How to read the pixel value of a single channel image in OpenCV using C++?

Digital images are made of pixels. Using OpenCV, it is easy to read the value of pixels. However, if we want to get the pixel values, we have to handle a single channel separately.

Here we are loading an image in the matrix named 'cimage', and then it converts the image using 'cvtColor(cimage, img, COLOR_BGR2GRAY); ' and store it in the matrix named 'img'.

The following program read the pixel value of an image and shows the values in console window.


using namespace std;
using namespace cv;
int main() {
   int x;//Declaring an integer variable to hold values of pixels//
   Mat cimage = imread("colors.jpg");//loading an image//
   Mat img;//Declaring an empty matrix to store converted image//
   cvtColor(cimage, img, COLOR_BGR2GRAY);//Converting loaded image to grayscale image//
   for (int i = 0; i < img.rows; i++)//loop for rows// {
      for (int j = 0; j < img.cols; j++)//loop for columns// {
         x = (int)<uchar>(i, j);//storing value of (i,j) pixel in variable//
         cout << "Value of pixel" << "(" << i << "," << j << ")" << "=" << x << endl;//showing the values in console window//
   imshow("Show", img);//showing the image//
   waitKey();//wait for keystroke from keyboard//
   return 0;


Updated on: 10-Mar-2021

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