OpenCv图像处理之resize(缩放)、transpose、rotate(旋转)、flip(翻转)介绍

OpenCv图像处理之resize(缩放)、transpose、rotate(旋转)、flip(翻转)介绍：

 

OpenCv图像处理之resize、transpose、rotate、flip介绍
cv::resize操作
cv::transpose操作
cv::rotate操作
cv::flip操作
cv::resize操作
缩放是处理图像中经常用到的方法，opencv中也专门封装了此类函数，就是cv::resize。

CV_EXPORTS_W void resize(InputArray src, OutputArray dst,
                             Size dsize, double fx = 0, double fy = 0,
                             int interpolation = INTER_LINEAR);

   InputArray src输入图像cv::Mat类型
   OutputArray dst输出图像cv::Mat类型
   Size dsize缩放后的尺寸
   double fx = 0x缩放比例，默认为0
   double fy = 0y缩放比例，默认为0
   int interpolation = INTER_LINEAR插值法，默认为双线性插值
再来看一个例子：

#include <opencv2/opencv.hpp>

using namespace std;
using namespace cv;

int main() {
    Mat frame, clone_frame;
    frame = imread("D:/cat.jpg", 3);
    clone_frame = frame.clone();
    cout << "front of the scale image.rows:" << clone_frame.rows << " " << "image.cols:"
         << clone_frame.cols << endl;
    double scale = 0.5;
    //放缩会导致图像失真，缩小时interpolation使用INTER_AREA，放大时使用INTER_LINEAR减少失真
    resize(clone_frame, clone_frame, Size(int(frame.cols * scale),
                                          int(frame.rows * 0.5)), 0, 0,
           INTER_AREA);
    cout << "behind of the scale image.rows:" << clone_frame.rows << " " << "image.cols:"
         << clone_frame.cols << endl;
    imshow("resize_img", clone_frame);
    waitKey(0);
    return 0;
}

front of the scale image.rows:745 image.cols:746
behind of the scale image.rows:372 image.cols:373

效果显示

注意使用resize进行缩放的时候，会出现图像失真问题，插值法有利于减少失真。

常见插值法

 

 

#include <iostream>
#include "opencv2/opencv.hpp"

using namespace std;
using namespace cv;


int main() {
    Mat frame, clone_frame;
    frame = imread("D:/cat.jpg", 3);
    clone_frame = frame.clone();
    double scale = 0.5;
    resize(clone_frame, clone_frame, Size(int(frame.cols * scale),
                                          int(frame.rows * scale)),
           0, 0, INTER_AREA);
    transpose(clone_frame, clone_frame);
    imshow("transpose_frame", clone_frame);
    waitKey(0);
    return 0;
}

 

 

cv::rotate操作

先来看一下源码种rotate的函数原型

CV_EXPORTS_W void rotate(InputArray src, OutputArray dst, int rotateCode);
enum RotateFlags {
    ROTATE_90_CLOCKWISE = 0, //!<Rotate 90 degrees clockwise
    ROTATE_180 = 1, //!<Rotate 180 degrees clockwise
    ROTATE_90_COUNTERCLOCKWISE = 2, //!<Rotate 270 degrees clockwise
};

源码描述：

/** @brief Rotates a 2D array in multiples of 90 degrees.
The function cv::rotate rotates the array in one of three different ways:
*   Rotate by 90 degrees clockwise (rotateCode = ROTATE_90_CLOCKWISE).
*   Rotate by 180 degrees clockwise (rotateCode = ROTATE_180).
*   Rotate by 270 degrees clockwise (rotateCode = ROTATE_90_COUNTERCLOCKWISE).
@param src input array.
@param dst output array of the same type as src.  The size is the same with ROTATE_180,
and the rows and cols are switched for ROTATE_90_CLOCKWISE and ROTATE_90_COUNTERCLOCKWISE.
@param rotateCode an enum to specify how to rotate the array; see the enum #RotateFlags
@sa transpose , repeat , completeSymm, flip, RotateFlags
*/

     上面这段话大概意思就是rotate函数能够按照顺时针的方法以三种不同的角度进行旋转，三种角度分别是90度，180度，270度。rotateCode参数可以取枚举类型RotateFlags中的值，0表示90度，1表示180度，2表示270度
    接下来我们使用cv::rotate来演示一下顺时针旋转180度的操作：

#include <iostream>
#include "opencv2/opencv.hpp"

using namespace std;
using namespace cv;


int main() {
    Mat frame, clone_frame;
    frame = imread("D:/cat.jpg", 3);
    clone_frame = frame.clone();
    double scale = 0.5;
    resize(clone_frame, clone_frame, Size(int(frame.cols * scale),
                                          int(frame.rows * scale)),
           0, 0, INTER_AREA);
    cv::rotate(clone_frame, clone_frame, 1);
    imshow("rotate_180_frame", clone_frame);
    waitKey(0);
    return 0;
}

效果显示

 

 

 

 

 

#include <iostream>
#include "opencv2/opencv.hpp"

using namespace std;
using namespace cv;


int main() {
    Mat frame, clone_frame;
    frame = imread("D:/cat.jpg", 3);
    clone_frame = frame.clone();
    double scale = 0.5;
    resize(clone_frame, clone_frame, Size(int(frame.cols * scale),
                                          int(frame.rows * scale)),
           0, 0, INTER_AREA);
    //y
    flip(clone_frame, clone_frame, 1);
    //x,y
    //flip(clone_frame,clone_frame,-1);
    //x
    //flip(clone_frame,clone_frame,0);
    imshow("flip_y_frame", clone_frame);
    waitKey(0);
    return 0;
}

以y轴为对称轴

分别以x轴,y轴为对称轴

以x轴为对称轴