opencv remap pixel remapping

The input to the remap() function is a source image and a mapping matrix. The mapping matrix contains new coordinates for each pixel, specifying the position of each pixel in the output image.

Suppose the coordinates of a pixel in the original image are $(x,y)$ , its new coordinates in the output image are$(x^{\prime },y^{\text{'}})$. To compute$(x^{\prime },y^{\prime })$, we need to define a mapping function$f(x,y)=(x^{\prime },y^{\prime })$, the original coordinates$(x,y)$ is mapped to new coordinates$(x^{\prime },y^{\prime })$。

In the remap() function, the mapping matrix consists of two grid matrices $ma{p}_x$和$ma{p}_y$composition, each grid matrix has the same size as the original image. $ma{p}_x$和$ma{p}_y$Each element ( i , j ) in (i,j)$(i,j)$ contains the pixel$(i,j)$ new coordinates$(x^{\prime },y^{\prime })$。

Therefore, we can put the mapping function $f(x,y)$表示为$f(x,y)=(ma{p}_x[i,j],ma{p}_y[i,j])$ , where$(i,j)$ is the pixel ( x , y ) in the original image$(x,y)$ coordinates.

In the implementation of the cv2.remap() function, the cv2.meshgrid() function is used to create the grid matrix $ma{p}_x$和$ma{p}_y$, while the mapping function $f(x,y)$ to calculate the new coordinates$(x^{\prime },y^{\prime })$。

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

void salt(cv::Mat image,int n){
    
    
   //随机数生成器
   std::default_random_engine generator;
   std::uniform_int_distribution<int> randomRow(0,image.rows-1);
   std::uniform_int_distribution<int> randomCol(0,image.cols-1);

   int i,j;
   for(int k = 0; k<n;k++){
    
    
       //随机生成图形位置
       i = randomCol(generator);
       j = randomRow(generator);
       if(image.type() == CV_8UC1){
    
     //灰度图像
         image.at<uchar>(j,i) = 0;
       }else if(image.type() == CV_8UC3){
    
    
           image.at<cv::Vec3b>(j,i)[0] = 0;
           image.at<cv::Vec3b>(j,i)[1] = 0;
           image.at<cv::Vec3b>(j,i)[2] = 0;
       }
   }
}


void wave(const cv::Mat &image,cv::Mat &result){
    
    
   //映射参数
   cv::Mat srcX(image.rows,image.cols,CV_32F);
   cv::Mat srcY(image.rows,image.cols,CV_32F);
   //创建映射参数
   for(int i=0;i<image.rows;i++){
    
    
       for(int j=0;j<image.cols;j++){
    
    
           srcX.at<float>(i,j) =  float(image.cols - j - 1);;
           srcY.at<float>(i,j) = i;

       }
   }
   cv::remap(image,result,srcX,srcY,cv::INTER_LINEAR);
}



int main(){
    
    


   cv::Mat a = cv::imread("../../a.png",1);

   cv::Mat result_a;

   wave(a,result_a);

   cv::imshow("image",a);

   cv::imshow("image_remap",result_a);

   cv::waitKey(0);

   return 0;
}