The calibration of camera systems employing zoom lenses raises several challenges, as changes in lens control settings introduce various imaging conditions, especially different degrees of defocus. This article presents a Fourier-based defocus calibration method to calibrate a camera attached with an electronically focus-tunable lens (ETL). Different from the traditional method which requires changing the scale of the calibration object for sharp images, the proposed method is more concerned with the frequency characteristics of the captured images than the gray distributions. According to the invariance of the fundamental frequencies before and after defocusing the images, coordinates of feature points can be extracted accurately, even in different degrees of defocus. Therefore, one normal size target can also be qualified for zoom system calibration. Then polynomial approximation is used to account for the variation of the intrinsic and distortion parameters across the zoom range. Extensive simulations and experiments were implemented to demonstrate the proposed idea's robustness against defocus, flexibility, and accuracy.

中文翻译：

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电子可调焦镜头的灵活标定方法


采用变焦镜头的相机系统的校准提出了一些挑战，因为镜头控制设置的变化会引入各种成像条件，特别是不同程度的散焦。本文提出了一种基于傅里叶的散焦校准方法，用于校准配有电子可调焦镜头 (ETL) 的相机。与传统方法需要改变标定对象的尺度以获得清晰图像不同，该方法更关心捕获图像的频率特性而不是灰度分布。根据图像离焦前后基频的不变性，即使在不同的离焦程度下，也能准确提取特征点坐标。因此，一个正常尺寸的目标也可以满足变焦系统校准的要求。然后使用多项式近似来解释整个变焦范围内的固有参数和畸变参数的变化。进行了大量的模拟和实验，以证明所提出的想法对散焦的鲁棒性、灵活性和准确性。