A three-dimensional shape measurement method and system based on continuous vertical scanning structured illumination

Abstract

The application belongs to the technical field of three-dimensional topography measurement, and discloses a three-dimensional topography measurement method and system based on continuous vertical scanning structure illumination, which comprises the following steps: S1, collecting a structure light image of a sample to be measured at each scanning position; S2, estimating background light intensity by using adjacent structure light images in time domain, obtaining a uniform illumination image, and correcting the structure light image; S3, performing high-pass filtering on the uniform illumination image to obtain high-frequency in-focus information, and performing low-pass filtering on the corrected structure light image to obtain low-frequency in-focus information; fusing the two to obtain an optical tomographic image of the sample to be measured; and S4, obtaining the three-dimensional topography of the sample to be measured. The application adopts a continuous scanning structure light illumination measurement method, only one structure illumination phase shift cosine fringe pattern is collected at each scanning position, and high-precision tomographic extraction is performed, so that high-precision tomographic imaging in an uninterrupted continuous scanning mode can be realized, and the measurement speed and precision are greatly improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of three-dimensional topography measurement, and more particularly relates to a three-dimensional topography measurement method and system based on continuous vertical scanning structured illumination. BACKGROUND

[0002] Microstructure surface topography is an important geometric feature of manufactured products and scientific research samples, and its measurement, analysis and evaluation are of great significance to the guarantee of surface functional quality characteristics. Structured light illumination microscopic measurement technology (SIM) is based on the principle of wide-field microscopic imaging, uses structured light to modulate the surface or structural information of the measured sample, removes the interference of out-of-focus signals, and then uses a peak positioning algorithm to extract the peak value of the tomographic response curve to realize three-dimensional measurement. This method has the characteristics of non-contact, high efficiency and high precision, and can be applied not only to reflective surfaces but also to scattered surfaces.

[0003] Since the existing structured light illumination microscopic measurement method needs to stop at the fixed step position during scanning, the spatial light modulator (DMD) in the measurement system projects multiple sets of cosine fringe patterns onto the surface of the measured sample, and then continues to scan until the scanning is completed. This process takes a long time and cannot meet the demand for rapid measurement. In the paper "Better three-dimensional inspection with structured illumination: speed", GERD et al. proposed a flying phase method, which only needs single exposure at the fixed scanning step position of the camera, and can realize rapid three-dimensional reconstruction by calculating the axial tomographic response through the "flying phase method", greatly shortening the measurement time. However, due to the limited number of images collected, the stability of the calculated tomographic response signal decreases. In addition, factors such as local slope of the sample surface, material properties, and environmental light fluctuations can significantly interfere with the collected signal, resulting in severe noise in the tomographic response. In the presence of complex noise interference, it is difficult to accurately determine the position of the maximum tomographic response in the tomographic response (the maximum tomographic response position can determine the height of the sample surface), resulting in reduced measurement accuracy. SUMMARY

[0004] In view of the above limitations of the prior art, the present application proposes a three-dimensional topography measurement method and system based on continuous vertical scanning structured illumination, which uses the "flying phase method" to collect multiple phase-shifted fringe patterns at each step position without stopping, thereby improving the measurement speed. At the same time, an effective tomographic extraction algorithm is adopted to suppress the influence of noise and ensure the measurement accuracy, realizing rapid and high-precision three-dimensional topography measurement by continuous vertical scanning structured illumination.

[0005] To achieve the above objectives, according to one aspect of the present invention, a high-precision three-dimensional topography measurement method based on continuous vertical scanning structured illumination is provided, comprising:

[0006] S1, using the continuous vertical scanning structured light illumination measurement method, collects a phase-shifted cosine fringe structured light image of the sample to be measured at each vertical scanning position;

[0007] S2, using the adjacent structured light images in the time domain to estimate the background light intensity, and obtaining the estimated background light intensity as a uniformly illuminated image; and simultaneously, using the estimated background light intensity to correct the background light intensity of the structured light image, and obtaining the corrected structured light image;

[0008] S3, performing high-pass filtering on the uniformly illuminated image to obtain high-frequency in-focus information of the sample to be tested; performing low-pass filtering on the corrected structured light image to obtain low-frequency in-focus information of the sample to be tested; and fusing the high-frequency in-focus information and the low-frequency in-focus information to obtain an optical tomography image of the sample to be tested;

[0009] S4, obtaining a three-dimensional morphology of the sample to be tested based on the optical tomography image.

[0010] According to the three-dimensional shape measurement method based on continuous vertical scanning structured illumination provided by the present invention, S1 specifically includes:

[0011] A plurality of cosine fringe patterns with fixed phase shifts are preset, and one of the cosine fringe patterns is projected onto the surface of the sample to be tested at each vertical scanning position. During the scanning process of the sample to be tested, the plurality of cosine fringe patterns are projected in a cycle in sequence.

[0012] According to the three-dimensional shape measurement method based on continuous vertical scanning structured illumination provided by the present invention, in S2, the background light intensity is estimated by using the adjacent structured light images in the time domain, and the estimated background light intensity is obtained as a uniform illumination image, which specifically includes:

[0013] For any vertical scanning position, taking a plurality of adjacent structured light images around the vertical scanning position;

[0014] averaging a plurality of adjacent structured light images and filtering the average to obtain an estimated background light intensity at any scanning position as a uniformly illuminated image;

[0015] The number of the plurality of adjacent structured light images is consistent with the number of the preset cosine fringe patterns.

[0016] According to the three-dimensional shape measurement method based on continuous vertical scanning structured illumination provided by the present invention, the uniform illumination image at any vertical scanning position is specifically expressed as follows:

[0017]

[0018] Among them, I b Indicates background light intensity; I est represents a uniformly illuminated image; H represents a filter; z i represents the i-th scanning position; I represents the structured light image; and N represents the number of preset cosine fringe patterns.

[0019] According to the three-dimensional shape measurement method based on continuous vertical scanning structured illumination provided by the present invention, in S2, the background light intensity of the structured light image is corrected using the estimated background light intensity to obtain the corrected structured light image, specifically comprising:

[0020] The collected structured light image is subtracted from the uniformly illuminated image to obtain a corrected structured light image.

[0021] According to the three-dimensional topography measurement method based on continuous vertical scanning structured illumination provided by the present invention, high-pass filtering is performed on the uniformly illuminated image in S3 to obtain high-frequency in-focus information of the sample to be measured, specifically including:

[0022] The contrast of the modified structured light image is calculated using a Laplace operator, and contrast-weighted high-pass filtering is performed on the uniformly illuminated image to obtain high-frequency in-focus information of the sample to be tested.

[0023] According to the three-dimensional shape measurement method based on continuous vertical scanning structured illumination provided by the present invention, the corrected structured light image is low-pass filtered to obtain the low-frequency in-focus information of the sample to be measured, which is specifically shown in the following formula:

[0024] I in,Lo (x,y)=LP[I in (x,y)]≈LP[D(x,y)];

[0025] Among them, I in,Lo Represents the low-frequency in-focus information in the tomographic response image; LP[.] represents Gaussian low-pass filtering; I in (x, y) represents the in-focus portion of the image; D(x, y) represents the corrected structured light image; and (x, y) is the pixel coordinate.

[0026] According to the three-dimensional topography measurement method based on continuous vertical scanning structured illumination provided by the present invention, the uniform illumination image is subjected to high-pass filtering to obtain high-frequency in-focus information of the sample to be measured, which is specifically shown in the following formula:

[0027] I in,Hi (x,y)=HP[I b (x,y)]≈HP[I est (x,y)]·Nm (x,y);

[0028] Among them, I in,Hi Represents the high-frequency in-focus information in the tomographic response image; HP[.]=1-LP[.]; I b Indicates background light intensity; I est represents a uniformly illuminated image; (x, y) is the pixel coordinate; N m (x, y) represents the contrast calculated using the Laplace operator on the corrected structured light image.

[0029] According to the three-dimensional topography measurement method based on continuous vertical scanning structured illumination provided by the present invention, high-frequency in-focus information and low-frequency in-focus information are fused to obtain an optical tomographic image of the sample to be measured, which is specifically shown in the following formula:

[0030] m HiLo (x,y)=ηI in,Hi (x,y)+I in,Lo (x,y)

[0031] =ηHP[I est (x,y)]·N m (x,y)+LP[|I(x,y)-I est (x,y)|];

[0032] Among them, m HiLo (x, y) represents the optical tomography image; η represents the adjustment factor.

[0033] According to another aspect of the present invention, a three-dimensional shape measurement system based on continuous vertical scanning structured illumination is provided. The system includes a memory and a processor. The memory stores a computer program. When the processor executes the computer program, it performs any of the above-mentioned three-dimensional shape measurement methods based on continuous vertical scanning structured illumination.

[0034] In general, compared with the prior art, the above technical solutions conceived by the present invention provide a three-dimensional shape measurement method and system based on continuous vertical scanning structured illumination:

[0035] 1. We propose using adjacent structured light images in the temporal domain to estimate background light intensity. This avoids acquiring multiple structured light images at the same scanning position, enabling continuous scanning while accurately estimating background light intensity. By using the estimated background light intensity to correct the structured light image, we can eliminate camera acquisition intensity fluctuations caused by ambient stray light and imaging noise during the scanning process, achieving accurate correction of the structured light image.

[0036] Taking into account the fact that the background light intensity image contains high-frequency information of the tomographic image and the corrected structured light image contains low-frequency information of the tomographic image, a fusion method is proposed. By performing low-pass filtering on the corrected structured light image, the low-frequency in-focus information is extracted to obtain the low-frequency information of the tomographic image. By performing high-pass filtering on the uniformly illuminated image, the high-frequency noise is suppressed while the high-frequency part of the in-focus information in the image is extracted to obtain the high-frequency information of the tomographic image. The high-frequency information and the low-frequency information are fused to obtain a complete tomographic image with a high signal-to-noise ratio in the entire frequency domain. In this way, the tomographic image can be calculated from a single structured illumination fringe pattern, realizing fast and accurate optical tomographic measurement of the three-dimensional morphology and improving the measurement speed.

[0037] Continuous scanning structured light illumination measurement method can be used to collect only one structured illumination phase-shifted cosine fringe pattern at each scanning position, thus achieving uninterrupted continuous scanning mode and greatly improving measurement speed;

[0038] 2. A background light intensity estimation method that averages adjacent structured light images in the time domain and adds filtering is beneficial for reducing the interference of imaging noise. Considering that the defocus conditions of images collected at different scanning positions are not consistent, residual streaks may appear in the background light intensity image obtained by the mean calculation, which will affect the quality of background intensity estimation. Therefore, a filter is proposed to filter the axial background intensity response to suppress the influence of residual streaks.

[0039] 3. The background-corrected structured light image eliminates the influence of background light intensity fluctuations. The image retains the in-focus fringe information. However, due to the presence of fringe information, it cannot be used directly. It needs to be low-pass filtered to extract the low-frequency in-focus information. Low-pass filtering can effectively remove noise and retain only the low-frequency part of the tomographic image, that is, obtain the low-frequency information in the tomographic image.

[0040] 4. Considering that the uniformly illuminated image contains in-focus information and out-of-focus information, if the high-frequency part of the in-focus information of the uniformly illuminated image is extracted and fused with the low-frequency information in the tomographic image, a complete tomographic image can be obtained. At the same time, considering that the out-of-focus information in the uniformly illuminated image is generally low-frequency, and the in-focus information is the clear texture details on the sample, which is high-frequency information, a high-pass filter is used to extract only the high-frequency information of the in-focus content and eliminate the out-of-focus content, that is, to obtain the high-frequency information in the tomographic image. At the same time, the Laplace operator is used to calculate the contrast of the corrected structured light image, and the high-pass filtered image is contrast-weighted, which can further suppress the high-frequency noise in the image and improve the image signal-to-noise ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1Schematic diagram of the measurement principle of the three-dimensional shape measurement method based on continuous vertical scanning structured illumination provided by the present invention;

[0042] Figure 2 It is a schematic diagram of the measurement process of the three-dimensional shape measurement method based on continuous vertical scanning structured illumination provided by the present invention. DETAILED DESCRIPTION

[0043] 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.

[0044] See also Figure 1 and Figure 2 This embodiment provides a three-dimensional shape measurement method based on continuous vertical scanning structured illumination, the three-dimensional shape measurement method comprising:

[0045] S1, using the continuous vertical scanning structured light illumination measurement method, collects a phase-shifted cosine fringe structured light image of the sample to be measured at each vertical scanning position;

[0046] S2, using the adjacent structured light images in the time domain to estimate the background light intensity, and obtaining the estimated background light intensity as a uniformly illuminated image; and simultaneously, using the estimated background light intensity to correct the background light intensity of the structured light image, and obtaining the corrected structured light image;

[0047] S3, performing high-pass filtering on the uniformly illuminated image to obtain a high-frequency portion of in-focus information of the sample to be tested; performing low-pass filtering on the corrected structured light image to obtain a low-frequency portion of in-focus information of the sample to be tested; and fusing the high-frequency in-focus information and the low-frequency in-focus information to obtain an optical tomography image of the sample to be tested;

[0048] S4, obtaining three-dimensional morphological parameters of the sample to be measured based on the optical tomography image.

[0049] This embodiment calculates a tomographic image from a single structured illumination fringe pattern, or structured light image, achieving rapid optical tomographic measurement and improving measurement speed. Existing methods require the acquisition of multiple phase-shifted patterns at each scanning position to calculate the optical tomographic image, necessitating intermittent scanning, i.e., a "stop-go-stop" mode. However, the method of this embodiment only requires the acquisition of a single structured illumination fringe pattern at each scanning position, enabling uninterrupted continuous scanning, significantly improving measurement speed while suppressing the excessive noise introduced by continuous scanning. This method, in turn, achieves both increased measurement speed and a high signal-to-noise ratio. Furthermore, this embodiment does not require the addition of additional projection patterns or hardware.

[0050] In some specific embodiments, a three-dimensional shape measurement method based on continuous vertical scanning structured illumination is a continuous scanning structured illumination optical tomography measurement method based on sliding time window background estimation and fusion, and the specific steps of the method are as follows:

[0051] First, N cosine fringe patterns with a fixed phase shift of 2π / N are generated and input into the DMD for projection during the scanning process. Specifically, S1 includes: presetting multiple cosine fringe patterns with a fixed phase shift, projecting one of the cosine fringe patterns onto the surface of the sample to be tested at each scanning position, and during the scanning process of the sample to be tested, the multiple cosine fringe patterns are projected in sequence. That is, multiple cosine fringe patterns are projected one at each scanning position in order to capture the structured light image, and after the first to last patterns are projected, the projection is cyclically started from the first pattern. Specifically, the fringe pattern I DMD It can be expressed as:

[0052]

[0053] Where I0 represents the base light intensity, (x, y) represents the image pixel coordinates, ω represents the frequency of the fringe pattern, n represents the nth cosine fringe pattern, and N represents the number of preset phase-shifted cosine fringe patterns. In actual measurements, the collected signal is easily disturbed by fluctuations in background light intensity. Any point I(z) in the structured light image collected by the camera of a continuously scanning structured illumination microscope can be expressed as:

[0054]

[0055] Where z represents the scanning position, m(z) represents the tomographic response of the measurement system (i.e., the degree of modulation of the cosine fringes), and Δz represents the scanning step. b Indicates the background light intensity affected by ambient stray light and imaging noise during the scanning process.

[0056] Then the background light intensity needs to be estimated. According to the expression of the collected structured light image signal, the cosine function of the cosine term is periodic. Therefore, the sum of the points with a fixed phase shift of 2π / N within the cosine function period is 0. By using this, the mean of the adjacent N images can be calculated to eliminate the cosine term in formula 1.2. At the same time, during the scanning process, the background light intensity I b (z) changes slowly compared to the cosine term, so it can be considered that in the N adjacent images in the time domain, I b (z) can be considered constant, so by calculating the mean of N images, we can calculate I b (z).

[0057] The mean of adjacent frame images in the time domain window is calculated to reduce the interference of ambient stray light and imaging noise during the scanning process, and the sliding calculation can obtain the uniform illumination image of each scanning position. Since the defocus of the collected images at each scanning position is not consistent, there are residual stripes on the calculated uniform illumination image, which affects the quality of background intensity estimation. Therefore, a band-stop filter is used to filter the axial background intensity response to suppress the influence of residual stripes.

[0058] That is, in S2, the background light intensity is estimated by using the structured light images adjacent in the time domain, and the estimated background light intensity is obtained as a uniform illumination image, which specifically includes:

[0059] For any vertical scanning position, taking a plurality of adjacent structured light images around the vertical scanning position;

[0060] averaging a plurality of adjacent structured light images and filtering the average to obtain an estimated background light intensity at any scanning position as a uniformly illuminated image;

[0061] The number of the plurality of adjacent structured light images is consistent with the number of the preset cosine fringe patterns.

[0062] Specifically, the uniformly illuminated image at any vertical scanning position is expressed as follows:

[0063]

[0064] Among them, I b Indicates background light intensity; I est represents the estimated background light intensity, i.e., uniformly illuminated image; H represents the filter; z i represents the i-th scanning position; I represents the structured light image; and N represents the number of preset cosine fringe patterns.

[0065] Furthermore, in S2, the estimated background light intensity is used to correct the background light intensity of the structured light image to obtain the corrected structured light image, which specifically includes:

[0066] The collected structured light image is subtracted from the uniformly illuminated image to obtain a corrected structured light image.

[0067] Furthermore, in S3, high-pass filtering is performed on the uniformly illuminated image to obtain high-frequency in-focus information of the sample to be tested, which specifically includes:

[0068] The modulation contrast of the collected structured light image is calculated, and the uniform illumination image is subjected to modulation contrast weighted high-pass filtering to obtain high-frequency in-focus information of the sample to be tested.

[0069] In the case of low signal-to-noise ratio or complex sample texture, imaging noise and high-frequency artifacts will inevitably be introduced, thereby reducing the accuracy of surface topography measurement. From the perspective of defocus, the wide-field image, that is, the background light intensity distribution I b and the structured light image I can be expressed as:

[0070] I b (x,y)=I in (x,y)+I out (x,y) (1.4)

[0071] I(x,y)=I in (x,y)·cos(ωx)+I b (x,y) (1.5)

[0072] Among them, I in (x,y) and I out (x, y) are the in-focus and out-of-focus parts of the image, x is the pixel coordinate; ω represents the frequency of the fringe pattern. in The tomographic response image (i.e., in-focus image) can be obtained, thereby determining the focal plane position for reconstruction. The background intensity estimate can be determined by formula 1.3. By subtracting the estimated background intensity image from the acquired structured light image, the background intensity fluctuation caused by ambient stray light and imaging noise during the scanning process is eliminated, thereby achieving correction. The acquired stripe structured light image D(x, y) corrected by the estimated background intensity is established as follows:

[0073] D(x,y)=|I(x,y)-I est (x,y)|=I in (x,y)|cos(ωx)|(1.6)

[0074] According to formula 1.6, the corrected structured light image can be approximated as an in-focus image. However, due to the presence of fringe information, it cannot be used directly. Fringe information is high-frequency information, so low-pass filtering D(x, y) to eliminate fringe information can approximately obtain low-frequency information in the in-focus image. That is, low-pass filtering is performed on the corrected structured light image to obtain the low-frequency in-focus information of the sample to be tested, as shown in the following formula:

[0075] I in,Lo (x,y)=LP[I in (x,y)]≈LP[D(x,y)](1.7)

[0076] Among them, I in,Lo Indicates the low-frequency information of the in-focus image; LP[.] indicates Gaussian low-pass filtering; I in (x) represents the in-focus portion of the image; D(x, y) represents the corrected structured light image; and (x, y) is the pixel coordinate.

[0077] The tomographic image contains high-frequency information and low-frequency information. The background light intensity image contains the high-frequency information of the tomographic image, and the corrected structured light image contains the low-frequency information of the tomographic image. This embodiment adopts the idea of ​​fusion to fuse the high-frequency information of the tomographic image and the low-frequency information of the tomographic image to obtain a complete tomographic image of the full frequency domain. The background correction in D(x, y) eliminates the influence of background light intensity fluctuations. What is retained in the image is the stripe information. After the background correction, the stripe information retained in D(x, y) is in focus, but due to the existence of the stripe information, it cannot be used directly. It needs to be low-pass filtered to extract the low-frequency in-focus information (i.e., the low-frequency information in the tomographic image). I obtained by low-pass filtering in,Lo The noise is effectively removed while only the low-frequency information in the tomographic image is retained.

[0078] In addition, according to formula 1.4, it can be seen that the background light intensity calculated in formula 1.3 contains the in-focus information and out-focus information, and there is no fringe interference. Therefore, if I is extracted b The high frequency part of the in-focus information is related to I in,Lo By fusion, a complete tomographic image (complete in-focus image) can be obtained. b The defocus information is generally low frequency, while the in-focus information is the clear texture details on the sample, which is high frequency information. Therefore, a high-pass filter is used to remove the out-of-focus part of the image and extract the high-frequency information of the in-focus part of the image (i.e., the high-frequency information in the tomographic image). In order to restore I in The high-frequency components in the low-pass filter LP are applied to the high-pass filter HP complementary to the low-pass filter LP. b , considering that the information of the out-of-focus part is represented by low-frequency information, namely HP[Iout (x,y)]≈0, while the contrast of the modified structured light image is calculated using the Laplacian operator, and the Gaussian high-pass filtering of the noisy wide-field image is performed using a contrast-weighted filtering method, which can further suppress the high-frequency noise in the image, i.e., the high-frequency in-focus information of the sample under test is as follows:

[0079] I in,Hi (x,y)=HP[I b (x,y)]≈HP[I est (x,y)]·N m (x,y)(1.8)

[0080] where I in,Hi represents the high-frequency in-focus information in the tomographic response image; HP[.]=1-LP[.] ; I b represents the background light intensity; I est represents the uniform illumination image; (x,y) is the pixel coordinate; N m (x,y) represents the contrast of the modified structured light image calculated using the Laplacian operator. N m is the modulation contrast calculated from D(x,y), and the contrast image N m is weighted to effectively suppress the influence of high-frequency noise.

[0081] The signal-to-noise ratio level of the regions with different contrasts calculated from the modified structured light image is often not the same, and the pixels with low contrast often have lower signal-to-noise ratio than the pixels with high contrast, and when the contrast approaches zero, the high-frequency information will be completely overwhelmed by noise, so a contrast-weighted method is needed to suppress the high-frequency noise in different regions of the tomographic image, to suppress the influence of noise and retain most of the effective high-frequency information.

[0082] Therefore, the above formula suppresses the influence of high-frequency noise and retains most of the high-frequency information components I in,Hi of the tomographic image. Combining formulas 1.7 and 1.8, the full-frequency-domain expressed tomographic distribution m HiLo (x,y) can be obtained, i.e., the high-frequency in-focus information and the low-frequency in-focus information are fused to obtain the optical tomographic image of the sample under test, which is as follows:

[0083] m HiLo (x,y)=ηI in,Hi (x,y)+I in,Lo (x,y)

[0084] =ηHP[I est (x,y)]·N m (x,y)+LP[|I(x,y)-I est (x,y)|](1.9)

[0085] wherein m HiLo (x, y) represents the optical tomographic image; η represents an adjustment factor for ensuring m HiLo (x) continuity in the frequency domain, which can be adjusted between 0-1. Thus, the imaging noise is suppressed in the full frequency domain, and a tomographic response image m HiLo (x, y) with high signal-to-noise ratio is obtained.

[0086] Further, according to the research "Properties of a Defocused Optical System" by P. A. Stokseth, the structured illumination tomographic response m(z) can be approximated by a Gaussian function g(z), which is expressed as:

[0087]

[0088] wherein a represents the maximum value of the axial tomographic response curve, h represents the position of the maximum value of the tomographic response, σ FWHM represents a parameter related to the full width at half maximum (FWHM) of the tomographic response curve. Thus, by least square Gaussian fitting, the peak position of the axial tomographic response curve can be determined from the selected effective interval, and the sample height is reconstructed, which is expressed as:

[0089]

[0090] wherein h' represents the calculated sample surface height, m p (z i ) represents the z i scan position tomographic response intensity, z i FWHM represents that the data points greater than half of the peak intensity of the axial tomographic response curve are selected as effective data points for least square Gaussian fitting.

[0091] Further, the embodiment provides a three-dimensional topography measurement system based on continuous vertical scanning structured illumination, which comprises a memory and a processor, the memory stores a computer program, and the processor executes the computer program to execute the three-dimensional topography measurement method based on continuous vertical scanning structured illumination according to any one of the above embodiments.

[0092] The measurement system used in the embodiment is as shown in Figure 1As shown, it includes a spatial light modulator DMD (LightCrafter6500), a camera (acA1920-155um, Basler), a continuous scanning mechanism (a displacement mechanism for achieving continuous scanning), an LED light source (central wavelength of 518nm), a microscope objective lens (20×0.45 numerical aperture, Nikon Inc), and related lenses and fixed brackets.

[0093] First, generate N cosine fringe patterns with a fixed phase shift of 2π / N (N is at least 3, and 5 is generally selected) and input them into the DMD. Set the total scanning stroke of the axial scanning mechanism and set it at a fixed scanning step. After each scanning step, the DMD will project a pre-input cosine fringe pattern onto the sample surface and collect it by the camera. After the next scan step is moved, the next phase-shifted fringe pattern will be switched for projection. Repeat the above steps in sequence until the scan is completed.

[0094] After scanning is complete, a stack of acquired images is obtained. Using the continuous scanning structured illumination optical tomography method based on sliding time window background estimation and fusion proposed in this invention, the tomographic response image is calculated. The sample surface topography is then reconstructed according to Equation 1.11.

[0095] Aiming at the problem of low measurement efficiency of structured light illumination micro measurement technology, the present invention proposes a continuous scanning structured illumination optical tomography measurement method based on sliding time window background estimation and fusion.

[0096] First, a continuous scanning structured illumination measurement method is used, where only one structured illumination phase-shifted cosine fringe pattern is collected at each scanning position to improve measurement efficiency.

[0097] Then, the background light intensity is estimated using adjacent captured images in the time domain to obtain a uniformly illuminated image. At the same time, the estimated background light intensity is used to correct the background light intensity of the captured fringe pattern to suppress background light intensity fluctuations caused by ambient stray light and imaging noise during the scanning process.

[0098] The contrast of the corrected fringe pattern is calculated, and the uniformly illuminated image is subjected to contrast-weighted high-pass filtering to obtain the high-frequency in-focus information of the sample under test. The collected fringe pattern after background light intensity correction is low-pass filtered to eliminate the fringe information and obtain the low-frequency in-focus information of the sample under test. The above two are weightedly fused to obtain an optical tomography image, thereby realizing three-dimensional reconstruction of the sample surface under test.

[0099] 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 three-dimensional shape measurement method based on continuous vertical scanning structured illumination, characterized in that: include: S1, using continuous vertical scanning structured illumination, collects a phase-shifted cosine fringe structured light image of the sample to be tested at each vertical scanning position; S2, using the adjacent structured light images in the time domain to estimate the background light intensity, and obtaining the estimated background light intensity as a uniformly illuminated image; and simultaneously, using the estimated background light intensity to correct the background light intensity of the structured light image, and obtaining the corrected structured light image; S3, performing high-pass filtering on the uniformly illuminated image to obtain high-frequency in-focus information of the sample to be tested; performing low-pass filtering on the corrected structured light image to obtain low-frequency in-focus information of the sample to be tested; The high-frequency in-focus information and the low-frequency in-focus information are fused to obtain an optical tomographic image of the sample to be tested; S4, acquiring a three-dimensional morphology of the sample to be tested based on the optical tomography image; S1 specifically includes: Preset multiple cosine fringe patterns with fixed phase shifts, project one of the cosine fringe patterns onto the surface of the sample to be tested at each vertical scanning position, and during the scanning process of the sample to be tested, the multiple cosine fringe patterns are projected in a cyclic manner in sequence; In S2, the background light intensity is estimated by using the structured light images adjacent in the time domain, and the estimated background light intensity is obtained as a uniform illumination image, specifically including: For any vertical scanning position, taking a plurality of adjacent structured light images around the vertical scanning position; averaging a plurality of adjacent structured light images and filtering the average to obtain an estimated background light intensity at any scanning position as a uniformly illuminated image; The number of the plurality of adjacent structured light images is consistent with the number of the preset cosine fringe patterns; The high-frequency in-focus information and the low-frequency in-focus information are fused to obtain the optical tomography image of the sample to be tested, as shown in the following formula: ； in, m HiLo represents an optical tomographic image; η represents the adjustment factor; I in,Hi Represents high-frequency in-focus information in the tomographic response image; I in,Lo Represents the low-frequency in-focus information in the tomographic response image; ( x , y ) are pixel coordinates; LP [.] indicates Gaussian low-pass filtering; HP [.] = 1- LP [.]; I est represents a uniformly illuminated image; N m represents the contrast calculated for the corrected structured light image; I Represents a structured light image.

2. The three-dimensional shape measurement method based on continuous vertical scanning structured illumination according to claim 1, characterized in that: The uniformly illuminated image at any vertical scanning position is specifically expressed as follows: ； in, I b Indicates background light intensity; I est represents a uniformly illuminated image; H represents a filter; z i Indicates the i Scan positions; I Represents a structured light image; N Indicates the number of preset cosine fringe patterns.

3. The three-dimensional shape measurement method based on continuous vertical scanning structured illumination according to claim 1 or 2, characterized in that: In S2, the background light intensity of the structured light image is corrected using the estimated background light intensity to obtain the corrected structured light image, specifically including: The collected structured light image is subtracted from the uniformly illuminated image to obtain a corrected structured light image.

4. The three-dimensional shape measurement method based on continuous vertical scanning structured illumination according to claim 1 or 2, characterized in that: In S3, high-pass filtering is performed on the uniformly illuminated image to obtain high-frequency in-focus information of the sample to be tested, specifically including: The contrast of the modified structured light image is calculated using a Laplace operator, and contrast-weighted high-pass filtering is performed on the uniformly illuminated image to obtain high-frequency in-focus information of the sample to be tested.

5. The three-dimensional shape measurement method based on continuous vertical scanning structured illumination according to claim 1 or 2, characterized in that: The corrected structured light image is subjected to low-pass filtering to obtain the low-frequency in-focus information of the sample to be tested, as shown in the following formula: ； in, I in,Lo Represents the low-frequency in-focus information in the tomographic response image; LP [.] indicates Gaussian low-pass filtering; I in Indicates the in-focus portion of the image; D represents the corrected structured light image; ( x , y ) are pixel coordinates.

6. The three-dimensional shape measurement method based on continuous vertical scanning structured illumination according to claim 4, characterized in that: The uniformly illuminated image is subjected to high-pass filtering to obtain the high-frequency in-focus information of the sample to be tested, as shown in the following formula: ； in, I in,Hi Represents high-frequency in-focus information in the tomographic response image; HP [.] = 1- LP [.]; I b Indicates background light intensity; I est represents a uniformly illuminated image; N m represents the contrast calculated for the corrected structured light image.

7. A three-dimensional shape measurement system based on continuous vertical scanning structured illumination, characterized in that: The system includes a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the three-dimensional shape measurement method based on continuous vertical scanning structured illumination according to any one of claims 1 to 6 is executed.

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