CN1302999A - Method for reconstructing 3D contour of digital projection based on phase-shifting method - Google Patents

Abstract

A method based on phase shifting for reconstructing 3D contour of digital projection includes such steps as pre-compiling projection pattern generation program, projecting the patterns onto the surface of object to be tested at time intervals by projector controlled by computer, taking the deformed image of each pattern by camera, then collecting, storing and processing the image data, and reconstructing the 3D contour based on the phase information of each point on the object and the geometric relation between projector, camera and object. Its advantages are the simplified projector and phase-shift unit, and high effect.

Description

A kind of method for reconstructing 3 D contour of digital projection based on phase-shifting method

The invention belongs to three-dimensional sensing and metering field, particularly the computer reconstruction technology of three-dimensional object surface pattern.

The computer reconstruction technology of three-dimensional object surface profile is one of focus of at present domestic and international three-dimensional sensing and quantitative study, and it is widely used in fields such as Aero-Space, machine-building, online detection and quality control, medical diagnosis, computer aided design/computer aided machine (CAD/CAM), robotic vision system.Phase-shifting method is the most ripe, the most reliable a kind of method in all three-dimensional appearance reconstructing method, it have calculated amount less, can be with reach very advantage such as high sensitivity and precision and anti-static noise than coarse grating, be the preferred option under the situation of conditions permit.

The principle of work of phase-shifting method is described below:

Shown in Fig. 1 a and Fig. 1 b is N step phase-shifting method.The sinusoidal grating striped that it will project to body surface moves N time, utilizes discrete phase shifting method to obtain the modulated image of the N width of cloth (N＞3), goes out the position according to the N-PHASE algorithm computation and distributes mutually, utilizes geometric relationship to try to achieve the height profile of body surface at last.

As shown in Figure 1a, sinusoidal light field 13 is with incident angle θ _iIncide on the reference planes 11, ccd image sensor 12 is at θ _vReceive on the direction by the light field after reference planes 11 modulation, wherein z is the light field cycle that receives.The cycle of supposing the sinusoidal light field of projection is x, and the plane moved Δ h, and shown in Fig. 1 b, at this moment z just has a variation delta z: Δ z=Δ h[tan (θ _i)+tan (θ _v)] cos (θ _v) (1) this can cause a phase change Δ φ in the light field in modulation: $\mathrm{\Δ\φ}=2\mathrm{\π}\frac{\mathrm{\Δz}}{z}=\frac{2\mathrm{\π}\•\mathrm{\Δh}\[\tan \left({\mathrm{\θ}}_i\right)+\tan \left({\mathrm{\θ}}_v\right)\]\cos \left({\mathrm{\θ}}_i\right)}{x}---\left(2\right)$

As can be seen from the above equation, the height change h in somewhere on the reference planes can be tried to achieve by the phase shift Δ φ of modulation light field.When ccd image sensor during perpendicular to reference planes, θ _vBe zero, so height change is: $\mathrm{\Δh}=\frac{x\•\mathrm{\Δ\φ}}{2\mathrm{\π}\sin \left({\mathrm{\θ}}_i\right)}---\left(3\right)$ As long as we get access to Δ φ, just can reconstruct the three-D profile of object.

When a light intensity of being regulated out by sinusoidal grating projected on the diffuse reflection body surface by two-dimensional projection's pattern of Sine distribution, the modulated image that is detected by imaging system can be described as: I _i(x, y)=a (x, y) [(l+m (and x, y) cos (φ (and x, y)+φ _i)] (4) ${\mathrm{\φ}}_i=i\•\frac{2\mathrm{\π}}{N},(i=1,2,\·\·\·,N)---\left(5\right)$

Wherein, (x y) represents bias light intensity to a, and (x y) represents fringe contrast to m, and (x y) has represented the feature of candy strip to phase function φ, thereby has comprised the information of profiling object surface, φ _iBe starting phase angle, N is the phase shift number of times.By regulating grating, can produce the sinusoidal projection pattern of different initial phases.Mobile grating N time (N 〉=3), the distance of each mobile P/N (P is the cycle of sinusoidal grating), then producing phase change is the N width of cloth projection pattern of 2 π/N.Note image after the modulation of each width of cloth pattern with ccd image sensor, have according to the N-PHASE algorithm: $\tan \left(\mathrm{\φ}(x,y)\right)=\frac{\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{I}_n(x,y)\•\sin (2\mathrm{\πn}/N)}{\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{I}_n(x,y)\•\cos (2\mathrm{\πn}/N)}---\left(6\right)$ So Δ φ can ask.

Traditional phase-shifting method measuring system is utilized sinusoidal grating to produce the projection light field and is shone on the testee, drive grating by stepper motor and move (N 〉=3) N time, the distance of each mobile P/N (P is the cycle of sinusoidal grating), produce the sinusoidal projection pattern of the different initial phases of the N width of cloth, note the deformation pattern that each width of cloth projection pattern is formed by the body surface modulation successively with video camera then; Computing machine is gathered video image by image pick-up card, and image data storage is got up; Handle these view data with N step phase-shifting method algorithm (N-PHASE algorithm), obtain the phase information of each point on the object; Reconstruct the three-D profile of object according to the geometric relationship between the phase information of each point on the object and projector, gamma camera, the testee.Because a variety of causes such as step-out of machining and stepper motor, the grating displacement of expectation usually can not accurately obtain, and this has brought very mistake to measurement result.Traditional phase changer as shown in Figure 2, the distance that mostly adopts the next real-time monitoring grating of accurate micro-displacement sensor to move, the distance that reality is moved feeds back to computing machine, and then does corresponding compensation according to deviation by servoamplifier drive stepping motor drive worktable.Though this method can be controlled phase shift accurately, the micro-displacement sensor of working stability costs an arm and a leg on the market, and volume is bigger, makes the design and installation of this cover feedback control system very inconvenient.

The objective of the invention is to for overcoming traditional phase-shifting method measuring system phase changer cost height, design, the complicated weak point of control, a kind of method of digital projection has been proposed, utilize computing machine to realize projection light field and phase shift from software, simplify projection, phase shift section in the traditional measurement system greatly, obtained result preferably.

The method for reconstructing 3 D contour of digital projection that the present invention proposes is characterized in that: work out the projection pattern generator program in advance, with generating the sinusoidal grating of fixed skew projection pattern is arranged more than three width of cloth; Move described program, the digital projector that computerizeds control projects projection pattern on the testee surface at interval successively by certain hour; Video camera is noted the deformation pattern that each width of cloth projection pattern is formed by the body surface modulation successively; Computing machine is gathered video image by image pick-up card, and image data storage is got up; With these view data of N step phase-shifting method algorithm process, obtain the phase information of each point on the object; Reconstruct the three-D profile of object according to the geometric relationship between the phase information of each point on the object and projector, gamma camera, the testee.

The generation of above-mentioned projection pattern can realize by various programming languages.Since on the projection pattern that generates from left to right light intensity change by the sinusoidal rule cycle, so can use computing machine programming Control projector, from left to right draw a series of straight lines by sinusoidal grey scale change successively and realize sinusoidal projection light field pattern.

The processing of steps such as the collection of projected image of the present invention, processing all can be adopted traditional disposal route.

The camera acquisition image is for different image pick-up cards, and its implementation also may be different.For example,, can programme so to be allowed to condition at and gather a few width of cloth images during every width of cloth pattern throws, select for use the best width of cloth of effect to enter down the Flame Image Process in step as the modulation image of this width of cloth projection pattern correspondence if used image pick-up card is programmable.If image pick-up card can not be programmed, can adopt the method for artificial control computer to carry out image acquisition.

The present invention is by adopting the method for digital projection, and it is higher effectively to have overcome traditional phase-shifting method measuring system phase changer cost, and design, the complicated deficiency of control have obtained good result.

Brief Description Of Drawings:

Fig. 1 is the phase-shifting method principle schematic.

Fig. 2 moves control chart for the grating of traditional phase changer.

Fig. 3 is an embodiment of the invention measurement mechanism synoptic diagram.

Fig. 4 is an embodiment of the invention measurement mechanism geometric relationship synoptic diagram.

Fig. 5 is the projection pattern automatically generating program process flow diagram of the embodiment of the invention.

Fig. 6 is the Flame Image Process process flow diagram of the embodiment of the invention.

A kind of computer control projector that the present invention proposes realizes that the embodiment of the method for reconstructing 3 D contour of projection light field and phase shift is described in detail as follows in conjunction with the accompanying drawings:

The present invention is embodiment with 4 width of cloth projection pattern, the measuring system of present embodiment as shown in Figure 3, projector 32 adopts EPSON7100 type LCD projector, resolution 1024 * 768 pixels, illumination 650 lumens; Imageing sensor 35 is quick logical TMC-56 type colored CCD gamma cameras, 640 * 480 pixels, 256 grades of gray scales (B/W output); Computing machine 31 performances are Pentium 233MHz, have programmable video input card, and 33,34,36 is respectively projection pattern, testee and the video image that collects.

The projection that above-mentioned measuring system adopts and the geometric relationship of imaging system as shown in Figure 4, P ₂And I ₂Emergent pupil and the entrance pupil of representing optical projection system and imaging system respectively, O are the intersection points of optical projection system and imaging system optical axis, and reference planes are vertical with the optical axis of imaging system.Testee should be placed in about on the point-symmetric position of O as far as possible, and the visual field of projection, imaging is evenly distributed.Under this situation, in the computing formula (3) $\sin \left({\mathrm{\&theta;}}_i\right)=d/\sqrt{{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="A0110416300081.png"\; state="\{\{state\}\}">d</figure-callout>}}^2+{\mathrm{<figure-callout\; id="2"\; label="l"\; filenames="A0110416300081.png"\; state="\{\{state\}\}">l</figure-callout>}}^2}$ , remaining measures Δ φ with phase-shifting method exactly.

The specific implementation step of the method for reconstructing 3 D contour of digital projection of present embodiment comprises: at first, establishment projection pattern generator program, its step as shown in Figure 5, defining variable at first, initialize; Define drawing area then, finish initialization; Adopt Visual Basic language to recirculate initial phase according to each width of cloth image by the setting-out of sinusoidal gray scale rule again by three.The projection pattern of definition control earlier number, every width of cloth projection pattern projection number of cycles, interior setting-out number of each projection cycle and their control threshold value variablees separately are respectively n, i, j, c, b, a, compose zero for n, i, j.Define a time-delay variable, assignment is 5 seconds in the present embodiment.Define 0.7 times of full frame width, full frame altitude range is a drawing area, and drawing area is provided with between two parties, finishes the drawing initialization.Present embodiment is drawn 128 lines by each in grey scale change cycle in drawing area, 7 cycles of picture draw altogether, so only needs be taken as 127 to a among Fig. 6, and b is taken as 6, and c is taken as 3, realizes that with Visual Basic Programming with Pascal Language this three recirculates and get final product.

Secondly, the program that operation is finished above, the LCD projector that computerizeds control projects the projection pattern that generates on the body surface successively by 5 second time interval setting.Read the Programming Notes of programmable vision capture card, work out corresponding program, during this period of time at interval in, allow the CCD gamma camera note the deformation pattern that each width of cloth projection pattern is formed by the body surface modulation successively, and they be stored as the BMP file.

At last, carry out Flame Image Process, its process as shown in Figure 6.At first will read in the image file of acquisition, wherein gradation data is saved as matrix, present embodiment uses the imread () function under the Matlab directly to read in the BMP file, and gradation data wherein is saved as matrix; Next the data that obtain are carried out filtering, remove noise wherein, present embodiment has utilized under the Matlab powerful wavelet filtering and Fourier transform kit to finish this work; When reading in successively, after Filtering Processing crosses each width of cloth view data, obtaining the phase information of each point on the object, obtain the height of each point by the geometric relationship of system by formula (3), thereby reconstruct the three-D profile of object according to N-PHASE algorithmic formula (6).

Experiment shows that method of the present invention has been simplified projection, the phase shift section in the traditional measurement system greatly, has obtained gratifying result.

Claims (1)

1, a kind of method for reconstructing 3 D contour of digital projection based on phase-shifting method is characterized in that may further comprise the steps:

(1) works out the projection pattern generator program in advance, the sinusoidal grating of fixed skew projection pattern is arranged more than three width of cloth with generating;

(2) move described program, the digital projector that computerizeds control projects projection pattern on the testee surface at interval successively by certain hour;

(3) video camera is noted the deformation pattern that each width of cloth projection pattern is formed by the body surface modulation successively;

(4) computing machine is gathered video image by image pick-up card, and image data storage is got up;

(5), obtain the phase information of each point on the object with these view data of N step phase-shifting method algorithm process;

(6) reconstruct the three-D profile of object according to the geometric relationship between the phase information of each point on the object and projector, gamma camera, the testee.

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