OpenCV和C++实现图像的翻转（镜像）、平移、旋转、仿射与透视变换
目录
一、翻转（镜像）
二、仿射扭曲
获取变换矩阵
仿射扭曲函数 warpAffine
旋转
平移
三、仿射变换
四、透视变换
综合示例
总结
官网教程
一、翻转（镜像）头文件 quick_opencv.h：声明类与公共函数
#pragma once
#include <opencv2\opencv.hpp>
using namespace cv;
class QuickDemo {
public:
...
void flip_Demo(Mat& image);
void rotate_Demo(Mat& image);
void move_Demo(Mat& image);
void Affine_Demo(Mat& image);
void toushi_Demo(Mat& image);
void perspective_detect(Mat& image);
};
主函数调用该类的公共成员函数
#include <opencv2\opencv.hpp>
#include <quick_opencv.h>
#include <iostream>
using namespace cv;
int main(int argc, char** argv) {
Mat src = imread("D:\\Desktop\\pandas.jpg");
if (src.empty()) {
printf("Could not load images...\n");
return -1;
}
namedWindow("input", WINDOW_NORMAL);
imshow("input", src);
QuickDemo qk;
...
qk.Affine_Demo(src);
qk.move_Demo(src);
qk.flip_Demo(src);
qk.toushi_Demo(src);
qk.perspective_detect(src);
waitKey(0);
destroyAllWindows();
return 0;
}
源文件 quick_demo.cpp：实现类与公共函数
void QuickDemo::flip_Demo(Mat& image) {
Mat dst0, dst1, dst2;
flip(image, dst0, 0);
flip(image, dst1, 1);
flip(image, dst2, -1);
imshow("dst0_上下翻转", dst0);
imshow("dst1_左右翻转", dst1);
imshow("dst2_对角线翻转", dst2); //旋转180度
}
二维图像一般情况下的变换矩阵（旋转+平移），当我们只需要平移的时候，取 θ 的值为0，a和b的值就代表了图像沿x轴和y轴移动的距离；其中原图 
(原图大小，不执行缩放)
变换矩阵计算：
其中： 
仿射扭曲函数 warpAffineMat getRotationMatrix2D( Point2f center, 源图像中旋转的中心
double angle, 角度以度为单位的旋转角度。正值表示逆时针旋转（坐标原点假定为左上角）。
double scale 各向同性比例因子。
)
函数签名
void warpAffine( InputArray src, 输入矩阵
OutputArray dst, 输出矩阵
InputArray M, 2×3 变换矩阵
Size dsize, 输出图像大小
int flags = INTER_LINEAR, 插值方式：默认线性插值
int borderMode = BORDER_CONSTANT, 边缘处理方式
const Scalar& borderValue = Scalar() 边缘填充值，默认=0
);
保留所有原图像素的旋转，原理： 
void QuickDemo::rotate_Demo(Mat& image) {
Mat dst_0, dst_1, M;
int h = image.rows;
int w = image.cols;
M = getRotationMatrix2D(Point(w / 2, h / 2), 45, 1.0);
warpAffine(image, dst_0, M, image.size());
double cos = abs(M.at<double>(0, 0));
double sin = abs(M.at<double>(0, 1));
int new_w = cos * w + sin * h;
int new_h = cos * h + sin * w;
M.at<double>(0, 2) += (new_w / 2.0 - w / 2);
M.at<double>(1, 2) += (new_h / 2.0 - h / 2);
warpAffine(image, dst_1, M, Size(new_w, new_h), INTER_LINEAR, 0, Scalar(255, 255, 0));
imshow("旋转演示0", dst_0);
imshow("旋转演示1", dst_1);
}
依次为：原图，旋转45度，保留所有原图像素的旋转45度
void QuickDemo::move_Demo(Mat& image) {
Mat dst_move;
Mat move_mat = (Mat_<double>(2, 3) << 1, 0, 10, 0, 1, 30);//沿x轴移动10沿y轴移动30
warpAffine(image, dst_move, move_mat, image.size());
imshow("dst_move", dst_move);
double angle_ = 3.14159265354 / 16.0;
cout << "pi=" << cos(angle_) << endl;
Mat rota_mat = (Mat_<double>(2, 3) << cos(angle_), -sin(angle_), 1, sin(angle_), cos(angle_), 1);
warpAffine(image, rotate_dst, rota_mat, image.size());
imshow("rotate_dst", rotate_dst);
}
Mat getAffineTransform( 返回变换矩阵
const Point2f src[], 变换前三个点的数组
const Point2f dst[] 变换后三个点的数组
);
void
void QuickDemo::Affine_Demo(Mat& image) {
Mat warp_dst;
Mat warp_mat(2, 3, CV_32FC1);
Point2f srcTri[3];
Point2f dstTri[3];
/// 设置源图像和目标图像上的三组点以计算仿射变换
srcTri[0] = Point2f(0, 0);
srcTri[1] = Point2f(image.cols - 1, 0);
srcTri[2] = Point2f(0, image.rows - 1);
for (size_t i = 0; i < 3; i++){
circle(image, srcTri[i], 2, Scalar(0, 0, 255), 5, 8);
}
dstTri[0] = Point2f(image.cols * 0.0, image.rows * 0.13);
dstTri[1] = Point2f(image.cols * 0.95, image.rows * 0.15);
dstTri[2] = Point2f(image.cols * 0.15, image.rows * 0.9);
warp_mat = getAffineTransform(srcTri, dstTri);
warpAffine(image, warp_dst, warp_mat, warp_dst.size());
imshow("warp_dst", warp_dst);
}
获取透射变换的矩阵：
Mat getPerspectiveTransform( 返回变换矩阵
const Point2f src[], 透视变换前四个点的 数组
const Point2f dst[], 透视变换后四个点的 数组
int solveMethod = DECOMP_LU
)
透射变换
void warpPerspective( InputArray src, 原图像
OutputArray dst, 返回图像
InputArray M, 透视变换矩阵
Size dsize, 返回图像的大小（宽，高）
int flags = INTER_LINEAR, 插值方法
int borderMode = BORDER_CONSTANT, 边界处理
const Scalar& borderValue = Scalar() 缩放处理
)
void QuickDemo::toushi_Demo(Mat& image) {
Mat toushi_dst, toushi_mat;
Point2f toushi_before[4];
toushi_before[0] = Point2f(122, 220);
toushi_before[1] = Point2f(397, 121);
toushi_before[2] = Point2f(133, 339);
toushi_before[3] = Point2f(397, 218);
int width_0 = toushi_before[1].x - toushi_before[0].x;
int height_0 = toushi_before[1].y - toushi_before[0].y;
int width_1 = toushi_before[2].x - toushi_before[0].x;
int height_1 = toushi_before[2].y - toushi_before[0].y;
int width = (int)sqrt(width_0 * width_0 + height_0 * height_0);
int height = (int)sqrt(width_1 * width_1 + height_1 * height_1);
Point2f toushi_after[4];
toushi_after[0] = Point2f(2, 2); // x0, y0
toushi_after[1] = Point2f(width+2, 2); // x1, y0
toushi_after[2] = Point2f(2, height+2); // x0, y1
toushi_after[3] = Point2f(width + 2, height + 2); // x1, y1
for (size_t i = 0; i < 4; i++){
cout << toushi_after[i] << endl;
}
toushi_mat = getPerspectiveTransform(toushi_before, toushi_after);
warpPerspective(image, toushi_dst, toushi_mat, Size(width, height));
imshow("toushi_dst", toushi_dst);
}
自动化透视矫正图像:
流程：
灰度化二值化
形态学去除噪点
获取轮廓
检测直线
计算直线交点
获取四个透视顶点
透视变换
inline void Intersection(Point2i& interPoint, Vec4i& line1, Vec4i& line2) {
// x1, y1, x2, y2 = line1[0], line1[1], line1[2], line1[3]
int A1 = line1[3] - line1[1];
int B1 = line1[0] - line1[2];
int C1 = line1[1] * line1[2] - line1[0] * line1[3];
int A2 = line2[3] - line2[1];
int B2 = line2[0] - line2[2];
int C2 = line2[1] * line2[2] - line2[0] * line2[3];
interPoint.x = static_cast<int>((B1 * C2 - B2 * C1) / (A1 * B2 - A2 * B1));
interPoint.y = static_cast<int>((C1 * A2 - A1 * C2) / (A1 * B2 - A2 * B1));
}
void QuickDemo::perspective_detect(Mat& image) {
Mat gray_dst, binary_dst, morph_dst;
// 二值化
cvtColor(image, gray_dst, COLOR_BGR2GRAY);
threshold(gray_dst, binary_dst, 0, 255, THRESH_BINARY_INV | THRESH_OTSU);
//形态学操作
Mat kernel = getStructuringElement(MORPH_RECT, Size(5, 5));
morphologyEx(binary_dst, morph_dst, MORPH_CLOSE, kernel, Point(-1, -1), 3);
bitwise_not(morph_dst, morph_dst);
imshow("morph_dst2", morph_dst);
//轮廓查找与可视化
vector<vector<Point>> contours;
vector<Vec4i> hierarches;
int height = image.rows;
int width = image.cols;
Mat contours_Img = Mat::zeros(image.size(), CV_8UC3);
findContours(morph_dst, contours, hierarches, RETR_TREE, CHAIN_APPROX_SIMPLE);
for (size_t i = 0; i < contours.size(); i++){
Rect rect = boundingRect(contours[i]);
if (rect.width > width / 2 && rect.width < width - 5) {
drawContours(contours_Img, contours, i, Scalar(0, 0, 255), 2, 8, hierarches, 0, Point());
}
}
imshow("contours_Img", contours_Img);
vector<Vec4i> lines;
Mat houghImg;
int accu = min(width * 0.5, height * 0.5);
cvtColor(contours_Img, houghImg, COLOR_BGR2GRAY);
HoughLinesP(houghImg, lines, 1, CV_PI / 180, accu, accu*0.6, 0);
Mat lineImg = Mat::zeros(image.size(), CV_8UC3);
for (size_t i = 0; i < lines.size(); i++){
Vec4i ln = lines[i];
line(lineImg, Point(ln[0], ln[1]), Point(ln[2], ln[3]), Scalar(0, 0, 255), 2, 8, 0);
}
// 寻找与定位上下左右四条直线
int delta = 0;
Vec4i topline = { 0, 0, 0, 0 };
Vec4i bottomline;
Vec4i leftline, rightline;
for (size_t i = 0; i < lines.size(); i++) {
Vec4i ln = lines[i];
delta = abs(ln[3] - ln[1]); // y2-y1
//topline
if (ln[3] < height / 2.0 && ln[1] < height / 2.0 && delta < accu - 1) {
if (topline[3] > ln[3] && topline[3] > 0) {
topline = lines[i];
}
else {
topline = lines[i];
}
}
if (ln[3] > height / 2.0 && ln[1] > height / 2.0 && delta < accu - 1) {
bottomline = lines[i];
}
if (ln[0] < width / 2.0 && ln[2] < width / 2.0) {
leftline = lines[i];
}
if (ln[0] > width / 2.0 && ln[2] > width / 2.0) {
rightline = lines[i];
}
}
cout << "topline: " << topline << endl;
cout << "bottomline: " << bottomline << endl;
cout << "leftline: " << leftline << endl;
cout << "rightline: " << rightline << endl;
// 计算上述四条直线交点（两条线的交点:依次为左上，右上，左下,右下）
Point2i p0, p1, p2, p3;
Intersection(p0, topline, leftline);
Intersection(p1, topline, rightline);
Intersection(p2, bottomline, leftline);
Intersection(p3, bottomline, rightline);
circle(lineImg, p0, 2, Scalar(255, 0, 0), 2, 8, 0);
circle(lineImg, p1, 2, Scalar(255, 0, 0), 2, 8, 0);
circle(lineImg, p2, 2, Scalar(255, 0, 0), 2, 8, 0);
circle(lineImg, p3, 2, Scalar(255, 0, 0), 2, 8, 0);
imshow("Intersection", lineImg);
//透视变换
vector<Point2f> src_point(4);
src_point[0] = p0;
src_point[1] = p1;
src_point[2] = p2;
src_point[3] = p3;
int new_height = max(abs(p2.y - p0.y), abs(p3.y - p1.y));
int new_width = max(abs(p1.x - p0.x), abs(p3.x - p2.x));
cout << "new_height = " << new_height << endl;
cout << "new_width = " << new_width << endl;
vector<Point2f> dst_point(4);
dst_point[0] = Point(0,0);
dst_point[1] = Point(new_width, 0);
dst_point[2] = Point(0, new_height);
dst_point[3] = Point(new_width, new_height);
Mat resultImg;
Mat wrap_mat = getPerspectiveTransform(src_point, dst_point);
warpPerspective(image, resultImg, wrap_mat, Size(new_width, new_height));
imshow("resultImg", resultImg);
}
关键步骤可视化
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