CN100491938C - Moire filtering synthetic process for digital moire phase shifting interference technology - Google Patents

Abstract

The invention includes following procedures: removing background (DC component) of virtual interference fringe and actual interference fringe respectively; carrying out morie synthetic method including digital multiplication and superposition; removing background interference fringe from morie fringe; extending bandwidth of morie fringe; simplified lowpass filtering process for saving time of filtering process in order to obtain morie interference fringe in sine distribution in real time through hardware.

Description

The More's filtering synthetic method that is used for digital More's movable phase interfere art

Affiliated technical field

The present invention is a kind of More's filtering synthetic method that is used for digital More's movable phase interfere art, belongs to optical measurement and technical field of image processing.

Background technology

Numeral More interferometry is the interference technique that a kind of new development is got up, its principle is to utilize computing machine to calculate interferogram (virtual interfere figure) according to the light path and the complicated tested corrugated of standard of actual interferometer, when actual detected, gather the interferogram (actual interferogram) of the actual tested corrugated formation of actual interferometer in real time, with the synthetic Moire fringe that obtains of this two width of cloth interferogram More, thereby realize the directly relevant of complicated corrugated, and can Real Time Observation and employing digital phase shift method fast processing Moire fringe.This digital More's movable phase interfere art is mainly used in directly and complicated standard corrugated occasion relatively.As: aspheric surface detects, and optical system is debug, the detection of aspects such as profile measurement and structural mechanics, fluid mechanics, thermodynamics.

Numeral More interferometry requires the energy Real Time Observation and handles Moire fringe, and therefore requiring More's Moire fringe intensity distributions synthetic and that filtering speed is quick and filtering is later is cosine distribution, and Moire fringe density is enough big, to increase the measurement range on corrugated.The numeral synthetic method is actual interference fringe numeral to be gathered become digital quantity, and the More is synthetic with the digital computation realization, specifically is divided into two kinds of methods of hardware and software digital processing again, synthesizes because speed limit is made numeral with hardware usually.Moire fringe after synthetic also will be made Filtering Processing, can do digital phase shift and calculate.

The virtual interfere striped:

Actual interference fringe:

Usually the synthetic Moire fringe that two stripeds directly multiplied each other, its light distribution is

(3)

(3) in the formula, the 4th

Being Moire fringe, is Useful Information, and other several need filtering to remove.Second and the 3rd is the background interference striped, and its bandwidth and the 4th differ not very big, makes to be difficult to leach the 4th fast simply, perhaps will limit the bandwidth of the 4th Moire fringe, thus the measurement range of dwindling the corrugated.Therefore, its wavefront measurement scope of existing More's synthetic method is still waiting to improve.

Summary of the invention

More's filtering synthetic method that the present invention proposes, its purpose is when synthesizing Moire fringe, directly remove second and the 3rd in (3) formula, promptly remove the background interference striped that is superimposed upon in the Moire fringe, measure the corrugated bandwidth to increase, be convenient to digital filtering, revise first to improve the contrast of Moire fringe, improve the signal to noise ratio (S/N ratio) of signal, thereby improved the precision that Moire fringe is handled in phase shift.That is: the Filtering Processing in the simplification More filtering synthetic method is saved the filtering time, fast the real-time Moire fringe that obtains cosine distribution.

To achieve these goals, respectively the DC component in virtual interfere striped and the actual interference fringe is removed, thereby removed cross term in the Moire fringe after synthetic, to reach the purpose of removing the background interference striped.

Implementation procedure of the present invention is: earlier the virtual interfere striped is gone DC component; Actual interference fringe is carried out pre-service, promptly gather the reference path light intensity, the reference path light intensity is carried out normalized, and the correction factor that utilizes normalized to obtain carries out homogenising to the light path of actual interference fringe to be handled, and the computing method during again with even illumination obtain pretreated parameter; Utilization is carried out the actual interference fringe DC component that parameter that pre-service obtains is removed real-time collection to actual interference fringe; Virtual interfere striped and the actual interference fringe of removing DC component are respectively made More's synthetic method that numeral multiplies each other and superposes, remove the background interference striped in the Moire fringe; Fill the DC component of Moire fringe again,, obtain the Moire fringe of cosine distribution by the low-pass filtering treatment in spatial domain.

The digital picture formula (1) of virtual interfere striped is deducted DC component a to be become:

With the digital picture formula (2) of actual interference fringe deduct DC component c (x y) becomes:

To remove two width of cloth image digitizations after the background multiplies each other and obtains Moire fringe

(6)

Following formula has negative intensity level, can not more can't directly show as the light distribution expression formula of Moire fringe, need fill suitable DC component, to increase the contrast of Moire fringe as far as possible.In the ideal case, the amplitude factor of Moire fringe is 1/2 of a direct current background, thus DC component numerical value should be bd (x, y).Moire fringe I ' then _mFor

(7)

(7) formula is reduced to

Second and the 3rd background striped in (3) formula in (8) formula, have been removed, (8) second (Moire fringe) is bigger with the 3rd band separation in the formula, cutoff frequency that can corresponding raising low-pass filtering, thereby the bandwidth of corresponding increase Moire fringe has also promptly increased the measurement range on tested corrugated.Improved simultaneously the effect of filtering again and shortened the filtering time, be convenient to real-time Moire fringe demonstration and phase shift Moire fringe and handle.

The fringe contrast of actual interferogram is often less than 1, just d (x, y)＜c (x, y).(3) in the formula

A(x，y)＝ac(x，y) (9)

D(x，y)＝1/2bd(x，y) (10)

D (x, y)/(x, y)＜1/2, contrast is lower than theoretical value to A.

In the formula (8)

A′(x，y)＝bd(x，y) (11)

D′(x，y)＝1/2bd(x，y) (12)

D ' (x, y)/(x, y)=1/2, contrast reaches theoretical value to A ', so the Moire fringe contrast in (8) formula will be higher than the represented Moire fringe of (3) formula.Thereby increased signal intensity, helped improving phase shift More processing accuracy.

When stating principle on the implementation, a, b, c (x, y) and d (x, numerical value y) determine very crucial, because the virtual interfere striped is the interferogram that a numerical evaluation goes out, a and b can be that available constant is represented uniformly.And the c in the actual interferogram (x, y) and d (x, y) with regard to complexity how, (x y) is influenced by the inhomogeneous and system's veiling glare of illuminating bundle mainly to c.D (x, y) main with two to restraint the coherence of the beam intensity ratio of coherent lights and laser instrument relevant.In addition, c (x, y) and d (x, numerical stability y) is relevant with the power stability of laser instrument, if adopt frequency stabilization power stabilize laser instrument, then c (x, y) and d (x, numerical stability y) still is higher, can think constant substantially.If (x y) can be used as constant and handles the even c of illumination, and (x y) also can think a constant to d.Because actual interferogram striped is very close, (x y) can adopt the method that the each point light intensity is averaged on the interferogram to try to achieve to c.

(x y) is calculated by formula (12) d

$d=\frac{I_{0\max }-I_{0\min }}{2}---\left(12\right)$

I wherein _OmaxAnd I _OminBe light intensity maximal value and the minimum value in the actual interferogram.If illumination unevenness is similar to actual interference field light distribution because of the reference path light distribution, gather the light distribution I that the interferometer reference path is returned in advance _r(x y), and obtains correction factor as normalized

$K(x,y)=\frac{I_r(x,y)}{I_{r\max }}---\left(13\right)$

I in the formula _RmaxBe maximal value in the reference light distribution.Light intensity value I with actual interferogram ₀(x, y) divided by K (x y) then obtains the uniform interferogram of a width of cloth, the computing method formula during then with even illumination obtain c (x, y) and d (x, y).

After c and d determine, just can realize that the digital filtering of Moire fringe is synthetic.

Virtual interfere figure goes DC component a to finish in advance, as long as optical interference circuit is determined, (x y) also determines with regard to corresponding K, also can measure in advance, c (x, y) and d (x y) can calculate by the actual interferogram of first pilot production one width of cloth, also is constant to tested corrugated c and the d that determines, they can be existed in the internal memory, when actual measurement, c be deducted from actual interferogram in real time.

For improving processing speed, remove c, the More is synthetic, mend A ' (x, y) and process such as spatial domain smothing filtering to realize with hardware.

Effective benefit of the present invention is:

1, is simple and easy to realize.More's filtering synthetic method is simple and easy to realize, goes the background interference stripe effect remarkable.

2, expanded the measurement range of Moire measuring method.Improve the cutoff frequency of low-pass filtering, simplified filtering method, can expand the measurement range of Moire measuring method simultaneously.

Description of drawings

Fig. 1 is the digital filtering synthetic schemes of Moire fringe of the present invention;

Fig. 2 is actual interference fringe pretreatment process figure.

Embodiment

Below in conjunction with accompanying drawing technical scheme of the present invention is described further:

As shown in Figure 1, earlier the virtual interfere striped is removed background DC component a, gather in real time parameter that actual interference fringe utilizes pre-service to obtain remove background DC component c (x, y); Then virtual interfere striped and the actual interference fringe of removing DC component are respectively done synthetic calculating of More that numeral multiplies each other and superposes, remove the background interference striped in the Moire fringe; (x y), by the low-pass filtering treatment in spatial domain, just obtains having only the Moire fringe of cosine light distribution to fill background DC component A ' again.

Synthetic for ease of More's filtering in real time, in advance pre-service is done in actual interference fringe collection, obtaining the correlation parameter of actual interference fringe, and then gather the correlation parameter that actual interference fringe utilization measures in advance, it is synthetic to carry out More's filtering.

As shown in Figure 2, gather the reference path light intensity I similar earlier to actual interference field light distribution _r(x y) carries out normalized, calculates to revise the uneven correction factor of actual interference field light intensity $K(x,y)=\frac{I_r(x,y)}{I_{r\max }},$ I _Rmax(x is with reference to the light distribution maximal value y), the actual interference fringe light intensity value I that will gather again ₀(x, y) (x y) just obtains the actual interference fringe I ' of light intensity homogenising divided by K ₀(x, y), its DC component c (x, y) and amplitude d (x y) all can think constant c and d, and c is I ' ₀(x, mean value y), $d=\frac{I_{0\max }^{\′}-I_{0\min }^{\′}}{2},$

Be respectively light intensity I ' after the pre-service ₀(x, y) maximal value in and minimum value, A ' (x, y)=bd, b is the amplitude of virtual interfere striped, with c, d, (x y) stores as the stand-by parameter that the More synthesizes A '.

Claims (1)

1. More's filtering synthetic method that is used for digital More's movable phase interfere art is characterized in that this method comprises:

The first step goes the virtual interfere striped to DC component;

Actual interference fringe is carried out pre-service: gather the reference path light intensity I similar earlier to actual interference field light distribution _r(x y) carries out normalized, calculates to revise the uneven correction factor of actual interference field light intensity $K(x,y)=\frac{I_r(x,y)}{I_{r\max }},$ I _Rmax(x is with reference to the light distribution maximal value y), the actual interference fringe light intensity value I that will gather again ₀(x, y) (x y) just obtains the actual interference fringe I ' of light intensity homogenising divided by K ₀(x, y), its DC component c (x, y) and amplitude d (x y) all can think constant c and d, and c is I ' ₀(x, mean value y), $d=\frac{I_{0\max }^{\′}-I_{0\min }^{\′}}{2},$ Be respectively light intensity I ' after the pre-service ₀(x, y) maximal value in and minimum value, A ' (x, y)=bd, b is the amplitude of virtual interfere striped, with c, d, (x y) stores as the stand-by parameter that the More synthesizes A ';

Utilization is carried out the parameter that pre-service obtains to actual interference fringe, removes the DC component of the actual interference fringe of real-time collection;

Second step, virtual interfere striped and the actual interference fringe of removing DC component are respectively done synthetic calculating of More that numeral multiplies each other and superposes, remove the background interference striped in the Moire fringe;

In the 3rd step, (x y), by the low-pass filtering treatment in spatial domain, obtains the Moire fringe of cosine distribution to fill the background DC component A ' of Moire fringe.

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