一、仿射变换
举例：基于离散点求最小外接轮廓
其主要思路是先把图像二值化，得到一系列离散的前景像素点集合，然后利用轮廓的最小外接矩形函数，得到偏斜的矩形大小与角度，通过仿射变换完成校正。代码实现如下：
int main() { Mat src, gray,dst; src = imread("D:\\cv_study\\Exercise\\文字倾斜\\text.png"); cvtColor(src, gray, CV_BGR2GRAY); threshold(gray, dst, 0, 255, CV_THRESH_BINARY_INV | CV_THRESH_OTSU); vector<Point>points; findNonZero(dst, points); RotatedRect box = minAreaRect(points); double angle = box.angle; if (angle < -45.) angle += 90.; printf("angle : %.2f\n", angle); Point2f vertices[4]; box.points(vertices); for (int i = 0; i < 4; ++i) line(src, vertices[i], vertices[(i + 1) % 4], Scalar(0, 0, 255), 2); Mat rot_mat = getRotationMatrix2D(box.center, angle, 1); Mat rotated; warpAffine(src, rotated, rot_mat, src.size(), cv::INTER_CUBIC, 0, Scalar(255, 255, 255)); waitKey(); return 0; }
二、透视变换
透视变换的一般过程：读入图片，获取边界点，定义目标边界点，获取转换矩阵，执行转换。
int main() { Mat src = imread("D:\\cv_study\\Exercise\\Perspective Transformation\\1.jpg"); vector<Point2f>src_coners(4); src_coners[0] = Point2f(13, 134); src_coners[1] = Point2f(271, 24); src_coners[2] = Point2f(180, 411); src_coners[3] = Point2f(398, 362); circle(src, src_coners[0], 3, Scalar(0, 0, 255), 3, 8); circle(src, src_coners[1], 3, Scalar(0, 0, 255), 3, 8); circle(src, src_coners[2], 3, Scalar(0, 0, 255), 3, 8); circle(src, src_coners[3], 3, Scalar(0, 0, 255), 3, 8); vector<Point2f>dst_coners(4); dst_coners[0] = Point2f(0, 300); dst_coners[1] = Point2f(0, 0); dst_coners[2] = Point2f(400, 300); dst_coners[3] = Point2f(400, 0); Mat warpMatrix = getPerspectiveTransform(src_coners, dst_coners); Mat dst; warpPerspective(src, dst, warpMatrix, dst.size(), INTER_LINEAR, BORDER_CONSTANT); waitKey(); return 0; }
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参考文献：
https://blog.csdn.net/zhangjunp3/article/details/80318533
https://blog.csdn.net/zhangjunp3/article/details/80036310
