CN102620667A - Method and device for measuring pixel pitch of image sensor based on point-target image splicing technology - Google Patents
Method and device for measuring pixel pitch of image sensor based on point-target image splicing technology Download PDFInfo
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Abstract
A method and a device for measuring the pixel pitch of an image sensor based on the point-target image splicing technology, which belong to the length, width or thickness metering field included in the field of metering equipment which is characterized by using an optical method. The method includes placing the point targets in different fields of view, and performing twice imaging of the point targets; constructing linear images according to the two point-target images; searching value ranges of the pixel pitch in the frequency domain, and calculating to obtain the pixel pitch by means of the search algorithm according to the best contact ratio of the actual modulation transfer function(MTF) curve related to the pixel pitch and the theoretical MTF curve related to the pixel pitch under the condition of the least square. Sliders bearing the point targets are arranged on a first guide rail and a second guide rail, and the movement of the slider on the first guide rail matches with the movement of the slider on the second guide rail so that the point targets can be focused correctly to form images on the surface of the image sensor at the position of any field of view. The method and the device for measuring the pixel pitch of the image sensor are favorable for reducing errors among results of single measurements, so that repetition of measuring results can be increased.
Description
Technical field
Utilizing point target to belong to the employing optical means as the image sensor pixel measurement method for distance of amalgamation and device is the field that is used for gauge length, width or thickness in the metering outfit field of characteristic, relates in particular to a kind of at image sensor pixel measurement method for distance and the device of frequency domain based on two frame static point target image combination methods.
Background technology
The image sensor pixel spacing is the very important technical indicator in precision measurement field.For example; A size known target is passed through optical system imaging; Based target is as shared image sensor pixel number, and pel spacing, promptly knows the size of target picture; Be the merchant through the size and the target size of target picture at last, just can demarcate the lateral magnification of this optical system; In addition, piece image is carried out spectrum analysis, only know pel spacing, just possibly accurately obtain the frequency spectrum of this image.
Yet; The product description of a lot of imageing sensors has only provided the pixel dimension of imageing sensor, and has not provided pel spacing; Like the MV-1300UM type industrial digital camera of Shaanxi dimensional view picture, it is 5.2 μ m * 5.2 μ m that product description has only been given the size of pixel; The IR113 type non-refrigeration focal surface movement of Wuhan Gao De and for example, its pixel dimension is 25 μ m * 25 μ m, though provide fill factor, curve factor＞80% simultaneously, still can't obtain pel spacing according to a uncertain fill factor, curve factor numerical value.If the frequency spectrum that we utilize above-mentioned imageing sensor to go to demarcate the lateral magnification of optical system or obtain certain image, pel spacing must become technical bottleneck.So it is very important that the pel spacing of measurement image sensor seems.
One, image sensor pixel measurement method for distance background technology
For the measuring method of image sensor pixel spacing, what at first expect is exactly in theory, can utilize one to project to the linear image that image sensor surface and length can be known, divided by this linear image institute covered pixels number, obtains pel spacing.Under perfect condition, this method has following two characteristics:
1) pixel that line source is covered fully, its gray-scale value is as the benchmark gray-scale value.
The edge pixel that 2) can not cover fully for line source, according to the ratio of its gray-scale value and benchmark gray-scale value, judge can the cover part scale.
Yet this method but has inevitable disturbing factor, has a strong impact on the accuracy of measurement result.
1) if the pixel that covers fully is saturated; Then gray-scale value will keep 255 constant; Gray-scale value between edge pixel that can not cover fully and the complete covered pixels will no longer have proportionate relationship, and the ratio of edge pixel that line source covers is judged mistake will occur.
2) in the line source process for imaging; Be bound to the to have powerful connections influence of light, random noise and imageing sensor dark current receives the influence of these disturbing factors, can make the pixel that line source covers fully; Gray-scale value is also all inequality, will bring difficulty to the judgement of benchmark gray-scale value like this.
Though these shortcomings can increase the length of line source in theory, remedied through sharing error equally with more pixel, the length that increases line source also can be brought new problem:
1) for the big optical lens of distortion, increase the length of line source, may make the line source picture that serious deformation takes place on length, in this case, not only can not share error equally, and can make the error in judgement of number of pixels bigger on the contrary.
2) in the optical system debug process, can make imageing sensor that the target of same intensity under the different visual fields is had different responses.Increased the judgement of benchmark gray-scale value so again.
Have above-mentioned a series of problem just because of this method, therefore in actual mechanical process, this method seldom is used, and the substitute is another serial method.
In April, 2005; College of Military Engineering journal the 17th volume is published an article for No. 2 " pel spacing of measuring the ccd image acquisition system based on Joint Fourier Transformation ", and this piece article has been introduced a kind of utilization centrosymmetric two square target are carried out the method that twice Fourier transform method tried to achieve the image capturing system pel spacing.This method is centrosymmetric two square-shaped image of output on spatial light modulator at first, through the fourier lense imaging, obtain the power spectrum of this width of cloth image on the CCD surface | S (u, v) |
2, this power spectrum obtains the real power spectrum after amplifying p times through image capturing system | S ' (u ', v ') |
2To respectively | S (u, v) |
2Compose with real power | S ' (u ', v ') |
2Be presented at once more on the spatial light modulator, form images, scheme electric acquisition system once more through fourier lense and amplify, obtain respectively | S (u, v) |
2Power spectrum o (ξ, η) and | S ' (u ', v ') |
2Power spectrum o (ξ ', η '), here, o (ξ '; η ') and o (ξ η) is the center for brighter square, and symmetrical is darker relatively square pattern in the both sides, center, and o (ξ '; η ') through p after doubly amplifying be exactly o (ξ, η), therefore, o (ξ; η) shared image capturing system pixel count D be the shared image capturing system pixel count D ' of o (ξ ', η ') p doubly, so, can utilize the ratio of D and D ' to calibrate the enlargement ratio p of image capturing system; After the p value is confirmed, | S ' (u ', v ') |
2And o (ξ ', η ') can confirm in succession, just can obtain among the o (ξ ', η ') between two squares apart from d ', utilize d '/D ' to obtain the pel spacing of ccd image acquisition system at last.The shortcoming of this method is: o (ξ, η) and o (ξ ', η ') can not guarantee that all square just in time covers on the pixel of ccd image acquisition system just; And very greatly may be across two pixels; This judgement to D and D ' will bring difficulty, all occurs ± 1 error during judgement easily, thereby makes the calibration result of the enlargement ratio p of ccd image acquisition system have error; And then have influence on o (ξ '; η ') judgement of the spacing d ' of two specks in, owing to utilized d '/D ', so can make the judgement of ccd image acquisition system pel spacing have inevitable error.
In Dec, 2005, College of Military Engineering journal the 17th volume is published an article for No. 6 " the CCD pel spacing based on the circular hole Fraunhofer diffraction is demarcated ", and a kind of method of utilizing the Fraunhofer diffraction distribution plan to demarcate the CCD pel spacing introduced in this piece article.This method utilizes the directional light irradiation to place the circular hole at collimator objective focal length place, and at the Fraunhofer diffraction distribution plan of collimator objective surface formation circular hole, this distribution plan incides the picture that the CCD surface forms this Fraunhofer diffraction distribution plan through the parallel ejaculation of collimator objective.Diameter a according to circular hole; Incident light wave length λ; And collimator objective focal distance f; Can obtain central bright spot diameter L=1.22f λ/a in the circular hole Fraunhofer diffraction distribution plan, again according to the number N of the shared CCD pixel of diameter of central bright spot in the Fraunhofer diffraction distribution plan ', the pel spacing that obtains CCD is δ '=L/N '.The shortcoming of this method is: the edge that can not guarantee central bright spot just in time drops on the pixel of CCD; And very greatly may be across two pixels; This just brings difficulty to the judgement of the shared CCD number of pixels of central bright spot diameter N ' in the Fraunhofer diffraction distribution plan; Occur ± 1 error easily, make the judgement of CCD pel spacing have inevitable error.
In June, 2008; Photon journal the 37th volume is published an article for No. 6 " pel spacing that utilizes TFT-LCD pixel mechanism diffraction test ccd image acquisition system ", and a kind of principle and method of utilizing Thin Film Transistor-LCD (TFT-LCD) test ccd image acquisition system pel spacing introduced in this piece article.This method at first forms the object space signal through TFT-LCD; According to TFT-LCD pixel zone printing opacity, the lighttight characteristic in non-pixel zone; Can it be regarded as one by orthogonal two two-dimensional gratings that the cycle rectangular raster constitutes; Be placed on the front focal plane of fourier lense, then on the back focal plane of this fourier lense, can obtain the spectrum intensity distribution plan of two-dimensional grating.This frequency spectrum profile is multistage spectrum distribution form; Wherein, Areal coordinate initial point place is composed in being centered close to of zero level frequency spectrum; The distribution form of each senior frequency spectrum and width are identical with the zero level frequency spectrum, but intensity reduces rapidly with the rising of level time, according to m level frequency spectrum center to the distance of initial point do | m λ f/d|.Gather this two-dimensional grating spectrum intensity distribution plan through the ccd image acquisition system, and arrive the shared pixel count N of initial point according to m level frequency spectrum center
m, the pel spacing that can obtain the ccd image acquisition system does | m λ f/dN
m|.This method also has with the identical shortcoming of above prior art: can not guarantee that zero level frequency spectrum and m level frequency spectrum center just in time drop on the pixel of CCD, therefore, N
mCan occur equally ± 1 error, make the judgement of ccd image acquisition system pel spacing have inevitable error.In order to solve N
mThe problem that has ± 1 error has adopted a kind of method of averaging of repeatedly measuring in the literary composition, under the situation of not considering enlargement factor, the pel spacing of the ccd image acquisition system of trying to achieve is:
This method is alleviated N to a certain extent
m± 1 error problem.
In October, 2008; Photoelectric technology is used the 29th volume and is published an article for No. 5 " the CCD pel spacing based on double direction shear is interfered is demarcated ", and this piece article has been introduced and a kind ofly interfered the relativeness of two half-court widths of fringe to measure the method for ccd image acquisition system pel spacing through double direction shear.This method is through directional light irradiation wedge shape mirror W, and the reflected light on the forward and backward surface of wedge shape mirror W is because the effect of wedge shape mirror W forms the shearing of x axle forward, again through mirror M
1Reflection back transmission is crossed wedge shape mirror W and is imaged on the ccd detector, and the width of fringe of this shear interference striped is d
1=λ R/ (s+2n β R), wherein, d
1=N
1Q; Simultaneously, the transmitted light on the forward and backward surface of wedge shape mirror W is through mirror M
2Incide again after the reflection on the wedge shape mirror W, form the shearing of x axle negative sense, the width of fringe of this shear interference striped is d
2=λ R/ (s+2n β R), wherein, d
2=N
2Q.These two equations all are the equations about CCD pel spacing q, radius R, shearing displacement s, and these two equations are constituted system of equations, and the expression formula that can obtain ccd image acquisition system pel spacing is:
Wherein, λ is the wavelength of incident light wave, and n is the refractive index of wedge shape mirror W, and β is the angle of wedge of wedge shape mirror W, all can be given by calibration system; N
1, N
2Be respectively the pixel count of the adjacent shear interference ccd image sensor that width of fringe covers of the positive negative sense of x axle, through to N
1, N
2Measurement, can obtain ccd image acquisition system pel spacing q.The shortcoming of this method is: can not guarantee that adjacent stripes covers on the pixel of CCD just, therefore, N
1, N
2All can occur ± 1 error, make the judgement of ccd image acquisition system pel spacing have inevitable error.
More than the common trait of these four kinds of methods be:
1) forms a shape and the big or small figure that all can know in image sensor surface;
2) figure has tangible boundary characteristic;
3) boundary position of figure is thought in the center of graphic limit institute respective pixel.
Than desirable measuring method, the advantage of this serial of methods is:
1), and avoided through judging and the process of edge pixel can make this method can bear the influence of larger interference factor with the proportionate relationship of benchmark gray-scale value because avoided the judgement of benchmark gray-scale value;
2),, reduced for the requirement of image also in the judgement that does not influence the graphic limit position even image is in state of saturation to a certain extent.
But this method also has the problem of self:
For the judgement of number of pixels, can only be that integer is judged, the judgement of each side can exist ± error of 0.5 pixel, and two edges will exist ± error of 1 pixel, line source length is short more, and error will be big more.
Though these shortcomings can increase the length of line source in theory, remedied through sharing error equally with more pixel, the length that increases line source can be brought new problem equally:
1) for the big optical lens of distortion, increase the length of line source, may make the line source picture that serious deformation takes place on length, in this case, not only can not share error equally, and can make the error in judgement of number of pixels bigger on the contrary;
2) in the optical system debug process, can make imageing sensor that the target of same intensity under the different visual fields is had different responses.Increased the judgement of benchmark gray-scale value so again.
The drawback of existing method is for the big optical lens of distortion, to be not suitable under big visual field, measuring; And the measurement under the small field of view, therefore error is bigger between the single measurement result, makes the measurement result poor repeatability.
Two, image sensor pixel gap measuring device background technology
The field tests of international Patent classificating number G01M 11/02 optical property discloses forming of moving image modulation transfer function measurement mechanism by two patents of invention:
Patent No. ZL200810137150.1; At on 09 29th, 2010 Granted publication day; Patent of invention " dynamic target modulation transfer function measurement method and device "; Disclose a kind of moving image modulation transfer function measurement mechanism of high-accuracy multifunctional, also had the structure of light source, optical system and imageing sensor in this device, and be that light source arrives image sensor surface through optical system imaging equally.
Patent No. ZL201010252619.3; At on 01 11st, 2012 Granted publication day; Patent of invention " moving image modulation transfer function measurement mechanism " on the basis of a last disclosed device of patent, further defines the coupling scheme of optical lens in the device and the method for synchronization of measurement.
But the movement locus that these two characteristic feature of an inventions are light sources is perpendicular to the straight line of optical axis; For the optical system that the curvature of field is arranged, in the process of light source motion, will inevitably cause the out of focus of image; If these two the disclosed measurement mechanisms of invention are applied directly among the present invention; Can't overcome problem of image blurring and gradation of image value variation issue that out of focus causes, this problem can cause the locational skew of cutoff frequency, and the accuracy of measurement result is affected.
Summary of the invention
The present invention is exactly the problem that is not suitable for measurement in the small field of view scope to above-mentioned existing measuring method; And there is the problem of out of focus in existing measurement mechanism; Proposed a kind of image sensor pixel spacing frequency domain measuring method and device, this method can improve measurement result repeatability in the small field of view scope; This device can be eliminated the influence of out of focus to measurement result.
The objective of the invention is to realize like this:
Utilize the image sensor pixel measurement method for distance of point target as amalgamation, step is following:
A. imageing sensor forms images to the static point target for the first time, obtains the first frame initial static point target image, and extracts point target picture place pixel coordinate position (x
1, y
1);
Point target is moved along image sensor line or column direction, and displacement is h, and keeping point target afterwards is stationary state;
C. keep the imageing sensor time shutter constant, imageing sensor forms images to the static point target for the second time, obtains the second frame initial static point target image, and extracts point target picture place pixel coordinate position (x
2, y
2);
D. remove point target and keep the imageing sensor time shutter constant, imageing sensor forms images to background, obtains interfering picture, and with the maximal value of gray-scale value in the interfering picture as threshold value;
E. a goes on foot the first frame initial static point target image that obtains, and gray-scale value is modified to 0 less than the gray-scale value that d goes on foot the pixel of gained threshold value, obtains the first frame correction static point target image; The second frame initial static point target image that the c step obtains is modified to 0 with gray-scale value less than the gray-scale value that d goes on foot the pixel of gained threshold value, obtains the second frame correction static point target image;
F. the first frame correction static point target image and the second frame correction static point target image that e step are obtained are superimposed, and all grey scale pixel value phase adductions that two point target pictures are expert at or are listed as in the back new images of will superpose obtain new gray-scale value divided by 2; And the pixel coordinate position (x that a step is obtained
1, y
1) and the pixel coordinate position (x that obtains of c step
2, y
2) gray-scale value of line institute covered pixels replaces with new gray-scale value, obtains constructing the point spread function image;
G. f goes on foot the structure point spread function image that obtains, and the full line or the permutation information that the wire hot spot are belonged to row or row extract, and as tectonic line spread function image, this tectonic line spread function image has n element;
H. the tectonic line spread function image that g step is obtained is 1 to carry out discrete Fourier transformation and delivery by spacing; Obtain initial modulation transport function image; This initial modulation transport function image has the identical element number n of tectonic line spread function image that obtains with the g step; Be n discrete spectrum component, be respectively M according to spatial frequency order from small to large
0, M
1, M
2..., M
N-1, at this in proper order down, it is M that the initial modulation transfer function values reaches the pairing modulating transfer function value of minimal value for the first time
i, footnote sequence number is i under it;
I. according to the displacement h in b step, calculate be the optical system of β through lateral magnification after, the distance between two point target pictures is: d=h β;
J. the pairing modulation transfer function model M of the tectonic line spread function TF (f) that obtains apart from d and g step between two point target pictures that obtain according to i step=| sinc (π fd) |, the cutoff frequency that obtains g step tectonic line spread function image spectrum is: f=1/d=1/ (h β);
It is M that the cutoff frequency f of the tectonic line spread function image spectrum that k. obtains according to j step goes on foot the modulating transfer function value that obtains with h
I-1And M
I+1Pairing spatial frequency values is equal respectively, that is: f=(i-1)/(nl
Min) and f=(i+1)/(nl
Max), the pel spacing span that obtains imageing sensor is: l
Min=(i-1)/(nf)=(i-1) d/n=(i-1) h β/n and l
Max=(i+1)/(nf)=(i+1) d/n=(i+1) h β/n;
1. the pel spacing span that obtains according to the k step is divided into N part with pel spacing, is respectively l
1, l
2..., l
N, l wherein
1=l
Min, l
N=l
Max
Choose the individual data as a comparison of K in the functional value of n the modulated terminal that m. obtains in h step, this K modulating transfer function value is respectively M
K1, M
K2..., M
KK, N the pel spacing that the 1st step was obtained is updated to following formula respectively:
In the resulting N of this formula the value, the pairing pel spacing l of minimum value is institute and asks.
The above-mentioned image sensor pixel measurement method for distance that utilizes point target as amalgamation, e step, f step replace with:
E '. the second frame initial static point target image that first frame initial static point target image that a step is obtained and c step obtain is superimposed; And gray-scale value is modified to 0 less than the gray-scale value that d goes on foot the pixel of 2 times of gained threshold values in the back image that will superpose, and obtains revising superimposed image;
F '. all grey scale pixel value phase adductions that two point target pictures are expert at or are listed as in the correction superimposed image that e ' step is obtained obtain new gray-scale value divided by 2; And the pixel coordinate position (x that a step is obtained
1, y
1) and the pixel coordinate position (x that obtains of c step
2, y
2) gray-scale value of line institute covered pixels replaces with new gray-scale value, obtains constructing the point spread function image.
Utilize the image sensor pixel gap measuring device of point target as amalgamation, comprise axial first guide rail of point target, optical system, imageing sensor, slide block and vertical light, described point target arrives image sensor surface through optical system imaging; And; This device also comprises second guide rail along optical axis direction; The slide block of bearing point target is installed on first guide rail and second guide rail; Slide block matches with the motion of slide block on second guide rail in the motion on first guide rail, makes point target be imaged onto image sensor surface any all accurate Jiao of field positions.
The invention has the beneficial effects as follows:
1) measuring method of the present invention's employing is different from traditional spatial domain measuring method; This method is target with the pointolite; Point target is under the different visual fields and to its twice imaging, looks like to construct linear image, in frequency domain, seek the span of pel spacing according to two width of cloth point targets; And best according to the actual modulated transfer curve relevant and theoretical modulation transfer function curve registration under least square condition with pel spacing, utilize searching algorithm to calculate pel spacing; When this characteristic make to adopt the short and small line source of length, can obtain higher cutoff frequency, thereby share the error of cutoff frequency equally, make that the error between the single measurement result is littler, and then improve measurement result repeatability;
2) measurement mechanism of the present invention's employing comprises second guide rail along optical axis direction; The slide block of bearing point target is installed on first guide rail and second guide rail; Slide block matches with the motion of slide block on second guide rail in the motion on first guide rail, makes point target be imaged onto image sensor surface any all accurate Jiao of field positions; This characteristic makes the modulation transfer function curve that measures more near true curve, and the cutoff frequency position that actual measurement obtains is more accurate, can further reduce the error between the single measurement result, improves measurement result repeatability.
Description of drawings
Fig. 1 utilizes the image sensor pixel gap measuring device structural representation of point target as amalgamation
Fig. 2 utilizes the image sensor pixel measurement method for distance process flow diagram of point target as amalgamation
Among the figure: 1 point target, 2 optical systems, 3 imageing sensors, 4 slide blocks, 5 first guide rails, 6 second guide rails
Embodiment
Below in conjunction with accompanying drawing the specific embodiment of the invention is described in further detail.
Fig. 1 utilizes the image sensor pixel gap measuring device structural representation of point target as amalgamation; This device comprises axial first guide rail 5 of point target 1, optical system 2, imageing sensor 3, slide block 4 and vertical light, and described point target 1 is imaged onto imageing sensor 3 surfaces through optical system 2; And; This device also comprises second guide rail 6 along optical axis direction; The slide block 4 of bearing point target 1 is installed on first guide rail 5 and second guide rail 6; Slide block 4 matches with the motion of slide block 4 on second guide rail 6 in the motion on first guide rail 5, makes point target 1 be imaged onto imageing sensor 3 surfaces any all accurate Jiao of field positions; Wherein, point target 1 is the pin hole of diameter 15 μ m, and the lateral magnification of optical system 2 is 0.0557.
Utilize the image sensor pixel measurement method for distance of point target as amalgamation, process flow diagram is as shown in Figure 2, and this method step is following:
A. 3 pairs of static point targets of imageing sensor 1 imaging for the first time obtains the first frame initial static point target image, and extracts point target picture place pixel coordinate position (x
1, y
1);
Point target 1 is moved along imageing sensor 3 line directions, and displacement is h=1.526mm, keeps point target 1 to be stationary state afterwards;
C. keep 3 time shutter of imageing sensor constant, 3 pairs of static point targets of imageing sensor 1 imaging for the second time obtains the second frame initial static point target image, and extracts point target picture place pixel coordinate position (x
2, y
2);
D. remove point target 1 and keep 3 time shutter of imageing sensor constant, the imaging of the 3 pairs of backgrounds of imageing sensor obtains interfering picture, and with the maximal value of gray-scale value in the interfering picture as threshold value, this threshold value is 10;
E. a goes on foot the first frame initial static point target image that obtains, and gray-scale value is modified to 0 less than the gray-scale value that d goes on foot the pixel of gained threshold value, obtains the first frame correction static point target image; The second frame initial static point target image that the c step obtains is modified to 0 with gray-scale value less than the gray-scale value that d goes on foot the pixel of gained threshold value, obtains the second frame correction static point target image;
F. the first frame correction static point target image and the second frame correction static point target image that e step are obtained are superimposed, and all grey scale pixel value phase adductions that two point target pictures are expert in the back new images of will superpose obtain new gray-scale value divided by 2; And the pixel coordinate position (x that a step is obtained
1, y
1) and the pixel coordinate position (x that obtains of c step
2, y
2) gray-scale value of line institute covered pixels replaces with new gray-scale value, obtains constructing the point spread function image;
G. f goes on foot the structure point spread function image that obtains, and the full line information of being gone in wire hot spot place extracts, and as tectonic line spread function image, this tectonic line spread function image has n=1280 element;
H. the tectonic line spread function image that g step is obtained is 1 to carry out discrete Fourier transformation and delivery by spacing; Obtain initial modulation transport function image; This initial modulation transport function image has the identical element number n of tectonic line spread function image that obtains with the g step; Be n discrete spectrum component, be respectively M according to spatial frequency order from small to large
0, M
1, M
2..., M
N-1, at this in proper order down, it is M that the initial modulation transfer function values reaches the pairing modulating transfer function value of minimal value for the first time
i, footnote sequence number is i under it;
I. according to the displacement h in b step, calculate be the optical system 2 of β through lateral magnification after, the distance between two point target pictures is: d=h β=1.526 * 0.0557=0.085mm;
J. the pairing modulation transfer function model M of the tectonic line spread function TF (f) that obtains apart from d and g step between two point target pictures that obtain according to i step=| sinc (π fd) |, the cutoff frequency that obtains g step tectonic line spread function image spectrum is:
It is M that the cutoff frequency f of the tectonic line spread function image spectrum that k. obtains according to j step goes on foot the modulating transfer function value that obtains with h
I-1And M
I+1Pairing spatial frequency values is equal respectively, that is: f=(i-1)/(nl
Min) and f=(i+1)/(nl
Max), the pel spacing span that obtains imageing sensor 3 is: l
Min=(i-1)/(nf)=(i-1) d/n=(i-1) h β/n and l
Max=(i+1)/(nf)=(i+1) d/n=(i+1) h β/n;
L. the pel spacing span that obtains according to the k step is divided into N part with pel spacing, is respectively l
1, l
2..., l
N, l wherein
1=l
Min, l
N=l
Max
M. according to spatial frequency order from small to large, n the modulating transfer function value that the h step is obtained is depicted as a curve, chooses on this curve from M
0Begin to first maximum value, and do not comprise first minimizing all modulating transfer function values, data are compared in K conduct altogether, and this K modulating transfer function value is respectively M
K1, M
K2..., M
KK, N the pel spacing that the l step is obtained is updated to following formula respectively:
In the resulting N of this formula the value, the pairing pel spacing l of minimum value is institute and asks.
According to top thinking pel spacing has been carried out 100 times and measured, the measurement result that obtains is listed in the table below:
The above-mentioned image sensor pixel measurement method for distance that utilizes point target as amalgamation, e step, f step replace with:
E '. the second frame initial static point target image that first frame initial static point target image that a step is obtained and c step obtain is superimposed; And gray-scale value is modified to 0 less than the gray-scale value that d goes on foot the pixel of 2 times of gained threshold values in the back image that will superpose, and obtains revising superimposed image;
F '. all grey scale pixel value phase adductions that two point target pictures are expert in the correction superimposed image that e ' step is obtained obtain new gray-scale value divided by 2; And the pixel coordinate position (x that a step is obtained
1, y
1) and the pixel coordinate position (x that obtains of c step
2, y
2) gray-scale value of line institute covered pixels replaces with new gray-scale value, obtains constructing the point spread function image.
Claims (3)
1. utilize the image sensor pixel measurement method for distance of point target, it is characterized in that said method step is following as amalgamation:
A. imageing sensor forms images to the static point target for the first time, obtains the first frame initial static point target image, and extracts point target picture place pixel coordinate position (x
1, y
1);
Point target is moved along image sensor line or column direction, and displacement is h, and keeping point target afterwards is stationary state;
C. keep the imageing sensor time shutter constant, imageing sensor forms images to the static point target for the second time, obtains the second frame initial static point target image, and extracts point target picture place pixel coordinate position (x
2, y
2);
D. remove point target and keep the imageing sensor time shutter constant, imageing sensor forms images to background, obtains interfering picture, and with the maximal value of gray-scale value in the interfering picture as threshold value;
E. a goes on foot the first frame initial static point target image that obtains, and gray-scale value is modified to 0 less than the gray-scale value that d goes on foot the pixel of gained threshold value, obtains the first frame correction static point target image; The second frame initial static point target image that the c step obtains is modified to 0 with gray-scale value less than the gray-scale value that d goes on foot the pixel of gained threshold value, obtains the second frame correction static point target image;
F. the first frame correction static point target image and the second frame correction static point target image that e step are obtained are superimposed, and all grey scale pixel value phase adductions that two point target pictures are expert at or are listed as in the back new images of will superpose obtain new gray-scale value divided by 2; And the pixel coordinate position (x that a step is obtained
1, y
1) and the pixel coordinate position (x that obtains of c step
2, y
2) gray-scale value of line institute covered pixels replaces with new gray-scale value, obtains constructing the point spread function image;
G. f goes on foot the structure point spread function image that obtains, and the full line or the permutation information that the wire hot spot are belonged to row or row extract, and as tectonic line spread function image, this tectonic line spread function image has n element;
H. the tectonic line spread function image that g step is obtained is 1 to carry out discrete Fourier transformation and delivery by spacing; Obtain initial modulation transport function image; This initial modulation transport function image has the identical element number n of tectonic line spread function image that obtains with the g step; Be n discrete spectrum component, be respectively M according to spatial frequency order from small to large
0, M
1, M
2..., M
N-1, at this in proper order down, it is M that the initial modulation transfer function values reaches the pairing modulating transfer function value of minimal value for the first time
i, footnote sequence number is i under it;
I. according to the displacement h in b step, calculate be the optical system of β through lateral magnification after, the distance between two point target pictures is: d=h β;
J. the pairing modulation transfer function model M of the tectonic line spread function TF (f) that obtains apart from d and g step between two point target pictures that obtain according to i step=| sinc (π fd) |, the cutoff frequency that obtains g step tectonic line spread function image spectrum is: f=1/d=1/ (h β);
It is M that the cutoff frequency f of the tectonic line spread function image spectrum that k. obtains according to j step goes on foot the modulating transfer function value that obtains with h
I-1And M
I+1Pairing spatial frequency values is equal respectively, that is: f=(i-1)/(nl
Min) and f=(i+1)/(nl
Max), the pel spacing span that obtains imageing sensor is: l
Min=(i-1)/(nf)=(i-1) d/n=(i-1) h β/n and l
Max=(i+1)/(nf)=(i+1) d/n=(i+1) h β/n;
1. the pel spacing span that obtains according to the k step is divided into N part with pel spacing, is respectively l
1, l
2..., l
N, l wherein
1=l
Min, l
N=l
Max
Choose the individual data as a comparison of K in the functional value of n the modulated terminal that m. obtains in h step, this K modulating transfer function value is respectively M
K1, M
K2..., M
KK, N the pel spacing that the 1st step was obtained is updated to following formula respectively:
In the resulting N of this formula the value, the pairing pel spacing l of minimum value is institute and asks.
2. the image sensor pixel measurement method for distance that utilizes point target as amalgamation according to claim 1 is characterized in that e step, f go on foot and replace with:
E '. the second frame initial static point target image that first frame initial static point target image that a step is obtained and c step obtain is superimposed; And gray-scale value is modified to 0 less than the gray-scale value that d goes on foot the pixel of 2 times of gained threshold values in the back image that will superpose, and obtains revising superimposed image;
F '. all grey scale pixel value phase adductions that two point target pictures are expert at or are listed as in the correction superimposed image that e ' step is obtained obtain new gray-scale value divided by 2; And the pixel coordinate position (x that a step is obtained
1, y
1) and the pixel coordinate position (x that obtains of c step
2, y
2) gray-scale value of line institute covered pixels replaces with new gray-scale value, obtains constructing the point spread function image.
3. utilize the image sensor pixel gap measuring device of point target as amalgamation; Comprise point target (1), optical system (2), imageing sensor (3), slide block (4) and axial first guide rail of vertical light (5), described point target (1) is imaged onto imageing sensor (3) surface through optical system (2); It is characterized in that: this device also comprises second guide rail (6) along optical axis direction; The slide block (4) of bearing point target (1) is installed on first guide rail (5) and second guide rail (6); Slide block (4) matches with the motion of slide block (4) on second guide rail (6) in the motion on first guide rail (5), makes point target (1) be imaged onto imageing sensor (3) surface any all accurate Jiao of field positions.
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