Nonlinear Distortion Correction of Endoscope Images with Digital Technology
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摘要: 内窥镜普遍采用了大视场的广角物镜, 其图像存在桶形畸变。在对畸变产生原因和校正原理进行分析的基础上, 提出一种新的内窥镜图像畸变数字校正方法。结合点阵样板校正的方法, 根据畸变图像中圆点之间相互位置关系构造出理想图像圆点的位置, 采用三次B样条插值函数分别对畸变图像像素在x坐标轴和y坐标轴方向上的偏移量曲面进行插值。利用曲面插值得到每个像素的偏移量, 对各像素进行坐标转换得到校正图像, 采用双线性插值方法对坐标转换时没有赋值的像素进行灰度插值。实验结果表明该方法原理简单, 易于实现, 可有效用于内窥镜图像畸变校正。Abstract: Because of restriction of the size, endoscope adopts wide-angle objective lens in order to enlarge the field of view. As a result, the endoscope images show barrel-type spatial distortion obviously. A new method for distortion correction of endoscope images is proposed based on the analyses of distortion and correction theory. The spatial distortion causes the pixels to shift, which makes the object distorted. A standard dot array calibration template comes into use for correcting the pixel offset in Cartesian coordinate. The cubic B-spline interpolating function is adopted to interpolate the curved faces of the pixel offset in X- and Y- axis separately. Thus, the offsets of each pixel are obtained in the distorted image. Furthermore, the pixels shift is rectified to achieve an undistorted image by coordinate conversion. A modified bilinear interpolation is used to evaluate the gray level of pixels, which is not assigned in coordinate conversion. The proposed method is applied to several endoscope images. The results show that the proposed method can correct the nonlinear distortion of endoscope images effectively.
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