CN101655358A

CN101655358A - Improved dynamic characteristic of phase measuring profilometry of cross compound grating by color coding

Info

Publication number: CN101655358A
Application number: CN200910059846A
Authority: CN
Inventors: 曹益平; 何宇航; 苏显渝; 向立群; 陈文静; 张启灿; 刘元坤
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2009-07-01
Filing date: 2009-07-01
Publication date: 2010-02-24

Abstract

The invention is a method for real-time measurement of the three-dimensional surface shape and deformation of an object by adopting color-coded orthogonal composite grating phase measurement profilometry in the three-dimensional sensing technology. Using a computer to design and encode, using a color digital projector, the color-coded surface structure modulation template is instantly imaged on the surface of the object, and then the color-coded object deformation fringe pattern is recorded with a color camera device, and then the fringe pattern is obtained by color decoding The orthogonal composite grating with ^2.15 gray levels improves the dynamic characteristics of the orthogonal composite grating from ^2.8 bit depth to ^2.15 bit depth, and can accurately restore the three-dimensional surface shape of the object. Further analysis of the data processing results can Obtain some digitized information such as object deformation. The invention can be used for the measurement and research of the surface features of objects with diffuse reflection characteristics. The invention has the advantages of high measurement precision, fast response time, real-time acquisition of three-dimensional surface shape data of objects, and the like.

Description

Improving Dynamic Properties of Orthogonal Composite Grating Phase Measurement Profilometry Using Color Coding

一、技术领域1. Technical field

本发明涉及光学三维传感技术，特别是涉及基于位相测量轮廓术方法的采用颜色编码的正交复合光栅实现对物体的实时三维面形的测量。The invention relates to an optical three-dimensional sensing technology, in particular to a phase measurement profilometry method using a color-coded orthogonal compound grating to realize real-time three-dimensional surface measurement of an object.

二、技术背景2. Technical background

三维面形测量，在机器视觉、生物医学、工业检测、快速成型、影视特技、产品质量控制等领域具有重要意义。光学三维传感技术，由于其具有非接触、精度高、大面积测量、易于自动控制等优点获得广泛的研究和应用。现有的光学三维传感方法主要包括：三角测量法、莫尔条纹法(MoiréTopography，简称MT)、傅里叶变换轮廓术(Fourier Transform Profilometry，简称FTP)、空间相位检测术(Spatial Phase Detection，简称SPD)、位相测量轮廓术(Phase MeasuringProfilometry，简称PMP)等，这些方法都是通过对受三维物体面形调制的空间结构光场进行解调制，来获得物体的三维面形信息。其中最常用的空间结构光场三维传感方法是傅立叶变换轮廓术和位相测量轮廓术。傅里叶变换轮廓术是通过对变形条纹图像进行傅里叶变换、频域滤波和逆傅里叶变换等步骤实现的。傅里叶变换轮廓术只需要用一帧条纹图来重建三维面形，实时性较好，可以用于动态过程的三维传感；但由于其涉及到滤波操作，频谱混叠会降低测量精度，该方法对环境光也比较敏感。位相测量轮廓术则需要从多帧相移条纹图形来重建三维面形，具有很高的精度，但由于采用多次相移，实时性较差。基于正交复合光栅的位相测量轮廓术综合了位相测量轮廓术和傅里叶变换轮廓术的优点，使用一帧条纹就可以重建物体的三维面形，并能达到较高的精度要求；但该方法由于从一帧条纹中提取三帧以上的相移条纹，受到投影系统和成像系统空间带宽积的限制，解调出来的相移条纹具有较小的灰度动态范围，降低了位相提取和三维测量的精度，应用本发明提及的方法就可以解决这一关键技术难题。Three-dimensional surface measurement is of great significance in the fields of machine vision, biomedicine, industrial inspection, rapid prototyping, film and television special effects, and product quality control. Optical three-dimensional sensing technology has been widely researched and applied due to its advantages of non-contact, high precision, large-area measurement, and easy automatic control. Existing optical three-dimensional sensing methods mainly include: triangulation, Moiré Topography (MT for short), Fourier Transform Profilometry (FTP for short), Spatial Phase Detection (Spatial Phase Detection, SPD for short), Phase Measuring Profilometry (PMP for short), etc. These methods obtain the three-dimensional surface shape information of the object by demodulating the spatially structured light field modulated by the three-dimensional object surface shape. The most commonly used three-dimensional sensing methods of spatially structured light field are Fourier transform profilometry and phase measurement profilometry. Fourier transform profilometry is realized through the steps of Fourier transform, frequency domain filtering and inverse Fourier transform on the deformed fringe image. Fourier transform profilometry only needs to use one frame of fringe images to reconstruct the three-dimensional surface shape, which has good real-time performance and can be used for three-dimensional sensing of dynamic processes; but because it involves filtering operations, spectral aliasing will reduce the measurement accuracy, This method is also sensitive to ambient light. Phase measurement profilometry needs to reconstruct the three-dimensional surface shape from multiple frames of phase-shifted fringe patterns, which has high accuracy, but due to the use of multiple phase shifts, the real-time performance is poor. Phase measurement profilometry based on orthogonal composite grating combines the advantages of phase measurement profilometry and Fourier transform profilometry, and can reconstruct the three-dimensional surface shape of an object with one frame of fringes, and can achieve high precision requirements; but this Due to the extraction of more than three frames of phase-shifted fringes from one frame of fringes, the demodulated phase-shifted fringes have a small gray-scale dynamic range due to the limitation of the spatial bandwidth product of the projection system and the imaging system, which reduces the phase extraction and three-dimensional For the accuracy of measurement, this key technical problem can be solved by applying the method mentioned in the present invention.

三、发明内容3. Contents of the invention

本发明的目的则是针对对一帧正交复合条纹进行解码相移条纹灰度变化范围较低的缺陷，提出一种在三维传感技术测量中采用颜色编码提高正交复合光栅位相测量轮廓术的动态特性的方法。这种方法能非常好地做到扩大相移条纹的灰度域，实时获得物体表面变形条纹分布的图像信息，具有较高的测量精度，能真正地实现动态和瞬态测量。The purpose of the present invention is to solve the defect that the range of gray scale of the phase-shift fringes is relatively low when decoding a frame of orthogonal composite fringes, and propose a method of using color coding to improve the phase measurement profilometry of orthogonal composite gratings in the measurement of three-dimensional sensing technology. method of dynamic properties. This method can very well expand the gray scale of the phase shift fringe, obtain real-time image information of the distribution of deformation fringes on the surface of the object, has high measurement accuracy, and can truly realize dynamic and transient measurement.

本发明的目的是采用下述技术方案来实现的：The object of the present invention is to adopt following technical scheme to realize:

采用计算机设计编码产生所需要的彩色光栅图案，即对透射光场进行面结构和颜色编码，然后运用彩色数字投影设备将光栅图案投影在物体上，降低了正交复合光栅位相测量轮廓术对系统空间带宽积的要求。Computer design and coding are used to generate the required color grating pattern, that is, surface structure and color coding of the transmitted light field, and then the color digital projection device is used to project the grating pattern on the object, which reduces the impact of orthogonal compound grating phase measurement profilometry on the system Space bandwidth product requirements.

本发明与现有技术相比有如下优点：Compared with the prior art, the present invention has the following advantages:

1.本发明使用颜色编码的正交复合光栅，扩大了相移条纹的灰度域，提高了正交复合光栅位相测量轮廓术的测量精度。1. The present invention uses a color-coded orthogonal compound grating to expand the gray scale of the phase-shift fringes and improve the measurement accuracy of the orthogonal compound grating phase measurement profilometry.

2.同样是获取一帧变形条纹图案，本发明相比傅立叶变换轮廓术具有更高的测量精度；而相比位相测量轮廓术则不需要进行相移，以及不需要采集多帧变形条纹图案。2. Also to obtain a frame of deformed fringe pattern, the present invention has higher measurement accuracy than Fourier transform profilometry; and phase measurement profilometry does not require phase shifting, and does not need to collect multiple frames of deformed fringe pattern.

3.本发明通过计算机软件可以灵活设计所需要的彩色光栅编码，因此可以在很短的时间内得到所需要的光栅图案。3. The present invention can flexibly design the required color grating code through computer software, so the required grating pattern can be obtained in a very short time.

四、附图说明4. Description of drawings

图1位相测量轮廓术的光路示意图。Figure 1 Schematic diagram of the optical path of phase measurement profilometry.

图2通过计算机设计编码的彩色正交复合光栅。Figure 2 Color orthogonal compound grating coded by computer design.

图3受到物体面形调制的彩色正交复合光栅变形条纹。Figure 3 is the deformed fringe of color orthogonal compound grating modulated by the shape of the object.

图4用上述技术方案恢复的物体。Fig. 4 The object recovered by the technical solution described above.

五、具体实施方式5. Specific implementation

下面结合附图、工作原理对本发明作进一步详细说明。The present invention will be described in further detail below in conjunction with the accompanying drawings and working principles.

先说明用正交复合光栅位相测量轮廓术实现实时三维面形的测量。用正交复合光栅实现实时三维面形测量的光路与传统的位相测量轮廓术的光路相似。图1是PMP方法的投影光路，P₁和P₂是投影系统的入瞳和出瞳，I₂和I₁是成像系统的入瞳和出瞳。成像光轴垂直于参考平面，并与投影光轴的夹角为θ，它们相交于参考平面上的O点，d为探测器光心到投影设备光心之间的距离，l为探测器光心到参考平面之间的距离。Firstly, the real-time three-dimensional surface shape measurement is realized by using the orthogonal composite grating phase measurement profilometry. The optical path of real-time three-dimensional surface measurement with orthogonal composite grating is similar to that of traditional phase measurement profilometry. Figure 1 is the projection optical path of the PMP method, P ₁ and P ₂ are the entrance pupil and exit pupil of the projection system, I ₂ and I ₁ are the entrance pupil and exit pupil of the imaging system. The imaging optical axis is perpendicular to the reference plane, and the included angle with the projection optical axis is θ, they intersect at point O on the reference plane, d is the distance between the optical center of the detector and the optical center of the projection device, l is the detector light The distance from the center to the reference plane.

用计算机设计一组满周期等步相移光栅，其投影强度像表示为：Design a group of full-period equal-step phase-shift gratings by computer, and the projection intensity image is expressed as:

$I_{n}^{0} (x, y) = a + b \cos (2 π η_{y} y - 2 πn / N),$ (n＝1，2…，N) (1) $I_{no}^{0} (x, the y) = a + b \cos (2 π η_{the y} the y - 2 πn / N),$ (n=1, 2..., N) (1)

a表示直流偏置，b/a表示条纹对比度，将这组等步相移光栅分别调制在一组载频正弦光栅上，载频光栅的栅线方向和相移光栅的栅线方向垂直，将各个调制成分叠加，得到的正交复合光栅的投影强度像为：a represents the DC bias, and b/a represents the fringe contrast. This group of equal-step phase shift gratings is respectively modulated on a group of carrier frequency sinusoidal gratings. The direction of the grid lines of the carrier frequency grating is perpendicular to the direction of the phase shift grating lines. Each modulation component is superimposed, and the projected intensity image of the obtained orthogonal compound grating is:

$I^{0} (x, y) = c + d Σ_{n = 1}^{N} I_{n}^{0} (x, y) \cdot \cos (2 π ξ_{n} x)$ (2) $I^{0} (x, the y) = c + d Σ_{no = 1}^{N} I_{no}^{0} (x, the y) &Center Dot; \cos (2 π ξ_{no} x)$ (2)

$= = c c + + d d \cdot &Center Dot; {Σ Σ}_{n no = = 11}^{N N} [[a a + + b b cos cos ((22 π π {η η}_{y the y} y the y - - 22 πn πn / / N N))]] \cdot \cdot cos cos ((22 π π {ξ ξ}_{n no} x x))$

频率ξ_n为载频正弦光栅的频率，c为正交光栅的直流偏置，d/c为条纹对比度。当一帧正交复合光栅图案被投影到物体表面时，不考虑物体的反射率和环境光强度，CCD得到的变形条纹可以表示为：Frequency ξ _n is the frequency of the carrier frequency sinusoidal grating, c is the DC bias of the orthogonal grating, and d/c is the fringe contrast. When a frame of orthogonal composite grating pattern is projected onto the surface of an object, regardless of the reflectivity of the object and the intensity of ambient light, the deformed fringes obtained by the CCD can be expressed as:

$I I ((x x,, y the y)) = = c c + + d d \cdot &Center Dot; {Σ Σ}_{n no = = 11}^{N N} [[a a + + b b cos cos (({22 πη πη}_{y the y} y the y + + φ φ - - 22 πn πn / / N N))]] \cdot &Center Dot; cos cos ((22 π π {ξ ξ}_{n no} x x)) - - - - - - ((33))$

其中φ为物体的高度引起的相移光栅条纹的相位变化。对(3)进行二维快速傅里叶变换(FFT)，得到的频谱I_FFT(ξ，η)如下：where φ is the phase change of the phase-shifted grating fringes caused by the height of the object. Carry out two-dimensional fast Fourier transform (FFT) to (3), the frequency spectrum I _FFT (ξ, η) that obtains is as follows:

${I I}_{FFT FFT} ((ξ ξ,, η η)) = = &Integral; &Integral; &Integral; &Integral; I I ((x x,, y the y)) {e e}^{- - j j 22 π π ((ξx ξx + + ηy ηy))} dxdy dxdy$

$= = &Integral; &Integral; &Integral; &Integral; {{c c + + d d \cdot \cdot {Σ Σ}_{n no = = 11}^{N N} [[a a + + b b cos cos ((22 {πη πη}_{y the y} + + φ φ - - 22 πn πn / / N N))]] \cdot \cdot cos cos ((22 π π {ξ ξ}_{n no} x x))}} {e e}^{- - j j 22 π π ((ξx ξx + + ηy ηy))} dxdy dxdy$

$= = cδ cδ ((x x,, y the y)) + + d d \cdot \cdot {Σ Σ}_{n no = = 11}^{N N} {{\frac{11}{22} aδ aδ ((ξ ξ + + {ξ ξ}_{n no},, η η)) + + \frac{11}{22} aδ aδ ((ξ ξ - - {ξ ξ}_{n no},, η η)) + + \frac{11}{44} bδ bδ ((ξ ξ - - {ξ ξ}_{n no},, η η - - {η η}_{y the y})) {e e}^{j j ((φ φ - - 22 πn πn / / N N))}$

$+ + \frac{11}{44} bδ bδ ((ξ ξ - - {ξ ξ}_{n no},, η η + + {η η}_{y the y})) {e e}^{- - j j ((φ φ - - 22 πn πn / / N N))} + + \frac{11}{44} bδ bδ ((ξ ξ + + {ξ ξ}_{n no},, η η - - {η η}_{y the y})) {e e}^{j j ((φ φ - - 22 πn πn / / N N))}$

$+ + \frac{11}{44} bδ bδ ((ξ ξ + + {ξ ξ}_{n no},, η η + + {η η}_{y the y})) {e e}^{- - j j ((φ φ - - 22 πn πn / / N N))}}} - - - - - - ((44))$

式中ξ，η为空间频率，从(4)式可知I(x，y)经过FFT后得到的频谱图中一共有6N+1个的频谱成分，其中cδ(ξ，η)为携带背景信息的零频；含有η_y的才是携带相移信息的频谱。为了能够有效提取出相应的相移光栅，要求尽可能的使各个频谱成分相互独立，没有混叠，因此可通过选择合适的载频光栅的频率来使各个频谱在频谱图中尽量独立。当满足上述条件时，选择适当的滤波器，可从整个频谱中提取第n个相移光栅变形条纹的频谱成分I_FFTn(x，y)：In the formula, ξ, η are the spatial frequencies. It can be seen from the formula (4) that I(x, y) has a total of 6N+1 spectral components in the spectrogram obtained after FFT, where cδ(ξ, η) is the background information The zero frequency of ; the spectrum containing η _y is the spectrum carrying phase shift information. In order to effectively extract the corresponding phase shift grating, it is required to make each spectrum component independent of each other as much as possible without aliasing. Therefore, the frequency of each frequency grating can be selected to make each spectrum as independent as possible in the spectrum diagram. When the above conditions are met, the appropriate filter can be selected to extract the spectral component I _FFTn (x, y) of the nth phase-shifted grating deformation fringe from the entire spectrum:

${I I}_{FFTn FFTn} = = \frac{11}{22} adδ adδ ((ξ ξ - - {ξ ξ}_{n no},, η η))$

(5)

$= = \frac{11}{22} adδ adδ ((ξ ξ - - {ξ ξ}_{n no},, η η))$

对(5)进行快速逆傅里叶变换(IFFT)得I_Rn，即：Perform fast inverse Fourier transform (IFFT) to (5) to get I _Rn , namely:

${I I}_{Rn n} = = {&Integral; &Integral; &Integral; &Integral; I I}_{FFTn FFTn} {e e}^{j j 22 π π ((xξ xξ + + yη yη))} dξdη dξdη$

I_Rn是一虚数，对I_Rn取模即可解调出一相移光栅变形条纹I_IMAGn：I _Rn is an imaginary number, taking the modulus of I _Rn can demodulate a phase-shifted grating deformed fringe I _IMAGn :

${I I}_{IMAGn IMAGn} = = | | {I I}_{Rn Rn} | |$

可以看出，从相移正交光栅中解调出的相移变形光栅I_IMAGn与用传统的满周期等步位相测量轮廓术直接获取的相移变形光栅像I_n(x，y)只是在强度上有一个倍数关系。因此，可以用传统的位相测量轮廓术的方法对解调后的变形光栅像进行处理，从而获得物体的三维面形分布。It can be seen that the phase _- shifted deformed grating I _IMAGn demodulated from the phase-shifted orthogonal grating is only in the There is a multiplier relationship in intensity. Therefore, the demodulated deformed grating image can be processed by the traditional method of phase measurement profilometry, so as to obtain the three-dimensional surface shape distribution of the object.

下面说明颜色编码的原理。由于投影系统和成像系统空间带宽积的限制，从正交复合条纹中分离出来的相移条纹只有少量的灰度级次，相移的次数越多，相移条纹的灰度域越小，这严重地影响了位相提取和三维重建的精度。由于颜色具有较高的动态范围，可以用颜色替代光强对物体的三维信息进行传递，即对正交复合光栅的条纹像进行颜色编码。如果红、绿、蓝三基色的色值范围是[0，255]，即8位bit的数据，理论上讲，彩色数字投影仪总共可以投出2²⁴种颜色，考虑到噪声和彩色摄象机的响应特性，只选取其中2¹⁵种颜色，即取8位bit数据的前5位。将(2)式对应的条纹像强度分成2¹⁵等份，让每一种强度值对应一种颜色，建立查找表。彩色摄象机接收到变形的彩色条纹，根据查找表找到每种颜色对应的光强值，按照传统的正交复合光栅位相测量轮廓术，可以获得物体的三维面形。The principle of color coding is explained below. Due to the limitation of the space-bandwidth product of the projection system and the imaging system, the phase-shifted fringes separated from the orthogonal compound fringes have only a small number of gray levels, and the more the number of phase shifts, the smaller the gray-scale domain of the phase-shifted fringes. It seriously affects the accuracy of phase extraction and 3D reconstruction. Because the color has a high dynamic range, the three-dimensional information of the object can be transmitted by using the color instead of the light intensity, that is, the color coding of the fringe image of the orthogonal composite grating. If the color value range of the three primary colors of red, green, and blue is [0, 255], that is, 8-bit data, theoretically speaking, a color digital projector can cast a total of 2 to ²⁴ colors. Considering noise and color imaging According to the response characteristics of the machine, only 2 to ¹⁵ colors are selected, that is, the first 5 bits of 8-bit data are taken. Divide the fringe image intensity corresponding to formula (2) into 2 ¹⁵ equal parts, let each intensity value correspond to a color, and establish a lookup table. The color camera receives the distorted color fringes, finds the light intensity value corresponding to each color according to the look-up table, and obtains the three-dimensional surface shape of the object according to the traditional orthogonal compound grating phase measurement profilometry.

图2是用计算机设计生成的彩色正交复合光栅。Figure 2 is a color orthogonal composite grating designed and generated by computer.

图3是受到物体面形调制的彩色正交复合光栅变形条纹。Fig. 3 is the deformed fringes of the color orthogonal compound grating modulated by the shape of the object.

图4是用上述技术方案恢复的物体。Fig. 4 is the object recovered with the above-mentioned technical scheme.

Claims

1. A method suitable for three-dimensional reconstruction using color coding to improve the dynamic characteristics of orthogonal composite grating phase measurement profilometry, characterized in that digital projection equipment is used to project the template pattern of the color-coded orthogonal composite grating onto the object surface , use the imaging device to record the deformed light field image, and process the obtained light field image to obtain the instantaneous three-dimensional surface shape distribution of the object.

2. according to the described method of claim 1, it is characterized in that adopting the RGB color coding of 24 bit depths to replace traditional 8 bit deep gray scale coding, and consider the crosstalk of RGB three primary colors, realize 15 bit deep color codings, Effectively improve the dynamic characteristics of orthogonal compound grating phase measurement profilometry.

3. according to the described method of claim 1, it is characterized in that the template pattern of the orthogonal composite grating through the said color code refers to the projection surface structure modulation template that utilizes computer design coding, comprises orthogonal modulation sinusoidal grating, positive Coding templates such as alternating modulating Roche gratings.

4. according to the described method of claim 1, it is characterized in that said deformed light field image that is obtained is processed, is to utilize the method for fast Fourier transform to carry out color decoding, Fourier transform, filtering, Inverse Fourier transform, phase extraction and expansion and other processing and operations are aimed at obtaining the surface shape distribution of the object by demodulating the phase, and also including processing the deformed light field by using the spatial phase detection method to obtain the surface shape distribution of the object .

5. according to the described method of claim 1, it is characterized in that adopting color coding to improve the dynamic characteristic of orthogonal composite grating phase measurement profilometry, research the instantaneous state of object, carry out pattern recognition or extract some characteristic parameters of object, as surface shape, attitude, deformation, feature point distance, etc.