Nonlinear Distortion Correction of Endoscope Images with Digital Technology

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.