CN102620671A - Method and device for measuring pixel pitches of image sensor by utilizing line light source - Google Patents

Abstract

The method and device for measuring the pixel pitch of an image sensor using a line light source belong to the field of measuring length, width or thickness in the field of measuring equipment characterized by the use of optical methods; Find the value range of the pixel pitch in the domain, and according to the best coincidence between the actual modulation transfer function curve and the theoretical modulation transfer function curve related to the pixel pitch under the least squares condition, the pixel pitch is calculated by using the search algorithm; the device is in In the plane determined by the optical axis direction of the device and the row or column direction of the image sensor, the line light source is curved, and any position on the line light source is quasi-focused and imaged on the surface of the image sensor; the pixel pitch of the image sensor is measured by using the present invention , which is beneficial to reduce the error between single measurement results, thereby improving the repeatability of measurement results.

Description

Image sensor pixel pitch measurement method and device using line light source

technical field

The method and device for measuring the pixel pitch of an image sensor using a line light source belong to the field of measuring length, width or thickness in the field of measuring equipment characterized by the use of optical methods, and in particular relate to a line light source as the target, using line in the frequency domain A measurement method and device for measuring the pixel pitch of an image sensor by using a light source image.

Background technique

Image sensor pixel pitch is a very important technical indicator in the field of precision measurement. For example, if a target with a known size is imaged through an optical system, the size of the target image can be known according to the number of pixels of the image sensor occupied by the target image and the pixel pitch, and finally the size of the target image can be compared with the target size to obtain The lateral magnification of the optical system can be calibrated; in addition, when performing spectrum analysis on an image, it is possible to accurately obtain the spectrum of the image only if the pixel pitch is known.

However, the product manuals of many image sensors only give the pixel size of the image sensor, but not the pixel pitch, such as the MV-1300UM industrial digital camera of Shaanxi Vision Image, the product manual only gives the pixel size It is 5.2μm×5.2μm; another example is Wuhan Gaode’s IR113 uncooled focal plane core, its pixel size is 25μm×25μm, although it also gives a fill factor > 80%, but it still cannot be based on an uncertain Fill factor value to get pixel pitch. If we use the above-mentioned image sensor to calibrate the lateral magnification of the optical system or obtain the spectrum of an image, the pixel pitch must become a technical bottleneck. Therefore, it is very important to measure the pixel pitch of the image sensor.

1. Background Technology of Image Sensor Pixel Pitch Measurement Method

For the measurement method of the pixel pitch of the image sensor, the first thing that comes to mind is that in theory, a linear image projected onto the surface of the image sensor and whose length is known can be divided by the number of pixels covered by the linear image to obtain the pixel pitch. Ideally, this method has the following two characteristics:

1) The gray value of the pixel completely covered by the line light source is used as the reference gray value.

2) For the edge pixels that cannot be completely covered by the line light source, the proportion of the part that can be covered is judged according to the ratio of its gray value to the reference gray value.

However, this method has inevitable interference factors, which seriously affect the accuracy of the measurement results.

1) If the fully covered pixel is saturated, the gray value will remain unchanged at 255, and the gray value between the edge pixel that cannot be completely covered and the fully covered pixel will no longer have a proportional relationship, and the edge covered by the line light source There will be errors in judging the ratio of pixels.

2) In the process of imaging the line light source, there must be background light, random noise, and dark current of the image sensor. Affected by these interference factors, the pixels completely covered by the line light source will have different gray values. , which will bring difficulties to the judgment of the reference gray value.

Although these shortcomings can theoretically increase the length of the line light source and compensate for the error by using more pixels to amortize the error, increasing the length of the line light source will also bring new problems:

1) For an optical lens with large distortion, increasing the length of the line light source may cause serious deformation of the line light source image in length. big.

2) During the debugging process of the optical system, the image sensor will have different responses to targets of the same intensity in different fields of view. This increases the judgment of the reference gray value.

It is precisely because this method has the above-mentioned series of problems, so in the actual operation process, this method is rarely used, and another series of methods are used instead.

In April 2005, the Journal of Military Engineering Academy Vol. 17 No. 2 published an article "Measurement of Pixel Pitch of CCD Image Acquisition System Based on Joint Fourier Transform". This article introduced a method of using two square targets symmetrical to the center The method of obtaining the pixel pitch of the image acquisition system by performing two Fourier transforms. In this method, two center-symmetrical square images are first output on the spatial light modulator, imaged through a Fourier lens, and the power spectrum |S(u, v)| ² of the image is obtained on the surface of the CCD, the power spectrum The actual power spectrum |S′(u′, v′ ⁾ | ² is obtained after the image acquisition system is magnified by p times; the |S(u, v)| | ² is displayed on the spatial light modulator again, imaged again by the Fourier lens and ^amplified by the electrograph acquisition system, and the power spectrum o(ξ, η) and |S′( u′, v′)| ² power spectrum o(ξ′, η′), here, both o(ξ′, η′) and o(ξ, η) are brighter squares in the center, symmetrical between the two The side is a relatively dark square pattern, and o(ξ′, η′) is o(ξ, η) after being enlarged by p times. Therefore, the number of pixels D of the image acquisition system occupied by o(ξ, η) is o( ξ', η') account for p times of the pixel number D' of the image acquisition system, so the ratio of D and D' can be used to calibrate the magnification p of the image acquisition system; after the value of p is determined, |S'(u' , v′)| ² and o(ξ′, η′) can be determined successively, and the distance d′ between the two squares in o(ξ′, η′) can be obtained, and finally the d′/D′ can be used to obtain The pixel pitch of the CCD image acquisition system. The disadvantage of this method is that neither o(ξ, η) nor o(ξ′, η′) can guarantee that the square just covers one pixel of the CCD image acquisition system, and it is very likely that it will straddle two pixels , this will bring difficulties to the judgment of D and D′, and the error of ±1 will easily appear in the judgment, so that there will be errors in the calibration result of the magnification p of the CCD image acquisition system, and then affect o(ξ′, η′ In the judgment of the distance d' of two bright spots in ), due to the use of d'/D', there will be inevitable errors in the judgment of the pixel distance of the CCD image acquisition system.

In December 2005, the Journal of the Academy of Military Engineering, Volume 17, No. 6 published an article "Calibration of CCD Pixel Pitch Based on Circular Fraunhofer Diffraction". The method of CCD pixel pitch. In this method, parallel light is used to irradiate a circular hole placed at the focal length of the collimating objective lens, and the Fraunhofer diffraction distribution pattern of the circular hole is formed on the surface of the collimating objective lens. An image of the Fraunhofer diffraction profile. According to the diameter a of the circular hole, the wavelength λ of the incident light, and the focal length f of the collimating objective lens, the diameter of the central bright spot in the Fraunhofer diffraction distribution diagram of the circular hole can be obtained L=1.22fλ/a, and then according to the Fraunhofer diffraction The diameter of the central bright spot in the distribution diagram occupies the number N' of CCD pixels, and the pixel pitch of the CCD is obtained as δ'=L/N'. The disadvantage of this method is: there is no guarantee that the edge of the central bright spot falls on one pixel of the CCD, and it is likely to span two pixels, which affects the diameter of the central bright spot in the Fraunhofer diffraction distribution diagram. The judgment of the number N' of CCD pixels occupied is difficult, and errors of ±1 are prone to occur, so that the judgment of the CCD pixel pitch has inevitable errors.

In June 2008, the Acta Photonica Sinica published an article "Using TFT-LCD Pixel Mechanism to Diffraction Test the Pixel Pitch of CCD Image Acquisition System" in Volume 37, No. 6. The principle and method of testing the pixel pitch of CCD image acquisition system. In this method, the object-side signal is first formed through the TFT-LCD. According to the characteristics of the TFT-LCD pixel area being transparent and the non-pixel area being opaque, it can be regarded as a binary system composed of two mutually perpendicular periodic rectangular gratings. If the two-dimensional grating is placed on the front focal plane of the Fourier lens, then the spectral intensity distribution map of the two-dimensional grating can be obtained on the back focal plane of the Fourier lens. The spectrum distribution diagram is a multi-level spectrum distribution form, in which the center of the zero-level spectrum is located at the origin of the spectrum surface coordinates, and the distribution form and width of each high-level spectrum are the same as the zero-level spectrum, but the intensity increases rapidly with the increase of the order Decrease, according to the distance from the center of the mth-level spectrum to the origin is |mλf/d|. The two-dimensional grating spectrum intensity distribution map is collected by the CCD image acquisition system, and according to the number N _m of pixels occupied by the m-th order spectrum center to the origin, the pixel pitch of the CCD image acquisition system can be obtained as |mλf/dN _m |. This method also has the same shortcoming as above prior art: can not guarantee that the center of the zero-order spectrum and the m-th order spectrum just falls on a pixel of the CCD, therefore, ±1 error can occur equally in N _m , makes the pixel of the CCD image acquisition system There are inevitable errors in the judgment of spacing. In order to solve the problem of ±1 error in N _m , a method of taking the average value of multiple measurements is adopted in this paper. Without considering the magnification, the obtained pixel pitch of the CCD image acquisition system is:

${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; wxya</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 6</span>}}<span\; class="notranslate">\; |</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; \&lambda;f</span>}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&lambda;\; f</span>}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; \&lambda;f</span>}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; \&lambda;f</span>}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&lambda;\; f</span>}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; \&lambda;f</span>}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}<span\; class="notranslate">\; |</span>$

This method alleviates the ±1 error problem of N _m to a certain extent.

In October 2008, the article "CCD Pixel Pitch Calibration Based on Two-way Shear Interference" was published in Volume 29 No. 5 of Photoelectric Technology Application. A method for measuring the pixel pitch of a CCD image acquisition system. In this method, the wedge mirror W is irradiated with parallel light, and the reflected light on the front and rear surfaces of the wedge mirror W forms a shear in the positive direction of the x-axis due to the action of the wedge mirror W, and then is reflected by the mirror _M1 and transmitted through the wedge mirror W to form an image On the CCD detector, the fringe width of the shear interference fringe is d ₁ =λR/(s+2nβR), where d ₁ =N ₁ q; at the same time, the transmitted light from the front and rear surfaces of the wedge mirror W passes through the mirror M ₂ After reflection, it is re-incident on the wedge mirror W, forming a shear in the negative direction of the x-axis, and the fringe width of the shear interference fringe is d ₂ =λR/(-s+2nβR), where, d ₂ =N ₂ q . Both of these two equations are equations about CCD pixel spacing q, radius R, and shear amount s. Combining these two equations into a system of equations, the expression of the pixel spacing of the CCD image acquisition system can be obtained as:

$\mathrm{<span\; class="notranslate">\; q</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; n\&beta;</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="N"\; filenames="HSA00000691844200011.png"\; state="\{\{state\}\}">N</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

Among them, λ is the wavelength of the incident light wave, n is the refractive index of _the wedge mirror W, and β is the wedge angle of the wedge mirror W, _both of which can be given by the calibration system; The number of pixels of the CCD image sensor covered by the interference fringe width can be obtained by measuring N ₁ and N ₂ to obtain the pixel spacing q of the CCD image acquisition system. The disadvantage of this method is that it cannot guarantee that the adjacent stripes just cover one pixel of the CCD. Therefore, there will be ±1 error in both N ₁ and N ₂ , which makes the judgment of the pixel pitch of the CCD image acquisition system inevitable.

The common features of the above four methods are:

1) Form a figure with known shape and size on the surface of the image sensor;

2) The graph has obvious boundary features;

3) The center position of the pixel corresponding to the graphic boundary is regarded as the boundary position of the graphic.

The advantages of this family of methods over ideal measurement methods are:

1) Because the judgment of the reference gray value is avoided, and the process of judging the edge pixels through the proportional relationship with the reference gray value is avoided, this method can withstand the influence of larger interference factors;

2) Even if the image is in a saturated state to a certain extent, it does not affect the judgment of the boundary position of the graphic, and the requirements for the image are reduced.

But this approach has its own problems:

For the judgment of the number of pixels, it can only be an integer judgment. There will be an error of ±0.5 pixels in the judgment of each side, and there will be an error of ±1 pixel in the two edges. The shorter the length of the line light source, the greater the error will be. big.

Although these shortcomings can theoretically increase the length of the line light source and compensate for the error by using more pixels to amortize the error, increasing the length of the line light source will also bring new problems:

1) For an optical lens with large distortion, increasing the length of the line light source may cause serious deformation of the line light source image in length. big;

2) During the debugging process of the optical system, the image sensor will have different responses to targets of the same intensity in different fields of view. This increases the judgment of the reference gray value.

The common disadvantage of the existing methods is that the optical lens with large distortion is not suitable for measurement in a large field of view; while the measurement in a small field of view has a large error between single measurement results, which makes the repeatability of the measurement results poor.

2. Image Sensor Pixel Pitch Measuring Device Background Technology

International Patent Classification No. G01M 11/02 In the field of testing optical properties, two invention patents disclose the composition of the moving image modulation transfer function measurement device:

Patent No. ZL200810137150.1, authorized announcement date September 29, 2010, invention patent "Modulation Transfer Function Measurement Method and Device for Dynamic Objects", discloses a high-precision and multi-functional dynamic image modulation transfer function measurement device. It also has the structure of a light source, an optical system, and an image sensor, and the light source is also imaged to the surface of the image sensor through the optical system.

Patent No. ZL201010252619.3, authorized announcement date January 11, 2012, invention patent "moving image modulation transfer function measurement device", on the basis of the device disclosed in the previous patent, it further limits the coupling method of the optical lens in the device and The synchronization method of the measurement.

However, the characteristic of these two inventions is that the movement trajectory of the light source is a straight line perpendicular to the optical axis. For an optical system with field curvature, the image will inevitably be defocused during the movement of the light source. If these two inventions are disclosed If the measuring device is directly applied to the present invention, it cannot overcome the problem of image blur caused by defocusing and the problem of image gray value change. This problem will cause a shift in the position of the cutoff frequency, which will affect the accuracy of the measurement result.

Contents of the invention

The present invention aims at the problem that the above-mentioned existing measurement method is not suitable for measurement in a small field of view, and the problem that the existing measurement device has defocus, and proposes a method and device for measuring the pixel pitch of an image sensor in the frequency domain. Improve the repeatability of measurement results within the field range; the device can eliminate the influence of defocus on measurement results.

The purpose of the present invention is achieved like this:

The method for measuring the pixel pitch of an image sensor using a line light source, the steps are as follows:

a. Place a line light source with a length of h on the object side. The direction is parallel to the row or column direction of the image sensor. Calculate the theoretical movement displacement of the line light source image on the surface of the image sensor after the line light source passes through the optical system with a lateral magnification rate β: d=h·β;

b. According to the theoretical motion displacement d obtained in step a and the line light source image spectrum model MTF(f)=|sin c(πfd)|, the cutoff frequency of the line light source image spectrum is: f=1/d;

c. The image sensor images the line light source as the initial point spread function image, and extracts the entire row or column information of the row or column where the line light source image is located, as the initial line spread function image, and the initial line spread function image has n element;

d. Remove the line light source and keep the exposure time of the image sensor unchanged. The image sensor images the background to obtain the interference image, and the maximum value of the gray value in the interference image is used as the threshold;

e. For the initial line spread function image obtained in step c, the gray value of the pixel whose gray value is smaller than the threshold obtained in step d is corrected to 0 to obtain a corrected line spread function image, which has the same The same number of elements n as the initial line spread function image obtained in the first step;

f. Carry out discrete Fourier transform and modulo the modified line spread function image obtained in step e with a pitch of 1 to obtain an initial modulation transfer function image, which has the same initial line extension obtained in step c The number n of the same elements in the function image, that is, n discrete spectral components, are respectively M ₀ , M ₁ , M ₂ , ..., M _n-1 in the order of spatial frequency from small to large. In this order, the initial The modulation transfer function value corresponding to the modulation transfer function value reaching the minimum value for the first time is M _i , and its subscript number is i;

g. according to the cut-off frequency value f obtained in the b step and the modulation transfer function value obtained in the f step, the corresponding spatial frequency frequency values of M _i-1 and M _i+1 are equal respectively, namely: f=(i-1 )/(nl _min ) and f=(i+1)/(nl _max ), the value range of the pixel pitch of the image sensor is: l _min =(i-1)/(nf)=(i-1)d /n=(i-1)hβ/n and _lmax =(i+1)/(nf)=(i+1)d/n=(i+1)hβ/n;

h. According to the value range of the pixel pitch obtained in step g, divide the pixel pitch into N parts on average, namely l ₁ , l ₂ , ..., l _N , where l ₁ =l _min , l _N =l _max ;

该公式所得到的N个值中，最小值所对应的像素间距l即为所求。i. Select K from the n modulation transfer function values obtained in step f as comparison data, and these K modulation transfer function values are M _K1 , M _K2 , ..., M _KK respectively, and the obtained in step h The N pixel pitches of are substituted into the following formulas:

Among the N values obtained by this formula, the pixel spacing l corresponding to the minimum value is the desired value.

In the method for measuring the pixel pitch of an image sensor using a line light source, step c, step d, and step e are replaced by:

c'. The image sensor images the line light source as the initial point spread function image;

d'. Remove the line light source and keep the exposure time of the image sensor unchanged, the image sensor images the background, obtains the interference image, and uses the maximum value of the gray value in the interference image as the threshold;

e'. The initial point spread function image obtained in step c', the gray value of the pixel whose gray value is smaller than the threshold obtained in step d' is corrected to 0, and the entire row or column of the row or column where the line light source image is located The information is extracted to obtain the corrected line spread function image, and the corrected line spread function image has the same element number n as the initial line spread function image obtained in step c.

An image sensor pixel pitch measuring device utilizing a line light source, comprising a line light source, an optical system, and an image sensor, the line light source is imaged to the surface of the image sensor through the optical system, and, in the direction of the optical axis of the device and the row or column direction of the image sensor In the determined plane, the line light source is curved, and any position on the line light source is quasi-focused and imaged on the surface of the image sensor.

The beneficial effects of the present invention are:

1) The measurement method used in the present invention is different from the traditional spatial measurement method. This method takes the line light source as the target to obtain a linear image, searches for the value range of the pixel pitch in the frequency domain, and according to the actual modulation transfer function related to the pixel pitch The coincidence degree between the curve and the theoretical modulation transfer function curve is the best under the condition of least squares, and the pixel spacing is calculated by using the search algorithm; this feature makes it possible to obtain a higher cutoff frequency when using a short-length line light source, thereby amortizing the cutoff frequency Error, making the error between single measurement results smaller, thereby improving the repeatability of measurement results;

2) In the measuring device adopted by the present invention, in the plane determined by the optical axis direction of the device and the row or column direction of the image sensor, the line light source is curved, and any position on the line light source is quasi-focused and imaged on the surface of the image sensor ; This feature makes the measured modulation transfer function curve closer to the real curve, and the cutoff frequency position obtained by actual measurement is more accurate, which can further reduce the error between single measurement results and improve the repeatability of measurement results.

Description of drawings

Figure 1 is a schematic structural diagram of an image sensor pixel pitch measurement device using a line light source

Figure 2 is a plane light path diagram of an image sensor pixel pitch measurement device using a line light source

Fig. 3 is a flow chart of a method for measuring the pixel pitch of an image sensor using a line light source

In the figure: 1 line light source 2 optical system 3 image sensor

Detailed ways

The specific embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Fig. 1 is a schematic structural diagram of an image sensor pixel pitch measuring device utilizing a line light source, and its planar optical path diagram is shown in Fig. 2; the device includes a line light source 1, an optical system 2, and an image sensor 3, and the line light source 1 passes through the optical system 2 is imaged on the surface of the image sensor 3, and in the plane determined by the optical axis direction of the device and the row direction of the image sensor 3, the line light source 1 is in a curved shape, and any position on the line light source 1 can be imaged in quasi-focus The surface of the image sensor 3; wherein, the lateral length of the line light source 1 is 1.526 mm, and the lateral magnification of the optical system 2 is 0.0557.

The method for measuring the pixel pitch of an image sensor using a line light source, the flow chart is shown in Figure 3, and the steps of the method are as follows:

a. Place a line light source 1 with a length of h=1.526mm on the object side, and its direction is parallel to the direction of the image sensor 3 rows. After calculating the line light source 1 passes through the optical system 2 with a lateral magnification rate of β=0.0557, the image of the line light source on the image sensor 3 The theoretical motion displacement of the surface is:

d=h·β=1.526×0.0557=0.085mm;

b. According to the theoretical motion displacement d=0.085mm obtained in step a and the line light source image spectrum model MTF(f)=|sin c(πfd)|, the cutoff frequency of the line light source image spectrum is obtained as:

$\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; \&beta;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 0.085</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 11.76471</span>}\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; mm</span>}<span\; class="notranslate">\; ;</span>$

c. The image sensor 3 images the line light source 1 as an initial point spread function image, and extracts the entire line information of the line where the line light source image is located, as an initial line spread function image, and the initial line spread function image has n=1280 element;

d. Remove the line light source 1 and keep the exposure time of the image sensor 3 unchanged. The image sensor 3 images the background to obtain an interference image, and the maximum value of the gray value in the interference image is used as a threshold value, and the threshold value is 10;

e. For the initial line spread function image obtained in step c, the gray value of the pixel whose gray value is smaller than the threshold obtained in step d is corrected to 0 to obtain a corrected line spread function image, which has the same The same element number n=1280 of the initial line spread function image that step obtains;

f. Carry out discrete Fourier transform and modulo the modified line spread function image obtained in step e with a pitch of 1 to obtain an initial modulation transfer function image, which has the same initial line extension obtained in step c The number of the same elements in the function image is n=1280, that is, 1280 discrete spectral components, which are respectively M ₀ , M ₁ , M ₂ , ..., M _n-1 in the order of spatial frequency from small to large, in this order , the MTF value corresponding to the initial MTF value reaching the minimum value for the first time is M _i , and its subscript number is i;

g. According to the cut-off frequency value f=11.7647lp/mm obtained in the b step and the modulation transfer function value obtained in the f step, the corresponding spatial frequency frequency values of M _i-1 and M _i+1 are respectively equal, namely: f =(i-1)/(nl _min ) and f=(i+1)/(nl _max ), the value range of the pixel pitch of the image sensor is: l _min =(i-1)/(nf)=( i-1)d/n=(i-1)hβ/n and _lmax =(i+1)/(nf)=(i+1)d/n=(i+1)hβ/n;

h. According to the value range of the pixel pitch obtained in step g, divide the pixel pitch into N parts on average, namely l ₁ , l ₂ , ..., l _N , where l ₁ =l _min , l _N =l _max ;

该公式所得到的N个值中，最小值所对应的像素间距l即为所求。i. According to the order of spatial frequency from small to large, draw the n modulation transfer function values obtained in step f into a curve, and select this curve from M ₀ to the first maximum value, and does not include the first pole All the modulation transfer function values of small values, a total of K are used as comparison data, these K modulation transfer function values are M _K1 , M _K2 , ..., M _KK respectively, and the N pixel spacings obtained in the hth step are respectively Substitute into the following formula:

Among the N values obtained by this formula, the pixel spacing l corresponding to the minimum value is the desired value.

According to the above ideas, the pixel pitch was measured 100 times, and the obtained measurement results are listed in the following table:

In the method for measuring the pixel pitch of an image sensor using a line light source, step c, step d, and step e are replaced by:

c'. The image sensor 3 images the line light source 1 as an initial point spread function image;

d'. Remove the line light source 1 and keep the exposure time of the image sensor 3 unchanged. The image sensor 3 images the background to obtain an interference image, and the maximum value of the gray value in the interference image is used as a threshold value, and the threshold value is 10;

e'. From the initial point spread function image obtained in step c', the gray value of the pixel whose gray value is smaller than the threshold value obtained in step d' is corrected to 0, and the entire row information of the row where the line light source image is located is extracted, The corrected line spread function image is obtained, and the corrected line spread function image has the same number of elements n=1280 as the initial line spread function image obtained in step c.

Claims (3)

1. utilize the image sensor pixel measurement method for distance of line source, it is characterized in that said method step is following:

A. placing length at object space is the line source of h, and direction is parallel with image sensor line or column direction, and after the calculating line source was the optical system of β through lateral magnification, the line source picture in the theory movement displacement of image sensor surface was: d=h β;

B. the theory movement displacement d that obtains according to a step and line source picture frequency spectrum model MTF (f)=| sin c (π fd) |, obtain the cutoff frequency that the line source picture frequency composes and be: f=1/d;

C. imageing sensor forms images to line source, as initial point spread function image, and full line or the permutation information that the line source picture is expert at or is listed as is extracted, and as initial line spread function image, this initial line spread function image has n element;

D. remove line source 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. c goes on foot the initial line spread function image that obtains; Gray-scale value is modified to 0 less than the gray-scale value that d goes on foot the pixel of gained threshold value; Obtain modified line spread function image, this modified line spread function image has the identical element number n of initial line spread function image that obtains with the c step;

F. the modified line spread function image that e 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 initial line spread function image that obtains with the c 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;

G. it is M that the cutoff frequency value f that obtains according to b step goes on foot the modulating transfer function value that obtains with f _I-1And M _I+1Pairing spatial frequency 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;

H. the pel spacing span that obtains according to the g step is divided into N part with pel spacing, is respectively l ₁, l ₂..., l _N, wherein, l ₁=l _Min, l _N=l _Max

I. go on foot at f and choose K in n the modulating transfer function value that obtains as the comparison data, this K modulating transfer function value is respectively M _K1, M _K2..., M _KK, N the pel spacing that the h 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.

2. the image sensor pixel measurement method for distance that utilizes line source according to claim 1 is characterized in that c step, d step, e go on foot and replace with:

C '. imageing sensor forms images to line source, as initial point spread function image;

D '. remove line source 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 '. the initial point spread function image that the c ' step obtains; Gray-scale value is modified to 0 less than the gray-scale value that d ' goes on foot the pixel of gained threshold value; And full line or the permutation information that the line source picture is expert at or is listed as extracted; Obtain modified line spread function image, this modified line spread function image has the identical element number n of initial line spread function image that obtains with the c step.

3. utilize the image sensor pixel gap measuring device of line source; Comprise line source (1), optical system (2), imageing sensor (3); Described line source (1) is imaged onto imageing sensor (3) surface through optical system (2); It is characterized in that: in this device optical axis direction and imageing sensor (3) row or the determined plane of column direction, line source (1) is bending, and last accurate Jiao in optional position of described line source (1) is imaged onto imageing sensor (3) surface.

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