CN113281979B - Lensless laminated diffraction image reconstruction method, system, device and storage medium - Google Patents
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Abstract
The invention provides a method, a system, equipment and a storage medium for reconstructing a lens-free laminated diffraction image. The method comprises the following steps: s1, acquiring a gray-phase amplitude curve of a spatial light modulator and physical parameters of a system; s2, obtaining a target pattern, and carrying out K-1 times of lamination translation on the target pattern to obtain K modulation patterns; s3, inputting the K modulation patterns obtained in the step S2 into a spatial light modulator, and carrying out intensity acquisition on a diffraction image of an object subjected to scattering on a sensor plane to obtain a diffraction intensity image sequence (I)1，…Ii，…IK(iv) a complementary portion; and S4, combining the gray scale-phase amplitude curve obtained in the step S1, the physical parameters of the system and the diffraction intensity image sequence obtained in the step S3 with an ePIE algorithm to carry out iterative reconstruction, and obtaining the high-resolution amplitude and phase distribution information of the object. The method and the system can reconstruct the high-resolution amplitude and phase distribution information of the object without mechanical scanning or medium replacement, and have the advantages of less required image quantity, high robustness and strong flexibility.
Description
Technical Field
The present invention relates to lens-Less Coherent Diffraction Imaging (LCDI), and in particular, to a method for reconstructing a stacked diffraction image based on wavefront modulation, and more particularly, to a method, a system, a computer device, and a computer-readable storage medium for reconstructing a lens-less stacked diffraction image.
Background
Lens-free microscopy is a technique that directly brings a sample into close proximity with a photosensor, such as a charge-coupled device (CCD) or a complementary metal-oxide semiconductor Chip (CMOS), and directly images the sample without the need for optical elements. In a classical lensless microscope system, the main components are the light source, the sample and the photosensor, and therefore the resolution of the photosensor will directly limit the resolution of the image. Because any lens is not added in the lensless microscope system, the problem that the traditional optical microscope imaging needs to compromise between a field of view and resolution is well solved, and the problem of aberration caused by the lens can be well avoided. Simultaneously compare with the traditional analysis and detection instrument that the price is expensive, the volume is big and need professional technical staff to operate, the no lens microtechnical principle is simple, and the low price conveniently carries, helps the testing personnel to carry out real-time observation analysis to the object. However, if the coherent domain is involved, the mainstream GS or HIO algorithm has high requirements on the isolation of the object and the coherence of the light source in order to recover the phase information of the object. Therefore, the traditional lens-free coherent diffraction imaging is mainly tested on an X-ray synchrotron radiation platform with harsh light source conditions.
In 1969, Hoppe first proposed the concept of stacked-layer scanning imaging (ptychodography), whose purpose was to be able to deterministically solve the phase information of complex-amplitude objects. The laminated scanning coherent diffraction imaging system obtains a plurality of intensity diffraction patterns corresponding to different parts of a sample through a two-dimensional moving aperture diaphragm or the sample. Stack imaging improves the convergence of the phase recovery algorithm and reduces the requirements on experimental conditions by recording a high redundancy of data. With the development of the reconstruction algorithm, the imaging quality of the laminated scanning is remarkably improved, and the application range is continuously expanded. Rodenburg et al, 2004, proposed a stacked diffraction imaging algorithm (PIE) that uses multiple intensity patterns instead of a traditional single intensity pattern, taking advantage of the redundancy of data to greatly reduce the strict limitations of LCDI on objects and light sources, and greatly improve the convergence of the algorithm. The laminated scanning technology and the wavefront modulation technology provide possibility for realizing microscopic imaging of common biological tissue cell objects under the visible laser condition of a laboratory for lens-free coherent diffraction imaging.
The lens-free coherent diffraction imaging technology in the existing mainstream laboratory is generally divided into two types, one is a lens-free coaxial holographic imaging technology, which is also called on-chip holography. The distance between an object and a sensor in the system is very close, and then a plurality of groups of data are collected by changing the wavelength, the illumination angle and the like of an LED light source, but the interference-based method is not stable and robust. The other is a lensless imaging system based on scattering media that randomly modulates the wavefront in front of the sensor or behind the light source, resulting in better convergence of the object information. However, this method often requires a plurality of different scattering media, and for unknown scattering media, thousands of pictures are often acquired to reconstruct the object well.
Disclosure of Invention
In order to solve the above problems, the present invention provides a method, a system, a computer device and a computer readable storage medium for reconstructing a lens-free laminated diffraction image, which can reconstruct high-resolution amplitude and phase distribution information of an object without mechanical scanning or medium replacement, and require a small number of images; in addition, the method has the characteristics of high robustness and strong flexibility for parameter errors and modulation errors of the spatial light modulator.
The invention provides a method for reconstructing a lens-free laminated diffraction image, which comprises the following steps: s1, acquiring a gray-phase amplitude curve of a spatial light modulator and physical parameters of a system; s2, obtaining a target pattern, and carrying out K-1 times of lamination translation on the target pattern to obtain K modulation patterns; s3, inputting the K modulation patterns obtained in the step S2 into a spatial light modulator, and carrying out intensity acquisition on a diffraction image of an object subjected to scattering on a sensor plane to obtain a diffraction intensity image sequence (I)1，…Ii，…IK(iv) a complementary portion; and S4, combining the gray scale-phase amplitude curve obtained in the step S1, the physical parameters of the system and the diffraction intensity image sequence obtained in the step S3 with an ePIE (extended mental imaging iterative engine) algorithm to perform iterative reconstruction, and obtaining the amplitude and phase distribution information of the object with high resolution.
The present application further provides a lens-free laminated diffraction image reconstruction system, comprising, along an optical path direction: lasers, objects, spatial light modulators and sensors; the system employs the lensless stack diffraction image reconstruction method described above.
The invention also provides a computer device comprising a memory having a computer program stored therein and a processor which, when executing the computer program, implements the lens-free stack diffraction image reconstruction method as described above.
The present invention also provides a computer readable storage medium comprising a computer program stored thereon, which when executed by a processor, implements the lens-free stack diffraction image reconstruction method as described above.
The invention has the beneficial effects that:
(1) the reconstruction method of ePIE can effectively improve the convergence of GS algorithm, and simultaneously fully utilizes the programmable characteristic of the spatial light modulator to realize the phase recovery without lens. After the object diffraction complex amplitude of the incident surface of the spatial light modulator is reconstructed, digital refocusing can be easily performed on the object at each depth.
(2) Compared with other stack scanning or Fourier stack scanning methods, the method has the defects of low resolution caused by the fact that hundreds of pieces of acquired data are needed (the data requirement is large), mechanical scanning is needed or only a partially coherent LED matrix is used; or the method using the scattering medium in the prior art, the modulation function of the medium is required to be reconstructed again when the medium is replaced. The invention realizes random wavefront modulation by utilizing the spatial light modulator, and the spatial light modulator combines an ePIE algorithm, so that the number of required images is less than that of the traditional laminated scanning, and the amplitude and phase distribution of a sample can be reconstructed without any mechanical movement.
(3) Compared with the model using the GS algorithm in the prior art, the method can update the modulation function of the spatial light modulator, namely the spatial light modulator is used as a programmable scattering medium, and the modulation error of the spatial light modulator is corrected in the updating of the ePIE algorithm. It is also uniquely robust and flexible to initial system errors, including modulation planes and geometric parameters between sensor planes. In the conventional reconstruction method, the centers of the two planes are strictly aligned and parallel, but in practical application, a translation error on an X-Y plane and a rotation error on an X, Y and Z axis exist between the two planes, and the device does not need to adopt an additional algorithm for geometric parameter correction.
Drawings
Fig. 1 is a schematic structural diagram of a lensless stacked diffraction imaging optical path based on a spatial light modulator in an embodiment of the present invention.
Fig. 2 is an overall framework of the lens-free stacked diffraction imaging reconstruction method in the embodiment of the invention.
Fig. 3 is one of the diffraction intensity images of the USAF sample collected by the sensor of the present invention.
Fig. 4 is a plot of amplitude and phase for reconstructed USAF samples of the present invention.
Fig. 5 is one of the diffraction intensity images of maple leaf samples collected by the sensor of the present invention.
Fig. 6 is a graph of amplitude and phase of reconstructed maple leaf samples according to the present invention.
Detailed Description
The present invention is described in further detail below with reference to specific embodiments and with reference to the attached drawings, it should be emphasized that the following description is only exemplary and is not intended to limit the scope and application of the present invention.
As shown in fig. 1, the present embodiment provides a lens-less stacked diffraction image reconstruction system, the optical elements along the optical path direction sequentially including: a light source, a collimating mirror, a diaphragm, a polarizer, an object, a Spatial Light Modulator (SLM), a polarizer, and a sensor.
The light beam emitted by the light source is collimated by the collimating mirror and then enters the surface of the diaphragm, the size of the light spot is controlled by the diaphragm, and the front polaroid and the rear polaroid play roles of a polarizer and an analyzer, so that the polarization direction of the light passing through the spatial light modulator is parallel to liquid crystal molecules in the spatial light modulator, and the modulation relation is met. The modulated light carrying the object information then reaches the sensor where the intensity is recorded.
The light source may be a laser light source, such as green light with a wavelength of 532 nm.
Spatial Light Modulator (SLM)) is a programmable Modulator that can modulate the amplitude and phase of an object wavefront, which can effectively simulate the scattering effect of various scattering media on Light. The principle of operation of a spatial light modulator is that a current adjusts the turning of the liquid crystal cell molecules, which rotate in the plane of the optical axis to change the magnitude of the modulating action. The modulation of the SLM is typically controlled by outputting a gray pattern to the SLM, with a current value for each gray value of 0-255, in a manner similar to controlling a display. However, the magnitude relationship between the gray value and the phase or amplitude modulation is not linear or even positive, and the modulation effect is not effective for o-polarized light parallel to the optical axis, so that a polarizer and an analyzer are often required in a transmissive SLM to realize the modulation of the wavefront.
The sensor is used for collecting the intensity of the scattered diffraction image of the object passing through the spatial light modulator to obtain a diffraction intensity image, and the sensor comprises a CCD or a CMOS.
Based on the optical path, the system adopts the following method for reconstructing the lens-free laminated diffraction image.
S1, acquiring a gray-phase amplitude curve of a spatial light modulator and physical parameters of a system;
the gray-phase amplitude profile of a spatial light modulator can sometimes be obtained directly from the specifications of the purchased spatial light modulator, but it may not be accurate or complete. In order to further improve the accuracy and precision, after the spatial light modulator applied in the system is determined, the gray-phase amplitude curve of the spatial light modulator can be obtained through a beam splitting interference experiment.
The physical parameters of the system include: the wavelength of the light source, the internal and external parameters of the spatial light modulator and the sensor, such as: the respective pixel cell sizes of the spatial light modulator and the sensor, the distance d1 from the object to the plane of the spatial light modulator, the distance d2 from the plane of the spatial light modulator to the plane of the sensor, etc.
S2, obtaining a target pattern, and carrying out K-1 times of lamination translation on the target pattern to obtain K modulation patterns.
The stack shift refers to a portion where K modulation patterns have an overlap with each other after the original pattern is shifted. K is set according to actual needs.
S3, inputting the K modulation patterns obtained in the step S2 into a spatial light modulator to form K times of modulation patternsModulating a function, and carrying out intensity acquisition on a diffraction image of an object subjected to scattering on a sensor plane to obtain a diffraction intensity image sequence (I)1，…Ii，…IK﹜。
Diffraction intensity image IiThe calculation formula of (2), namely the physical model based on the whole system, is as follows:
Ii＝|propd2(SLMi·O)|2formula (1)
Wherein, Ii(i 1.., K) represents a diffraction intensity pattern acquired by the sensor; o ═ propd1(X), X is the object plane complex amplitude distribution; d1 and d2 are the distance from the object to the plane of the spatial light modulator and the distance from the plane of the spatial light modulator to the plane of the sensor respectively; prop is expressed as a fresnel propagation formula, specifically formula (2) as follows:
formula (2) is a propagation process of Fresnel diffraction between two planes, wherein U represents a plane light complex amplitude distribution; ξ, η and x, y are the two-dimensional coordinates of the diffraction and object planes, respectively, which are related to the respective pixel cell sizes of the spatial light modulator and the sensor; z denotes a distance between the spatial light modulator plane and the sensor plane (in the present embodiment, Z ═ d2), λ is a light wavelength, k is a wave vector, and j denotes an imaginary unit.
Fresnel diffraction describes the propagation law of paraxial approximation of the complex amplitude of light in free space, due to the propagation distance being much larger than the object plane.
And S4, combining the gray scale-phase amplitude curve obtained in the step S1, the physical parameters of the system and the diffraction intensity image sequence obtained in the step S3 with an ePIE algorithm to carry out iterative reconstruction, and obtaining the high-resolution amplitude and phase distribution information of the object.
In particular, iterative reconstruction includes initialization and iterative optimization.
S41, initialization: obtaining an object diffraction complex amplitude distribution O of an initial spatial light modulator plane0And an initial modulation function P0. The method specifically comprises the following steps:
s411, generating an initial modulation function P according to the gray-phase amplitude curve and the target pattern0；
S412, reversely propagating the diffraction intensity image sequence back to the incident surface of the spatial light modulator, summing the sum, and averaging to obtain object diffraction complex amplitude distribution O of the initial spatial light modulator plane0Said O is0Is calculated as in equation (3):
S42, iterative optimization: according to the complex amplitude distribution O0And an initial modulation function P0Combining with ePIE algorithm, the complex amplitude of the incident plane of the spatial light modulator is updated for N times to obtain the modulation function PNAnd object diffraction complex amplitude distribution ONThen, the object is diffracted to have a complex amplitude distribution ONAnd reversely propagating to the object plane to obtain high-resolution amplitude and phase distribution information of the object.
As shown in fig. 2, the iterative optimization process is to implement N times of complex amplitude updates on the SLM incident plane based on the optical model formula (1) in combination with the iterative projection principle of the ePIE algorithm, where the nth time of complex amplitude update is taken as an example:
s421. in the nth iteration, OnAnd PnRepresenting O and P obtained after the end of the last iteration. P is translated according to the translation amount of the ith modulation pattern translationnPerforming translation with the same translation amount to obtain corresponding
The calculation formula is as follows:
wherein the content of the first and second substances,
the modulation function adopted by the ith modulation in the nth iteration is shown; x (i), y (i) denotes the ith modulation function
Relative to PnThe amount of translation of; pnIndicating the modulation function in the nth iteration, updated from the (n-1) th iteration.
S422, according to the modulation function adopted by the ith modulation in the nth iteration
Transmitting the complex amplitude of the space optical sensor plane to the sensor plane by utilizing Fresnel transmission to obtain the complex amplitude of the sensor plane
The calculation formula of (a) is as follows:
s423, utilizing the diffraction intensity image I collected in the step S3iAmplitude versus complex amplitude of
Amplitude value replacement is carried out to obtain replaced complex amplitude
The calculation formula of (a) is as follows:
where j represents an imaginary unit.
S424, replacing the complex amplitude obtained in the step S423
Back-propagating to the spatial light modulator plane, and calculating to obtain an updated modulation function Pn+1And object diffraction complex amplitude distribution On+1(ii) a The P isn+1And On+1The calculation formula of (a) is as follows:
wherein, alpha represents the updating step length, represents the gradient updating rate and can be adjusted by self;
represents the updated ith modulation function, according to which the modulation function P used in the next iteration is updatedn+1。
S425, repeating the steps S421 to S424 until N iterations are carried out to obtain the modulation function PNAnd object diffraction complex amplitude distribution ON；
Wherein N is 0 … N-1; when n is equal to 0, the compound is,
is composed of
Represents the first iteration according to P0Carrying out the ith translation to obtain a modulation function; the equations (1) to (9) use the object diffraction complex amplitude distribution O in step S410And an initial modulation function P0. S426, distributing the diffraction complex amplitude of the object to obtain an ONAnd reversely propagating to the object plane to obtain high-resolution amplitude and phase distribution information of the object. N is a positive integer and can be set according to actual needs.
According to the above system and method, a USAF (United States Air Force) and maple leaves are respectively used as samples to perform the reconstruction of the lens-free laminated diffraction image, as shown in fig. 3, which is one of the diffraction intensity images of the USAF sample collected by the sensor, and the amplitude and phase distribution graph obtained after the reconstruction is shown in fig. 4; as shown in fig. 5, which is one of the diffraction intensity images of the maple leaf sample acquired by the sensor, the amplitude and phase distribution map obtained after reconstruction is shown in fig. 6.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by a computer program, which can be stored in a computer-readable storage medium, and can include the processes of the embodiments of the methods described above when the computer program is executed. The storage medium may be a non-volatile storage medium such as a magnetic disk, an optical disk, a Read-Only Memory (ROM), or a Random Access Memory (RAM).
The present embodiments also provide a computer device including a memory, a processor, and the like communicatively connected to each other through a system bus. As will be understood by those skilled in the art, the computer device is a device capable of automatically performing numerical calculation and/or information processing according to a preset or stored instruction, and the hardware includes, but is not limited to, a microprocessor, an Application Specific Integrated Circuit (ASIC), a Programmable Gate Array (FPGA), a Digital Signal Processor (DSP), an embedded device, and the like.
The computer device may be a desktop computer, a notebook, a palm computer, a cloud server, or other computing devices. The computer equipment can carry out man-machine interaction with a user through a keyboard, a mouse, a remote controller, a touch panel or voice control equipment and the like.
The memory includes at least one type of readable storage medium including a flash memory, a hard disk, a multimedia card, a card type memory (e.g., SD or DX memory, etc.), a Random Access Memory (RAM), a Static Random Access Memory (SRAM), a Read Only Memory (ROM), an Electrically Erasable Programmable Read Only Memory (EEPROM), a Programmable Read Only Memory (PROM), a magnetic memory, a magnetic disk, an optical disk, etc. In some embodiments, the storage may be an internal storage unit of the computer device, such as a hard disk or a memory of the computer device. In other embodiments, the memory may also be an external storage device of the computer device, such as a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) Card, a Flash memory Card (Flash Card), or the like provided on the computer device. Of course, the memory may also include both internal and external storage devices of the computer device. In the embodiment of the present invention, the memory is generally used for storing an operating system installed in the computer device and various types of application software, such as the program codes of the above method for reconstructing a lens-free laminated diffraction image. In addition, the memory may also be used to temporarily store various types of data that have been output or are to be output.
The processor may be a Central Processing Unit (CPU), controller, microcontroller, microprocessor, or other data Processing chip in some embodiments. The processor 92 is typically used to control the overall operation of the computer device. In an embodiment of the invention, the processor is configured to execute the program code stored in the memory or to process data, for example, execute the program code of the method for reconstructing a lens-free laminated diffraction image as described above.
The foregoing is a more detailed description of the invention in connection with specific/preferred embodiments and is not intended to limit the practice of the invention to those descriptions. It will be apparent to those skilled in the art that various substitutions and modifications can be made to the described embodiments without departing from the spirit of the invention, and these substitutions and modifications should be considered to fall within the scope of the invention.
Claims (10)
1. A method for reconstructing a lens-free laminated diffraction image, comprising:
s1, acquiring a gray-phase amplitude curve of a spatial light modulator and physical parameters of a system;
s2, obtaining a target pattern, and carrying out K-1 times of lamination translation on the target pattern to obtain K modulation patterns;
s3, transmitting the K modulation patterns obtained in the step S2Entering a spatial light modulator and carrying out intensity acquisition on a diffraction image of an object subjected to scattering on a sensor plane to obtain a diffraction intensity image sequence (I)1，…Ii，…IK﹜；
And S4, combining the gray scale-phase amplitude curve obtained in the step S1, the physical parameters of the system and the diffraction intensity image sequence obtained in the step S3 with an ePIE algorithm to carry out iterative reconstruction, and obtaining the high-resolution amplitude and phase distribution information of the object.
2. The method of claim 1, wherein the physical parameters of the system comprise:
internal and external parameters between the spatial light modulator and the sensor, and the wavelength of the light source; the internal and external parameters between the spatial light modulator and the sensor include: the respective pixel cell sizes of the spatial light modulator and the sensor, the distance of the object to the plane of the spatial light modulator, the distance of the plane of the spatial light modulator to the plane of the sensor.
3. The method of claim 1, wherein the diffraction intensity image I in step S3iObtained by the following formula:
Ii-＝|propd2(SLMi.o)|2
wherein O is propdi(X), X is the object plane complex amplitude distribution; d1 and d2 are the distance from the object to the plane of the spatial light modulator and the distance from the plane of the spatial light modulator to the plane of the sensor respectively; prop is expressed as fresnel propagation, and the formula is as follows:
wherein U represents a planar light complex amplitude distribution; ξ, η and x, y are the two-dimensional coordinates of the diffraction and object planes, respectively, Z represents the distance between the spatial light modulator plane and the sensor plane, λ is the wavelength of the light, k is the wave vector, and j represents the imaginary unit.
4. The method of claim 1, wherein the iterative reconstructing comprises:
s41, initialization: obtaining an object diffraction complex amplitude distribution O of an initial spatial light modulator plane0And an initial modulation function P0；
S42, iterative optimization: according to the complex amplitude distribution O0And an initial modulation function P0Combining with ePIE algorithm, the complex amplitude of the incident plane of the spatial light modulator is updated for N times to obtain the modulation function PNAnd object diffraction complex amplitude distribution ONThen, the object is diffracted to have a complex amplitude distribution ONAnd reversely propagating to the object plane to obtain high-resolution amplitude and phase distribution information of the object.
5. The method of claim 4, wherein the step S41 initialization comprises:
s411, generating an initial modulation function P according to the gray-phase amplitude curve and the target pattern0；
S412, reversely propagating the diffraction intensity image sequence back to the incident surface of the spatial light modulator, summing the sum, and averaging to obtain object diffraction complex amplitude distribution O of the initial spatial light modulator plane0Said O is0The calculation formula of (a) is as follows:
wherein the content of the first and second substances,
according to P in the first iteration0And (5) performing the ith translation to obtain a modulation function, wherein conj is a conjugate function.
6. The method of claim 4, wherein said step S42 iterative optimization comprises:
s421, according to the translation amount of the ith modulation pattern translation, P is convertednPerforming translation with the same translation amount to obtain corresponding
The calculation formula is as follows:
wherein the content of the first and second substances,
the modulation function adopted by the ith modulation in the nth iteration is shown; x (i), y (i) denotes the ith modulation function
Relative to PnThe amount of translation of; pnRepresenting the modulation function in the nth iteration;
s422, according to the modulation function adopted by the ith modulation in the nth iteration
Transmitting the complex amplitude of the space optical sensor plane to the sensor plane by utilizing Fresnel transmission to obtain the complex amplitude of the sensor plane
The calculation formula of (a) is as follows:
s423. utilizing the diffraction collected in the step S3Intensity image IiAmplitude versus complex amplitude of
Amplitude value replacement is carried out to obtain replaced complex amplitude
The calculation formula of (a) is as follows:
wherein j represents an imaginary unit;
s424, replacing the complex amplitude obtained in the step S423
Back-propagating to the spatial light modulator plane, and calculating to obtain an updated modulation function Pn+1And object diffraction complex amplitude distribution On+1(ii) a The P isn+1And On+1The calculation formula of (a) is as follows:
wherein, alpha represents the updating step length, represents the gradient updating rate and can be adjusted by self;
represents the updated ith modulation function, according to which the modulation function P used in the next iteration is updatedn+1；
S425, repeating the steps S421 to S424 until N iterations are carried out to obtain the modulation function PNAnd object diffraction complex amplitude distribution ON；
Wherein N is 0, …, N-1; when n is equal to 0, the compound is,
is composed of
Represents the first iteration according to P0Carrying out the ith translation to obtain a modulation function;
s426, distributing the diffraction complex amplitude of the object to obtain an ONAnd reversely propagating to the object plane to obtain high-resolution amplitude and phase distribution information of the object.
7. A lensless stacked diffractive image reconstruction system comprising, along an optical path: a light source, an object, a spatial light modulator and a sensor; the system employs the lens-free stack diffraction image reconstruction method of any one of claims 1-6.
8. The lens-free laminated diffractive image reconstruction system of claim 7, further comprising, in order between said light source and object: a collimating lens, a diaphragm and a polaroid; and a polaroid is also arranged between the spatial light modulator and the sensor.
9. A computer device comprising a memory and a processor, wherein the memory has stored therein a computer program which, when executed by the processor, implements the lens-free stack diffraction image reconstruction method of any of claims 1-6.
10. A computer-readable storage medium, comprising a computer program stored thereon, which, when executed by a processor, implements the lens-free stack diffraction image reconstruction method of any one of claims 1-6.
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