aperture and the imaging lens, moving the encoding camera in the x-y plane by the motorized displacement platform, and simultaneously collecting images of the target to obtain the plurality of images; Reconstructing a target image by using a Fourier ptychographic imaging technology according to the plurality of images; The imaging processing module reconstructs a target image by using a Fourier ptychographic imaging technology according to the plurality of images, and the process comprises: Step 1, initializing a pupil function according to a numerical aperture of the imaging system, and initializing a target spectrum according to the plurality of images; Step 2, extracting local spectra of different sub-regions from the current target spectrum according to the camera positions corresponding to each image, and performing low-pass filtering on the local spectra by using the current pupil function to obtain filtered spectra; Step 3, propagating the filtered spectra to the encoding layer in a reverse direction and performing inverse Fourier transform to obtain a first exit wave front of the light wave reaching the encoding layer, and multiplying the first exit wave front by the complex amplitude of the encoding layer point by point to obtain a second exit wave front of the light wave leaving the encoding layer; Step 4, after propagating the second exit wave front to the image sensor in a forward direction, updating the amplitude information and keeping the phase unchanged to obtain a target complex amplitude; Step 5, propagating the target complex amplitude to the encoding layer in a reverse direction to obtain an updated second exit wave front; Step 6, updating the first exit wave front by using the rPIE algorithm according to the second exit wave front before and after the update and the complex amplitude of the encoding layer; Step 7, propagating the updated first exit wave front to the image sensor in a forward direction and performing Fourier transform to obtain an updated filtered spectrum; Step 8, reconstructing the local spectrum of the target by using the rPIE algorithm according to the filtered spectrum before and after the update, and updating the pupil function; Step 9, updating the target spectrum according to the reconstructed local spectrum, and judging whether a convergence condition is met; if the convergence condition is met, performing target imaging according to the updated target spectrum; if the convergence condition is not met, returning to step 2.

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