结构光测量中相机曝光优化与图像质量评估

Camera Exposure Optimization and Image Quality Assessment in Structured Light Measurement

为了解决结构光三维测量采集过程中无法准确确定曝光量的问题,提出了一种基于相机响应函数求解最优曝光时间的方法。该方法主要通过使用大津法(Otsu)对不同被测物体图像进行背景分割,然后利用相机响应函数求解真实像素值与曝光时间之间的关系,从而得到在理想像素均值下的最优曝光时间。此外,构建了通过计算图像过曝与欠曝像素点的占比与归一化的像素均值等其他基本图像质量评价参数的图像质量评价方法,该方法能够对被测物体图像进行有效评价。实验使用不同曝光时间进行双目结构光三维测量,对比了模型重建中相位匹配点数量与关键特征的测量结果。结果表明:使用最优曝光时间采集被测物,图像评价结果参数均在90%以上;在模型重建过程中相位匹配点数最多,关键特征测量结果准确,与其他测量方法的最大测量误差为0.02 mm;同时被测物图像质量评价结果与相位匹配点数呈正相关,证明了该评价方法的有效性。本研究为结构光三维测量中曝光量的选择提供了科学的依据。

To solve the problem that the exposure cannot be determined accurately in the acquisition process of structured light 3D measurement,we propose a method to solve the optimal exposure time based on the camera response function.The background segmentation of different measured object images is mainly performed by using the Otsu method,and then the camera response function is utilized to solve the relationship between the true pixel value and the exposure time,so as to obtain the optimal exposure time under the ideal pixel mean value.In addition,an image quality evaluation method is constructed by calculating the ratio of overexposed and underexposed pixel points in the image and the normalization of other basic image quality evaluation parameters such as pixel mean value,which is capable to effectively evaluate the measured object images.Experiments are conducted using different exposure times for binocular structured light 3D measurements to compare the number of phase-matched points and key feature measurements in the model reconstruction.The results show that when the optimal exposure time is used to acquire the measured object,the image evaluation values are above 90%,the number of phase-matched points are the highest during the model reconstruction process,and the key features are measured accurately with a maximum measurement error of 0.02 mm compared with other measuring methods.Meanwhile,the quality evaluation results of the measured object image are positively correlated with the number of phase-matched points,which proves the effectiveness of the evaluation method.This study provides a scientific basis for the selection of the exposure in structured light 3D measurement.