OpenCV图像几何变换之透视变换

2020-01-26 13:27:23

字体：大中小

来源：转载

供稿：网友

本文实例为大家分享了OpenCV图像几何变换之透视变换的具体代码，供大家参考，具体内容如下

1. 基本原理

透视变换（Perspective Transformation）的本质是将图像投影到一个新的视平面，其通用变换公式为：

（u，v）为原始图像像素坐标，（x=x'/w'，y=y'/w'）为变换之后的图像像素坐标。透视变换矩阵图解如下：

仿射变换（Affine Transformation）可以理解为透视变换的特殊形式。透视变换的数学表达式为：

所以，给定透视变换对应的四对像素点坐标，即可求得透视变换矩阵；反之，给定透视变换矩阵，即可对图像或像素点坐标完成透视变换，如下图所示：

2. OpenCV透视变换函数

Mat getPerspectiveTransform(const Point2f* src, const Point2f* dst)// Calculate a perspective transform from four pairs of the corresponding points.// src  Coordinates of quadrangle vertices in the source image.// dst  Coordinates of the corresponding quadrangle vertices in the destination image. void warpPerspective(InputArray src, OutputArray dst, InputArray M, Size dsize, int flags=INTER_LINEAR, int borderMode=BORDER_CONSTANT, const Scalar& borderValue=Scalar())// Apply a perspective transform to an image.// src  Source image.// dst  Destination image that has the size dsize and the same type as src.// M  3*3 transformation matrix.// dsize  Size of the destination image.// flags  Combination of interpolation methods and the optional flag WARP_INVERSE_MAP that means that M is the inverse transformation (dstsrc).// borderMode  Pixel extrapolation method. When borderMode=BORDER_TRANSPARENT, it means that the pixels in the destination image that corresponds to the “outliers” in the source image are not modified by the function.// borderValue  Value used in case of a constant border. By default, it is 0.

3. 程序

#include <iostream> #include "highgui.h"#include "opencv2/imgproc/imgproc.hpp" int main(){ // get original image. cv::Mat originalImage = cv::imread("road.png");   // perspective image. cv::Mat perspectiveImage;   // perspective transform cv::Point2f objectivePoints[4], imagePoints[4];  // original image points. imagePoints[0].x = 10.0; imagePoints[0].y = 457.0; imagePoints[1].x = 395.0; imagePoints[1].y = 291.0; imagePoints[2].x = 624.0; imagePoints[2].y = 291.0; imagePoints[3].x = 1000.0; imagePoints[3].y = 457.0;  // objective points of perspective image. // move up the perspective image : objectivePoints.y - value . // move left the perspective image : objectivePoints.x - value. double moveValueX = 0.0; double moveValueY = 0.0;  objectivePoints[0].x = 46.0 + moveValueX; objectivePoints[0].y = 920.0 + moveValueY; objectivePoints[1].x = 46.0 + moveValueX; objectivePoints[1].y = 100.0 + moveValueY; objectivePoints[2].x = 600.0 + moveValueX; objectivePoints[2].y = 100.0 + moveValueY; objectivePoints[3].x = 600.0 + moveValueX; objectivePoints[3].y = 920.0 + moveValueY;  cv::Mat transform = cv::getPerspectiveTransform(objectivePoints, imagePoints);  // perspective. cv::warpPerspective(originalImage,      perspectiveImage,      transform,      cv::Size(originalImage.rows, originalImage.cols),      cv::INTER_LINEAR | cv::WARP_INVERSE_MAP);  // cv::imshow("perspective image", perspectiveImage); // cvWaitKey(0);  cv::imwrite("perspectiveImage.png", perspectiveImage);  return 0;}

原始图像及其透视变换结果：