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Elimination method of crosstalk and chromatic aberration between color channels for composite surface measurement
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摘要:
为实现漫反射表面和镜面复合表面的快速测量，基于条纹投影和条纹反射的复合表面测量系统通过相机的多颜色通道快速获得绝对相位。针对复合表面形貌测量中相机、投影仪、显示屏所引入颜色通道间的串扰和色差，研究了基于矩阵的串扰消除方法和绝对相位对应像素偏差的色差消除方法。基于串扰矩阵，分别建立投影仪和显示屏的串扰矩阵，完成颜色通道间的串扰消除。通过彩色正交条纹获得各颜色通道水平和竖直方向的绝对相位，建立颜色通道间相位差和像素偏差之间的关系，实现每一像素点的像素偏差校正，消除色差的影响。实验结果证明，所提色差和串扰消除方法使复合台阶的测量均方根误差从0.479 mm降至0.030 mm，提高了测量效率和测量精度。
Abstract:In order to realize the rapid measurement of composite surfaces with diffuse and mirror reflection, the composite surface measurement system based on fringe projection and fringe reflection can obtain the absolute phase rapidly through the multi-color channel of the camera. Aiming at the crosstalk and chromatic aberration between the color channels introduced by the camera, projector, and display in the composite surface topography measurement, this paper studies the crosstalk elimination method based on the matrix and the chromatic aberration elimination method of the absolute phase corresponding pixel deviation. Based on the crosstalk matrix, the crosstalk matrix of the projector and display screen is established. The crosstalk intensity from other channels in the desired color channel is eliminated to complete the crosstalk elimination between color channels. The absolute phase in the horizontal and vertical directions of each color channel is obtained by color orthogonal stripes. The relationship between phase difference and pixel deviation is established to realize the pixel deviation correction of each pixel point and eliminate the influence of color difference. The experimental results show that the proposed method reduces the average measurement error of the composite step from 0.479 mm to 0.030 mm, and improves the efficiency and accuracy of measurement.
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Overview: Due to the large dynamic range and high precision, the optical 3D measurement technology based on phase calculation is widely used in aerospace, automobile manufacturing, biomedicine, cultural relics protection, and other fields to measure a type of surface. For example, fringe projection profilometry and phase measurement deflectometry are used to measure diffuse and specular surfaces, respectively. With the development of advanced manufacturing technology, the measurement of one type of surface cannot meet the current situation. In the existing research on diffuse and specular composite surfaces, 3D topography restoration of large gradient and discontinuous composite surfaces has been achieved. The composite surface measurement system based on fringe projection and fringe reflection can obtain absolute phase rapidly through the multi-color channel of the camera. However, the multi-color channel of the camera not only realizes the rapid measurement but also introduces the errors such as crosstalk and chromatic aberration into the system, which limits the accuracy of 3D topography restoration of composite surface objects. Crosstalk mainly comes from the process of simultaneously shooting different color stripes projected by the projector to the diffuse part of the object and displayed by the transparent display screen on the mirror part of the object. The color difference mainly comes from the different color stripes displayed by the double screen transmission of the mirror part, and there is a phase difference between the absolute phase of the two colors. Therefore, this paper studies the crosstalk elimination method based on the matrix and the color difference elimination method of absolute phase corresponding pixel deviation. Based on the crosstalk matrix, the crosstalk matrix of the projector and the transparent screen is calculated respectively according to the color light intensity relationship between the color camera, projector, and transparent screen. The stripes of different colors projected on the diffuse surface and mirror of the composite object are separated, and the absolute phase of the two parts is obtained. The absolute phase in the horizontal and vertical directions of each color channel was obtained by color orthogonal stripes, and the relationship between phase difference and pixel deviation between color channels was established to complete the pixel matching of different color channels. Finally, the pixel matching points are converted into the matrix obtained by two-dimensional interpolation to realize the pixel deviation correction of each pixel point and eliminate the influence of color difference. The experimental results show that the proposed method reduces the root mean square error of the composite step from 0.479 mm to 0.030 mm, and improves the measurement efficiency and accuracy.
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图 1 复合测量系统色差原理图
Figure 1. Color difference schematic of the composite measurement system
图 5 串扰消除前后的绝对相位图。(a) 同时拍摄的条纹图; (b) 处理前的蓝色通道绝对相位图; (c) 处理前的绿色通道绝对相位图; (d) 处理后的蓝色通道绝对相位图; (e) 处理后的绿色通道绝对相位图
Figure 5. Absolute phase diagram before and after crosstalk elimination. (a) A fringe map taken at the same time; (b) Absolute phase map of the blue channel before processing; (c) Absolute phase diagram of the green channel before processing; (d) Absolute phase diagram of the processed blue channel; (e) Absolute phase diagram of the processed green channel
图 6 传统方法色差校正前后的像素偏差图。(a) 色差校正前的像素偏差; (b) 色差校正后的像素偏差
Figure 6. Image of pixel deviation before and after color correction by the traditional method. (a) Image of pixel deviation before chromatic correction; (b) Image of pixel deviation after chromatic aberration correction
图 7 正交条纹及展开相位图。(a) 绿色正交条纹图; (b) 竖直条纹展开相位; (c) 水平条纹展开相位;(d) 红色正交条纹图; (e) 竖直条纹展开相位; (f) 水平条纹展开相位
Figure 7. Orthogonal fringe and unwrapping phase diagram. (a) Green orthogonal fringe pattern; (b) Vertical stripe unwrapping phase; (c) Horizontal fringe unwrapping phase; (d) Red orthogonal stripe pattern; (e) Vertical stripe unwrapping phase; (f) Horizontal fringe unwrapping phase
图 8 色差校正前后的像素偏差图。(a) 色差校正前的像素偏差图; (b) 色差校正后的像素偏差图
Figure 8. Image of pixel deviation before and after chromatic aberration correction. (a) Image of pixel deviation before chromatic correction; (b) Image of pixel deviation after chromatic aberration correction
图 9 重建深度图。(a) 误差校正前深度图; (b) 误差校正后深度图
Figure 9. Reconstructed depth map. (a) Depth map before error correction; (b) Error corrected depth map
图 11 重建深度图。(a) 误差处理前镜面深度图; (b) 误差处理后镜面深度图; (c) iPad标识重建深度图
Figure 11. Reconstructed depth map. (a) Mirror depth map before error processing; (b) Mirror depth map after error processing; (c) iPad logo rebuild depth map
表 1 复合台阶相邻台阶面的测量
Table 1. Measurement results of adjacent step surfaces of composite reflection steps (unit: mm)
Step
surfaceCMM
measurement
resultsMeasurement
results before
correctionCorrected
measurement
resultsAbsolute error
before
correctionCorrected
absolute
error1-2 3.000 2.646 2.975 0.354 0.025 2-3 4.000 4.381 4.021 0.381 0.021 3-4 5.000 4.409 4.961 0.592 0.039 4-5 5.500 5.979 5.523 0.479 0.023 5-6 6.500 5.957 6.463 0.543 0.037 
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