Tang Zhongwei, von Gioi Rafael Grompone, Monasse Pascal, Morel Jean-Michel
Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455, USA.
J Opt Soc Am A Opt Image Sci Vis. 2012 Oct 1;29(10):2134-43. doi: 10.1364/JOSAA.29.002134.
This paper addresses the high-precision measurement of the distortion of a digital camera from photographs. Traditionally, this distortion is measured from photographs of a flat pattern that contains aligned elements. Nevertheless, it is nearly impossible to fabricate a very flat pattern and to validate its flatness. This fact limits the attainable measurable precisions. In contrast, it is much easier to obtain physically very precise straight lines by tightly stretching good quality strings on a frame. Taking literally "plumb-line methods," we built a "calibration harp" instead of the classic flat patterns to obtain a high-precision measurement tool, demonstrably reaching 2/100 pixel precisions. The harp is complemented with the algorithms computing automatically from harp photographs two different and complementary lens distortion measurements. The precision of the method is evaluated on images corrected by state-of-the-art distortion correction algorithms, and by popular software. Three applications are shown: first an objective and reliable measurement of the result of any distortion correction. Second, the harp permits us to control state-of-the art global camera calibration algorithms: it permits us to select the right distortion model, thus avoiding internal compensation errors inherent to these methods. Third, the method replaces manual procedures in other distortion correction methods, makes them fully automatic, and increases their reliability and precision.
本文探讨了通过照片对数码相机畸变进行高精度测量的问题。传统上，这种畸变是通过包含对齐元素的平面图案照片来测量的。然而，制造一个非常平坦的图案并验证其平整度几乎是不可能的。这一事实限制了可达到的测量精度。相比之下，通过在框架上紧密拉伸高质量的绳子来获得物理上非常精确的直线要容易得多。我们从字面上理解“铅垂线方法”，构建了一个“校准竖琴”来替代传统的平面图案，从而获得了一种高精度测量工具，其精度可达2/100像素。竖琴辅以从竖琴照片中自动计算两种不同且互补的镜头畸变测量值的算法。该方法的精度在经过最先进的畸变校正算法和流行软件校正的图像上进行了评估。展示了三个应用：第一，对任何畸变校正结果进行客观可靠的测量。第二，竖琴使我们能够控制最先进的全局相机校准算法：它使我们能够选择正确的畸变模型，从而避免这些方法固有的内部补偿误差。第三，该方法取代了其他畸变校正方法中的手动操作，使其完全自动化，并提高了其可靠性和精度。
