CN102169201B - Sinusoidal phase plate and field depth extension imaging system based on same - Google Patents

Abstract

The utility model relates to a sinusoidal phase plate used for extending the field depth of an optical imaging system and a field depth extension imaging system employing the phase plate. The field depth extension imaging system comprises a phase plate, an imaging lens, and an imaging detector; the phase plate, the imaging lens, and the imaging detector are arranged on a same optical axis. The invention provides a phase plate which can effectively reduce the sensitivity of the system on defocussing, can not cause loss of image details information, can obtain sharp and clear big field depth images, and is used for extending the field depth. The invention also provides a field depth extension imaging system based on the phase plate.

Description

The sinusoidal pattern phase-plate reaches the field depth extension imaging system based on this phase-plate

Technical field

The invention belongs to optical field, relate to a kind of phase-plate and based on the imaging system of this phase-plate, relate in particular to a kind of for the sinusoidal pattern phase-plate of expanding field depth of optical imaging system and the field depth extension imaging system of using this phase-plate.

Background technology

The depth of field of expansion optical imaging system always is the focus of academia's research.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, although panoramic method is proposed for the expansion imaging system depth of field, but until after doctor E.R.Dowski of Univ Colorado-Boulder USA proposed wavefront coded concept in nineteen ninety-five, depth of field continuation had just had breakthrough truly.

By add the phase-plate of a cube type on aperture plane, entrance pupil plane or the emergent pupil plane of imaging system, the modulation transfer function of system just can become to out of focus and 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 just has to a certain degree decline in amplitude within effective frequency range, and does not have zero point or nearly zero point.This just shows, when there was out of focus in system, the information that exceeds the primal system field depth was not lost, and just had been carried out coding in a kind of known mode, just can effectively be recovered by 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 a kind of novel field depth extension imaging technology that is different from very much reduced bore method, central obscuration method or apodization.

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

$H(u,W_{20})=\frac{1}{2}\&CenterDot;\underset{-(1-|u|/2)}{\overset{1-\left|u\right|/2}{\&Integral;}}\exp (j\&CenterDot;(2k{\mathrm{<figure-callout\; id="20"\; label="W"\; filenames="HDA0000066141070000031.png,HDA0000066141070000041.png"\; state="\{\{state\}\}">W</figure-callout>}}_{20}\mathrm{ux}+fx(x+u/2)-f(x-u/2)))\mathrm{dx}$

Wherein, u and x are respectively normalized spatial frequency and aperture plane lateral coordinates; W ₂₀It is maximum defocus wave aberration coefficient; K is 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 expression that therefore can easily obtain out of focus OTF is:

$H(u,W_{20})=\frac{\sin (2\mathrm{<figure-callout\; id="20"\; label="k\; W"\; filenames="HDA0000066141070000031.png,HDA0000066141070000041.png"\; state="\{\{state\}\}">k</figure-callout>}{W}_{}{}_{20}\&CenterDot;(1-\frac{\left|u\right|}{2}))}{2k{W}_{20}u}u\&NotEqual;0$

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

$H(u,W_{20})\&ap;\frac{1}{2}\&CenterDot;\sqrt{\frac{\mathrm{\&pi;}}{\left|3\mathrm{\&alpha;u}\right|}}\&CenterDot;\exp (j\&CenterDot;(\frac{\mathrm{\&alpha;}{u}^3}{4}-\frac{k^{2}u{{\mathrm{<figure-callout\; id="2"\; label="W"\; filenames="HDA0000066141070000031.png,HDA0000066141070000042.png"\; state="\{\{state\}\}">W</figure-callout>}}^2}_{20}}{3\mathrm{\&alpha;}})+j\&CenterDot;\mathrm{sgn}\left(u\right)\&CenterDot;\frac{\mathrm{\&pi;}}{4})u\&NotEqual;0$

Obviously, this moment out of focus OTF mould, namely 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; Although the phase bit position of OTF and degree of blur W ₂₀Relevant, but as long as modulation factor α increases, it is to W ₂₀Dependency degree 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, except the cube type phase-plate that doctor Dowski proposes, also has the logarithmic phase-plate, many types such as exponential type phase-plate, high order square phase-plate.Although phase-plate can make the MTF of system become insensitive to out of focus, but compare with the diffraction limited imaging system, the value of its MTF has larger decline, thereby the intermediate image that causes this novel imaging system to obtain presents the fuzzy of uniformity, must use digital image restoration method with ambiguity removal to obtain large depth of field picture rich in detail.Come that the intermediate image of all out of focus positions is all had efficient recovery with a digital filter, the out of focus MTF of the corresponding system of phase-plate must stablize as much as possible, and this also is the basic point of departure of phase-plate design.

Summary of the invention

In order to solve the above-mentioned technical matters that exists in the background technology, the invention provides a kind of can effectively reduce system to the susceptibility of out of focus, can not cause losing and can obtaining the phase-plate that is used for depth of field continuation of sharp keen clearly large depth image and based on the field depth extension imaging system of this phase-plate of image detail information.

Technical solution of the present invention is: the invention provides a kind of sinusoidal pattern phase-plate, its special character is: the surface structure of described phase-plate is described by sine function, and the expression formula of described sine function is:

f(x)＝α·sin(β·x+θ)，x∈[-1，1]

In the formula, α, β and θ are the parameters of the PHASE DISTRIBUTION function of described phase-plate, are used for controlling the phase-modulation intensity that the sinusoidal pattern phase-plate is introduced; X is the normalization coordinate of imaging system aperture plane.

A kind of field depth extension imaging system based on above-mentioned sinusoidal pattern phase-plate, its special character is: described field depth extension imaging system comprises phase-plate, imaging lens and imaging detector; Described phase-plate, imaging lens and imaging detector are on the same optical axis.

Above-mentioned phase-plate separates setting with imaging lens.

Described phase-plate is arranged at aperture plane, emergent pupil face or the entrance pupil face of imaging lens.

Distance between described phase-plate and the imaging lens is not less than 3～5mm.

Above-mentioned field depth extension imaging system also comprises graphics processing unit; Described graphics processing unit links to each other with imaging detector.

Above-mentioned graphics processing unit is the graphics processing unit that deconvolutes.

Advantage of the present invention is:

Field depth extension imaging system involved in the present invention can reduce system effectively to the susceptibility of out of focus, great variation can not occur with the change of degree of blur 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 clearly large depth image.Compare with the cube type phase-plate of classics, sinusoidal pattern phase-plate proposed by the invention can reduce system more effectively to the susceptibility of out of focus, is a kind of better selection of expanding the imaging system depth of field therefore.

Description of drawings

Fig. 1 is cube type phase-plate and sinusoidal pattern phase-plate one dimension phase function proposed by the invention the first schematic diagram relatively.

Fig. 2 is cube type phase-plate and sinusoidal pattern phase-plate one dimension phase function proposed by the invention the second schematic diagram relatively.

Fig. 3 is cube type phase-plate and sinusoidal pattern phase-plate one dimension phase function proposed by the invention the 3rd schematic diagram relatively.

Fig. 4 estimates schematic diagram with the out of focus invariant feature that Fisher information aligns chordwise phase-plate and classical cube type phase-plate.

Fig. 5 is the structural representation of field depth extension imaging system embodiment involved in the present invention;

Wherein, 1-object; The 2-phase-plate; The 3-imaging lens; The 4-imaging detector; The 5-graphics processing unit.

Embodiment

The present invention relates to a kind of sinusoidal pattern phase-plate, compare with the cube type phase-plate of classics, the sinusoidal pattern phase-plate has better out of focus unchangeability, can expand better the depth of field of imaging system.Before the depth of field extension capability of dissimilar phase-plate is estimated, be the first step based on the face type optimization under the uniform principles.Because the decline meeting of the MTF that the introducing of phase-plate causes produces adverse influence to follow-up image restoration, so the optimization of face type should be with minimum acceptable degeneration MTF, namely the Th in the table 1 carries out for constraint.

Phase-plate PHASE DISTRIBUTION function proposed by the invention can be described by the standard sine function, and expression is:

f(x)＝α·sin(β·x+θ)，x∈[-1，1]

In the formula, α, β and θ are the parameters of the PHASE DISTRIBUTION function of described phase-plate, are used for controlling the phase-modulation intensity that the sinusoidal pattern phase-plate is introduced; X is the normalization coordinate of imaging system aperture plane.

After use simulated annealing is carried out multi-parameters optimization to above-mentioned phase-plate, just can obtain the optimum face shape parameter under the corresponding various boundary conditions of phase-plate, as shown in table 1.

Table 1

Th	α	β	ω
				0.21	395.761	1.370	0.042
0.23	186.875	1.634	6.363
				0.25	239.912	1.438	0.059
0.27	645.356	0.957	6.333
				0.29	186.889	1.412	15.633
0.31	117.900	1.632	18.927
				0.33	67.886	1.836	3.007
0.35	78.721	1.676	19.072

In table 1, symbol Th is a threshold value, and satisfies ∫ MTF (u, W ₂₀=0, P) du 〉=Th, wherein MTF is the modulation transfer function of wavefront coded system; U, W ₂₀And P is respectively the normalization spatial frequency, out of focus wave aberration coefficient and phase-plate parameter.Th is the degree that reduces at phase-plate face type optimizing process for constrained system MTF, and namely the Th value is larger, and the corresponding MTF curve of system after optimizing is just higher, otherwise lower.

Fig. 1, Fig. 2 and Fig. 3 have provided the optimum face type of cube type phase-plate and sinusoidal pattern phase-plate curve and have equaled respectively 0.21,0.27 and 0.33 o'clock contrast at Th.In Fig. 1, two kinds of phase-plate parameters are corresponding to the situation of Th=0.21 in the table 1, and horizontal ordinate represents the aperture plane coordinate after the normalization.In Fig. 2, two kinds of phase-plate parameters are corresponding to the situation of Th=0.27 in the table 1, and horizontal ordinate represents the aperture plane coordinate after the normalization.In Fig. 3, two kinds of phase-plate parameters are corresponding to the situation of Th=0.33 in the table 1, and horizontal ordinate represents the aperture plane coordinate after the normalization.

Can see, difference between the corresponding optimum face type curve of phase-plate still clearly, and this just the sinusoidal pattern phase-plate can obtain the root of better out of focus invariant feature.

Fig. 4 has provided the sinusoidal pattern phase-plate, and the Fisher curve during corresponding to different Th value is relatively from cube type phase-plate.According to the Fisher information definition, its value is less, and system is just more insensitive to degree of blur so.Can see, no matter how many values of Th is, when existing medium or during serious out of focus, comparing with cube type phase-plate, the sinusoidal pattern phase-plate is more obvious to the inhibiting effect of out of focus, because the value of its corresponding Fisher curve is less.Wherein, Fig. 4 (1)～(8) respectively corresponding Th equal 0.21,0.23, and 0.25,0.27,0.29,0.31,0.33,0.35 situation, out of focus scope 0-9 π.Wherein, solid line represents the sinusoidal pattern phase-plate, and dotted line then represents cube type phase-plate, and horizontal ordinate is degree of blur, and ordinate is Fisher information size.

The present invention also provides a kind of field depth extension imaging system based on above-mentioned sinusoidal pattern phase-plate, and this system comprises imaging lens 3, imaging detector 4 and is co-located on phase-plate 2 on the same optical axis with the two, comprises in addition convolved image processing unit 5; 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 fuzzy intermediary image through imaging lens 3 at imaging detector 4 after modulating through phase-plate more like this, relies on afterwards the picture rich in detail of the graphics processing unit 5 rear acquisition objects 1 that deconvolute again.

The PHASE DISTRIBUTION function of phase-plate 2 is described by sine function, and its one dimension phase function expression formula is:

f(x)＝α·sin(β·x+θ)，x ∈[-1，1]

In the formula, α, β and θ are the parameters of the PHASE DISTRIBUTION function of described phase-plate, are used for controlling the phase-modulation intensity that the sinusoidal pattern phase-plate is introduced; X is the normalization coordinate of imaging system aperture plane.

Phase-plate 2 and imaging lens 3 are split settings, Fig. 5 has provided the situation of phase-plate 2 and imaging lens 3 splits setting, when phase-plate 2 and imaging lens 3 are that split is when arranging, phase-plate 2 is arranged on aperture plane or the entrance pupil of system, and the distance of any one lens center is controlled at 3～5mm at least in the Range Imaging camera lens 3, decides according to applied environment.In addition, also phase-plate can be arranged on the emergent pupil face of imaging lens, the position of setting should determine according to practical situations, and the image processing process at imaging detector 4 and convolved image processing unit 5 is identical with said process thereafter.

Sinusoidal pattern phase-plate proposed by the invention can effectively suppress out of focus through after optimizing, thus the depth of field of expansion optical imaging system.According to the Fisher information definition, to compare with traditional cube type phase-plate, the sinusoidal pattern phase-plate can make imaging system more insensitive to out of focus.Therefore, the field depth extension imaging system of application sinusoidal pattern phase-plate involved in the present invention can reduce system effectively to the susceptibility of out of focus, great variation can not occur with the change of degree of blur 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 clearly large depth image.

Claims (7)

1. sinusoidal pattern phase-plate, it is characterized in that: the surface structure of described phase-plate is described by sine function, and the expression formula of described sine function is:

f(x)=α·sin(β·x+θ),x∈[-1,1]

In the formula, α, β and θ are the parameters of the PHASE DISTRIBUTION function of described phase-plate, are used for controlling the phase-modulation intensity that the sinusoidal pattern phase-plate is introduced; X is the normalization coordinate of imaging system aperture plane.

2. field depth extension imaging system based on sinusoidal pattern phase-plate claimed in claim 1, it is characterized in that: described field depth extension imaging system comprises phase-plate, imaging lens and imaging detector; Described phase-plate, imaging lens and imaging detector are on the same optical axis.

3. field depth extension imaging system according to claim 2, it is characterized in that: described phase-plate is to separate setting with imaging lens.

4. field depth extension imaging system according to claim 3, it is characterized in that: described phase-plate is arranged at aperture plane, emergent pupil face or the entrance pupil face of imaging lens.

5. field depth extension imaging system according to claim 4, it is characterized in that: the distance between described phase-plate and the imaging lens is 3 ~ 5mm.

6. the described field depth extension imaging system of arbitrary claim according to claim 2-5, it is characterized in that: described field depth extension imaging system also comprises graphics processing unit; Described graphics processing unit links to each other with imaging detector.

7. field depth extension imaging system according to claim 6, it is characterized in that: described graphics processing unit is the graphics processing unit that deconvolutes.

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