CN106950222A - A kind of big depth field imaging method - Google Patents

Abstract

The invention discloses a kind of big depth field imaging method, belong to optical imaging field.The present invention uses specified wavelength light irradiation different object distances object using the lens characteristic different to different wave length optical index by calculating, and makes its imaging plane overlapping so as to extended depth of field.The present invention is solved for having space thickness object can not be imaged in optimal imaging plane, the problems such as White-light LED illumination easily produces aberration, contrast common white-light illuminating this method can be obviously improved image resolution ratio, it is low cost, widely applicable.

Description

A kind of big depth field imaging method

Technical field

The present invention relates to a kind of big depth field imaging method, belong to optical imaging field.

Background technology

Big depth field imaging has two aspects of microcosmic and macroscopic view, and this case belongs to the big depth field imaging of macroscopic aspect, for Be not microcosmic micro-imaging.The lifting imaging system depth of field mainly includes following several method at present：1) code aperture skill is used Art, because each region in image is to defocus PSF function deblurring by what is estimated, institute in this way effect by estimation of Depth Precision influence it is larger；2) increase phase-plate increase Depth of field, wherein Dowski et. propose a kind of cube phase-plate, Because this kind of phase-plate can retain more detail of the high frequency, so there is more preferable effect compared to circular phase-plate；3) adopt The depth of field is expanded with digital image processing techniques, wherein having scholar by the way that the sharpness information that color component is focused in the colors of RGB tri- is opened up Other color components are opened up, lifting definition is so as to increase the depth of field；4) big scape is produced by the mechanical movement of imaging optic element It is deep.

More than in addition to four kinds of methods, because common non-achromatic lens has aberration, the Focus Club of lens is with incident light wave Long different produce offsets, and foreign countries have scholar to utilize this characteristic, have been invented for barcode scanning machine and have expanded Depth of field using aberration System, the system using infrared light and other wavelength lights collocation illumination bar code, imaging sensor acquisition order image can Realize from 1.5 inches to 8 inches apart from upper reading bar code information.But it is due to the machine-readable characteristic for taking image information of barcode scanning, should System can not be by the object with certain depth of field while blur-free imaging.

The content of the invention

The present invention is intended to provide a kind of big depth field imaging method, is to utilize the lens spy different to different wave length optical index Property, specified wavelength light irradiation different object distances object is used by calculating, makes the image distance of each object distance object identical, i.e., each target The imaging plane of thing is overlapping so as to extended depth of field.

Methods described, comprises the following steps：

(1) for any simple lens, the lens material wavelength X of the lens and refractive index n relation is determined, n=f is expressed as (λ)；And the refractive index n and focal length f' of the lens relation are determined, it is expressed as f'=g (n)；So that it is determined that the focal length f' of the lens With the relation of wavelength X：F'=g (f (λ))；

(2) we adjust the distance lens for L₁And L₂Two object plane P₁、P₂Blur-free imaging, L₁＜ L₂；To object plane P₁, use ripple A length of λ₁Light irradiation, object plane P₁Image formula beL' is image distance；For object plane P₂, make

It is λ with wavelength₂Light irradiation, object plane P₂Image formula beTo make the image distance phase of two object planes Together, then have

(3) step (1), (2) are combined, L is obtained₂And λ₂Between relation, i.e., Wherein L₁And λ₁All be it is known, can be to obtain in object distance L by the formula₂Locate illumination wavelength λ needed for blur-free imaging₂。

When the simple lens is spherical mirror, in step (1), the relation of its refractive index and focal length is met：Wherein r₁、r₂Respectively surface curvature before and after lens, d is lens thickness；Then Step (3) obtains L₂And λ₂Between relation such as formula (1) shown in：

L in formula (1)₁、λ₁、r₁、r₂, a, b, c be all known parameters, determine L₂Afterwards, it is possible to try to achieve λ₂, it is λ with wavelength₂'s Light irradiation object plane P₂Just can be with blur-free imaging.

When the simple lens is for planoconvex spotlight, in step (1), the relation of its refractive index and focal length is met：Wherein r₁、r₂Respectively surface curvature before and after lens, d is lens thickness, and r₂=∞, then, the relation of focal length and refractive index are further simplified asThen step (3) obtains L₂And λ₂Between relation As shown in formula (2)：

L in formula (2)₁、λ₁、r₁, a, b, c be all known parameters, determine L₂Afterwards, it is possible to try to achieve λ₂, it is λ with wavelength₂Light Irradiate object plane P₂Just can be with blur-free imaging.

In the step (1), the relation of lens material refractive index and wavelength can be obtained by inquiring about material handbook, and one As, material handbook is to provide the corresponding refractive index of several wavelength lights, the method that we can be fitted by data, is found specific Relational expression.For spherical lens, the relation of usual material refractive index and wavelength meets Vcauchy dispersion formuia：Further, its refractive index and the relation of focal length are met：Its Middle r₁、r₂Respectively surface curvature before and after lens, d is lens thickness；, can without specific formula for non-spherical lens To characterize the relation of refractive index and focal length, but we can obtain its relation by the method tested and software is simulated.

The present invention propose it is a kind of need not addition or design customization optical element extended depth-of-field in optical imaging systems Method.We irradiate different object planes using different wavelengths of light, make each object plane image distance identical to obtain picture rich in detail, expand scape It is deep.The present invention solves the object with space thickness and can not be imaged in optimal imaging plane, and White-light LED illumination is easily produced The problems such as aberration, contrast common white-light illuminating, the inventive method can be obviously improved image resolution ratio, low cost, widely applicable.

The present invention can be applied in industrial automation detection, and detection is with many object planes or the big workpiece of longitudinal depth, product Deng.Under conditions of the depth of field needed for known target thing, the good illuminating lamp position of reasonable arrangement is automatic to calculate selection illumination wavelengths, from And realize Polaroid, completion Detection task.For example to domestic washing basin inner surface Defect Detection, because hand washing sink is matrix , with larger longitudinal depth, by the method for the present invention, by the way of the illumination of multi-wavelength subregion, it is possible to obtain clear Clear image, coordinates Machine Vision Detection algorithm, completes Detection task.

Brief description of the drawings

Fig. 1 is systematic schematic diagram.

Fig. 2 is system pictorial diagram.

Fig. 3 is the basic parameter for the biconvex lens that embodiment 1 is used.

Fig. 4 is imaging picture of the embodiment 1 using white-light illuminating.

Fig. 5 is imaging picture of the embodiment 1 using means of illumination of the present invention.

Fig. 6 is imaging picture of the embodiment 2 using white-light illuminating.

Fig. 7 is imaging picture of the embodiment 2 using means of illumination of the present invention.

Embodiment

Embodiment 1

We have a biconvex lens parameter such as Fig. 3：

From the figure, we can obtain, and the lens are biconvex spherical mirror, and standard focal length is 34.9mm, lens thickness d= 6.8mm, sphere curvature radius r₁=r₂=34.86mm, the lens material is H-K9L, and inquiry obtains the refractive index characteristic of the material As shown in table 1.

Table 1H-K9L parts wavelength refractive index

The relation satisfaction of the material wavelength and refractive index can be obtained by being fitted us by data：That is a=1.504, b=4621, c=-4.899 × 10⁷.We are with object plane P₁Using ripple Long λ₁=405nm purple lights are illuminated, L₁=-500mm, L₂=-700mm, L₃Exemplified by=- 800mm diaphragm diameters D=5mm.According to formula (1) we, which can calculate, obtains in object distance L₂Place should use 530nm wavelength optical illumination, in object distance L₃Place should use 598nm wavelength lights Illumination.

The reflective reflectance charts 1 of 0.5 times of ISO-12233 are being placed at lens 500mm, apart from lens 700mm With at 800mm respectively place test card 2,3.Test card 1,2, about 3 staggers placement.In order to contrast different optical illumination and same light The effect of illumination, we are chosen thereafter as far as possible close to calculated value wavelength first by the White-light LED illumination that many power are 1W LED illuminates different object planes respectively.We measured used LED light spectrum centre frequency be respectively 400nm, 530nm, 600nm.In order to be evenly illuminated effect, the position of LED and angle are all optimized, and the image of shooting is without appointing What software algorithm processing.The pixel black and white CMOS of CMOS chip model MT9M001 types 1,300,000, resolution ratio is 1280H × 1024V, 5.2 μm of 5.2 μ m of pixel dimension.Fig. 4 is uses white-light illuminating, and Fig. 5 is to use this case method illuminating effect.

We utilize the resolution ratio of the resolution test software I matest software test images of specialty, respectively in image It is each at 500mm, 700mm and 800mm to choose its MTF50 score of domain test at three.The region of selection will be as shown in figure 5, will be all Region is averaged as the region objective scoring.Fig. 4 and Fig. 5 objective scorings are as shown in table 1 below.

The evaluation result of table 2

It will be seen that using the methods experiment effect of this case than white-light illuminating high resolution from table 1, and object distance The effect of bigger lifting is more obvious, and resolution ratio improves 45.3%, 293.8% and 515.3% respectively.

Embodiment 2

We use biconvex lens to embodiment 1, and we obtain a plano-convex spherical lens in this example.The lens curvature Radius r₁=15.504mm, material is still K9 glass.We are with object plane P₁Using wavelength X₁=460nm blue illuminations, L₁=- 600mm, L₂=-800mm, L₃Exemplified by=- 1000mm diaphragm diameters D=5mm.According to formula (2), we, which can calculate, obtains in object distance L₂Place should use 559nm wavelength optical illumination, in object distance L₃Place should use 658nm wavelength optical illumination.

The reflective reflectance charts 1 of 0.5 times of ISO-12233 are being placed at lens 600mm, apart from lens 800mm With at 1000mm respectively place test card 2,3.Test card 1,2, about 3 staggers placement.In order to contrast different optical illumination and identical The effect of optical illumination, we are chosen thereafter as far as possible close to calculated value wavelength first by the White-light LED illumination that many power are 1W LED illuminate different object planes respectively.We measured used LED light spectrum centre frequency be respectively 460nm, 530nm, 650nm.In order to be evenly illuminated effect, the position of LED and angle are all optimized, and the image of shooting is without appointing What software algorithm processing.The pixel black and white CMOS of CMOS chip model MT9M001 types 1,300,000, resolution ratio is 1280H × 1024V, 5.2 μm of 5.2 μ m of pixel dimension.We have carried out cutting processing by the photo to shooting, have intercepted the less part of middle aberration Picture, Fig. 6 is uses white-light illuminating, and Fig. 7 is to use this case method illuminating effect.

We utilize the resolution ratio of the resolution test software I matest software test images of specialty, respectively in image It is each at 600mm, 800mm and 1000mm to choose its MTF50 score of domain test at three.The region of selection will be as shown in fig. 7, will be all Region is averaged as the region objective scoring.Fig. 6 and Fig. 7 objective scorings are as shown in table 2 below.

The evaluation result of table 3

It will be seen that using the methods experiment effect of this case than white-light illuminating high resolution from table 2, and object distance The effect of bigger lifting is more obvious, and resolution ratio improves 44.5%, 146.3% and 231.6% respectively.

Although the present invention is disclosed as above with preferred embodiment, it is not limited to the present invention, any to be familiar with this skill The people of art, without departing from the spirit and scope of the present invention, can do various changes and modification, therefore the protection model of the present invention Enclose being defined of being defined by claims.

Claims (7)

1. a kind of imaging method, it is characterised in that be using the lens characteristic different to different wave length optical index, using specified Wavelength light irradiation homologue makes the image distance of each object distance object identical away from object, i.e., the imaging plane of each object it is overlapping from And extended depth of field.

2. according to the method described in claim 1, it is characterised in that comprise the following steps：

(1) according to lens material refractive index properties, lens wavelength X and focal length f' relation are determined；

(2) the image equation of different object distances object is built；

(3) lens wavelength X and focal length f' relation are substituted into image equation, solves object distance and the relational expression of wavelength.

3. method according to claim 1 or 2, it is characterised in that comprise the following steps：

(1) for any simple lens, the lens material wavelength X of the lens and refractive index n relation are determined, n=f (λ) is expressed as； And the refractive index n and focal length f' of the lens relation are determined, it is expressed as f'=g (n)；So that it is determined that the focal length f' and ripple of the lens Long λ relation：F'=g (f (λ))；

(2) we adjust the distance lens for L₁And L₂Two object plane P₁、P₂Blur-free imaging, L₁＜ L₂；To object plane P₁, it is using wavelength λ₁Light irradiation, object plane P₁Image formula beL' is image distance；For object plane P₂, the use of wavelength is λ₂Illumination Penetrate, object plane P₂Image formula beTo make the image distance of two object planes identical, then have

(3) step (1), (2) are combined, L is obtained₂And λ₂Between relation, i.e.,Wherein L₁And λ₁All be it is known, can be to obtain in object distance L by the formula₂Locate illumination wavelength λ needed for blur-free imaging₂。

4. according to any described method of claims 1 to 3, it is characterised in that when the simple lens is spherical mirror, step (1) In, the relation of its refractive index and focal length is met：Wherein r₁、r₂Respectively before and after lens Surface curvature, d is lens thickness；Then step (3) obtains L₂And λ₂Between relation such as formula (1) shown in：

$\frac{1}{L_2}=\frac{1}{L_1}-\left(\frac{b}{{\mathrm{\λ}}_2^2}+\frac{c}{{\mathrm{\λ}}_2^4}-\frac{b}{{\mathrm{\λ}}_1^2}-\frac{c}{{\mathrm{\λ}}_1^4}\right)\left(\frac{1}{r_1}-\frac{1}{r_2}\right)+\frac{{\left(a+\frac{b}{{\mathrm{\λ}}_2^2}+\frac{c}{{\mathrm{\λ}}_2^4}-1\right)}^{2}d}{\left(a+\frac{b}{{\mathrm{\λ}}_2^2}+\frac{c}{{\mathrm{\λ}}_2^4}\right)r_1{r}_2}-\frac{{\left(a+\frac{b}{{\mathrm{\λ}}_1^2}+\frac{c}{{\mathrm{\λ}}_1^4}-1\right)}^{2}d}{\left(a+\frac{b}{{\mathrm{\λ}}_1^2}+\frac{c}{{\mathrm{\λ}}_1^4}\right)r_1{r}_2}---\left(1\right)$

L in formula (1)₁、λ₁、r₁、r₂, a, b, c be all known parameters, determine L₂Afterwards, it is possible to try to achieve λ₂, it is λ with wavelength₂Illumination Penetrate object plane P₂Just can be with blur-free imaging.

5. according to any described method of claims 1 to 3, it is characterised in that when the simple lens is planoconvex spotlight, step (1) in, the relation of its refractive index and focal length is met：Wherein r₁、r₂Respectively lens Front and rear surface curvature, d is lens thickness, and r₂=∞, then, the relation of focal length and refractive index are further simplified asThen step (3) obtains L₂And λ₂Between relation such as formula (2) shown in：

$\frac{b}{{\mathrm{\λ}}_2^2}+\frac{c}{{\mathrm{\λ}}_2^4}=\frac{r_1}{L_1}-\frac{r_1}{L_2}+\frac{b}{{\mathrm{\λ}}_1^2}+\frac{c}{{\mathrm{\λ}}_1^4}---\left(2\right)$

L in formula (2)₁、λ₁、r₁, a, b, c be all known parameters, determine L₂Afterwards, it is possible to try to achieve λ₂, it is λ with wavelength₂Light irradiation Object plane P₂Just can be with blur-free imaging.

6. according to any described method of claims 1 to 3, it is characterised in that when the simple lens is non-spherical lens, pass through Optical software is simulated and tested, and obtains the relation f'=F (λ) of the focal length of lens and wavelength, then step (3) obtains L₂And λ₂Between Shown in relation such as formula (3)：

$\frac{1}{L_2}=\frac{1}{L_1}+\frac{1}{F\left({\mathrm{\λ}}_1\right)}-\frac{1}{F\left({\mathrm{\λ}}_2\right)}---\left(3\right).$

7. a kind of imaging system, it is characterised in that be single lens, with lighting device, the lighting device can use specified The object of wavelength light irradiation different object distances, makes the image distance of the object of each object distance identical.