OpenCV中的图像几何变换

     OpenCV中图像几何变换包括图像的平移，旋转，尺度，剪切变换，所有的变换都可以借助于仿射变换矩阵CTM实现，CTM是一个2*3的矩阵：

1. 图像的尺度变换，缩放

    cv::Mat image = cv::imread("d:/QRImage.bmp", 1);
	//读取原始图像
	//1.尺度变换
	cv::Mat resize_image, resize_image_M;
	cv::resize(image, resize_image, cv::Size(0, 0), 0.5, 0.5, 1);

	cv::Mat warp_matrix_resize; //声明尺度变换 M 矩阵
	warp_matrix_resize = cv::Mat::zeros(2, 3, CV_32F);
	float cx = 0.2, cy = 0.3;  //设置尺度变换 M 矩阵
	warp_matrix_resize.at(0, 0) = cx;
	warp_matrix_resize.at(1, 1) = cy;
	
	cv::Size dsize = image.size();
	
	dsize.width *= cx;
	dsize.height *= cy;
	
	warpAffine(image, resize_image_M, warp_matrix_resize, dsize, INTER_LINEAR, 1);

	cv::imshow("original", image);
	cv::imshow("resize", resize_image);
	cv::imshow("M resize", resize_image_M);

    void cv::warpAffine    

   (   InputArray      src,
        OutputArray     dst,
        InputArray      M,
        Size    dsize,
        int     flags = INTER_LINEAR,
        int     borderMode = BORDER_CONSTANT,
        const Scalar &      borderValue = Scalar() 
    )的参数为：

  src: 输入图像
. dst: 输出图像，尺寸由dsize指定，图像类型与原图像一致
. M: 2X3的变换矩阵
. dsize: 指定图像输出尺寸
. flags: 插值算法标识符，有默认值INTER_LINEAR，如果插值算法为WARP_INVERSE_MAP,

2. 图像的平移变换

    cv::Mat temp_image = resize_image.clone(); //使用缩小后的图像进行变换
	cv::Mat translation_image; //声明目标图像变量
	cv::Mat warp_matrix_translation;  //声明平移变换 M 矩阵
	warp_matrix_translation = cv::Mat::eye(2, 3, CV_32F);

	float tx = 40, ty = 20; //设置平移变换参数
	warp_matrix_translation.at(0, 2) = tx;
	warp_matrix_translation.at(1, 2) = ty;
	cout << "M translation = " << endl << warp_matrix_translation << endl << endl;
	
	int top = 10, bottom = ty+20, left = 10, right = tx+20;
	cv::copyMakeBorder(temp_image, temp_image, top, bottom, left, right, BORDER_CONSTANT, cv::Scalar(200));//扩边

	cv::warpAffine(temp_image, translation_image, warp_matrix_translation, temp_image.size(), INTER_LINEAR, BORDER_TRANSPARENT);

	cv::imshow("source image", temp_image);
	cv::imshow("translation", translation_image);

3. 图像的旋转变换

    //旋转变换
	cv::Mat rotate_image; //声明目标图像变量
	cv::Mat temp_image = resize_image.clone();

	double angle = 45;    //设定旋转角度    
	int border = 0.207 * temp_image.cols;
	cv::copyMakeBorder(temp_image, temp_image, border, border, border, border, BORDER_CONSTANT, cv::Scalar(200));//扩边
	cv::Point2f center(temp_image.cols / 2., temp_image.rows / 2.);
	//指定旋转中心
	cv::Mat warp_rotate_matrix = cv::getRotationMatrix2D(center, angle, 1.0);
	//获取旋转变换M矩阵
	//根据旋转矩阵进行仿射变换
	cv::warpAffine(temp_image, rotate_image, warp_rotate_matrix, temp_image.size(), INTER_LINEAR, BORDER_REPLICATE);
	

	cv::imshow("rotate", rotate_image);  //显示图像

4. 图像的剪切变换

    cv::Mat shear_vertical_image, shear_horizontal_image;
	//声明目标图像变量
	cv::Mat temp_image = resize_image.clone();
	cv::Mat temp_image_vertical, temp_image_horizontal;
	int border = 40;
	cv::copyMakeBorder(temp_image, temp_image_vertical, 10, 2 * border, border, 10 + border, BORDER_CONSTANT, cv::Scalar(200));
	cv::copyMakeBorder(temp_image, temp_image_horizontal, border + 10, border, 10, 2 * border, BORDER_CONSTANT, cv::Scalar(200));
	
	cv::Mat warp_matrix_shear_vertical, warp_matrix_shear_horizontal;
	//声明剪切变换 M 矩阵
	warp_matrix_shear_vertical = cv::Mat::eye(2, 3, CV_32F);
	//垂直剪切变换矩阵
	warp_matrix_shear_horizontal = cv::Mat::eye(2, 3, CV_32F);
	//水平剪切变换矩阵
	float sv = 0.3, sh = 0.3;
	warp_matrix_shear_horizontal.at(0, 1) = sh;//水平偏移矩阵
	warp_matrix_shear_vertical.at(1, 0) = sv;  //垂直偏移矩阵
	//根据旋转矩阵进行仿射变换
	cv::warpAffine(temp_image_vertical, shear_vertical_image, warp_matrix_shear_vertical, temp_image_vertical.size(), INTER_LINEAR, BORDER_REPLICATE);
	cv::warpAffine(temp_image_horizontal, shear_horizontal_image, warp_matrix_shear_horizontal, temp_image_horizontal.size(), INTER_LINEAR, BORDER_REPLICATE);
	cv::imshow("shear vertical", shear_vertical_image);    //显示图像
	cv::imshow("shear horizontal", shear_horizontal_image);