Contrast demodulation method based on synchronous scanning phase shift

Abstract

The invention discloses a contrast demodulation method based on synchronous scanning phase shift, and belongs to the technical field of digital measurement, and the method comprises the following steps: a, building a structured light illumination measurement system; b, longitudinal scanning is carried out through a structured light illumination measurement system; c, acquiring a longitudinal light intensity response curve, and longitudinally extracting a light intensity value of each scanning position to obtain a light intensity function; step d, performing local Fourier transform processing to obtain frequency spectrum information of the light intensity curve; e, filtering the frequency spectrum information of the light intensity curve to obtain filtered fundamental frequency information; and f, carrying out inverse Fourier transform on the filtered fundamental frequency information, and carrying out modulus operation to obtain a contrast function of a single pixel point changing along with the scanning position. According to the invention, through parallel operation of projection fringe phase shift and scanning image acquisition, rapid and high-precision demodulation of the contrast is realized by using local Fourier transform.

Description

Technical Field

[0001] The invention relates to the technical field of digital measurement, and in particular to a contrast demodulation method based on synchronous scanning phase shift. Background Art

[0002] The microscopic three-dimensional measurement method based on structured light illumination has the characteristics of non-contact, non-destructive, high precision, high efficiency and wide adaptability. Its basic principle is to realize three-dimensional detection by using the characteristic that the contrast value of the sinusoidal grating fringes after imaging is sensitive to the height information of the object surface. The specific process is to project the sinusoidal grating fringes generated by the physical grating or digital micromirror array DMD onto the surface of the object through an optical microscope system. In this measurement system, the physical grating or digital micromirror array DMD is in an optical imaging conjugate position with the surface of the object to be measured. The grating imaging and the object surface imaging are synchronously clear or blurred. Therefore, the fringe contrast information representing the degree of grating blur can be used to characterize the focusing degree of the pixel points on the object surface. When the fringe contrast reaches the maximum value, it means that the grating fringe imaging is the clearest, that is, the corresponding area of ​​the object to be measured is the clearest. Subsequently, the longitudinal contrast response curve of the fringe is synchronously obtained by longitudinally scanning the object to be measured, and the height mapping of the object surface is realized by combining the peak fitting and peak location algorithms, thereby realizing the three-dimensional measurement of the object surface.

[0003] Among them, the contrast demodulation algorithm is the core step of the structured light illumination measurement method, and its demodulation accuracy and efficiency directly determine the final measurement accuracy and efficiency. The existing contrast demodulation algorithms are mainly divided into two categories: multiple scanning demodulation and single scanning demodulation. The former is represented by the modulation and demodulation algorithm based on phase shift technology, and the latter is represented by the contrast demodulation algorithm based on global Fourier transform technology. The former multiple scanning demodulation algorithm needs to collect multiple imaging pictures at the same scanning position to solve the contrast. Its characteristics are that the calculation process covers all the information of the image, the demodulation accuracy is high, the application range is wide, and the measurement objects are diverse. However, due to the complex image collection process and large data processing volume, its measurement efficiency is low, and it is not suitable for fast measurement and dynamic measurement. The latter single scanning demodulation algorithm only needs to collect one imaging picture at the same scanning position to solve the contrast. Its characteristics are simple measurement system, small data processing volume, and high measurement efficiency. However, the high-frequency information of the object is inevitably lost during the data processing process, resulting in low demodulation accuracy, which is not suitable for ultra-high precision measurement and steep edge detection.

[0004] A Chinese patent document with publication number CN102589479A and publication date July 18, 2012 discloses a three-dimensional shape central perturbation composite grating projection measurement method and device, the measurement method comprising the following steps: using four carrier gratings of different frequencies to modulate four frames of phase-shifted sinusoidal gratings perpendicular to their directions respectively, wherein the brightness of the central stripes of the fourth frame of the phase-shifted sinusoidal grating is changed, and superposition is formed to form a central perturbation composite grating; using an LCD display to project the central perturbation composite grating onto the object to be measured to obtain a deformed grating modulated by the surface shape of the object; performing a two-dimensional Fourier transform on the deformed grating, filtering it with a suitable bandpass filter, and then performing an inverse Fourier transform and taking the modulus value to obtain a deformed phase The invention discloses a method for obtaining a phase-shifted grating stripe by using a central perturbation composite grating. The method comprises the following steps: first, a phase-shifted grating stripe is formed by using a central perturbation composite grating, and second, a phase-shifted grating stripe is formed by using a central perturbation composite grating. The method comprises the following steps: the phase-shifted grating stripe is formed by using a central perturbation composite grating, and the phase-shifted grating stripe is formed by using a central perturbation composite grating. The method comprises the following steps: the inverses of the four carrier frequencies are in an arithmetic progression. The four frames of sinusoidal grating phase-shifted stripes are formed by using a full-cycle equal phase shift method, that is, the phase shift of adjacent sinusoidal grating phase-shifted stripes is π / 2. The brightness of the central stripe of the fourth frame of the sinusoidal grating is changed so that the stripe at the center contains coded information different from that of other stripes, thereby forming perturbation information.

[0005] The three-dimensional morphology center perturbation composite grating projection measurement method and device disclosed in this patent document can improve the optical three-dimensional measurement speed, but the accuracy is low. Summary of the invention

[0006] In order to overcome the defects of the above-mentioned prior art, the present invention provides a contrast demodulation method based on synchronous scanning phase shift. The present invention realizes fast and high-precision demodulation of contrast by using local Fourier transform through parallel operation of projection fringe phase shift and scanning acquisition.

[0007] The present invention is achieved through the following technical solutions: A contrast demodulation method based on synchronous scanning phase shift comprises the following steps: Step a, building a structured light illumination measurement system; Step b, longitudinal scanning is performed by a structured light illumination measurement system, a computer controls a digital micromirror array to generate a sinusoidal grating fringe pattern, a white light source is used to illuminate the digital micromirror array to generate a structured light field, the structured light field is projected onto the object to be measured, a CCD camera captures the reflected light field imaging, and the CCD camera records the reflected light field and stores the image in the computer; Step c, obtaining a longitudinal light intensity response curve, and extracting the light intensity value of each scanning position longitudinally to obtain a light intensity function; Formula 1 in, A single pixel changes with the scanning position The light intensity curve, is the background light intensity, is the grating fringe contrast information, is a fixed value, is the phase shift step number, is the scanning position; Step d, performing local Fourier transform processing on equation 1 to obtain spectrum information of the light intensity curve, including zero frequency information of the light intensity spectrum and fundamental frequency information of the light intensity spectrum; Formula 2 in, is the spectrum information of the light intensity curve, is the negative fundamental frequency information of the light intensity spectrum, is the zero-frequency information of the light intensity spectrum, is the positive fundamental frequency information of the light intensity spectrum; Step e, filtering the spectrum information of the light intensity curve, designing a rectangular filter window with the vertex of the fundamental frequency curve as the center and the half width of the fundamental frequency curve as the radius, and using the rectangular filter window to process the light intensity spectrum to obtain the filtered fundamental frequency information; Step f: The filtered baseband information is subjected to inverse Fourier transform and modulo to obtain a single pixel point with the scanning position. Varying contrast function; Formula 3 in, Maximum contrast ratio, is the spatial frequency of the projected fringe, is the point spread parameter.

[0008] In the step a, the structured light illumination measurement system includes a white light source, a digital micromirror array, a first lens, a CCD camera, a second lens, a beam splitter, a microscope objective lens and an objective stage. The white light source illuminates the digital micromirror array to generate a structured light field required for measurement. The structured light field is sequentially projected onto the object to be measured located on the objective stage through the first lens, the beam splitter and the microscope objective lens, and the reflected light field sequentially passes through the microscope objective lens, the beam splitter and the second lens to reach the CCD camera.

[0009] The stage is a piezoelectric ceramic displacement stage. In the step b, projecting the structured light field onto the object to be measured means that the structured light field is sequentially projected onto the object to be measured located on the piezoelectric ceramic translation stage through the first lens, the beam splitter and the microscope objective lens.

[0010] In the step b, the CCD camera captures the reflected light field for imaging, which means that the reflected light field passes through the microscope objective, the beam splitter and the second lens in sequence to reach the CCD camera, and is imaged by the CCD camera.

[0011] In the step b, the reflected light field refers to the reflected light formed after the light source projects the structured light field onto the surface of the object to be measured, including the surface morphology and reflectivity information of the object to be measured.

[0012] In the step b, the longitudinal scanning specifically means that each time the piezoelectric ceramic displacement stage scans once, the digital micromirror array simultaneously switches a sinusoidal grating fringe pattern containing a phase difference, and the CCD camera collects the image, and the operation is repeated until the entire scan is completed.

[0013] In the step d, the local Fourier transform refers to performing a Fourier transform on the light intensity curve of a single pixel.

[0014] In the step e, filtering the spectrum information of the light intensity curve specifically refers to filtering out the zero-frequency information of the light intensity spectrum and the fundamental frequency information of the light intensity spectrum.

[0015] In the step f, the point diffusion parameter Calculated by formula 4; Formula 4 in, For scanning position, is the scanning step, is the focal length of the microscope lens, Is a constant.

[0016] In the step f, taking the mold body means taking the absolute value after the inverse Fourier transform.

[0017] The CCD camera described in the present invention refers to a digital camera with a charge coupled device image sensor.

[0018] The beneficial effects of the present invention are mainly manifested in the following aspects: 1. Compared with the prior art, the present invention realizes fast and high-precision demodulation of contrast by performing phase shift of projection fringes and scanning acquisition in parallel, and utilizing local Fourier transform.

[0019] 2. The present invention performs scanning and phase shifting in parallel, thereby greatly reducing the amount of data compared to conventional multi-step phase shift demodulation, and has higher accuracy than conventional Fourier transform demodulation.

[0020] 3. The present invention effectively combines the traditional multi-step phase shift and global Fourier transform to achieve fast and high-precision demodulation of fringe contrast, laying a foundation for further improving the measurement performance of structured light illumination.

[0021] 4. Compared with the conventional contrast demodulation based on multi-step phase shift, the present invention can effectively improve the demodulation efficiency because the amount of data processing is greatly reduced.

[0022] 5. Compared with the traditional contrast demodulation based on global Fourier, in the present invention, during longitudinal scanning, each time the digital micromirror array simultaneously switches a sinusoidal grating fringe pattern with a phase difference, and the CCD camera collects the image, and the scanning and phase shift are performed in parallel and cyclically. The pixel point in the scanning direction shows an ideal modulation signal, which can be obtained by extracting the light intensity value of the pixel point in each image, which can save the time of projecting the sinusoidal grating fringe pattern at each position and realize fast and high-precision demodulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Figure 1 It is a flowchart of the present invention; Figure 2 It is a schematic diagram of the structure of the structured light illumination measurement system of the present invention; Markings in the figure: 1. white light source, 2. digital micromirror array, 3. first lens, 4. CCD camera, 5. second lens, 6. beam splitter, 7. microscope objective lens, 8. stage. DETAILED DESCRIPTION

[0024] Example 1 See also Figure 1 , a contrast demodulation method based on synchronous scanning phase shift, comprising the following steps: Step a, building a structured light illumination measurement system; Step b, longitudinal scanning is performed by a structured light illumination measurement system, a computer controls a digital micromirror array 2 to generate a sinusoidal grating fringe pattern, a white light source 1 is used to illuminate the digital micromirror array 2 to generate a structured light field, the structured light field is projected onto the object to be measured, a CCD camera 4 captures the reflected light field imaging, and the CCD camera 4 records the reflected light field and stores the image in the computer; Step c, obtaining a longitudinal light intensity response curve, and extracting the light intensity value of each scanning position longitudinally to obtain a light intensity function; Formula 1 in, A single pixel changes with the scanning position The light intensity curve, is the background light intensity, is the grating fringe contrast information, is a fixed value, is the phase shift step number, is the scanning position; Step d, performing local Fourier transform processing on equation 1 to obtain spectrum information of the light intensity curve, including zero frequency information of the light intensity spectrum and fundamental frequency information of the light intensity spectrum; Formula 2 in, is the spectrum information of the light intensity curve, is the negative fundamental frequency information of the light intensity spectrum, is the zero-frequency information of the light intensity spectrum, is the positive fundamental frequency information of the light intensity spectrum; Step e, filtering the spectrum information of the light intensity curve, designing a rectangular filter window with the vertex of the fundamental frequency curve as the center and the half width of the fundamental frequency curve as the radius, and using the rectangular filter window to process the light intensity spectrum to obtain the filtered fundamental frequency information; Step f: The filtered baseband information is subjected to inverse Fourier transform and modulo to obtain a single pixel point with the scanning position. Varying contrast function; Formula 3 in, Maximum contrast ratio, is the spatial frequency of the projected fringe, is the point spread parameter.

[0025] This embodiment is the most basic implementation method, which realizes fast and high-precision demodulation of contrast by performing phase shift of projection fringes and scanning acquisition in parallel and utilizing local Fourier transform.

[0026] Example 2 See also Figure 1 and Figure 2 , a contrast demodulation method based on synchronous scanning phase shift, comprising the following steps: Step a, building a structured light illumination measurement system; Step b, longitudinal scanning is performed by a structured light illumination measurement system, a computer controls a digital micromirror array 2 to generate a sinusoidal grating fringe pattern, a white light source 1 is used to illuminate the digital micromirror array 2 to generate a structured light field, the structured light field is projected onto the object to be measured, a CCD camera 4 captures the reflected light field imaging, and the CCD camera 4 records the reflected light field and stores the image in the computer; Step c, obtaining a longitudinal light intensity response curve, and extracting the light intensity value of each scanning position longitudinally to obtain a light intensity function; Formula 1 in, A single pixel changes with the scanning position The light intensity curve, is the background light intensity, is the grating fringe contrast information, is a fixed value, is the phase shift step number, is the scanning position; Step d, performing local Fourier transform processing on equation 1 to obtain spectrum information of the light intensity curve, including zero frequency information of the light intensity spectrum and fundamental frequency information of the light intensity spectrum; Formula 2 in, is the spectrum information of the light intensity curve, is the negative fundamental frequency information of the light intensity spectrum, is the zero-frequency information of the light intensity spectrum, is the positive fundamental frequency information of the light intensity spectrum; Step e, filtering the spectrum information of the light intensity curve, designing a rectangular filter window with the vertex of the fundamental frequency curve as the center and the half width of the fundamental frequency curve as the radius, and using the rectangular filter window to process the light intensity spectrum to obtain the filtered fundamental frequency information; Step f: The filtered baseband information is subjected to inverse Fourier transform and modulo to obtain a single pixel point with the scanning position. Varying contrast function; Formula 3 in, Maximum contrast ratio, is the spatial frequency of the projected fringe, is the point spread parameter.

[0027] Preferably, in step a, the structured light illumination measurement system includes a white light source 1, a digital micromirror array 2, a first lens 3, a CCD camera 4, a second lens 5, a beam splitter 6, a microscope objective lens 7 and an objective stage 8. The white light source 1 irradiates the digital micromirror array 2 to generate a structured light field required for measurement. The structured light field is projected onto the object to be measured located on the objective stage 8 through the first lens 3, the beam splitter 6 and the microscope objective lens 7 in sequence, and the reflected light field reaches the CCD camera 4 through the microscope objective lens 7, the beam splitter 6 and the second lens 5 in sequence.

[0028] The stage 8 is a piezoelectric ceramic displacement stage. This embodiment is a preferred implementation method. Since scanning and phase shifting are performed in parallel, the amount of data is greatly reduced compared to traditional multi-step phase shift demodulation, and it has higher accuracy than traditional Fourier transform demodulation.

[0029] Example 3 See also Figure 1 and Figure 2 , a contrast demodulation method based on synchronous scanning phase shift, comprising the following steps: Step a, building a structured light illumination measurement system; Step b, longitudinal scanning is performed by a structured light illumination measurement system, a computer controls a digital micromirror array 2 to generate a sinusoidal grating fringe pattern, a white light source 1 is used to illuminate the digital micromirror array 2 to generate a structured light field, the structured light field is projected onto the object to be measured, a CCD camera 4 captures the reflected light field imaging, and the CCD camera 4 records the reflected light field and stores the image in the computer; Step c, obtaining a longitudinal light intensity response curve, and extracting the light intensity value of each scanning position longitudinally to obtain a light intensity function; Formula 1 in, A single pixel changes with the scanning position The light intensity curve, is the background light intensity, is the grating fringe contrast information, is a fixed value, is the phase shift step number, is the scanning position; Step d, performing local Fourier transform processing on equation 1 to obtain spectrum information of the light intensity curve, including zero frequency information of the light intensity spectrum and fundamental frequency information of the light intensity spectrum; Formula 2 in, is the spectrum information of the light intensity curve, is the negative fundamental frequency information of the light intensity spectrum, is the zero-frequency information of the light intensity spectrum, is the positive fundamental frequency information of the light intensity spectrum; Step e, filtering the spectrum information of the light intensity curve, designing a rectangular filter window with the vertex of the fundamental frequency curve as the center and the half width of the fundamental frequency curve as the radius, and using the rectangular filter window to process the light intensity spectrum to obtain the filtered fundamental frequency information; Step f: The filtered baseband information is subjected to inverse Fourier transform and modulo to obtain a single pixel point with the scanning position. Varying contrast function; Formula 3 in, Maximum contrast ratio, is the spatial frequency of the projected fringe, is the point spread parameter.

[0030] In the step a, the structured light illumination measurement system includes a white light source 1, a digital micromirror array 2, a first lens 3, a CCD camera 4, a second lens 5, a spectroscope 6, a microscope objective lens 7 and an objective stage 8. The white light source 1 irradiates the digital micromirror array 2 to generate a structured light field required for measurement. The structured light field is projected onto the object to be measured located on the objective stage 8 through the first lens 3, the spectroscope 6 and the microscope objective lens 7 in sequence, and the reflected light field reaches the CCD camera 4 through the microscope objective lens 7, the spectroscope 6 and the second lens 5 in sequence.

[0031] The stage 8 is a piezoelectric ceramic displacement stage. Further preferably, in the step b, projecting the structured light field onto the object to be measured means that the structured light field is sequentially projected onto the object to be measured located on the piezoelectric ceramic translation stage through the first lens 3, the beam splitter 6 and the microscope objective lens 7.

[0032] In the step b, the CCD camera 4 captures the reflected light field for imaging, which means that the reflected light field passes through the microscope objective 7, the beam splitter 6 and the second lens 5 in sequence to reach the CCD camera 4 and is imaged by the CCD camera 4.

[0033] In the step b, the reflected light field refers to the reflected light formed after the light source projects the structured light field onto the surface of the object to be measured, including the surface morphology and reflectivity information of the object to be measured.

[0034] In step b, the longitudinal scanning specifically means that each time the piezoelectric ceramic displacement stage scans once, the digital micromirror array 2 simultaneously switches a sinusoidal grating fringe pattern containing a phase difference, and the CCD camera 4 collects images, and the operation is repeated until the entire scan is completed.

[0035] In the step d, the local Fourier transform refers to performing a Fourier transform on the light intensity curve of a single pixel.

[0036] This embodiment is another preferred implementation method, which effectively combines the traditional multi-step phase shift and global Fourier transform to achieve fast and high-precision demodulation of fringe contrast, laying a foundation for further improving the structured light illumination measurement performance.

[0037] Example 4 See also Figure 1 and Figure 2 , a contrast demodulation method based on synchronous scanning phase shift, comprising the following steps: Step a, building a structured light illumination measurement system; Step b, longitudinal scanning is performed by a structured light illumination measurement system, a computer controls a digital micromirror array 2 to generate a sinusoidal grating fringe pattern, a white light source 1 is used to illuminate the digital micromirror array 2 to generate a structured light field, the structured light field is projected onto the object to be measured, a CCD camera 4 captures the reflected light field imaging, and the CCD camera 4 records the reflected light field and stores the image in the computer; Step c, obtaining a longitudinal light intensity response curve, and extracting the light intensity value of each scanning position longitudinally to obtain a light intensity function; Formula 1 in, A single pixel changes with the scanning position The light intensity curve, is the background light intensity, is the grating fringe contrast information, is a fixed value, is the phase shift step number, is the scanning position; Step d, performing local Fourier transform processing on equation 1 to obtain spectrum information of the light intensity curve, including zero frequency information of the light intensity spectrum and fundamental frequency information of the light intensity spectrum; Formula 2 in, is the spectrum information of the light intensity curve, is the negative fundamental frequency information of the light intensity spectrum, is the zero-frequency information of the light intensity spectrum, is the positive fundamental frequency information of the light intensity spectrum; Step e, filtering the spectrum information of the light intensity curve, designing a rectangular filter window with the vertex of the fundamental frequency curve as the center and the half width of the fundamental frequency curve as the radius, and using the rectangular filter window to process the light intensity spectrum to obtain the filtered fundamental frequency information; Step f: The filtered baseband information is subjected to inverse Fourier transform and modulo to obtain a single pixel point with the scanning position. Varying contrast function; Formula 3 in, Maximum contrast ratio, is the spatial frequency of the projected fringe, is the point spread parameter.

[0038] In the step a, the structured light illumination measurement system includes a white light source 1, a digital micromirror array 2, a first lens 3, a CCD camera 4, a second lens 5, a spectroscope 6, a microscope objective lens 7 and an objective stage 8. The white light source 1 irradiates the digital micromirror array 2 to generate a structured light field required for measurement. The structured light field is projected onto the object to be measured located on the objective stage 8 through the first lens 3, the spectroscope 6 and the microscope objective lens 7 in sequence, and the reflected light field reaches the CCD camera 4 through the microscope objective lens 7, the spectroscope 6 and the second lens 5 in sequence.

[0039] The stage 8 is a piezoelectric ceramic displacement stage. In the step b, projecting the structured light field onto the object to be measured means that the structured light field is sequentially projected onto the object to be measured located on the piezoelectric ceramic displacement stage through the first lens 3, the beam splitter 6 and the microscope objective lens 7.

[0040] In the step b, the CCD camera 4 captures the reflected light field for imaging, which means that the reflected light field passes through the microscope objective 7, the beam splitter 6 and the second lens 5 in sequence to reach the CCD camera 4 and is imaged by the CCD camera 4.

[0041] In the step b, the reflected light field refers to the reflected light formed after the light source projects the structured light field onto the surface of the object to be measured, including the surface morphology and reflectivity information of the object to be measured.

[0042] In step b, the longitudinal scanning specifically means that each time the piezoelectric ceramic displacement stage scans once, the digital micromirror array 2 simultaneously switches a sinusoidal grating fringe pattern containing a phase difference, and the CCD camera 4 collects images, and the operation is repeated until the entire scan is completed.

[0043] More preferably, in step d, the local Fourier transform refers to performing a Fourier transform on the light intensity curve of a single pixel.

[0044] In the step e, filtering the spectrum information of the light intensity curve specifically refers to filtering out the zero-frequency information of the light intensity spectrum and the baseband information of the light intensity spectrum.

[0045] In the step f, the point diffusion parameter Calculated by formula 4; Formula 4 in, For scanning position, is the scanning step, is the focal length of the microscope lens, Is a constant.

[0046] In the step f, taking the mold body means taking the absolute value after the inverse Fourier transform.

[0047] This embodiment is the best implementation mode. Compared with the traditional contrast demodulation based on multi-step phase shift, the data processing amount is greatly reduced, thereby effectively improving the demodulation efficiency.

[0048] Compared with the traditional contrast demodulation based on global Fourier, during longitudinal scanning, the digital micromirror array 2 simultaneously switches a sinusoidal grating fringe pattern with a phase difference for each scan, and the CCD camera 4 collects images, and scanning and phase shifting are performed in parallel and cyclically. The pixel point in the scanning direction appears as an ideal modulation signal, which can be obtained by extracting the light intensity value of the pixel point in each image, which can save the time of projecting the sinusoidal grating fringe pattern at each position and realize fast and high-precision demodulation.

[0049] The basic principles of the present invention are as follows: In the basic principle of structured light measurement, phase shift must be used to achieve periodic transformation of sinusoidal grating fringes. The traditional measurement method is to continuously project multiple phase-shifted fringe patterns at a fixed position and continue scanning after the acquisition is completed.

[0050] In the longitudinal scanning process of the present invention, a digital micromirror array 2 is controlled by a computer to generate a sinusoidal grating fringe pattern, a white light source 1 irradiates the digital micromirror array 2 to generate a structured light field required for measurement, the structured light field is sequentially projected onto the object to be measured located on the stage 8 through the first lens 3, the beam splitter 6 and the microscope objective 7, the reflected light field sequentially passes through the microscope objective 7, the beam splitter 6 and the second lens 5 to reach the CCD camera 4, the CCD camera 4 captures the image, records the reflected light field and stores the image in the computer.

[0051] Each time a scan is performed, the digital micromirror array 2 simultaneously switches a sinusoidal grating fringe pattern with a phase difference, and the CCD camera 4 collects images. Scanning and phase shifting are performed in parallel and cyclically, and the pixel point in the scanning direction appears as an ideal modulation signal, which can be obtained by extracting the light intensity value of the pixel point in each image. Therefore, the present invention can save the time of projecting the sinusoidal grating fringe pattern at each position and realize fast and high-precision demodulation.

Claims

1. A contrast demodulation method based on synchronous scanning phase shift, characterized in that: The following steps are involved: Step a, building a structured light illumination measurement system; Step b, longitudinal scanning is performed by a structured light illumination measurement system, a computer controls a digital micromirror array (2) to generate a sinusoidal grating fringe pattern, a white light source (1) is used to illuminate the digital micromirror array (2) to generate a structured light field, the structured light field is projected onto the object to be measured, a CCD camera (4) captures the reflected light field image, and the CCD camera (4) records the reflected light field and stores the image in a computer; Step c, obtaining a longitudinal light intensity response curve, and extracting the light intensity value of each scanning position longitudinally to obtain a light intensity function; Formula 1 in, A single pixel changes with the scanning position The light intensity curve, is the background light intensity, is the grating fringe contrast information, is a fixed value, is the phase shift step number, is the scanning position; Step d, performing local Fourier transform processing on equation 1 to obtain spectrum information of the light intensity curve, including zero frequency information of the light intensity spectrum and fundamental frequency information of the light intensity spectrum; Formula 2 in, is the spectrum information of the light intensity curve, is the negative fundamental frequency information of the light intensity spectrum, is the zero-frequency information of the light intensity spectrum, is the positive fundamental frequency information of the light intensity spectrum; Step e, filtering the spectrum information of the light intensity curve, designing a rectangular filter window with the vertex of the fundamental frequency curve as the center and the half width of the fundamental frequency curve as the radius, and using the rectangular filter window to process the light intensity spectrum to obtain the filtered fundamental frequency information; Step f: The filtered baseband information is subjected to inverse Fourier transform and modulo to obtain a single pixel point with the scanning position. Varying contrast function; Formula 3 in, Maximum contrast ratio, is the spatial frequency of the projected fringe, is the point spread parameter.

2. The contrast demodulation method based on synchronous scanning phase shift according to claim 1, characterized in that: In step a, the structured light illumination measurement system comprises a white light source (1), a digital micromirror array (2), a first lens (3), a CCD camera (4), a second lens (5), a beam splitter (6), a microscope objective lens (7) and an object stage (8); the white light source (1) irradiates the digital micromirror array (2) to generate a structured light field required for measurement; the structured light field is sequentially projected onto an object to be measured located on the object stage (8) through the first lens (3), the beam splitter (6) and the microscope objective lens (7); and the reflected light field sequentially passes through the microscope objective lens (7), the beam splitter (6) and the second lens (5) to reach the CCD camera (4).

3. The contrast demodulation method based on synchronous scanning phase shift according to claim 2, characterized in that: The object carrier (8) is a piezoelectric ceramic displacement stage.

4. The contrast demodulation method based on synchronous scanning phase shift according to claim 1, characterized in that: In the step b, projecting the structured light field onto the object to be measured means that the structured light field is sequentially projected onto the object to be measured located on the piezoelectric ceramic displacement stage through the first lens (3), the beam splitter (6) and the microscope objective lens (7).

5. The contrast demodulation method based on synchronous scanning phase shift according to claim 2, characterized in that: In the step b, the CCD camera (4) captures the reflected light field for imaging, which means that the reflected light field passes through the microscope objective lens (7), the beam splitter (6) and the second lens (5) in sequence to reach the CCD camera (4), and is imaged by the CCD camera (4).

6. The contrast demodulation method based on synchronous scanning phase shift according to claim 1, characterized in that: In the step b, the reflected light field refers to the reflected light formed after the light source projects the structured light field onto the surface of the object to be measured, including the surface morphology and reflectivity information of the object to be measured.

7. The contrast demodulation method based on synchronous scanning phase shift according to claim 3, characterized in that: In the step b, the longitudinal scanning specifically means that each time the piezoelectric ceramic displacement stage scans once, the digital micromirror array (2) simultaneously switches a sinusoidal grating fringe pattern containing a phase difference, and the CCD camera (4) simultaneously collects an image, and the operation is repeated until the entire scan is completed.

8. The contrast demodulation method based on synchronous scanning phase shift according to claim 1, characterized in that: In the step d, the local Fourier transform refers to performing a Fourier transform on the light intensity curve of a single pixel.

9. The contrast demodulation method based on synchronous scanning phase shift according to claim 1, characterized in that: In the step e, filtering the spectrum information of the light intensity curve specifically refers to filtering out the zero-frequency information of the light intensity spectrum and the fundamental frequency information of the light intensity spectrum.

10. The contrast demodulation method based on synchronous scanning phase shift according to claim 1, characterized in that: In the step f, the point diffusion parameter Calculated by formula 4; Formula 4 in, For scanning position, is the scanning step, is the focal length of the microscope lens, Is a constant.

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