CN106842496B - The method of automatic adjustment focus based on frequency domain comparison method - Google Patents
The method of automatic adjustment focus based on frequency domain comparison method Download PDFInfo
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B7/00—Mountings, adjusting means, or light-tight connections, for optical elements
- G02B7/28—Systems for automatic generation of focusing signals
- G02B7/36—Systems for automatic generation of focusing signals using image sharpness techniques, e.g. image processing techniques for generating autofocus signals
- G02B7/365—Systems for automatic generation of focusing signals using image sharpness techniques, e.g. image processing techniques for generating autofocus signals by analysis of the spatial frequency components of the image
Abstract
The present invention relates to a kind of methods of automatic adjustment focus based on frequency domain comparison method, including following procedure: computer controlled machine tool stretches lens barrel, adjust digital camera, or imaging non-spherical lens, or the position of microcobjective, flexible lens barrel carries out telescopic moving on one side, and camera is shot on one side, obtains K width image data I0,…,Ii,…,Ij,…,Ik‑1, in the telescopic location for the mechanical lens barrel for obtaining the when of being focused by series of computation, the mechanical lens barrel of control, which stretches, can be realized auto-focusing to the position.Pass through the comparison and analysis of frequency components, picture noise be can be avoided to automatic focal adjustments precision bring adverse effect, the automatic focal adjustments being more suitable to transmission imaging, especially for capilary inside human skin in noninvasive situation, its shape and distribution have periodically, it is become apparent in the feature of frequency domain, therefore automatic focal adjustments of the invention are more accurate.In the operating aspect of device, this method is easier, is easy to actually use.
Description
Technical field
The present invention relates to field of image processings, specifically the method for the automatic adjustment focus based on frequency domain comparison method.
Background technique
Micro mirror head system and camera etc. may be implemented the acquisition of image, but image in collection process due to focus pair
The image that inaccurate problem will lead to acquisition is smudgy, and the meaning of Image Acquisition is not achieved.Therefore, being adjusted to for focus closes weight
It wants.
Focus is adjusted in order to facilitate user, improves the service efficiency of equipment, the Telescopic mirror of mechanical braking is added in a device
Cylinder, user control the flexible to adjust the distance between microlens system and camera of mechanical lens barrel by adjusting rocking bar, or
Person adjusts the distance between microcobjective and the non-spherical lens for imaging.Although the flexible lens barrel of mechanical braking can be one
Determine the complexity for reducing equipment focusing in degree, but be still difficult where confirming focus without the user of microexamination experience,
Automatic focal adjustments algorithm is just needed to calculate optimal focus position under such circumstances, to automatically control mechanical Telescopic mirror cylinder
Complete the auto-focusing process of equipment.
Currently, the method for automatic adjustment focus is broadly divided into two major classes, the automatic adjustment of active and passive type.Active coke
Point adjusting method need to install in equipment infrared ray perhaps ultrasonic transmitter-receiver using infrared ray or ultrasonic distance measurement method,
Actively measurement is observed the distance of object, according to the distance of calculating, automatically adjusts each eyeglass in lens system by mechanical device
Position, realize the automatic focal adjustments of equipment.Although active focus adjusting method focusing precision is higher, but needs
The hardware device for being simply possible to use in focusing is added in equipment, is unfavorable for the cost effective of device product and miniaturization.
Passive type focus adjusting method is the imaging directly received using equipment, using image processing techniques, automatic point
Be observed the clarity of object in analysis imaging, calculate the lens location of clearest imaging automatically, realize equipment from oving foci tune
Section.The most commonly used in the method for image processing and analyzing clarity is phase method and contrast method.Auto-focusing is utilized in phase method
Inductor realizes that auto-focusing is separated in a device with imaging optical system, and auto-focusing inductor is to being observed object
The phase pushing figure of picture is detected, and the smallest imaging lens position of offset is focusing position.Auto-focusing incudes body
Product is small, is easy to the miniaturization of equipment, but add additional equipment cost, is unfavorable for the cost effective of equipment.Contrast rule
It is to arrive continuously shot images out of focus again to focusing by out of focus, is detected in imaging automatically using image procossing and be observed object
Contour edge clarity is come the auto-focusing realized.Contrast method does not need additionally to increase the dedicated unit for being used for auto-focusing,
Conducive to the cost effective of equipment and miniaturization.In the automatic focal adjustments method of existing picture contrast, La Pula is utilized mostly
The Edge-Detection Algorithms such as this image filter realize the automatic detection of clarity, these image processing algorithms are calculating edge
It is also very sensitive to noise present in image while clarity, thus for example through surface to interior of articles carry out at
In the biggish situations of picture noises such as picture, it can not achieve accurate automatic focal adjustments.
Summary of the invention
In view of the above deficiencies, the present invention provides a kind of method of automatic adjustment focus based on frequency domain comparison method.
To achieve the above object, technical program of the present invention lies in the sides of the automatic adjustment focus based on frequency domain comparison method
Method, it is characterised in that: including following procedure:
Computer controlled machine tool stretches lens barrel, adjusts digital camera, or imaging non-spherical lens or microcobjective
Position, flexible lens barrel carries out telescopic moving on one side, and camera is shot on one side, obtains K width image data I0,…,i,…
,j,…,K-1, discrete Fourier transform is carried out to the horizontally or vertically ingredient of every piece image, the data after Fourier transformationIt is indicated with formula 1:
Wherein,Indicate the horizontally or vertically ingredient of the y row/column of the i-th width photographs, the unit of i is width；N is
Image laterally/longitudinal number of pixels, unit pixel, x be image laterally/longitudinal coordinate, y is that image is longitudinal/lateral
Coordinate, unit pixel, u are image data frequency domain coordinates, unit Hz；
It converts above-mentioned transformation results to using dB as the energy frequency spectrum of numerical value unit, then average meter is carried out to energy frequency spectrum
Calculation obtains the horizontal/vertical energy frequency spectrum of the image, that is, the frequency components of image, with Gi(u) [dB] is indicated, calculation formula
It is as follows:
In image, distance d (G between the i-th width image and the horizontal/vertical frequency components of jth width imagei,Gj) multiply using two it is flat
Mean square root acquires, as shown in Equation 4:
Wherein, d indicates that the frequency domain distance between two images, unit are [dB], Gi,GjRespectively the frequency domain of two images at
Point, unit is [dB]；
Theoretically, when the fog-level of two images is identical, that is, focal point position distance it is identical when, frequency domain distance
It is 0, in this case, formula 5 can be obtained according to formula 4:
Due to [Gi(u)-Gj(u)]2>=0, therefore:
(subscript j indicates the position of image, and unit is width；J in formula indicates complex symbol)
Because when shooting image, moving digital camera on one side, or non-spherical lens or microcobjective is imaged, one
Side shooting, so, the position of every piece image in image group, corresponding digital camera, or imaging non-spherical lens, or
The position of microcobjective namely the telescopic location of mechanical-stretching lens barrel, according to formula 6 it is found that two identical with focusing position non-
Focus image, they meet functional relation shown in formula 7 in the relationship on the telescopic location of mechanical-stretching lens barrel:
According to geometric optical theory, the image that non-focusing generates is fuzzy to be considered as having carried out low pass Gauss to focus image
Filtering processing, therefore the function in formula 7 can approximately see Gaussian function as, as shown in Equation 8:
Here, m indicate mechanical-stretching lens barrel telescopic location, unit be μm, mcIndicate the center of Gaussian function, i.e.,
Focusing position, unit are μm that K indicates that the number of shooting image, unit are width, and σ indicates a constant parameter about camera lens；
Absolute value and natural logrithm exploitation are carried out to formula 8, formula 9 can be obtained:
The calculating substrate of formula 9 is changed to 10, formula 9 can be changed to the form of formula 10:
According to formula 10, the function in formula 7 about m is obtained, as shown in Equation 11:
|fu(m) |=log | Fu(m) |=am2+ bm+c formula 11
It brings formula 11 into formula 7, can obtain:
Therefore, by the comparison to image frequency domain, available following two minimum:
According to formula 13, two minimums respectively represent two straight lines on plane coordinates, and the intersecting point coordinate of two straight lines is just
It is unique minimum, this unique minimum, the telescopic location of machinery lens barrel when being exactly the required focusing obtained；
It can be calculated the parameter of two straight lines in formula 13 by the minimum value line by line to 2-D data, then to two straight lines
Intersection point solution is carried out, horizontal axis/ordinate of orthogonal axes value is exactly the telescopic location of machinery lens barrel when focusing；
The mechanical lens barrel of control, which stretches, can be realized auto-focusing to the position.
The present invention also provides a kind of methods for carrying out auto-focusing using this calculation method, include the following steps:
(1) user controls the flexible of mechanical lens barrel using rocking bar, adjusts imaging module, imaging unit or lens unit
Focusing coarse adjustment is completed in position；
(2) user sends auto-focusing instruction to computer by rocking bar and other command devices；
(3) computer receives instruction, starts auto-focusing；
(4) computer controlled machine tool lens barrel, according to upward/lower movement of preset range, is reached pre- centered on current location
If stopping movement behind position；Camera start recording image, at the same mechanical lens barrel start using position after stopping as starting point to
Lower/upper movement；Mechanical lens barrel moves on one side, and camera records image on one side, and the image of record is stored in memory or hard disk
In memory；
(5) after shooting, computer reads image information, handles image information using frequency domain comparison method, obtains RMS points
Butut；
(6) computer uses algorithm, the calculated minimum point line by line in RMS distribution map, and connects these points and obtain two
The straight line of intersection；
(7) computer uses algorithm, calculates the intersecting point coordinate for acquiring the straight line of two intersections, utilizes RMS distribution map coordinate
The transformation between coordinate is acted to mechanical lens barrel, telescopic location when calculating machine lens barrel is focused；
(8) computer controls flexible lens barrel and is moved on the above position for calculating and acquiring, and completes auto-focusing.
The beneficial effects of the present invention are: using the method for the automatic adjustment focus of passive type, it is not required to dedicated focus tune
Regulating device is easy to devices with low cost and miniaturization.Relative to the generic contrast method using Image Edge-Detection, pass through frequency
The comparison and analysis of domain ingredient can be avoided picture noise to automatic focal adjustments precision bring adverse effect, be more suitable
To the automatic focal adjustments of transmission imaging, especially for capilary, shape and distribution inside human skin in noninvasive situation
It with periodicity, is become apparent in the feature of frequency domain, therefore automatic focal adjustments of the invention are more accurate.In the operation of device
Aspect, this method is easier, is easy to actually use.
Detailed description of the invention
Fig. 1 is frequency domain distance (frequency spectrum RMS) numeric distribution figure.
Specific embodiment
The present invention will be further described combined with specific embodiments below.
The method of automatic adjustment focus based on frequency domain comparison method, it is characterised in that: including following procedure:
Computer controlled machine tool stretches lens barrel, adjusts digital camera, or imaging non-spherical lens or microcobjective
Position, flexible lens barrel carries out telescopic moving on one side, and camera is shot on one side, obtains K width image data I0,…,i,…
,j,…,K-1, discrete Fourier transform is carried out to the horizontally or vertically ingredient of every piece image, the data after Fourier transformationIt is indicated with formula 1:
Wherein,Indicate the horizontally or vertically ingredient of the y row/column of the i-th width photographs, the unit of i is width；N is
Image laterally/longitudinal number of pixels, unit pixel, x be image laterally/longitudinal coordinate, y is that image is longitudinal/lateral
Coordinate, unit pixel, u are image data frequency domain coordinates, unit Hz；
It converts above-mentioned transformation results to using dB as the energy frequency spectrum of numerical value unit, then average meter is carried out to energy frequency spectrum
Calculation obtains the horizontal/vertical energy frequency spectrum of the image, that is, the frequency components of image, with Gi(u) [dB] is indicated, calculation formula
It is as follows:
In image, distance d (G between the i-th width image and the horizontal/vertical frequency components of jth width imagei,Gj) multiply using two it is flat
Mean square root acquires, as shown in Equation 4:
Wherein, d indicates that the frequency domain distance between two images, unit are [dB], Gi,GjRespectively the frequency domain of two images at
Point, unit is [dB]；
Theoretically, when the fog-level of two images is identical, that is, focal point position distance it is identical when, frequency domain distance
It is 0, in this case, formula 5 can be obtained according to formula 4:
Due to [Gi(u)-Gj(u)]2>=0, therefore:
(subscript j indicates the position of image, and unit is width；J in formula indicates complex symbol)；
Because when shooting image, moving digital camera on one side, or non-spherical lens or microcobjective is imaged, one
Side shooting, so, the position of every piece image in image group, corresponding digital camera, or imaging non-spherical lens, or
The position of microcobjective namely the telescopic location of mechanical-stretching lens barrel, according to formula 6 it is found that two identical with focusing position non-
Focus image, they meet functional relation shown in formula 7 in the relationship on the telescopic location of mechanical-stretching lens barrel:
According to geometric optical theory, the image that non-focusing generates is fuzzy to be considered as having carried out low pass Gauss to focus image
Filtering processing, therefore the function in formula 7 can approximately see Gaussian function as, as shown in Equation 8:
Here, i indicate mechanical-stretching lens barrel telescopic location, unit be μm, icIndicate the center of Gaussian function, i.e.,
Focusing position, unit are μm that K indicates that the number of shooting image, unit are width, σ indicate one about camera lens constant parameter；
Absolute value and natural logrithm exploitation are carried out to formula 8, formula 9 can be obtained:
The calculating substrate of formula 9 is changed to 10, formula 9 can be changed to the form of formula 10:
According to formula 10, the function in formula 7 about i is obtained, as shown in Equation 11:
|fu(i) |=log | Fu(i) |=ai2+ bi+c formula 11
It brings formula 11 into formula 7, can obtain:
Therefore, by the comparison to image frequency domain, available following two minimum:
According to formula 13, two minimums respectively represent two straight lines on plane coordinates, and the intersecting point coordinate of two straight lines is just
It is unique minimum, this unique minimum, the telescopic location of machinery lens barrel when being exactly the required focusing obtained；
It can be calculated the parameter of two straight lines in formula 13 by the minimum value line by line to 2-D data, then to two straight lines
Intersection point solution is carried out, horizontal axis/ordinate of orthogonal axes value is exactly the telescopic location of machinery lens barrel when focusing；
The mechanical lens barrel of control, which stretches, can be realized auto-focusing to the position.
The method that this calculation method carries out auto-focusing, includes the following steps:
(1) user controls the flexible of mechanical lens barrel using rocking bar, adjusts imaging module, imaging unit or lens unit
Focusing coarse adjustment is completed in position；
(2) user sends auto-focusing instruction to computer by rocking bar and other command devices；
(3) computer receives instruction, starts auto-focusing；
(4) computer controlled machine tool lens barrel, according to upward/lower movement of preset range, is reached pre- centered on current location
If stopping movement behind position；Camera start recording image, at the same mechanical lens barrel start using position after stopping as starting point to
Lower/upper movement；Mechanical lens barrel moves on one side, and camera records image on one side, and the image of record is stored in memory or hard disk
In memory；
(5) after shooting, computer reads image information, handles image information using frequency domain comparison method, obtains RMS points
Butut；
(6) computer uses algorithm, the calculated minimum point line by line in RMS distribution map, and connects these points and obtain two
The straight line of intersection；
(7) computer uses algorithm, calculates the intersecting point coordinate for acquiring the straight line of two intersections, utilizes RMS distribution map coordinate
The transformation between coordinate is acted to mechanical lens barrel, telescopic location when calculating machine lens barrel is focused；
(8) computer controls flexible lens barrel and is moved on the above position for calculating and acquiring, and completes auto-focusing.
Wherein, the horizontal axis in Fig. 1 indicates the image i for needing to be compared by frequency domain, and unit is width, and the longitudinal axis indicates what frequency domain compared
Sample image j, unit are width.Brightness expression frequency domain distance in figure, that is, the size of frequency spectrum RMS value, brighter value, also
It is the white portion in image, frequency domain illustrates that the similarity of image i at this moment and image j are lower apart from larger.Darker value,
Black portions namely in image, frequency domain distance is smaller, illustrates that the similarity of image i at this moment and image j are higher.Because burnt
Image at point position is relatively clear, minimum with the image similarity of other positions, so two slanting similar according to formula 13
The intersection point for spending higher black region is exactly required focal position.
Claims (2)
1. the method for the automatic adjustment focus based on frequency domain comparison method, it is characterised in that: including following procedure:
Computer controlled machine tool stretches lens barrel, adjusts digital camera or the position of non-spherical lens or microcobjective is imaged, stretch
Lens barrel carries out telescopic moving on one side, and camera is shot on one side, obtains K width image data I0,…,Ii,…,Ij,…,IK-1,
Discrete Fourier transform is carried out to the horizontally or vertically ingredient of every piece image, the data after Fourier transformationWith 1 table of formula
Show:
Wherein,Indicate the horizontally or vertically ingredient of the y row/column of the i-th width photographs, the unit of i is width；N is image
Laterally/longitudinal direction number of pixels, coordinate unit pixel, x lateral/longitudinal for image, y are image longitudinal direction/transverse direction seat
Mark, unit pixel, u are image data frequency domain coordinates, unit Hz；
It converts above-mentioned transformation results to using dB as the energy frequency spectrum of numerical value unit, then average computation is carried out to energy frequency spectrum and is obtained
To the horizontal/vertical energy frequency spectrum of the image, that is, the frequency components of image, with Gi(u) [dB] is indicated, calculation formula is as follows
It is shown:
In image, distance d (G between the i-th width image and the horizontal/vertical frequency components of jth width imagei,Gj) multiply using two and averagely put down
Root acquires, as shown in Equation 4:
Wherein, d indicates that the frequency domain distance between two images, unit are [dB], Gi,GjThe respectively frequency components of two images, it is single
Position is [dB]；
Theoretically, when the fog-level of two images is identical, that is, focal point position distance it is identical when, frequency domain distance is 0,
In this case, formula 5 can be obtained according to formula 4:
Due to [Gi(u)-Gj(u)]2>=0, therefore:
Wherein, subscript j indicates the position of image, and unit is width；J in formula indicates complex symbol；
Because when shooting image, moving digital camera or imaging non-spherical lens or microcobjective on one side, shooting on one side, so,
The position of every piece image in image group, corresponding digital camera, or the position of imaging non-spherical lens or microcobjective
It sets namely the telescopic location of mechanical-stretching lens barrel, according to formula 6 it is found that two non-focus images identical with focusing position, they
Meet functional relation shown in formula 7 in the relationship on the telescopic location of mechanical-stretching lens barrel:
|fu(m) |=| fu(n) | formula 7
|fu(m) |=log | Fu(m)|
|fu(n) |=log | Fu(n)|
According to geometric optical theory, the image that non-focusing generates is fuzzy to be considered as having carried out low pass gaussian filtering to focus image
Processing, therefore the function in formula 7 can approximately see Gaussian function as, as shown in Equation 8:
Here, m indicate mechanical-stretching lens barrel telescopic location, unit be μm, mcThe center for indicating Gaussian function, that is, focus
Position, unit are μm that K indicates that the number of shooting image, unit are width, and σ indicates a constant parameter about camera lens；
Absolute value and natural logrithm exploitation are carried out to formula 8, formula 9 can be obtained:
The calculating substrate of formula 9 is changed to 10, formula 9 can be changed to the form of formula 10:
According to formula 10, the function in formula 7 about m is obtained, as shown in Equation 11:
|fu(m) |=log | Fu(m) |=am2+ bm+c formula 11
It brings formula 11 into formula 7, can obtain:
Therefore, by the comparison to image frequency domain, available following two minimum:
According to formula 13, two minimums respectively represent two straight lines on plane coordinates, and the intersecting point coordinate of two straight lines is exactly only
One minimum, this unique minimum, the telescopic location of machinery lens barrel when being exactly the required focusing obtained；
It can be calculated the parameter of two straight lines in formula 13 by the minimum value line by line to 2-D data, then two straight lines carried out
Intersection point solves, and horizontal axis/ordinate of orthogonal axes value is exactly the telescopic location of machinery lens barrel when focusing；
The mechanical lens barrel of control, which stretches, can be realized auto-focusing to the position.
2. a kind of method for carrying out auto-focusing using the method as described in claim 1, it is characterised in that: including walking as follows
It is rapid:
(1) user controls the flexible of mechanical lens barrel, the position of adjustment imaging unit, imaging unit or lens unit using rocking bar
It sets, completes focusing coarse adjustment；
(2) user sends auto-focusing instruction to computer by rocking bar and other command devices, and computer receives instruction, starts
Auto-focusing；
(3) computer controlled machine tool lens barrel, according to upward/lower movement of preset range, reaches default position centered on current location
Postpone stopping movement；Camera start recording image, while mechanical lens barrel starts using position after stopping to be starting point to lower/upper
It is mobile；Mechanical lens barrel moves on one side, and camera records image on one side, and the image of record is stored in the memory of memory or hard disk
In；
(4) after shooting, computer reads image information, handles image information using frequency domain comparison method, obtains RMS distribution
Figure；
(5) computer uses algorithm, the calculated minimum point line by line in RMS distribution map, and connects these points and obtain two intersections
Straight line；
(6) computer uses algorithm, calculates the intersecting point coordinate for acquiring the straight line of two intersections, utilizes RMS distribution map coordinate to machine
Tool lens barrel acts the transformation between coordinate, telescopic location when calculating machine lens barrel is focused；
(7) computer controls flexible lens barrel and is moved on the above position for calculating and acquiring, and completes auto-focusing.
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| CN113852761B (en) * | 2021-09-27 | 2023-07-04 | 宁波华思图科技有限公司 | Automatic focusing method for intelligent digital microscope |
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