1、API
仿射变换API：
| src | 输入图像 |
| dst | 输出图像 |
| M | 2×3 transformation matrix，旋转矩阵，用getRotationMatrix2D来获取 |
| dsize | 输出图像尺寸定义 |
| flags | 插值方式combination of interpolation methods (see InterpolationFlags) and the optional flag WARP_INVERSE_MAP that means that M is the inverse transformation ( dst→src ). |
| borderMode | 边缘处理方式pixel extrapolation method (see BorderTypes); 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. |
旋转矩阵API
| center | 图像旋转中心，注意定义时用Point2f类型 |
| angle | 旋转角度 |
| scale | 决定是否对图像本身放缩，不放缩传入1.0即可。Isotropic scale factor. |
代码示例：
void QuickDemo::rotate_Demo(Mat& image)
{
Mat dst, M;
int w = image.cols;
int h = image.rows;
//获取旋转矩阵
M = getRotationMatrix2D(Point2f(w / 2, h / 2), 45, 1.0);
//获取旋转后图像的尺寸
double cos = abs(M.at<double>(0, 0));
double sin = abs(M.at<double>(0, 1));
int nw = cos * w + sin * h;
int nh = sin * w + cos * h;
//分别获取x，y方向的偏移量
M.at<double>(0, 2) += (nw / 2 - w / 2);
M.at<double>(1, 2) += (nh / 2 - h / 2);
//旋转
warpAffine(image, dst, M, Size(nh, nw), INTER_LINEAR, 0, Scalar(255, 0, 0));
imshow("旋转图像", dst);
}结果：
