Method, system, and storage medium for suppressing wrapped phase noise

Abstract

The application discloses a method, system and storage medium for suppressing wrapped phase noise, and relates to the technical field of digital holography, and comprises the following steps: simulating an illumination hologram of a target object based on object light, reference light and reproduced light, to obtain a complex amplitude distribution of a reproduced image surface of the illumination hologram; performing an inverse tangent calculation on a quotient of an imaginary part of the complex amplitude distribution divided by a real part of the complex amplitude distribution, to obtain a wrapped phase distribution; decomposing the wrapped phase distribution, to obtain a sine phase graph and a cosine phase graph; respectively performing discrete cosine transformation and threshold filtering calculation on the sine phase graph and the cosine phase graph, to obtain a first discrete cosine spectrum and a second discrete cosine spectrum after noise reduction; and performing discrete cosine inverse transformation and unwrapped phase calculation on the first discrete cosine spectrum and the second discrete cosine spectrum, to obtain a phase distribution image of the target object after noise reduction. The application can suppress speckle noise while improving the accuracy of the obtained phase distribution image, so that the accuracy of a digital holographic image is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of digital holography, and particularly relates to a method and system for suppressing wrapped phase noise and a storage medium. BACKGROUND

[0002] Digital holography has the advantages of non-contact, high sensitivity, real-time quantitative imaging and the like, and is widely applied to the detection field. In the process of digital holographic reconstruction, due to the high coherence of laser, when laser is irradiated to a rough surface, scattering occurs, thereby forming speckle noise, which will reduce the accuracy of the obtained digital holographic image.

[0003] In the related art, the holographic image is generally denoised by a sine-cosine filtering method based on an image processing algorithm. Although this method can retain the peak value information in the image, some useful information will be filtered or blurred when the speckle noise is filtered, and the accuracy of the obtained digital holographic image cannot be guaranteed. How to suppress the speckle noise while guaranteeing the accuracy of the obtained digital holographic image is a problem to be discussed and solved at present. SUMMARY

[0004] The present application aims to at least solve one of the technical problems in the prior art. To this end, the present application provides a method and system for suppressing wrapped phase noise and a storage medium, which can improve the accuracy of the obtained phase distribution image while suppressing the speckle noise, thereby guaranteeing the accuracy of the digital holographic image.

[0005] To solve the above technical problems, the present application provides the following technical solutions:

[0006] The first aspect of the present application provides a method for suppressing wrapped phase noise, comprising:

[0007] obtaining object light, reference light and reconstruction light of a target object, simulating an illumination hologram of the target object based on the object light, the reference light and the reconstruction light, and obtaining a complex amplitude distribution of a reconstruction image plane of the illumination hologram;

[0008] performing an inverse tangent calculation on a quotient of an imaginary part of the complex amplitude distribution divided by a real part of the complex amplitude distribution, to obtain a wrapped phase distribution;

[0009] decomposing the wrapped phase distribution to obtain a sine phase image and a cosine phase image;

[0010] respectively performing discrete cosine transform and threshold filtering calculation on the sine phase image and the cosine phase image to obtain a first discrete cosine spectrum and a second discrete cosine spectrum after noise reduction;

[0011] performing inverse discrete cosine transform and unwrapping phase calculation on the first discrete cosine spectrum and the second discrete cosine spectrum to obtain a phase distribution image of the target object after noise reduction.

[0012] The method for suppressing wrapped phase noise according to the first aspect of the present application has at least the following beneficial effects: the method for suppressing wrapped phase noise according to the present application can simulate an illumination hologram of a target object based on the intensity of object light, the intensity of reference light and the intensity of reproduced light, and by decomposing the wrapped phase distribution of the illumination hologram, a sine phase image and a cosine phase image are obtained, which converts the discontinuous wrapped phase distribution into a continuous quantity, thereby improving the accuracy; and after obtaining the sine phase image and the cosine phase image, discrete cosine transform and threshold filtering calculation are performed on the sine phase image and the cosine phase image to suppress noise, thereby obtaining a first discrete cosine spectrum and a second discrete cosine spectrum, and then inverse discrete cosine transform and unwrapping phase calculation are performed on the first discrete cosine spectrum and the second discrete cosine spectrum to obtain a continuous phase distribution, i.e., a phase distribution image of the target object after noise reduction. Based on this, the present application can suppress speckle noise while improving the accuracy of the obtained phase distribution image, thereby ensuring the accuracy of the digital holographic image.

[0013] According to some embodiments of the first aspect of the present application, simulating the illumination hologram of the target object based on the object light, the reference light and the reproduced light to obtain the complex amplitude distribution of the reproduction image plane of the illumination hologram comprises:

[0014] calculating the interference intensity of the object light and the reference light to obtain the light intensity distribution of the illumination hologram;

[0015] obtaining the complex amplitude distribution of the reproduction image plane of the illumination hologram based on the light intensity distribution, the reproduced light, a preset reproduction distance, a preset light wavelength and an angular spectrum reconstruction object light field of a preset observation plane;

[0016] wherein the complex amplitude distribution of the reproduction image plane is:

[0017]

[0018] wherein U z1 (x,y) represents the complex amplitude distribution of the reproduction image plane; I(x,y) represents the light intensity distribution; C(x,y) represents the reproduced light; z1 represents the reproduction distance; λ represents the light wavelength; f x and f y represent the angular spectrum of the observation plane; F represents Fourier transform; F -1 represents inverse Fourier transform.

[0019] According to some embodiments of the first aspect of the present application, the step of decomposing the wrapped phase distribution to obtain a sine phase image and a cosine phase image comprises:

[0020]

[0021]

[0022] wherein S(x, y) represents the sine phase map; C(x, y) represents the cosine phase map; represents the wrapped phase distribution.

[0023] According to some embodiments of the first aspect of the application, the discrete cosine transform and threshold filtering calculation on the sine phase map and the cosine phase map respectively to obtain the first and second discrete cosine spectra after noise reduction comprises:

[0024] discrete cosine transform on the sine phase map and the cosine phase map respectively to obtain the first and second frequency spectra;

[0025] screening the first and second frequency spectra by a preset threshold to obtain the first and second discrete cosine spectra after noise reduction.

[0026] According to some embodiments of the first aspect of the application, the first frequency spectrum is:

[0027]

[0028]

[0029]

[0030] 0≤u≤M-1;

[0031] 0≤v≤N-1;

[0032] wherein F S (u, v) represents the first frequency spectrum; S(x, y) represents the sine phase map; M represents the width of S(x, y); N represents the length of S(x, y);

[0033] the second frequency spectrum is:

[0034]

[0035]

[0036]

[0037] 0≤u≤M-1;

[0038] 0≤v≤N-1;

[0039] wherein F C(u,v) represents the second frequency spectrum; C(x,y) represents the cosine phase map; M represents the width of C(x,y); and N represents the length of C(x,y).

[0040] According to some embodiments of the first aspect of the present application, the filtering of the first frequency spectrum and the second frequency spectrum by the preset threshold to obtain the first discrete cosine spectrum and the second discrete cosine spectrum after noise reduction comprises:

[0041]

[0042]

[0043] wherein, F represents the first discrete cosine spectrum; F S (u,v) represents the first frequency spectrum; and thr represents the preset threshold. F represents the second discrete cosine spectrum; F C (u,v) represents the second frequency spectrum.

[0044] According to some embodiments of the first aspect of the present application, the inverse discrete cosine transformation and the unwrapping phase calculation of the first discrete cosine spectrum and the second discrete cosine spectrum to obtain the phase distribution image of the target object after noise reduction comprises:

[0045] respectively performing inverse discrete cosine transformation on the first discrete cosine spectrum and the second discrete cosine spectrum to obtain a sine wrapped phase and a cosine wrapped phase;

[0046] performing arctangent calculation on the quotient of the sine wrapped phase and the cosine wrapped phase to obtain a noise-reduced wrapped phase distribution;

[0047] performing phase unwrapping calculation on the noise-reduced wrapped phase distribution to obtain the phase distribution image of the target object after noise reduction.

[0048] According to some embodiments of the first aspect of the present application, after obtaining the phase distribution image of the target object after noise reduction, the method further comprises:

[0049] performing polynomial fitting on the phase in the phase distribution image to obtain a distortion coefficient;

[0050] correcting the phase distribution image by the distortion coefficient to obtain a corrected phase distribution image of the target object after noise reduction.

[0051] The second aspect of the present application provides a system for suppressing wrapped phase noise, comprising:

[0052] at least one memory;

[0053] at least one processor;

[0054] at least one program;

[0055] the program is stored in the memory, and the processor executes at least one of the programs to implement:

[0056] The method for suppressing wrapped phase noise according to any one of the first aspect of the application.

[0057] The third aspect of the application provides a computer readable storage medium, the computer readable storage medium stores computer executable signals, and the computer executable signals are used for executing:

[0058] The method for suppressing wrapped phase noise according to any one of the first aspect of the application.

[0059] Additional aspects and advantages of the application will be in part apparent and in part pointed out below. BRIEF DESCRIPTION OF DRAWINGS

[0060] Additional aspects and advantages of the application will be in part apparent and in part pointed out below.

[0061] Figure 1 Main flowchart of the method for suppressing wrapped phase noise provided for some embodiments of the application;

[0062] Figure 2 Subflowchart of the method for suppressing wrapped phase noise provided for some embodiments of the application;

[0063] Figure 3 Subflowchart of the method for suppressing wrapped phase noise provided for some embodiments of the application;

[0064] Figure 4 Subflowchart of the method for suppressing wrapped phase noise provided for some embodiments of the application;

[0065] Figure 5 Subflowchart of the method for suppressing wrapped phase noise provided for some embodiments of the application;

[0066] Figure 6 Main flowchart of the method for suppressing wrapped phase noise provided for another embodiment of the application;

[0067] Figure 7 Module block diagram of the system for suppressing wrapped phase noise provided for some embodiments of the application. DETAILED DESCRIPTION

[0068] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0069] It should be noted that although the logical order is shown in the flowchart, in some cases, the steps shown or described can be performed in an order different from that in the flowchart. The terms in the specification and claims and the above-described drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0070] In the description of the present application, if the first, second, and the like are described, they are used only for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the sequence of indicated technical features.

[0071] In the description of the present application, unless otherwise explicitly limited, the words such as arrangement, installation, connection, and the like should be broadly understood, and those skilled in the art can reasonably determine the specific meaning of the above words in the present application in combination with the specific content of the technical solution.

[0072] Before the embodiments of the present disclosure are further described in detail, the terms and terms involved in the embodiments of the present disclosure are explained, and the terms and terms involved in the embodiments of the present disclosure are applicable to the following explanations:

[0073] Speckle noise: due to the high coherence of laser, when laser is irradiated to a rough surface, scattering occurs to form speckle noise.

[0074] Wrapped phase: due to the introduction of the arctangent function when extracting the phase information, the obtained phase is called wrapped phase, that is, the phase value is between [-π, π].

[0075] Sine and cosine decomposition: the original noisy phase image with light and dark alternation is transformed by sine and cosine functions to decompose into sine and cosine phase images, and the jump information is converted into continuous quantities.

[0076] Discrete cosine transform: it is a transform related to Fourier transform, and its essence is discrete Fourier transform, but only real numbers are used. Discrete cosine transform is equivalent to a discrete Fourier transform with a length of about twice its length, which is performed on a real even function. In some transformations, the input or output position needs to be moved by half a unit.

[0077] Digital holography has the advantages of non-contact, high sensitivity and real-time quantitative imaging, and is widely used in detection field. In the process of digital holographic reconstruction, due to the high coherence of laser, when laser irradiates the rough surface, scattering will occur, and speckle noise will be formed, which will reduce the accuracy of the final digital holographic image.

[0078] At present, the method for suppressing speckle noise of wrapped phase can be divided into two categories. One is from the perspective of hardware, including: replacing the high-coherence laser light source with a low-coherence light source such as an LED light source in the experiment; or physically removing the high coherence of laser, such as using double rotating plates to remove coherence. The other is based on image processing algorithm for noise suppression, such as using sine-cosine filtering method to suppress the speckle noise of wrapped phase.

[0079] In the related art, the holographic image is filtered by the sine-cosine filtering method based on the image processing algorithm. Although this method can retain the peak value information in the image, it will filter or blur some useful information while filtering out the speckle noise, and cannot guarantee the accuracy of the final digital holographic image. How to suppress speckle noise while guaranteeing the accuracy of the final digital holographic image is a problem to be discussed and solved at present.

[0080] There are many methods for suppressing wrapped phase noise based on image processing algorithm, such as median filtering method, sine-cosine mean filtering method, windowed Fourier filtering method, etc. However, using the sine-cosine mean filtering method will lose the phase jump information and peak value information in the original phase diagram, and blur the boundaries of the fringes. Although the median filtering method can retain the phase jump information, it is not suitable for high noise level due to the noise statistical distribution assumption based on the bilateral exponential function, and the median filtering method needs to sort the size of each pixel value in the filtering window, which takes a long time to calculate. The wrapped phase and unwrapped phase obtained by using the windowed Fourier filtering method have no obvious noise residue, but the running speed is slow.

[0081] Therefore, the present application discloses a method for suppressing wrapped phase noise, which can quickly denoise the wrapped phase and obtain high-precision phase information.

[0082] Reference Figure 1 In a first aspect, the embodiments of the present application provide a method for suppressing wrapped phase noise, which includes but is not limited to steps S110, S120, S130, S140 and S150.

[0083] In step S110, the object light, reference light and reconstruction light of a target object are obtained, and the illumination hologram of the target object is simulated based on the object light, reference light and reconstruction light to obtain the complex amplitude distribution of the reconstruction image surface of the illumination hologram.

[0084] Step S120, the inverse tangent calculation is performed on the quotient of the imaginary part of the complex amplitude distribution divided by the real part of the complex amplitude distribution to obtain a wrapped phase distribution;

[0085] Step S130, the wrapped phase distribution is decomposed to obtain a sine phase graph and a cosine phase graph;

[0086] Step S140, the discrete cosine transform and threshold filtering calculation are respectively performed on the sine phase graph and the cosine phase graph to obtain a first discrete cosine spectrum and a second discrete cosine spectrum after noise reduction;

[0087] Step S150, the discrete cosine inverse transform and unwrapped phase calculation are performed on the first discrete cosine spectrum and the second discrete cosine spectrum to obtain a phase distribution image of the target object after noise reduction.

[0088] Referring to Figure 6 , Figure 6 The main flowchart of the method for suppressing wrapped phase noise provided by another embodiment of the present application; before simulating the illumination hologram, the intensity of the object light, the intensity of the reference light and the intensity of the reproduced light of the target object need to be obtained first, based on the principle of optical interference, the intensity of the interference of the object light and the reference light is calculated, and in the digital holographic reproduction process, the computer is used to simulate the reproduction light to illuminate the hologram, the angular spectrum diffraction theory is used to reconstruct the object light field to obtain the complex amplitude distribution of the reproduced image surface, the complex amplitude distribution contains the amplitude and the phase, and directly represents the distribution of the light wave in the space. After obtaining the complex amplitude distribution, the inverse tangent calculation is performed on the quotient of the imaginary part of the complex amplitude distribution divided by the real part of the complex amplitude distribution to obtain a wrapped phase distribution, specifically, the expression of the wrapped phase distribution is: Wherein, U represents the wrapped phase distribution; z1 (x, y) represents the complex amplitude distribution of the reproduced image surface; z1 (x, y) represents the imaginary part of the complex amplitude distribution; z1 (x, y) represents the real part of the complex amplitude distribution. After obtaining the wrapped phase distribution, considering that most of the wrapped phase distributions exist edge information loss, and the essence of the edge information loss is that the periodic function of the phase graph itself is discontinuous, in order to solve this problem, the discontinuous function can be converted into a continuous periodic function, that is, the discontinuous phase is converted into a continuous phase and then regularly denoised, before denoising, the original noisy phase graph with light and dark alternation needs to be transformed by a sine function, that is, the wrapped phase distribution is decomposed to obtain a sine phase graph and a cosine phase graph, and the jump information is converted into a continuous quantity.

[0089] After obtaining the sine phase map and the cosine phase map, the application also needs to perform discrete cosine transform on the sine phase map and the cosine phase map to calculate the two-dimensional cosine wave in the sine phase map and the cosine phase map. The discrete cosine transform can periodically expand the sine phase map and the cosine phase map, so that the sine phase map and the cosine phase map have better frequency energy concentration. However, due to the randomness of noise and the incoherence of the discrete cosine transform, noise usually penetrates the entire spectrum domain with very small coefficients. If the amplitude of the frequency spectrum coefficient is less than a preset threshold, the noise can be suppressed by discarding the frequency spectrum coefficient. Based on this, the application achieves the filtering effect through threshold filtering calculation to obtain the first discrete cosine spectrum and the second discrete cosine spectrum. At this time, the first discrete cosine spectrum and the second discrete cosine spectrum need to be inversely transformed to obtain the sine wrapped phase and the cosine wrapped phase after noise reduction, and the sine wrapped phase and the cosine wrapped phase need to be calculated to obtain the unwrapped phase, that is, the phase information wrapped between (-π, π) is unfolded and restored to continuous phase data to obtain continuous phase distribution and obtain a phase distribution image. After obtaining the phase distribution image, the application also compares and analyzes the final results obtained by the method for suppressing wrapped phase noise, the windowed Fourier filtering noise reduction method, the sine-cosine mean filtering method, and the median filtering method. Referring to Table 1, the discrete cosine transform noise reduction method based on sine-cosine decomposition is the method for suppressing wrapped phase noise of the application. It can be obviously observed that the PSNR (Peak Signal-to-Noise Ratio) and SIMM (Structural SIMilarity) of the final result of the application are higher than those of the final results obtained by other signal processing methods, and the time used by the application is also shorter.

[0090]

[0091]

[0092] Table 1: Performance comparison of different noise suppression methods

[0093] It should be noted that the method for suppressing wrapped phase noise provided in the application can simulate an illumination hologram based on the intensity of the object light, the intensity of the reference light and the intensity of the reproduced light, obtain a sine phase graph and a cosine phase graph by decomposing the wrapped phase distribution of the illumination hologram, convert the discontinuous wrapped phase distribution into a continuous quantity, and improve the accuracy; and after obtaining the sine phase graph and the cosine phase graph, the method performs discrete cosine transform and threshold filtering calculation on the sine phase graph and the cosine phase graph to suppress noise, and obtains a first discrete cosine spectrum and a second discrete cosine spectrum after noise reduction, and then performs inverse discrete cosine transform and unwrapped phase calculation on the first discrete cosine spectrum and the second discrete cosine spectrum to obtain a continuous phase distribution, i.e. a phase distribution image of the target object after noise reduction. Based on this, the application can improve the accuracy of the obtained phase distribution image while suppressing speckle noise, thereby ensuring the accuracy of the digital holographic image.

[0094] Reference Figure 2 In a first aspect, the embodiments of the application provide a method for suppressing wrapped phase noise, including but not limited to steps S210 and S220.

[0095] In step S210, the interference intensity of the object light and the reference light is calculated to obtain the light intensity distribution of the illumination hologram.

[0096] In step S220, the complex amplitude distribution of the reconstruction image plane of the illumination hologram is obtained based on the light intensity distribution, the reproduced light, a preset reconstruction distance, a preset light wavelength and an angular spectrum of a preset observation plane.

[0097] It can be understood that the complex amplitude distribution of the reconstruction image plane is:

[0098]

[0099] Wherein, U z1 (x,y) represents the complex amplitude distribution of the reconstruction image plane; I(x,y) represents the light intensity distribution; C(x,y) represents the reproduced light; z1 represents the reconstruction distance; λ represents the light wavelength; f x and f y represent the angular spectrum of the observation plane; F represents the Fourier transform; F -1 represents the inverse Fourier transform.

[0100] According to one embodiment of the application, when the object light and the reference light are acquired, the light intensity ratio of the acquired object light and reference light should be controlled. After the object light, the reference light and the reproduced light are acquired, the application first calculates the interference intensity of the object light and the reference light based on the principle of optical interference to obtain the light intensity distribution of the illumination hologram, and the expression of the light intensity distribution of the illumination hologram is: I(x,y) = |O+R| 2 = |O| 2 + |R| 2+2R*O; wherein, I(x,y) represents the light intensity distribution of the illumination hologram, O represents the object light; R represents the reference light.

[0101] It should be noted that holographic technology is a technology for recording and reproducing real three-dimensional images of an object by using interference and diffraction principles. "Holographic" means "all information", which refers to recording and reproducing all information of light emitted by the photographed object by projection. The holographic image technology is also commonly referred to as virtual imaging technology or holographic imaging technology. The imaging principle is to record the phase and amplitude of the light wave of the object by means of light wave interference, and at the same time, to display the light wave information of the object by means of diffraction principle, so as to achieve the effect of imaging. In the digital holographic reproduction process, in order to facilitate subsequent noise suppression, the distribution of the light wave in space needs to be obtained first. Therefore, after obtaining the light intensity distribution of the illumination hologram, the complex amplitude distribution of the reproduction image plane of the illumination hologram is obtained based on the light intensity distribution of the illumination hologram, the reproduction light, the preset reproduction distance, the preset wavelength of the light, and the angular spectrum of the preset observation plane. The object light field records the collection of light rays in space, including the position information and angle information of the light rays in space, and the complex amplitude distribution of the reproduction image plane represents the distribution of the light wave in space.

[0102] It can be understood that the wrapped phase distribution is decomposed to obtain the sine phase graph and the cosine phase graph, including:

[0103]

[0104]

[0105] wherein, S(x,y) represents the sine phase graph; C(x,y) represents the cosine phase graph; represents the wrapped phase distribution.

[0106] According to an embodiment of the present application, after obtaining the wrapped phase, the present application decomposes the wrapped phase by sine transformation and cosine transformation, converts the discontinuous wrapped phase image into continuous sine phase and cosine phase, specifically, the decomposition of the wrapped phase distribution includes: performing sine transformation on the phase value of any point in the wrapped phase distribution image to obtain the sine phase graph, and performing cosine transformation on the phase value of any point in the wrapped phase distribution image to obtain the cosine phase graph. The present application converts the discontinuous phase in the wrapped phase image into continuous phase by performing sine and cosine function transformation on the original noisy wrapped phase image with light and shade, which is convenient for subsequent regular noise removal processing.

[0107] Referring to Figure 3 , in a first aspect, the embodiments of the present application provide a method for suppressing wrapped phase noise, including but not limited to steps S310 and S320.

[0108] Step S310, respectively, on the sine phase map and cosine phase map discrete cosine transform, to obtain the first spectrum and the second spectrum;

[0109] Step S320, by a predetermined threshold for screening the first spectrum and the second spectrum, to obtain the first discrete cosine spectrum and the second discrete cosine spectrum after noise reduction.

[0110] It should be noted that the basis vector of the transform array of the discrete cosine transform can well describe the relevant characteristics of the speech signal and the image signal, in order to facilitate subsequent noise suppression, after obtaining the sine phase map and the cosine phase map, the sine phase map and the cosine phase map are respectively subjected to discrete cosine transform, i.e. the two-dimensional cosine wave in the sine phase map and the cosine phase map is calculated, the sine phase map and the cosine phase map are periodically expanded, the first spectrum and the second spectrum with better frequency energy concentration are obtained, after the sine phase map and the cosine phase map are subjected to discrete cosine transform, the unimportant frequency domain area and the coefficient can be filtered out, and the effect of noise suppression is achieved.

[0111] Moreover, due to the randomness of the noise and the incoherence of the discrete cosine transform, the noise usually penetrates the entire spectrum domain with a very small coefficient, if the amplitude of the frequency spectrum coefficient is less than the predetermined threshold, the noise can be suppressed by discarding the frequency spectrum coefficient, the present application sets a fixed threshold to discard the discrete cosine spectrum coefficient in the first spectrum and the discrete cosine spectrum coefficient in the second spectrum which is less than the predetermined threshold, to obtain the first discrete cosine spectrum and the second discrete cosine spectrum after threshold processing, and further suppress the noise.

[0112] It can be understood that the first spectrum is:

[0113]

[0114]

[0115]

[0116] 0≤u≤M-1;

[0117] 0≤v≤N-1;

[0118] Wherein, F S (u,v) represents the first spectrum; S(x,y) represents the sine phase map; M represents the width of S(x,y); N represents the length of S(x,y);

[0119] The second spectrum is:

[0120]

[0121]

[0122]

[0123] 0≤u≤M-1;

[0124] 0≤v≤N-1;

[0125] Among them, F C (u,v) represents the second spectrum; C(x,y) represents the cosine phase diagram; M represents the width of C(x,y); N represents the length of C(x,y).

[0126] It should be noted that a signal typically consists of a DC signal (a signal with a constant amplitude) and multiple AC signals (signals whose amplitudes change periodically at a certain frequency). Based on this, this application can decompose the sinusoidal phase diagram S(x,y) and cosine phase diagram C(x,y) into multiple DC and AC components by performing a two-dimensional discrete cosine transform. The corresponding components in different frequency domains of the sinusoidal and cosine phase diagrams are then obtained, yielding the first spectrum F. S (u,v) and the second spectrum F C (u,v).

[0127] It is understandable that by filtering the first and second spectra using a preset threshold, the denoised first and second discrete cosine spectra are obtained, including:

[0128]

[0129]

[0130] in, F represents the first discrete cosine spectrum; S (u,v) represents the first spectrum; thr represents the preset threshold. F represents the second discrete cosine spectrum; C (u,v) represents the second spectrum.

[0131] It should be noted that this application uses a preset threshold thr to divide the first spectrum F S Discrete cosine spectral coefficients and second spectrum F in (u,v) that are less than the threshold C Discrete cosine spectrum coefficients smaller than the threshold in (u,v) are discarded to achieve noise suppression, resulting in the first discrete cosine spectrum after noise reduction. Second Discrete Cosine Spectrum

[0132] Reference Figure 4In a first aspect, the embodiments of the present application provide a method for suppressing wrapped phase noise, including but not limited to steps S410, S420 and S430.

[0133] In step S410, inverse discrete cosine transform is performed on the first and second discrete cosine spectrums respectively to obtain the sine wrapped phase and the cosine wrapped phase.

[0134] In step S420, the arctangent calculation is performed on the quotient of the sine wrapped phase and the cosine wrapped phase to obtain the noise-reduced wrapped phase distribution.

[0135] In step S430, the phase unwrapping calculation is performed on the noise-reduced wrapped phase distribution to obtain the phase distribution image of the target object after noise reduction.

[0136] According to an embodiment of the present application, the purpose of performing the discrete cosine transform on the sine phase image and the cosine phase image in the above step is to convert the two-dimensional image from the spatial domain to the frequency domain, to calculate the two-dimensional cosine wave in the sine phase image and the cosine phase image, i.e., the first spectrum and the second spectrum, and to filter the first spectrum and the second spectrum to obtain the first discrete cosine spectrum and the second discrete cosine spectrum after filtering. At this time, in order to restore the first discrete cosine spectrum and the second discrete cosine spectrum obtained after noise reduction to the original data, inverse discrete cosine transform needs to be performed on the first discrete cosine spectrum and the second discrete cosine spectrum respectively to obtain the sine wrapped phase and the cosine wrapped phase.

[0137] Specifically, the formula for performing the inverse discrete cosine transform on the first discrete cosine spectrum is:

[0138]

[0139]

[0140]

[0141] 0≤x≤M-1;

[0142] 0≤y≤N-1;

[0143] wherein, represents the sine wrapped phase; represents the first discrete cosine spectrum; M represents the width of the first discrete cosine spectrum; and N represents the length of the first discrete cosine spectrum.

[0144] On the other hand, the formula for performing the inverse discrete cosine transform on the second discrete cosine spectrum is:

[0145]

[0146]

[0147]

[0148] 0≤x≤M-1;

[0149] 0≤y≤N-1;

[0150] wherein, denotes the cosine wrapped phase; denotes the second discrete cosine spectrum; M denotes the width of the; the length of the.

[0151] According to one embodiment of the present application, after obtaining the filtered component phase map, i.e., obtaining the sine wrapped phase and the cosine wrapped phase, the quotient of the sine wrapped phase and the cosine wrapped phase needs to be processed by the arctangent to obtain the denoised wrapped phase distribution, and specifically, the formula of the denoised wrapped phase distribution is:

[0152]

[0153] wherein, denotes the denoised wrapped phase distribution; denotes the sine wrapped phase; denotes the cosine wrapped phase.

[0154] According to another embodiment of the present application, the wrapped phase brings a problem that the phase change of the light is continuous, while the denoised wrapped phase distribution is a wrapped phase distributed in the interval (-π, π) and is a discontinuous jump signal, which needs to be unwrapped to unfold the phase information wrapped between (-π, π) and restore it into the continuously changed phase data to obtain the continuous phase distribution, i.e., to perform the phase unfolding calculation on the denoised wrapped phase distribution to obtain the displacement field distribution data of each point on the object surface, i.e., to obtain the continuous phase distribution image of the denoised target object.

[0155] With reference to Figure 5 , in a first aspect, the embodiments of the present application provide a method for suppressing wrapped phase noise, including but not limited to steps S510 and S520.

[0156] Step S510, polynomial fitting is performed on the phase in the phase distribution image to obtain a distortion coefficient;

[0157] Step S520, the distortion coefficient is used to correct the phase distribution image to obtain a corrected phase distribution image of the denoised target object.

[0158] According to one embodiment of the present application, after obtaining the phase distribution image, in order to further suppress noise, polynomial fitting is further needed to be performed on the phase in the phase distribution image, to find the coefficient of off-axis tilt distortion, i.e. the distortion coefficient, and the phase distribution image is corrected through the distortion coefficient, to remove the off-axis tilt distortion in the phase distribution image, to obtain the accurate original phase distribution of the object, i.e. to obtain the corrected phase distribution image of the target object after noise reduction. Specifically, the phase distribution image is corrected through the distortion coefficient, to further suppress noise and improve the accuracy of the digital holographic image.

[0159] In a second aspect, referring to Figure 7 The embodiment of the present application provides a system for suppressing wrapped phase noise, comprising:

[0160] at least one memory 200;

[0161] at least one processor 100;

[0162] at least one program;

[0163] The program is stored in the memory 200, and the processor 100 executes the at least one program to implement:

[0164] The method for suppressing wrapped phase noise according to any one of the embodiments of the first aspect of the present application.

[0165] The processor 100 and the memory 200 can be connected through a bus or other means.

[0166] The memory 200 is a non-transient readable storage medium, which can be used to store non-transient software instructions and non-transient instructions. In addition, the memory 200 can include a high-speed random access memory, and can also include a non-transient memory, such as at least one magnetic disk storage device, a flash memory device, or other non-transient solid-state memory device. It can be understood that the memory 200 can optionally include a memory 200 arranged remotely with respect to the processor 100, and these remote memories 200 can be connected to the processor 100 through a network. Examples of the above network include but are not limited to the Internet, an intranet, a local area network, a mobile communication network, and a combination thereof.

[0167] The processor 100 performs various functional applications and data processing by running the non-transient software instructions, instructions and signals stored in the memory 200, i.e. implements the method for suppressing wrapped phase noise according to the above first aspect embodiment.

[0168] The non-transitory software instructions required to implement the system for suppressing wrapped phase noise of the above embodiments and the instructions are stored in the memory 200, when executed by the processor 100, perform the method for suppressing wrapped phase noise of the first aspect of the application, for example, perform the method steps S110-S160 in the above description Figure 1 , the method steps S210-S220 in the above description Figure 2 , the method steps S310-S320 in the above description Figure 3 , the method steps S410-S430 in the above description Figure 4 , the method steps S510-S520 in the above description. Figure 5

[0169] In the third aspect, the embodiments of the present application provide a computer readable storage medium, the computer readable storage medium stores computer executable signals, and the computer executable signals are used to execute:

[0170] The method for suppressing wrapped phase noise of any one of the embodiments of the first aspect of the application.

[0171] For example, the method steps S110-S160 in the above description Figure 1 , the method steps S210-S220 in the above description Figure 2 , the method steps S310-S320 in the above description Figure 3 , the method steps S410-S430 in the above description Figure 4 , the method steps S510-S520 in the above description. Figure 5 The device embodiments described above are only schematic, wherein the units shown as separate components can or can not be physically separate, and the components shown as units can or can not be physical units, i.e., can be located in one place, or can be distributed to multiple network units. Part or all of the units can be selected according to actual needs to achieve the purpose of the embodiments.

[0172]

[0173] ​​From the description of the above embodiments, those skilled in the art can understand that all or some steps in the method disclosed above can be implemented as software, firmware, hardware and appropriate combinations thereof. Some or all physical components can be implemented as software executed by a processor such as a central processing unit, a digital signal processor or a microprocessor, or as hardware, or as an integrated circuit such as an application specific integrated circuit. Such software can be distributed on a readable medium, which can include computer storage media (or non-transitory media) and communication media (or transitory media). As known to those skilled in the art, the term computer storage media includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable signals, data structures, instruction modules or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tapes, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired information and can be accessed by a computer. Furthermore, as known to those skilled in the art, communication media typically includes computer readable signals, data structures, instruction modules or other data in modulated data signals such as carrier waves or other transport mechanisms, and can include any information delivery medium.

[0174] The above detailed description of the embodiments of the present application is made in conjunction with the accompanying drawings, but the present application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the purpose of the present application.

Claims

1. A method of suppressing wrapped phase noise, characterized by, The method comprises the following steps: acquiring object light, reference light and reproduction light of a target object, simulating an illumination hologram of the target object based on the object light, the reference light and the reproduction light, and obtaining a complex amplitude distribution of a reproduction image plane of the illumination hologram; performing an inverse tangent calculation on a quotient of an imaginary part of the complex amplitude distribution divided by a real part of the complex amplitude distribution to obtain a wrapped phase distribution; decomposing the wrapped phase distribution to obtain a sine phase map and a cosine phase map; performing discrete cosine transform and threshold filtering calculation on the sine phase map and the cosine phase map respectively to obtain a first discrete cosine spectrum and a second discrete cosine spectrum after noise reduction; performing discrete cosine inverse transform and unwrapped phase calculation on the first discrete cosine spectrum and the second discrete cosine spectrum to obtain a phase distribution image of the target object after noise reduction; wherein the performing discrete cosine transform and threshold filtering calculation on the sine phase map and the cosine phase map respectively to obtain the first discrete cosine spectrum and the second discrete cosine spectrum after noise reduction comprises: performing discrete cosine transform on the sine phase map and the cosine phase map respectively to obtain a first frequency spectrum and a second frequency spectrum; performing screening on the first frequency spectrum and the second frequency spectrum through a preset threshold to obtain the first discrete cosine spectrum and the second discrete cosine spectrum after noise reduction; the performing discrete cosine inverse transform and unwrapped phase calculation on the first discrete cosine spectrum and the second discrete cosine spectrum to obtain the phase distribution image of the target object after noise reduction comprises: performing discrete cosine inverse transform on the first discrete cosine spectrum and the second discrete cosine spectrum respectively to obtain a sine wrapped phase and a cosine wrapped phase; performing inverse tangent calculation on a quotient of the sine wrapped phase and the cosine wrapped phase to obtain a noise reduction wrapped phase distribution; performing phase unwrapping calculation on the noise reduction wrapped phase distribution to obtain the phase distribution image of the target object after noise reduction.

2. The method of suppressing a wrapped phase noise as claimed in claim 1, wherein, The simulating the illumination hologram of the target object based on the object light, the reference light and the reproduction light to obtain the complex amplitude distribution of the reproduction image plane of the illumination hologram comprises: calculating an interference intensity of the object light and the reference light to obtain a light intensity distribution of the illumination hologram; reconstructing an object light field based on the light intensity distribution, the reproduction light, a preset reproduction distance, a preset light wavelength and a preset observation plane angular spectrum to obtain the complex amplitude distribution of the reproduction image plane of the illumination hologram; wherein the complex amplitude distribution of the reproduction image plane is: ； wherein denotes the complex amplitude distribution of the reconstruction plane; denotes the light intensity distribution; denotes the reconstruction light; denotes the reconstruction distance; denotes the light wavelength; and denotes the angular spectrum of the observation plane; denotes the Fourier transform; denotes the inverse Fourier transform.

3. The method of suppressing a wrapped phase noise as claimed in claim 1, wherein, the decomposing the wrapped phase distribution to obtain the sine phase map and the cosine phase map comprises: ; ; wherein denotes the sine phase map; denotes the cosine phase map; denotes the wrapped phase distribution.

4. The method of suppressing a wrapped phase noise as claimed in claim 1, wherein, the first frequency spectrum is: wherein represents the first frequency spectrum; represents the sinusoidal phase map; represents the width of represents the length of the second frequency spectrum is: wherein represents the second frequency spectrum; represents the cosine phase map; represents the width of represents the length of 5. The method of suppressing a wrapped phase noise according to claim 4, wherein, the performing screening on the first frequency spectrum and the second frequency spectrum through the preset threshold to obtain the first discrete cosine spectrum and the second discrete cosine spectrum after noise reduction comprises: wherein, denotes the first discrete cosine spectrum; denotes the first frequency spectrum; denotes a predetermined threshold value; denotes the second discrete cosine spectrum; denotes the second frequency spectrum.

6. The method of suppressing a wrapped phase noise as claimed in claim 1, wherein, after obtaining the phase distribution image of the target object after noise reduction, the method further comprises: performing polynomial fitting on a phase in the phase distribution image to obtain a distortion coefficient; performing correction on the phase distribution image through the distortion coefficient to obtain a corrected phase distribution image of the target object after noise reduction.

7. A system for suppressing wrapped phase noise, characterized by The device comprises: at least one memory; at least one processor; at least one program; The program is stored in the memory, and the processor executes at least one of the programs to implement the method for suppressing wrapped phase noise according to any one of claims 1 to 6.

8. A computer-readable storage medium, characterized in that, The computer readable storage medium stores computer executable signals for executing the method for suppressing wrapped phase noise according to any one of claims 1 to 6.

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