Undistorted outspread method for annular images of the inner wall of borehole with a center offset

An undistorted outspread method for annular images of the inner wall of borehole with a center offset, comprising:

• a step S1 of putting a camera into the borehole and pushing the camera inward to carry out a video acquisition;
• a step S2 of selecting at least two frames of images, a first image and a second image, from the video obtained from the step S1;
• adjusting a second axis angle in the second image to an angle same as a first axis angle in the first image to obtain an adjusted second axis angle;
• a step S3 of adjusting the first axis angle and the adjusted second axis angle in the step S2 until difference between said angles is zero;
• a step S4 of calculating a first radius ratio of motion according to adjusted first image and second image in the step S3, and obtaining a second radius ratio of motion;
• a step S5 of obtaining a first radius ratio of axis distance according to the first radius ratio of motion in the step S4, and obtaining a second radius ratio of axis distance, wherein the first radius ratio of axis distance is ratio of the radius to a distance from a center of a circle to a center of the image;
• a step S6 of correcting the first image and the second image to obtain a corrected third image and a corrected fourth image according to the calculation of the first radius ratio of axis distance and the second radius ratio of axis distance in the step S5;
• a step S7 of matching the corrected third image in the step S6 along with the first image and matching the corrected fourth image in the step S6 along with the second image to obtain corrected undistorted images;
• and
• a step S8 of outspreading the corrected undistorted images from the step S7 to obtain an undistorted outspread image according to a polar coordinate formula
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