Department of Computer Science, National Tsing Hua University, Hsinchu 300, Taiwan.
IEEE Trans Biomed Eng. 2013 Sep;60(9):2603-13. doi: 10.1109/TBME.2013.2261816. Epub 2013 May 6.
Operation in minimally invasive surgery is more difficult since the surgeons perform operations without haptic feedback or depth perception. Moreover, the field of view perceived by the surgeons through endoscopy is usually quite limited. The goal of this paper is to allow surgeons to see wide-angle images from endoscopy without the drawback of lens distortion. The proposed distortion correction process consists of lens calibration and real-time image warping. The calibration step is to estimate the parameters in the lens distortion model. We propose a fully automatic Hough-entropy-based calibration algorithm, which provides calibration results comparable to the previous manual calibration method. To achieve real-time correction, we use graphics processing unit to warp the image in parallel. In addition, surgeons may adjust the focal length of a lens during the operation. Real-time distortion correction of a zoomable lens is impossible by using traditional calibration methods because the tedious calibration process has to repeat again if focal length is changed. We derive a formula to describe the relationship between the distortion parameter, focal length, and image boundary. Hence, we can estimate the focal length for a zoomable lens from endoscopic images online and achieve real-time lens distortion correction.
微创手术中的操作更加困难，因为外科医生在没有触觉反馈或深度感知的情况下进行手术。此外，外科医生通过内窥镜感知的视野通常非常有限。本文的目的是允许外科医生从内窥镜看到广角图像，而不会产生镜头失真的缺点。所提出的失真校正过程包括镜头校准和实时图像变形。校准步骤是估计镜头失真模型中的参数。我们提出了一种完全基于 Hough 熵的自动校准算法，该算法提供的校准结果可与以前的手动校准方法相媲美。为了实现实时校正，我们使用图形处理单元并行地对图像进行变形。此外，外科医生在手术过程中可能会调整镜头的焦距。如果使用传统的校准方法，对于可缩放镜头的实时失真校正则是不可能的，因为如果焦距发生变化，则必须再次重复繁琐的校准过程。我们推导出一个公式来描述失真参数、焦距和图像边界之间的关系。因此，我们可以从内窥镜图像在线估计可缩放镜头的焦距，并实现实时镜头失真校正。
