Method and system for measuring multi-band spatially varying point spread function of a simple lens for computational imaging

Abstract

The present invention discloses a method and system for measuring the multi-band spatially varying point spread function of a simple lens for computational imaging, belonging to the field of optical technology. A system for measuring the spatially varying point spread function is provided, as well as a specific method for compensating and correcting the measurement results. By measuring an appropriate number of horizontal field-of-view point spread images of a simple lens and performing operations such as interpolation and rotation on them, a full-field-of-view two-dimensional multi-band point spread function array is generated, greatly improving measurement efficiency and accuracy, and contributing to improving the quality of restored images. The method can accurately and quickly measure the point spread function of a simple lens, and can be directly used as input for simple lens deconvolution operations, as well as for evaluating the imaging quality of the lens.

Description

Technical Field

[0001] The present invention belongs to the field of optical technology, and in particular relates to a method and system for measuring the multi-band spatial variation point spread function of a simple lens for computational imaging. Background Art

[0002] Computational imaging technology has shown tremendous potential for improving the resolution and reducing the weight of optical systems. Simple lens imaging is a key research area in computational imaging. This approach eliminates the need to eliminate optical aberrations during the optical design phase, simplifying the design process. This allows the optical lens to produce a blurred image, and then, during image processing, a clear image is obtained through deconvolution algorithms. Obtaining a clear restored image relies not only on advanced deconvolution algorithms but also on an accurate estimation of the point spread function (PSF) of the optical lens. Because the PSF of a simple imaging lens depends on the system's wavelength and varies nonlinearly with the field of view, acquiring a complete PSF for each field of view and wavelength band is extremely time-consuming and labor-intensive.

[0003] Currently, the point spread function (PSF) is obtained by placing an array of luminous LEDs on the object plane, which improves measurement efficiency to a certain extent. However, this method cannot simulate an infinitely distant target and cannot compensate for the influence of the LED's own size on the measurement results, resulting in large measurement errors. Therefore, there is an urgent need to develop an accurate and fast PSF measurement method. Summary of the Invention

[0004] In response to the above-mentioned defects or improvement needs of the prior art, the present invention proposes a method and system for measuring the multi-band spatially varying point spread function of a simple lens for computational imaging, which can achieve accurate and rapid point spread function measurement.

[0005] To achieve the above objectives, according to one aspect of the present invention, a system for measuring the multi-band spatially varying point spread function of a simple lens for computational imaging is provided, comprising: a light source, a filter, an off-axis collimator, a simple lens to be measured, a microscopic imaging assembly, an electrically controlled turntable, and an image acquisition module;

[0006] The light emitted by the light source is filtered to limit the measurement band range to achieve measurement of multiple bands. The light after passing through the filter is collimated by an off-axis collimator to simulate an infinite star point target. The infinite star point target is imaged by the simple lens under test, magnified by the micro-imaging component, and the point spread function image is saved by the image acquisition module.

[0007] The electrically controlled turntable drives the simple lens and microscopic imaging components to be measured to rotate, so as to achieve measurement of different fields of view.

[0008] According to another aspect of the present invention, a method for measuring a multi-band spatially varying point spread function of a simple lens for computational imaging is provided, comprising:

[0009] After the simple lens and the micro-imaging assembly to be tested are rotated horizontally to the target measurement field position by the electric-controlled turntable, the point spread function image is saved by the image acquisition module and the point spread function image is corrected;

[0010] After completing the point spread function image measurement and correction of all bands and the measurement field corresponding to each band, a multi-band point spread function image is obtained;

[0011] The corresponding image height and the rotation angle of the corresponding point spread function in the two-dimensional space are obtained from the two-dimensional plane field of view position;

[0012] The multi-band point spread function image is interpolated according to the corresponding image height in the two-dimensional space, and the interpolated multi-band point spread function image is rotated according to the rotation angle of the corresponding point spread function. Then, the point spread function images are spliced ​​to obtain a full-field multi-band spatially varying point spread function image.

[0013] In some optional embodiments, the correcting the point spread function image includes:

[0014] In the frequency domain, the point spread function image is compensated for the first time by the frequency domain distribution of the pinhole diffraction to compensate for the error caused by the pinhole size on the point spread function measurement;

[0015] The frequency domain representation sampled by the detector of the microscopic imaging component in the frequency domain performs a second compensation on the point spread image after the first compensation to compensate for the error caused by the detector sampling in the point spread function measurement.

[0016] In some optional embodiments, Perform the first compensation on the point spread function image, where U w represents the point spread function image after the first compensation, represents the Fourier transform, represents the inverse Fourier transform, P w Represents the point spread function image, H w represents the frequency domain distribution of pinhole diffraction, D is the diameter of the hole, f is the spatial frequency, and J1(x) is the first-order Bessel function.

[0017] In some optional embodiments, The second compensation is performed on the point spread image after the first compensation, where V w represents the point spread function image after the second compensation, represents the Fourier transform, represents the inverse Fourier transform, K w represents the representation of detector sampling in the frequency domain, S is the size of the detector pixel of the microscopic imaging component, and f is the spatial frequency.

[0018] In some optional embodiments, Get the two-dimensional plane field of view position, where h m is the maximum image height of the simple lens under test, and the imaging field of view of the simple lens under test is divided into N*N blocks, i∈[1,N], j∈[1,N].

[0019] In some optional embodiments, Get the corresponding image height L in two-dimensional space rc and the corresponding point spread function rotation angle θ rc .

[0020] In some optional embodiments, based on cubic spline interpolation, the point spread functions of different fields of view are interpolated to obtain the value of each image height L. rc Point spread function image G at rc .

[0021] In some optional embodiments, The interpolated multi-band point spread function image G rc Perform a rotation.

[0022] In some optional embodiments, The point spread function is downsampled, where the convolution kernel E is an all-one matrix, the convolution step is t, and t is the downsampling rate. n is G' rc The resolution of the microscope is S, the pixel size of the detector of the microscope imaging component is M, the magnification of the microscope imaging component is d, the pixel size of the imaging detector is Q' rc is the point spread function image at the position (r,c) after downsampling according to the size of the imaging detector.

[0023] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0024] (1) The measurement band range is limited by the filter, and the infinite star point target is simulated by the off-axis collimator. The simple lens and microscopic imaging components under test are driven to rotate by the electric control turntable to achieve measurement of different fields of view. It can accurately and quickly perform multi-band and spatially varying point spread function measurements.

[0025] (2) By measuring an appropriate number of horizontal field-of-view point spread images of a simple lens and performing operations such as interpolation and rotation on the point spread images, a multi-band point spread function array in two-dimensional space with a full field of view is generated. This can accurately and quickly measure the point spread function of a simple lens, which can be directly used as the input for the deconvolution operation of a simple lens and can also be used to evaluate the imaging quality of the lens. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 1 is a diagram of a point spread function measurement system provided by an embodiment of the present invention;

[0027] Figure 2 This is a flow chart of a method for measuring multi-band spatially varying point spread function of a simple lens for computational imaging provided by an embodiment of the present invention;

[0028] Figure 3 This is a flow chart of another method for measuring multi-band spatially varying point spread function of a simple lens for computational imaging provided by an embodiment of the present invention;

[0029] Figure 4 This is a comparison diagram before and after on-axis point spread function compensation provided by an embodiment of the present invention;

[0030] Figure 5 This is a schematic diagram of point spread function rotation provided by an embodiment of the present invention;

[0031] Figure 6 This is a picture of the measurement results of a multi-band spatially varying point spread function provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0033] In this embodiment, the following Figure 1 The multi-band, spatially varying point spread function measurement system shown includes a light source 101, a filter 102, an off-axis collimator 103, a simple lens to be measured 104, a microscopic imaging component 105, an electrically controlled turntable 106 and an image acquisition module 107.

[0034] Specifically, the filter 102 is used to limit the measurement wavelength range, enabling measurement of point spread functions in the 0.486µm, 0.546µm, and 0.656µm imaging bands. An off-axis collimator 103 collimates the pinhole target emitted by the light source, simulating an infinitely distant star point target. The infinitely distant star point target is imaged by the simple lens 104 under test, magnified by the microscopic imaging assembly 105, and finally captured by the image acquisition center 107. An electrically controlled turntable 106 drives the simple lens 104 under test and the microscopic imaging assembly 105 to rotate, enabling measurement of different fields of view.

[0035] Furthermore, in this embodiment, based on Figure 2 The flowchart shown in the figure completes the measurement of the full-band spatial variation point spread function of a simple lens, including the following steps:

[0036] After the simple lens and the micro-imaging assembly to be tested are rotated horizontally to the target measurement field position by the electric-controlled turntable, the point spread function image is saved by the image acquisition module and the point spread function image is corrected;

[0037] After completing the point spread function image measurement and correction of all bands and the measurement field corresponding to each band, a multi-band point spread function image is obtained;

[0038] The corresponding image height and the rotation angle of the corresponding point spread function in the two-dimensional space are obtained from the two-dimensional plane field of view position;

[0039] The multi-band point spread function image is interpolated according to the corresponding image height in the two-dimensional space, and the interpolated multi-band point spread function image is rotated according to the rotation angle of the corresponding point spread function. Then, the point spread function images are spliced ​​to obtain a full-field multi-band spatially varying point spread function image.

[0040] Furthermore, in this embodiment, based on Figure 3 As shown in the flowchart, first, the electric control turntable 106 drives the simple lens 104 to rotate horizontally to the starting measurement field position w1, w∈[w1 w2…w n ], n is the number of horizontal measurement fields. In the specific implementation of the present invention, the electric control turntable 106 drives the simple lens 104 to rotate horizontally to the starting measurement field position w=0, w∈[0,-0.5h m , 0.5h m , -0.707h m ,0.707h m ,-h m ,h m ], h m =3.0 mm, and the point spread function image P is saved by the image acquisition module 107 w , the point spread function is saved as Figure 4As shown in (a).

[0041] Furthermore, in this embodiment, the size of the star point cannot be infinitesimal, while the point spread function lens responds to an infinitesimal pulse. Therefore, it is necessary to compensate for the error caused by the aperture size in the point spread function measurement. Specifically, compensation is performed in the frequency domain using the following calculation method:

[0042]

[0043] Among them, U w represents the point spread function image after the first compensation, represents the Fourier transform, represents the inverse Fourier transform, H w The frequency domain distribution of the pinhole diffraction is calculated as follows: D = 0.310 mm is the diameter of the pinhole, f is the spatial frequency, J1(x) is the first-order Bessel function,

[0044]

[0045] Furthermore, in this embodiment, the point spread function image is collected by the detector of the microscopic imaging assembly 105. The sampling process of the detector is equivalent to convolving the energy distribution with a rectangular window function, which will cause image blur. Therefore, it is necessary to compensate for the error caused by detector sampling in the point spread function measurement. Specifically, compensation is performed in the frequency domain, and the calculation method is as follows:

[0046]

[0047] Among them, V w represents the point spread function image after the second compensation, represents the Fourier transform, represents the inverse Fourier transform, K w The detector sampling is represented in the frequency domain. The calculation method is as follows: S = 4.54 μm is the size of the detector pixel of the microscopic imaging component, f is the spatial frequency,

[0048] After aperture size compensation and detector sampling compensation, the point spread function is as follows: Figure 4 As shown in (b), it can be clearly observed that the point spread function size before and after compensation is smaller than the original point spread function.

[0049] Furthermore, the electric-controlled turntable 106 is controlled to drive the simple lens 104 to rotate horizontally to the next field of view position, and the above steps are repeated to complete the acquisition of point spread function images of all fields of view.

[0050] Furthermore, in this embodiment, the filter 102 at the light source is replaced, and the above steps are repeated until the measurement of the three bands of 0.486um, 0.546um, and 0.656um is completed, and the measured multi-band point spread function image is saved, which is expressed as K=[K1…K n ].

[0051] Furthermore, in this embodiment, the maximum image height h of the simple lens 104 under test is m =3.0mm, divide the lens imaging field of view into 9*9 blocks, and calculate the two-dimensional image height position (r, c) of each measurement field of view. The specific method is as follows, where i∈[1,9], j∈[1,9]:

[0052] r=i·h m / N

[0053] c=j·h m / N

[0054] Furthermore, in this embodiment, since the simple lens 104 under test based on computational imaging consists of one or two lenses, its center deviation can be easily eliminated through adjustment. Assuming that the point spread function is spatially rotationally invariant, the point spread function at the same image height at different spatial positions can be obtained by rotating the point spread function in the horizontal direction. Therefore, by measuring the point spread function in the horizontal direction and then rotating it, the point spread function with spatial variation across the entire field of view can be obtained. Figure 5 As shown, the point spread function of the A1 field of view can be obtained by rotating the point spread function of the horizontal field of view A1', and the point spread function of the B1 field of view can be obtained by rotating the point spread function of the horizontal field of view B1'. The same applies to the remaining non-axis points. The image height L corresponding to a certain field of view (r, c) in two-dimensional space rc and the corresponding point spread function rotation angle θ rc Both can be calculated from the field of view position coordinates (r, c), the specific method is as follows:

[0055]

[0056] Furthermore, in this embodiment, based on cubic spline interpolation, the point spread function K of different fields of view is interpolated to obtain the value of each image height L. rc Point spread function image G at rc .

[0057] Furthermore, in this embodiment, according to the rotation angle θ corresponding to each view point position (r, c), rc , for each field of view after interpolation, the point spread function G rc The specific calculation method is as follows:

[0058]

[0059] Furthermore, in this embodiment, since the microscopic imaging component 105 in the measurement system magnifies the PSF image by a factor of M = 10, this is equivalent to upsampling the PSF. The PSF is then sampled by the detector of the microscopic imaging component 105. Since the detector pixel size d adapted for the simple lens 104 under test is 2.75 μm, the PSF needs to be downsampled to match the actual imaging detector pixel size. The calculation method for downsampling the PSF image is as follows:

[0060]

[0061] Among them, the convolution kernel E is an all-one matrix, and the convolution step size is t. t is the downsampling rate, which is calculated as follows, and n is G' rc The resolution of the microscope, S is the pixel size of the detector of the microscope imaging component, Q' rc The point spread function image at the position (r, c) is downsampled according to the size of the imaging detector. The magnification of the microscope imaging component is M = 10, and the pixel size of the imaging detector is d = 2.75 μm.

[0062]

[0063] Furthermore, in this embodiment, the point spread functions at all positions are spliced ​​to obtain a point spread function image with full field of view and multi-band spatial variation, as shown in FIG. Figure 6 As shown, (a) is the point spread function image of the 0.486 band, (b) is the point spread function image of the 0.546 band, (c) is the point spread function image of the 0.656 band, and (d) is the merged point spread function image.

[0064] It should be pointed out that, according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, or two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0065] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for measuring a multi-band spatially varying point spread function of a simple lens based on a system for computational imaging, the system comprising: A light source, a filter, an off-axis collimator, a simple lens to be measured, a microscopic imaging component, an electrically controlled turntable, and an image acquisition module; light emitted by the light source is passed through the filter to limit the measurement band range to achieve measurement of multiple bands; the light after passing through the filter is collimated by the off-axis collimator to simulate an infinitely distant star point target; the infinitely distant star point target is imaged by the simple lens to be measured, amplified by the microscopic imaging component, and the point spread function image is stored by the image acquisition module; The electric-controlled turntable drives the simple lens and the microscopic imaging assembly to rotate to achieve measurement of different fields of view. The method is characterized in that the method includes: After the simple lens and the micro-imaging assembly to be tested are rotated horizontally to the target measurement field position by the electric-controlled turntable, the point spread function image is saved by the image acquisition module and the point spread function image is corrected; After completing the point spread function image measurement and correction of all bands and the measurement field corresponding to each band, a multi-band point spread function image is obtained; The corresponding image height and the rotation angle of the corresponding point spread function in the two-dimensional space are obtained from the two-dimensional plane field of view position; The multi-band point spread function image is interpolated according to the corresponding image height in the two-dimensional space, the interpolated multi-band point spread function image is rotated according to the rotation angle of the corresponding point spread function, and then each point spread function image is spliced ​​to obtain a full-field multi-band spatially varying point spread function image; Correcting the point spread function image includes: In the frequency domain, the point spread function image is compensated for the first time by the frequency domain distribution of the pinhole diffraction to compensate for the error caused by the pinhole size on the point spread function measurement; The frequency domain representation sampled by the detector of the microscopic imaging component in the frequency domain performs a second compensation on the point spread image after the first compensation to compensate for the error caused by the detector sampling in the point spread function measurement.

2. The method according to claim 1, characterized in that Depend on The point spread function image is compensated for the first time, where represents the point spread function image after the first compensation, represents the Fourier transform, represents the inverse Fourier transform, represents the point spread function image, represents the frequency domain distribution of pinhole diffraction, , is the diameter of the small hole, is the spatial frequency, is a first-order Bessel function.

3. The method according to claim 2, characterized in that Depend on The point spread image after the first compensation is compensated for the second time, where represents the point spread function image after the second compensation, represents the Fourier transform, represents the inverse Fourier transform, represents the representation of detector sampling in the frequency domain, , is the size of the detector pixel of the microscopic imaging component, is the spatial frequency.

4. The method according to any one of claims 1 to 3, characterized in that Depend on Get the two-dimensional plane field of view position, where is the maximum image height of the simple lens under test, and the imaging field of the simple lens under test is divided into N*N blocks. , .

5. The method according to claim 4, characterized in that Depend on Get the corresponding image height in two-dimensional space and the rotation angle of the corresponding point spread function .

6. The method according to claim 5, characterized in that Based on cubic spline interpolation, the point spread functions of different fields of view are interpolated to obtain the value of each image height. Point spread function image at .

7. The method according to claim 6, characterized in that Depend on Interpolated multi-band point spread function image Perform a rotation.

8. The method according to claim 7, characterized in that Depend on The point spread function is downsampled, where the convolution kernel is an all-one matrix, the convolution step is t, t is the downsampling rate, , for resolution, is the pixel size of the detector of the microscopic imaging component, is the magnification of the microscope imaging component, is the pixel size of the imaging detector, is the point spread function image at the position (r,c) after downsampling according to the size of the imaging detector.

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