Abstract Fringe projection techniques have been widely used in three-dimensional (3D) microscopic measurement; however, the working volume is severely restricted due to the shallow depth-of-field (DOF) of the telecentric lenses used. In this paper, a large-DOF 3D measurement method for use with a microscopic structured-light system was proposed. By employing a precisely controlled moving platform, the height of the camera can be adjusted to capture several sets of fringe patterns with different amounts of defocusing. Then the proposed focusing map generation algorithm was employed to calculate the focusing degree of each pixel and generate a focusing map for each set of fringe patterns. Subsequently, local 3D shape data corresponding to in-focus pixels were merged with the guidance of the focusing maps, and global fine 3D measurement data without the influence of lens blur can be obtained. Specifically, to guide the compositing of the 3D shape data, a novel, simple focusing map generation algorithm was proposed to calculate the focusing degree of each set of captured fringe patterns. In contrast to existing DOF-extending 3D measurement techniques using multiple focal distances, the proposed algorithm does not need the object’s texture to calculate the gray-level gradient; hence, complex convolution or iteration is not required. The experimental results demonstrate that the proposed technique can increase the measurement DOF to approximately three times that of a conventional system.

中文翻译：

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使用微观结构光系统进行大景深 3D 测量

摘要 条纹投影技术已广泛应用于三维（3D）显微测量；然而，由于使用的远心镜头的景深 (DOF) 较浅，工作体积受到严重限制。在本文中，提出了一种用于微观结构光系统的大自由度 3D 测量方法。通过采用精确控制的移动平台，可以调整相机的高度，以捕获具有不同散焦量的多组条纹图案。然后采用所提出的聚焦图生成算法计算每个像素的聚焦度，并为每组条纹图案生成聚焦图。随后，与聚焦像素对应的局部 3D 形状数据与聚焦图的引导合并，并且可以获得不受镜头模糊影响的全局精细3D测量数据。具体来说，为了指导 3D 形状数据的合成，提出了一种新颖、简单的聚焦图生成算法来计算每组捕获的条纹图案的聚焦度。与现有使用多焦距的扩展自由度的 3D 测量技术相比，所提出的算法不需要对象的纹理来计算灰度梯度；因此，不需要复杂的卷积或迭代。实验结果表明，所提出的技术可以将测量自由度增加到传统系统的大约三倍。提出了简单的聚焦图生成算法来计算每组捕获的条纹图案的聚焦度。与现有使用多焦距的DOF扩展3D测量技术相比，所提出的算法不需要对象的纹理来计算灰度梯度；因此，不需要复杂的卷积或迭代。实验结果表明，所提出的技术可以将测量自由度增加到传统系统的大约三倍。提出了简单的聚焦图生成算法来计算每组捕获的条纹图案的聚焦度。与现有使用多焦距的DOF扩展3D测量技术相比，所提出的算法不需要对象的纹理来计算灰度梯度；因此，不需要复杂的卷积或迭代。实验结果表明，所提出的技术可以将测量自由度增加到传统系统的大约三倍。