Create a negative image in OpenCV

The following code shows how to create a negative in OpenCV.

#include <iostream> //preprocessor directive

#include "opencv2/opencv.hpp" //include OpenCV libraries




//Main function (starting point of execution)
  int main(int argc, char argv[])



{
  // Read the image from file (replace the image file name in your code)

cv::Mat imgIn = cv::imread("snow.jpg");

//Check if the image is empty

if ( imgIn.empty() )



{
  //Print error message

std::cout << "Error occured when loading the image" << std::endl;

//Return negative 1 to indicate an error has occured in the program

return -1;



}
  //Scan all the rows of the image

for (int row=0;row<imgIn.rows;row++)



{
  //Scan all the columns of the image

for (int col=0;col<imgIn.cols;col++)



{
  //Invert each colour channel

imgIn.at<cv::Vec3b>(row,col)[0]=255-imgIn.at<cv::Vec3b>(row,col)[0];

imgIn.at<cv::Vec3b>(row,col)[1]=255-imgIn.at<cv::Vec3b>(row,col)[1];

imgIn.at<cv::Vec3b>(row,col)[2]=255-imgIn.at<cv::Vec3b>(row,col)[2];



}

}
  //Create a window

cv::namedWindow("My Window", 1);

//Display the image

imshow("My Window", imgIn);

// Wait until a key is pressed



cv::waitKey(0);
  //Return 0 to indicate normal run of the program

return 0;



}