CN115128762B - Automatic focusing measurement method based on light intensity gradient number - Google Patents
Automatic focusing measurement method based on light intensity gradient number Download PDFInfo
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- CN115128762B CN115128762B CN202210821316.1A CN202210821316A CN115128762B CN 115128762 B CN115128762 B CN 115128762B CN 202210821316 A CN202210821316 A CN 202210821316A CN 115128762 B CN115128762 B CN 115128762B
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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
- G02B7/285—Systems for automatic generation of focusing signals including two or more different focus detection devices, e.g. both an active and a passive focus detecting device
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B21/00—Microscopes
- G02B21/24—Base structure
- G02B21/241—Devices for focusing
- G02B21/245—Devices for focusing using auxiliary sources, detectors
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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
- G02B7/282—Autofocusing of zoom lenses
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Abstract
The invention provides an automatic focusing measurement method based on light intensity gradient number, which utilizes the image characteristics of a PSF function and uses a fitting function to fit, utilizes the fitting function to fit light spot images under different defocusing amounts, and obtains a first order derivative function; taking the extreme value of the first order derivative function as the difference to obtain a function curve of the defocus quantity-derivative function extreme value difference; fitting a function curve of the defocus quantity-derivative function extremum difference by using a fitting function; the calibrated defocus amount-derivative function extremum difference function is obtained, and a function curve of defocus amount-first-order derivative function extremum difference is drawn by finding the characteristic that the fitted Gaussian function has the first-order derivative function extremum difference and is different under different defocus amounts, so that focusing accuracy is improved, quick focusing is realized, and universality is improved.
Description
Technical Field
The invention relates to the field of focusing, in particular to an automatic focusing measurement method based on light intensity gradient number.
Background
At present, the existing micro focusing method mainly starts from image ambiguity, and whether a camera focuses or not is determined by judging the edge ambiguity degree of an image or the edge size of an image facula. The method has great limitation in a scene requiring high-precision measurement, wherein the degree of blurring is not clearly defined, so that the precision of a measurement system is reduced, and the size of the light spot edge is influenced by artificial subjective threshold segmentation.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides an automatic focusing measurement method based on the light intensity gradient number, which is used for drawing a function curve of defocus quantity-first order derivative function extremum difference by finding out the characteristic that the first order derivative function extremum difference exists in a Gaussian function fitted under different defocus quantities, thereby improving focusing accuracy and realizing quick focusing.
The invention adopts the following technical scheme:
an automatic focusing measurement method based on light intensity gradient number comprises the following steps: an automatic focusing measurement system based on a light intensity gradient number, comprising:
the light source is used for emitting laser; leveling the emitted laser by the leveling lens group to enable the emitted horizontal parallel light to be emitted; the semi-transparent semi-reflective lens reflects incident light in the horizontal parallel light and transmits measurement light; the objective lens is used for measuring an object to be measured, the converging lens is used for converging measuring light, and the photosensitive device is used for imaging;
the measuring method comprises a calibration stage and a measuring stage;
wherein the calibration phase comprises:
placing a calibration sample with the same material property as the measured sample on an objective table of the objective lens, and collecting light spot images before and after focusing within a focal plane threshold distance by the objective table to obtain light spot images under different defocusing amounts;
fitting the light spot images under different defocus amounts by using a fitting function, and solving a first order derivative function;
taking the extreme value of the first order derivative function as the difference to obtain a function curve of the defocus quantity-derivative function extreme value difference;
fitting a function curve of the defocus quantity-derivative function extremum difference by using a fitting function; obtaining a calibrated defocus amount-derivative function extremum difference function; wherein, the independent variable of the defocus amount-derivative function extremum difference function is defocus distance, and the dependent variable is defocus amount-derivative function extremum difference;
the measuring stage comprises the following steps:
placing an object to be measured on an objective table of an objective lens, driving the object to be measured to move by the objective table, photographing two positions before and after the movement in the moving process by a photosensitive device, and recording the moving direction and the coordinate position of the objective table;
performing Gaussian function fitting on the collected two light spot pictures at two positions before and after movement, and obtaining a first derivative;
substituting the obtained two first order derivative function extremum differences into a calibrated defocus amount-derivative function extremum difference function, and calculating defocus amount according to the moving direction and the coordinate position of the objective table, namely moving the objective table to finish automatic focusing.
Specifically, the light source is a point light source or a parallel light source.
Specifically, the photosensitive device is a camera.
Specifically, the fitting function includes, but is not limited to, a gaussian function, a cauchy function, or a gauss-cauchy function.
As can be seen from the above description of the present invention, compared with the prior art, the present invention has the following advantages:
the invention provides an automatic focusing measurement method based on light intensity gradient number, which draws a function curve of defocus-first order derivative function extremum difference by finding out the characteristic that the difference exists between the first order derivative function extremum differences of a fitted Gaussian function under different defocus amounts, thereby improving focusing accuracy, realizing quick focusing and improving universality.
Drawings
FIG. 1 is a schematic diagram of a system optical path architecture according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a point spread function of a microsystem according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a Gaussian distribution function;
FIG. 4 is a graph of the first derivative of a standard Gaussian distribution function;
FIG. 5 is a schematic diagram of a function curve of the defocus amount-derivative function extremum difference provided by the embodiment of the present invention;
the invention is further described in detail below with reference to the drawings and the specific examples.
Detailed Description
The invention is further described below by means of specific embodiments.
FIG. 1 is a schematic diagram of a system optical path architecture according to an embodiment of the present invention; comprises 1 a light source (a point light source and a parallel light source can be used for emitting laser; 2 straightening lens group (used for flattening incident light to make it appear horizontal parallel light to be emitted); 3 semi-transparent semi-reflective lens (incident light reflection, measurement light transmission); 4 objective lens (for measuring object); 5, an object to be detected; 6, converging lenses; 7 photosensitive devices (positioned at the light converging point); an aperture diaphragm is arranged in front of the converging lens and the straightening lens group 2;
the light source 1 is used for emitting laser; leveling the emitted laser by the straightening lens group 2 to enable the emitted horizontal parallel light to be emitted; the half-transmitting and half-reflecting lens 3 reflects incident light in the horizontal parallel light and transmits measurement light; the objective lens 4 is used for measuring an object 5 to be measured, the converging lens 6 is used for converging measuring light, and the photosensitive device 7 is used for imaging; the two aperture diaphragms are used for realizing a confocal measurement principle;
measurement principle:
the microscope system is a linear time-invariant system, the imaging process of which can be described by means of a point spread function
Wherein D (r) is the intensity distribution of the light field at the detector end, E (r) is the intensity distribution of the light field of the light emitted by the sample after being illuminated,
for convolution operation, the PSF (r) is the point spread function of the microscope system, which can be expressed by the following equation:
J 1 (. Cndot.) a first class of first order Bessel function equations;
na—the numerical aperture of the objective;
lambda-the wavelength of the illumination light;
r——r＝(x 2 +y 2 ) 1/2 and x and y are coordinates of a sample plane.
The point spread function of the microscopy system described according to equation 2 is shown in figure 2 below;
in the measurement field, it is difficult to measure a specific PSF function, so that the PSF function is approximated by a multi-purpose gaussian function, and a standard gaussian function (average value is 0 and standard deviation is 1) is shown in fig. 3.
Because of the certain value change of the maximum light intensity at different distances from the focal plane, namely the peak value and variance change of the Gaussian function fitted to the light field graph collected at different positions from the focal plane. Based on this variation, a first derivative of the fitted gaussian function is derived, as shown in fig. 4, which is a first derivative graph of a standard gaussian distribution function. Finding that two extreme points (one maximum value and one minimum value) exist in the first-order derivative function, extracting extreme values of the two extreme points, performing difference making (or not performing difference making, wherein the difference making is to enlarge the difference on the first-order derivative of the Gaussian function), and performing curve calibration on the obtained extreme value difference and the defocusing distance when the light spots are collected, wherein the abscissa is the defocusing distance, and the ordinate is the Gaussian fit-derivative function extreme value difference. The pattern change is shown in fig. 5.
Based on the principle, the technical scheme of the invention is as follows:
the measuring method comprises a calibration stage and a measuring stage;
wherein the calibration phase comprises:
placing a calibration sample with the same material property as the measured sample on an objective table of the objective lens, and collecting light spot images before and after focusing within a focal plane threshold distance by the objective table to obtain light spot images under different defocusing amounts;
fitting the light spot images under different defocus amounts by using a fitting function, and solving a first order derivative function;
taking the extreme value of the first order derivative function as the difference to obtain a function curve of the defocus quantity-derivative function extreme value difference;
fitting a function curve of the defocus quantity-derivative function extremum difference by using a fitting function; obtaining a calibrated defocus amount-derivative function extremum difference function; wherein, the independent variable of the defocus amount-derivative function extremum difference function is defocus distance, and the dependent variable is defocus amount-derivative function extremum difference;
the measuring stage comprises the following steps:
placing an object to be measured on an objective table of an objective lens, driving the object to be measured to move by the objective table, photographing two positions before and after the movement in the moving process by a photosensitive device, and recording the moving direction and the coordinate position of the objective table;
performing Gaussian function fitting on the collected two light spot pictures at two positions before and after movement, and obtaining a first derivative;
substituting the obtained two first order derivative function extremum differences into a calibrated defocus amount-derivative function extremum difference function, and calculating defocus amount according to the moving direction and the coordinate position of the objective table, namely moving the objective table to finish automatic focusing.
The light source 1 may be a parallel light source or a point light source; either as a single light source or as light sources with a certain spacing, either by reflection during other optical periods or spontaneously generated; the number of the lights is not limited to one but may be plural.
In addition, the photosensitive device is a camera, and can also be replaced by a photosensitive device capable of sensing light intensity conversion.
Furthermore, the fitting function includes, but is not limited to, a Gaussian function, a cauchy function, or a Gaussian-cauchy function; the Gaussian function is adopted in the embodiment of the invention.
The invention provides an automatic focusing measurement method based on light intensity gradient number, which draws a function curve of defocus-first order derivative function extremum difference by finding out the characteristic that the difference exists between the first order derivative function extremum differences of a fitted Gaussian function under different defocus amounts, thereby improving focusing accuracy, realizing quick focusing and improving universality.
The foregoing is merely illustrative of specific embodiments of the present invention, but the design concept of the present invention is not limited thereto, and any insubstantial modification of the present invention by using the design concept shall fall within the scope of the present invention.
Claims (4)
1. An automatic focusing measurement method based on the number of light intensity steps is characterized by comprising the following steps: an automatic focusing measurement system based on a light intensity gradient number, comprising:
the light source is used for emitting laser; leveling the emitted laser by the leveling lens group to enable the emitted horizontal parallel light to be emitted; the semi-transparent semi-reflective lens reflects incident light in the horizontal parallel light and transmits measurement light; the objective lens is used for measuring an object to be measured, the converging lens is used for converging measuring light, and the photosensitive device is used for imaging;
the measuring method comprises a calibration stage and a measuring stage;
wherein the calibration phase comprises:
placing a calibration sample with the same material property as the measured sample on an objective table of the objective lens, and collecting light spot images before and after focusing within a focal plane threshold distance by the objective table to obtain light spot images under different defocusing amounts;
fitting the light spot images under different defocus amounts by using a fitting function, and solving a first order derivative function;
taking the extreme value of the first order derivative function as the difference to obtain a function curve of the defocus quantity-derivative function extreme value difference;
fitting a function curve of the defocus quantity-derivative function extremum difference by using a fitting function; obtaining a calibrated defocus amount-derivative function extremum difference function; wherein, the independent variable of the defocus amount-derivative function extremum difference function is defocus distance, and the dependent variable is defocus amount-derivative function extremum difference;
the measuring stage comprises the following steps:
placing an object to be measured on an objective table of an objective lens, driving the object to be measured to move by the objective table, photographing two positions before and after the movement in the moving process by a photosensitive device, and recording the moving direction and the coordinate position of the objective table;
performing Gaussian function fitting on the collected two light spot pictures at two positions before and after movement, and obtaining a first derivative;
substituting the obtained two first order derivative function extremum differences into a calibrated defocus amount-derivative function extremum difference function, and calculating defocus amount according to the moving direction and the coordinate position of the objective table, namely moving the objective table to finish automatic focusing.
2. The method of claim 1, wherein the light source is a point light source or a parallel light source.
3. The method of claim 1, wherein the photosensitive device is a camera.
4. The method of claim 1, wherein the fitting function includes, but is not limited to, a gaussian function, a cauchy function, or a gauss-cauchy function.
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| US6091075A (en) * | 1997-06-04 | 2000-07-18 | Hitachi, Ltd. | Automatic focus detection method, automatic focus detection apparatus, and inspection apparatus |
| JP2007163461A (en) * | 2005-11-15 | 2007-06-28 | Olympus Corp | Lens evaluation system |
| CN101852970A (en) * | 2010-05-05 | 2010-10-06 | 浙江大学 | Automatic focusing method for camera under imaging viewing field scanning state |
| CN105049723A (en) * | 2015-07-13 | 2015-11-11 | 南京工程学院 | Auto-focusing method based on defocus distance difference qualitative analysis |
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| JP5692969B2 (en) * | 2008-09-01 | 2015-04-01 | 浜松ホトニクス株式会社 | Aberration correction method, laser processing method using this aberration correction method, laser irradiation method using this aberration correction method, aberration correction apparatus, and aberration correction program |
| US8970850B2 (en) * | 2012-12-14 | 2015-03-03 | University Of New Brunswick | Method and apparatus for surface profilometry |
| US20150205088A1 (en) * | 2014-01-23 | 2015-07-23 | U&U Engineering Inc. | Bevel-axial auto-focusing microscopic system and method thereof |
| JP6914977B2 (en) * | 2019-01-31 | 2021-08-04 | 日本電子株式会社 | Scanning transmission electron microscope and aberration correction method |
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Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH08160284A (en) * | 1994-12-07 | 1996-06-21 | Olympus Optical Co Ltd | Automatic focusing device and method therefor |
| US6091075A (en) * | 1997-06-04 | 2000-07-18 | Hitachi, Ltd. | Automatic focus detection method, automatic focus detection apparatus, and inspection apparatus |
| JP2007163461A (en) * | 2005-11-15 | 2007-06-28 | Olympus Corp | Lens evaluation system |
| CN101852970A (en) * | 2010-05-05 | 2010-10-06 | 浙江大学 | Automatic focusing method for camera under imaging viewing field scanning state |
| CN105049723A (en) * | 2015-07-13 | 2015-11-11 | 南京工程学院 | Auto-focusing method based on defocus distance difference qualitative analysis |
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