CN201812089U - Phase plate and field depth expanding imaging system applying same - Google Patents

Abstract

The utility model relates to a phase plate and field depth expanding imaging system using the same, wherein the imaging system comprises a phase plate arranged on an optical axis of the phase plate; the phase distribution function of the phase plate is obtained by multiplying a 4 th power function and a logarithm function, and the one-dimensional function expression of the phase distribution function is as follows: α · x⁴·sgn(x)·log(β·|x|)，x∈[-1，1]Wherein α and β are parameters of a phase distribution function of the phase plate, and x is a normalized coordinate; sgn represents a sign function, whose value is 1 when x > 0 and-1 when x < 0; adopt the utility model relates to a depth of field expands its defocusing modulation transfer function MTF that corresponds of imaging system and all has good stability in high frequency region still in the low frequency region to two kinds of logarithmic phase boards that are obviously better than known, thereby allow the deconvolution processing unit only to use a digital filter just can obtain the clear image of all out of focus positions departments.

Description

A kind of phase-plate and the depth of field expansion imaging system of using this phase-plate

Technical field

The utility model relates to a kind of depth of field expansion imaging system that is used for the logarithmic phase-plate of depth of field continuation and uses this phase-plate.

Background technology

The depth of field of expansion optical system always is the focus of academia's research, and the relative aperture of reduction system can play the effect of depth of field continuation, but meeting heavy losses luminous flux and resolution, so practicality is not strong.Since 20th century the mid-80, though being suggested, panoramic method is used for depth of field expansion, but after doctor E.R.Dowski of Univ Colorado-Boulder USA proposed wavefront coded notion in nineteen ninety-five, depth of field continuation had just had breakthrough truly.

By on aperture plane, entrance pupil or the emergent pupil of imaging system, adding the phase-plate of a cube type, the modulation transfer function MTF of system can become to out of focus and may cause that the factor of out of focus is insensitive, thereby reach the purpose of extended depth-of-field, and the most important thing is, after having added phase-plate, MTF is in the decline that just has on amplitude within the effective frequency range to a certain degree, and do not have zero point or nearly zero point.This just shows that when there was out of focus in system, the information that exceeds the primal system field depth was not lost, and just has been encoded in a kind of known mode, just can be recovered effectively by the corresponding digital Image Restoration Algorithm afterwards.Simultaneously, because phase-plate is just encoded to the imaging phase of line in the aperture plane, logical light quantity and resolution to system can not impact theoretically, thus wavefront coded be that a kind of novel depth of field that is different from very much reduced bore method, central obscuration method or apodization is expanded imaging technique.

With the one dimensional optical system is example, and its out of focus optical transfer function OTF can obtain by the auto-correlation computation of generalized pupil function, and is as follows:

$H(u,W_{20})=\frac{1}{2}\&CenterDot;\underset{-(1-|u|/2)}{\overset{1-\left|u\right|/2}{\&Integral;}}\exp (j\&CenterDot;(2k{W}_{20}\mathrm{ux}+f(x+u/2)-f(x-u/2)))\mathrm{dx}$

Wherein, u and x are respectively normalized spatial frequency and aperture plane lateral coordinates; W ₂₀It is maximum defocus wave aberration coefficient; K is a wave number; F then represents phase-plate universal expression formula.

For traditional imaging system, the f item in the following formula does not exist, and the formula that embodies that therefore can easily obtain out of focus OTF is:

$H(u,W_{20})=\frac{\sin (2k{W}_{20}\&CenterDot;(1-\frac{\left|u\right|}{2}))}{2k{W}_{20}u}u\&NotEqual;0$

Can see that when system did not introduce phase-plate, its OTF was highstrung to out of focus, and zero point can periodically occur, thereby cause irreversible information loss in the frequency space.But in case with the cube phase-plate (f (x)=α x of doctor E.R.Dowski institute utility model ³) introduce, just can obtain a diverse out of focus OTF by static phase is approximate so, as follows:

$H(u,W_{20})\&ap;\frac{1}{2}\&CenterDot;\sqrt{\frac{\mathrm{\&pi;}}{\left|3\mathrm{\&alpha;u}\right|}}\&CenterDot;\exp (j\&CenterDot;(\frac{{\mathrm{\&alpha;u}}^3}{4}-\frac{k^2\mathrm{<figure-callout\; id="2"\; label="u\; W"\; filenames="DEST\_PATH\_HSB00000220896800011.png,DEST\_PATH\_HSB00000220896800012.png"\; state="\{\{state\}\}">u</figure-callout>}{W^{}}_{}{{}^2}_{20}}{3\mathrm{\&alpha;}})j\&CenterDot;\mathrm{sgn}\left(u\right)\&CenterDot;\frac{\mathrm{\&pi;}}{4})u\&NotEqual;0$

Obviously, this moment out of focus OTF mould, promptly MTF and out of focus wave aberration coefficient have nothing to do, and that is to say that the cube phase-plate can make the MTF of system insensitive to out of focus; Though the phase bit position of OTF is relevant with out of focus parameter W20, as long as modulation factor α increases, its dependency degree to W20 will significantly reduce.Therefore, the depth of field that wavefront coding technology really can expanding system.The phase-plate that is used for depth of field continuation is of a great variety, and logarithmic only is a class wherein.

But, the pairing out of focus MTF curve of two kinds of logarithmic phase-plates that exists all shows instability in the low frequency position at present, the consistance that is the modulation transfer function under the different defocusing amounts is very poor, therefore is difficult to use a wave filter to come the intermediate image of all out of focus positions is recovered.

The utility model content

For the problem of the out of focus MTF poor stability that solves the logarithmic phase-plate that exists in the prior art, the utility model provides a kind of depth of field that is used for the phase-plate of depth of field continuation and uses this phase-plate to expand imaging system.

A kind of phase-plate that the utility model is related, its special character is: the PHASE DISTRIBUTION function of described phase-plate is to be multiplied each other by 4 rank power functions and logarithmic function to obtain, and its one dimension function expression is:

f(x)＝α·x ⁴·sgn(x)·log(β·|x|)，x∈[-1，1]

In the formula, α and β are the parameters of this phase-plate, are used for the phase modulation (PM) intensity that the control phase plate is introduced, and x is the normalization coordinate; Sgn conventional letter function, when x＞0, its value is 1, and its value is-1 when x＜0.

A kind of depth of field of using above-mentioned phase-plate is expanded imaging system, described imaging system comprises the imaging lens of being made up of one or more lens, its special character is: also comprise the phase-plate that is arranged on the imaging lens optical axis, described phase-plate can be arranged between aperture plane, entrance pupil face, emergent pupil face or the entrance pupil face and the aperture plane of imaging lens or the optional position between emergent pupil face and the aperture plane; The PHASE DISTRIBUTION function of described phase-plate is to be multiplied each other by 4 rank power functions and logarithmic function to obtain, and its one dimension function expression is:

f(x)＝α·x ⁴·sgn(x)·log(β·|x|)，x∈[-1，1]

In the formula, α and β are the parameters of this phase-plate, are used for the phase modulation (PM) intensity that the control phase plate is introduced, and x is the normalization coordinate; Sgn conventional letter function, when x＞0, its value is 1, and its value is-1 when x＜0.

Imaging system will and cause that the factor of out of focus is insensitive to out of focus like this, when three-dimensional scenic or target during through such system imaging, at first can be modulated at and form the fuzzy intermediary image of homogeneous on the sensor, rely on the graphics processing unit that deconvolutes just can obtain big depth of field picture rich in detail afterwards again through phase-plate.

Above-mentioned phase-plate its center minimum apart from lens when being arranged on the position of closing on any one lens in the imaging lens should be 3～5MM, and the reliable installation of element preferably can be guaranteed near aperture plane, entrance pupil face or emergent pupil face in the phase-plate present position simultaneously.

Above-mentioned phase-plate also can be the surface of arbitrary lens, and the surface of lens is set to the phase-plate surface structure of above-mentioned PHASE DISTRIBUTION function, but preferably select camera lens surface, to guarantee the insensitivity of system to out of focus near aperture plane, emergent pupil face or entrance pupil face.

The related depth of field of the utility model is expanded imaging system and can be reduced the susceptibility of system to out of focus effectively, great variation can not take place with the change of out of focus parameter in the modulation transfer function (MTF) that is whole optical system, and zero point or nearly zero point can not appear, so can not cause losing of image detail information in the passband scope.After middle blurred picture process deconvolution processing, just can obtain sharp keen big clearly depth image.

Description of drawings

Fig. 1 is the corresponding out of focus MTF of a kind of logarithmic phase-plate of the prior art (being proposed by E.R.Dowski team), and wherein phase-plate face type function is: f (x)=α x ²Sgn (x) 1og (| x|+ β), parameter is α=244.08 and β=0.78.Horizontal ordinate is represented the spatial frequency after the normalization, and out of focus parameter span is 0-9 π.

Fig. 2 is the pairing out of focus MTF of another kind of logarithmic phase-plate in the prior art, and wherein phase-plate face type function is: f (x)=α x ²Sgn (x) log (|| x|+ β |), parameter is α=165.92 and β=-1.22.Horizontal ordinate is represented the spatial frequency after the normalization, and out of focus parameter span is 0-9 π.

Fig. 3 is the pairing out of focus MTF of the related phase-plate of the utility model, and wherein the phase-plate parameter is α=112.27 and β=0.10.Horizontal ordinate is represented the spatial frequency after the normalization, and out of focus parameter span is 0-9 π.

Fig. 4 is the related phase-plate of the utility model pairing one dimension PHASE DISTRIBUTION when special parameter (α=112.27 and β=0.10); Wherein horizontal ordinate is represented normalized aperture coordinate, and ordinate is then represented phase modulation (PM) intensity f.

Fig. 5 is the structural representation that the related depth of field of the utility model is expanded first kind of embodiment of imaging system;

Fig. 6 is the structural representation that the related depth of field of the utility model is expanded second kind of embodiment of imaging system;

Description of drawings: 1-object; The 2-phase-plate; The 3-imaging lens; The 4-imaging detector; The 5-graphics processing unit.

Embodiment

The phase-plate that the utility model is related, its PHASE DISTRIBUTION function are multiplied each other by 4 rank power functions and logarithmic function and obtain, and function expression is:

f(x)＝α·x ⁴·sgn(x)·log(β·|x|)，x∈[-1，1]

In the formula, α and β are the parameters of this phase-plate, are used for the phase modulation (PM) intensity that the control phase plate is introduced, and x is the normalization coordinate; Sgn conventional letter function, when x＞0, its value is 1, and its value is-1 when x＜0.

When the phase-plate parameter is α=112.27 and β=0.10, when out of focus parameter span is 0-9 π, its pairing out of focus MTF curve and one dimension PHASE DISTRIBUTION, as shown in Figure 3 and Figure 4, obviously, the pairing out of focus MTF curve of existing two kinds of logarithmic phase-plates, as shown in Figure 1 and Figure 2, all show instability in the low frequency position, wherein the phase-plate that proposed by E.R.Dowski research team of Fig. 1 shows then more obviously.Become sharp contrast with it be the utility model propose based on the logarithmic phase-plate of 4 rank power functions modulation to out of focus more insensitive, the pairing out of focus MTF of imaging system that promptly carries this phase-plate is very stable in whole frequency space from the low frequency to the high frequency.

With reference to Fig. 5, the related depth of field of the utility model is expanded imaging system, comprises imaging lens 3 and the phase-plate 2 that is arranged on its optical axis, also has imaging detector 4 and convolved image processing unit 5 in addition; Wherein imaging lens 3, imaging detector 4 and convolved image processing unit 5 are according to the distribution of the imaging system of normal conventional and distribute, phase-plate 2 is arranged on the entrance pupil face of imaging lens 3, object forms the fuzzy intermediary image of homogeneous through imaging lens 3 after modulating through phase-plate again on imaging detector 4 like this, relies on the picture rich in detail of the graphics processing unit 5 back acquisition objects 1 that deconvolute afterwards again.

The PHASE DISTRIBUTION function of above-mentioned phase-plate 2 is to be multiplied each other by 4 rank power functions and logarithmic function to obtain, and its one dimension function expression is:

f(x)＝α·x ⁴·sgn(x)·log(β·|x|)，x∈[-1，1]

In the formula, α and β are the parameters of this phase-plate, are used for the phase modulation (PM) intensity that the control phase plate is introduced, and x is the normalization coordinate; Sgn conventional letter function, when x＞0, its value is 1, and its value is-1 when x＜0.

In addition, also phase-plate 2 can be arranged on the aperture plane, emergent pupil face of imaging lens 3 or between emergent pupil face and the aperture plane or the optional position between entrance pupil face and the aperture plane, but preferably on the optical axis that is arranged on imaging lens 3, the particular location of its setting should be determined according to practical situations.But when above-mentioned phase-plate 2 is arranged on the adjacent locations of any one lens of imaging lens 3, itself and lens center be controlled at 3～5MM apart from minimum, decide according to applied environment.Thereafter the image processing process at imaging detector 4 and convolved image processing unit 5 is identical with said process.

In addition, phase-plate 2 also can be exactly the surface of arbitrary camera lens of imaging lens 3, but the surface of described lens is set to the phase-plate surface structure of above-mentioned PHASE DISTRIBUTION function, and referring to Fig. 6, imaging afterwards, processing procedure are identical with processing procedure in the above-mentioned embodiment.But the surface of these lens can be determined the position of its setting according to practical situations preferably near the surface of the camera lens of aperture plane, emergent pupil face or entrance pupil face.

The related depth of field of the utility model is expanded imaging system and can be reduced the susceptibility of system to out of focus effectively, great variation can not take place with the change of out of focus parameter in the modulation transfer function (MTF) that is whole optical system, and zero point or nearly zero point can not appear, so can not cause losing of image detail information in the passband scope.After middle blurred picture process deconvolution processing, we just can obtain sharp keen big clearly depth image.

Claims (5)

1. phase-plate, it is characterized in that: the PHASE DISTRIBUTION function of described phase-plate is to be multiplied each other by 4 rank power functions and logarithmic function to obtain, and its one dimension function expression is:

f(x)＝α·x ⁴·sgn(x)·log(β·|x|)，x∈[-1，1]

In the formula, α and β are the PHASE DISTRIBUTION function parameters of described phase-plate, and x is the normalization coordinate; Sgn conventional letter function is 1 for its value when x＞0, and its value is-1 when x＜0.

2. an application rights requires the depth of field of 1 described phase-plate to expand imaging system, comprises the imaging lens of being made up of one or more lens, and it is characterized in that: described imaging system also comprises the phase-plate on the optical axis that is arranged on described imaging lens; Described phase-plate is arranged between aperture plane, entrance pupil face, emergent pupil face, entrance pupil face and the described aperture plane of imaging lens or the optional position between emergent pupil face and the described aperture plane.

3. the depth of field according to claim 2 is expanded imaging system, and it is characterized in that: the distance at the position of described phase-plate setting and adjacent lens center is 3～5MM at least.

4. the depth of field according to claim 2 is expanded imaging system, and it is characterized in that: described phase-plate is the surface of arbitrary lens, and the surface of described lens is set to the phase-plate surface structure.

5. the depth of field according to claim 4 is expanded imaging system, it is characterized in that: the surface of described lens is the lens surfaces near aperture plane, emergent pupil face or entrance pupil face.

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