OpenCV仿射变换——平移

OpenCV仿射变换——平移

公式及原理

定义原坐标为(x,y)，平移后(xoffect,yoffset)后的坐标为(x^*,y^* ):
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也就是说，原来在(x,y)位置的像素值，被平移到(x^’,y^’ )位置处，为方便计算机运算，可以写成矩阵样式：

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在OpenCV中的防射变换矩阵M就是:

OpenCV函数

通过cv::getAffineTransform函数得到变换矩阵
cv::Mat getAffineTransform(cv::InputArray src, cv::InputArray dst)
输入
InputArray src：表示输入的三个点
InputArray dstL:表示输出的三个点
返回
cv::Mat对象
通过cv::warpAffine得到平移或旋转的cv::Mat对象
void warpAffine(InputArray src, OutputArray dst, InputArray M, Size dsize, int flags=INTER_LINEAR, int borderMode=BORDER_CONSTANT, const Scalar& borderValue=Scalar());
src : Source image.
**dst **: Destination image that has the size dsize and the same type as src .
M –:2\times 3 transformation matrix.
dsize : Size of the destination image.
flags : Combination of interpolation methods (see resize() ) and the optional flag WARP_INVERSE_MAP that means that M is the inverse transformation ( \texttt{dst}\rightarrow\texttt{src} ).
borderMode : Pixel extrapolation method (see borderInterpolate() ). When borderMode=BORDER_TRANSPARENT , it means that the pixels in the destination image corresponding 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.
无返回值

实现代码

#include<iostream>
#include<opencv2/core.hpp>
#include<opencv2/imgproc.hpp>
#include<opencv2/highgui.hpp>

int main() {
	cv::Mat src = cv::imread("D:\\Windows\\WorkSpace\\imageTest\\OIP.jpg",cv::IMREAD_COLOR);
	if (src.empty()) {
		std::cout << "failed to read image." << std::endl;
		return EXIT_FAILURE;
	}

	cv::Point2f pt1[3], pt2[3];
	float xoffset = src.cols / 5;
	float yoffset = src.rows / 3;

	/*平移前的位置*/
	pt1[0] = cv::Point2f(0, 0);//            0  0
	pt1[1] = cv::Point2f(xoffset, 0);//      x  0
	pt1[2] = cv::Point2f(0, yoffset);//      0  y
	/*平移后的位置*/
	pt2[0] = cv::Point2f(xoffset, yoffset);//         x  y
	pt2[1] = cv::Point2f(xoffset * 2, yoffset);//    2x  y
	pt2[2] = cv::Point2f(xoffset, yoffset * 2);//     x  2y

	//生成只有平移的防射矩阵
	cv::Mat M;
	M = cv::getAffineTransform(pt1, pt2);

	std::cout << M << std:: endl;

	int col = src.cols;
	int row = src.rows;

	//std::cout << src.size() << std::endl;

	//生成新的显示结果的矩阵（图）
	cv::Mat dst = cv::Mat::zeros(col + xoffset, row + yoffset, CV_32FC1);
	//std::cout << dst.size() << std::endl;
	//平移
	cv::warpAffine(src, dst, M, dst.size());
	
	cv::namedWindow("平移前", cv::WINDOW_AUTOSIZE);
	cv::imshow("平移前", src);
	cv::namedWindow("平移后", cv::WINDOW_AUTOSIZE);
	cv::imshow("平移后", dst);
	cv::waitKey(0);
}

代码执行效果

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