CN110108230A - Two-value optical grating projection defocus degree assessment method based on image difference Yu LM iteration - Google Patents
Two-value optical grating projection defocus degree assessment method based on image difference Yu LM iteration Download PDFInfo
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- CN110108230A CN110108230A CN201910372643.1A CN201910372643A CN110108230A CN 110108230 A CN110108230 A CN 110108230A CN 201910372643 A CN201910372643 A CN 201910372643A CN 110108230 A CN110108230 A CN 110108230A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
- G01B11/2433—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures for measuring outlines by shadow casting
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Abstract
The invention discloses a kind of two-value optical grating projection defocus degree assessment method based on image difference Yu LM iteration, the defocusing degree appraisal procedure is the following steps are included: adjust the parameter of projector output grating before test；Difference operation first is executed to the image obtained by camera during the test, and then iterative operation is executed to difference image by LM method for the objective function of sinusoid；The absolute error of data and real image when obtaining iteration ends at image each point, and be corrected with image grayscale range, reduce fluctuating error.The present invention evaluates defocusing degree from the angle of experiment, have many advantages, such as to judge the accuracy of defocus degree is high, required equipment is simple, it is convenient and practical, can real-time display.
Description
Technical field
The present invention relates to flash ranging experimental solid mechanics fields, and in particular to a kind of two-value based on image difference Yu LM iteration
Optical grating projection defocus degree assessment method.
Background technique
In optical measurement mechanics field, tunneling leakage current is a kind of basic optical morphology measurement method.Tunneling leakage current is direct
Using the three-dimensional information of object is obtained by the phase distortion information of modulation grid line, using the method demodulation phase of mathematics, and
It can be with the concavity and convexity of automatic discrimination object.Therefore image procossing is easy to automate, accuracy and sensitivity with higher.
For the ease of measurement, in tunneling leakage current, projector be two-dimensional structure pattern (candy strip) rather than
The sinusoidal pattern of 3D shape, then binary mode is blurred into quasi sinusoid by suitably making projector's defocus to realize
Pattern, this technology are known as binary system defocus technology.It can not only eliminate gradation distortion, also achieve high speed 3D measurement.However
There are some problems for binary system defocus technology: if defocus degree is too small, pattern is not sine curve, humorous comprising many high orders
Wave.If projector's defocus, the contrast of pattern is lower too many.Non-sine structure causes binary system defocus technology by high-order
In harmonic wave introduce error into demodulation phase, can reduce 3D measurement precision.Furthermore in practical applications, it is desirable to improve measurement
Accuracy, it is necessary to consider that the distortion of β existing for electronic device itself causes the image received to have certain non-sinusoidal character
Problem.Such issues that affect the precision of measurement, be unfavorable for the development of high-precision optical measurement mechanics.
Summary of the invention
It is commented the purpose of the present invention is to provide a kind of based on image difference and the two-value optical grating projection defocus degree of LM iteration
Estimate method.
The technical solution for realizing the aim of the invention is as follows: a kind of two-value optical grating projection based on image difference Yu LM iteration
Defocus degree assessment method, the experimental provision of this method include camera, camera lens, optical platform, computer, projector and mark
Fixed board, the appraisal procedure the following steps are included:
The fixation of step 1, experimental provision: scaling board, camera and projector are fixed on optical platform, and camera lens hang down
Directly in scaling board plane, the maximum planes direction of projector lens alignment scaling board is positioned；
The acquisition of step 2, raster image: sharp using projector to the raster image of calibration one width binaryzation of planar projective
The image of scaling board and grating is acquired with camera；
Step 3, pre-processing image data: determining the best use length, and one piece on image is chosen on the basis of the length
Rectangular area generates feature array needed for evaluating the image；
The evaluation of step 4, current defocus degree: assessing characteristics of image array, obtains assessment numerical value；
The selection of step 5, best defocus degree: changing focal length and aperture, repeats step 2- step 4, optimal assessment number
The lower corresponding defocusing degree of value is best defocus degree.
Compared with prior art, the present invention its remarkable advantage are as follows: (1) present invention judges defocus from the angle of experiment
Degree accuracy is high, best being obtained using this method for one without the system that radian fluctuation is ± 0.05rad under defocus
Fluctuating error be can reach under defocus degree less than ± 0.01rad；(2) equipment required for the present invention is simple, convenient and practical；(3)
Algorithm speed of the invention is per second up to 50 frames, meets the requirement calculated in real time, can be with real-time display, and intuitive is strong.
Detailed description of the invention
Fig. 1 is experimental provision schematic diagram of the present invention.
Fig. 2 is that the present invention is based on the two-value optical grating projection defocus degree assessment method flow charts of image difference and LM iteration.
Specific embodiment
A kind of two-value optical grating projection defocus degree assessment method based on image difference Yu LM iteration, the experiment dress of this method
Set including camera, camera lens, optical platform, computer, projector and scaling board, the appraisal procedure the following steps are included:
The fixation of step 1, experimental provision: scaling board, camera and projector are fixed on optical platform, and camera lens hang down
Directly in scaling board plane, the maximum planes direction of projector lens alignment scaling board is positioned；
The acquisition of step 2, raster image: sharp using projector to the raster image of calibration one width binaryzation of planar projective
The image of scaling board and grating is acquired with camera；
Step 3, pre-processing image data: determining the best use length, and one piece on image is chosen on the basis of the length
Rectangular area generates feature array needed for evaluating the image；
The evaluation of step 4, current defocus degree: assessing characteristics of image array, obtains assessment numerical value；
The selection of step 5, best defocus degree: changing focal length and aperture, repeats step 2- step 4, optimal assessment number
The lower corresponding defocusing degree of value is best defocus degree.
Further, in step 3 the best use length L calculation method are as follows:
The row or column in original image with spectra features is chosen, chooses therein one if being vertical grating if projection
Row chooses a column therein if being horizontal raster if what is projected；It is defaulted as vertical grating in following steps, if horizontal raster
It then only needs to exchange the narration of row and column；
Wherein, k is periodic coefficient, and π is pi, GmaxFor the maximum gradation value in initial pictures institute selection area, Gmin
For the minimum gradation value in initial pictures institute selection area, A1=Gmax-Gmin；For the selected area of original image first-order difference image
Maximum gradation value in domain,For the minimum gradation value in first-order difference image institute selection area,
Further, the rectangular area selection method in step 3 is as follows:
With the best use length L, chosen area size is the rectangular area of L × R pixel, 50≤R≤200, if image
Total line number is less than 50, then using line number as the longitudinal side length of selected rectangular area, selected rectangular area is completely in light
In the region of grid projection.
Further, the generation method of feature array is as follows in step 3:
(1) with the standard of behaviour, difference operation is carried out to each row of image, obtaining the numerical value on new images every bit is G*
(x, y)=G (x+1, y)-G (x, y), wherein 1≤x≤(L-1), 1≤y≤R；Generate the difference diagram that a width size is (L-1) × R
Picture；
(2) to arrange as benchmark, average operations are carried out to each row, the feature array ultimately generated is
Further, step 4 specifically:
Feature array is fitted using LM iterative method, objective function are as follows:
F (x)=a0+a1cos(a2x+a3)
Wherein a0, a1, a2, a3For the coefficient of objective function, the initial value of LM iterative method are as follows:
Pass through the sum of the absolute error for obtaining primitive image features array and being fitted between array
Final defocus degree evaluation value are as follows:
Wherein α is correction factor.
The following describes the present invention in detail with reference to examples.
Embodiment
As shown in Figure 1, a kind of two-value optical grating projection for being based on image difference and LM (Levenberg-Marquardt) iteration
Defocus degree assessment method, this method experimental provision include following equipment: an industrial camera 1, high-resolution lens 2, optics
Platform 4, electronic computer 6, projector 5, low reflecting rate plane reference plate and its clamping device 3.It is used in test experiments
Industrial camera pixel is 4,000,000 pixels, lens focus 35mm.As shown in Fig. 2, the appraisal procedure the following steps are included:
The fixation of step 1, experimental provision: by scaling board, camera and projector are tightly fixed on optical platform, and limitation is each
Relative displacement between part；It, should be by camera lens perpendicular to scaling board plane, and by projector lens pair during this
The maximum planes direction of fiducial mark fixed board is positioned.
The acquisition of step 2, raster image: using projector to calibration one width binaryzation of planar projective raster image, into
And utilize the image of camera acquisition scaling board and grating.
Step 3, pre-processing image data: the data line of selection image first is handled, and determines the optimal work of method
Use length.One piece of region on image is chosen on the basis of the length, generates feature array needed for evaluating the image.It is optimal
Action length L calculation method is as follows:
The row or column in original image with spectra features is chosen, chooses therein one if being vertical grating if projection
Row chooses a column therein if being horizontal raster if what is projected.Defaulted by taking vertical grating as an example in the following description, if cross
It then only needs to exchange the narration of row and column to grating.Assuming that the columns of image is C, then the length for the row chosen should control
0.2C~C, and selected part is completely in the region of optical grating projection.
Wherein, k is periodic coefficient, is typically chosen 2 (1.5~3)；π is pi；GmaxFor initial pictures institute selection area
Interior maximum gradation value, GminFor the minimum gradation value in initial pictures institute selection area, A1=Gmax-Gmin；For original image
As the maximum gradation value in first-order difference image institute selection area,For the minimum in first-order difference image institute selection area
Gray value,
Regional selection method is as follows:
First to optimal action length, chosen area size is the rectangular area of L × R (50≤R≤200), if figure
Total line number of picture is less than 50, then directly using line number as the longitudinal side length of selected rectangular area, selected part is located completely
In in the region of optical grating projection.
The generation method of feature array is as follows:
First with the standard of behaviour, difference operation is carried out to each row of image, obtaining the numerical value on new images every bit is G*
(x, y)=G (x+1, y)-G (x, y), wherein 1≤x≤(L-1), 1≤y≤R.Ultimately generate the difference that a width size is (L-1) × R
Image；And then to arrange as benchmark, average operations are carried out to each row, the feature array ultimately generated is
Wherein 1≤x≤(L-1).
The evaluation of step 4, current defocus degree: characteristics of image array is assessed using algorithm, is specifically commented
Estimate numerical value.
LM iterative method is fitted feature array, objective function are as follows:
F (x)=a0+a1cos(a2x+a3)
The wherein initial value of LM iterative method are as follows:
Pass through the sum of the absolute error for obtaining primitive image features array and being fitted between array
Final defocus degree evaluation value are as follows:
Wherein α is correction factor, and specific value can be gone out by experimental calibration.The scaling method of α is as follows:
System is fixed first, in accordance with the step 1 described in claim 1.By camera focusing to obscuring, according to six step phases
The phase reconstruction of shifting method progress scaling board plane.The phase information restored is subjected to 5 surface fittings, and is subtracted with former data
Fitting data generates error matrix F0.Acquire the variance D under current defocus degree0.Continue to adjust camera focus, fuzzy-clear
It is clear-obscure this during, discrete is sampled, 5 groups of sample size or more.The selection of α, it is only necessary to so that D and every
The evaluation of estimate P of group is positively correlated.For 8 cameras, the value of α is between 0~2.
The selection of step 5, best defocus degree: slightly changing current focus and aperture, repeats step 2- step
4, corresponding defocusing degree is the optimum position to be chosen under optimal assessment numerical value.
Claims (5)
1. a kind of two-value optical grating projection defocus degree assessment method based on image difference Yu LM iteration, which is characterized in that the party
The experimental provision of method includes camera, camera lens, optical platform, computer, projector and scaling board, and the appraisal procedure includes
Following steps:
The fixation of step 1, experimental provision: scaling board, camera and projector are fixed on optical platform, camera lens perpendicular to
The maximum planes direction of scaling board plane, projector lens alignment scaling board is positioned；
The acquisition of step 2, raster image: using projector to the raster image of calibration one width binaryzation of planar projective, phase is utilized
Machine acquires the image of scaling board and grating；
Step 3, pre-processing image data: determining the best use length, and one piece of rectangle on image is chosen on the basis of the length
Region generates feature array needed for evaluating the image；
The evaluation of step 4, current defocus degree: assessing characteristics of image array, obtains assessment numerical value；
The selection of step 5, best defocus degree: changing focal length and aperture, repeatedly step 2- step 4, under optimal assessment numerical value
Corresponding defocusing degree is best defocus degree.
2. the two-value optical grating projection defocus degree assessment method according to claim 1 based on image difference Yu LM iteration,
It is characterized in that, in step 3 the best use length L calculation method are as follows:
The row or column in original image with spectra features is chosen, chooses a line therein if being vertical grating if projection,
A column therein are chosen if being horizontal raster if what is projected；It is defaulted as vertical grating in following steps, then if horizontal raster
It only needs to exchange the narration of row and column；
Wherein, k is periodic coefficient, and π is pi, GmaxFor the maximum gradation value in initial pictures institute selection area, GminIt is first
Minimum gradation value in beginning image institute selection area, A1=Gmax-Gmin；For original image first-order difference image institute selection area
Interior maximum gradation value,For the minimum gradation value in first-order difference image institute selection area,
3. the two-value optical grating projection defocus degree assessment method according to claim 2 based on image difference Yu LM iteration,
It is characterized in that, the rectangular area selection method in step 3 is as follows:
With the best use length L, chosen area size is the rectangular area of L × R pixel, 50≤R≤200, if the head office of image
Number is less than 50, then using line number as the longitudinal side length of selected rectangular area, selected rectangular area is completely in grating throwing
In the region of shadow.
4. the two-value optical grating projection defocus degree assessment method according to claim 3 based on image difference Yu LM iteration,
It is characterized in that, the generation method of feature array is as follows in step 3:
(1) with the standard of behaviour, difference operation is carried out to each row of image, obtaining the numerical value on new images every bit is G*(x, y)
=G (x+1, y)-G (x, y), wherein 1≤x≤(L-1), 1≤y≤R；Generate the difference image that a width size is (L-1) × R；
(2) to arrange as benchmark, average operations are carried out to each row, the feature array ultimately generated is
5. the two-value optical grating projection defocus degree assessment method according to claim 4 based on image difference Yu LM iteration,
It is characterized in that, step 4 specifically:
Feature array is fitted using LM iterative method, objective function are as follows:
F (x)=a0+a1 cos(a2x+a3)
Wherein a0, a1, a2, a3For the coefficient of objective function, the initial value of LM iterative method are as follows:
a3=0
Pass through the sum of the absolute error for obtaining primitive image features array and being fitted between array
Final defocus degree evaluation value are as follows:
Wherein α is correction factor.
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