Assessing the pixel values of an image

Functions:

Vec3b, imshow, imread, namedWindow, waitKey.

Example:

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#include "opencv2/core/core.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "iostream"

using namespace cv;
using namespace std;

int main( )
{

    Mat src1;
    src1 = imread("lena.jpg", CV_LOAD_IMAGE_COLOR); 
    namedWindow( "Original image", CV_WINDOW_AUTOSIZE ); 
    imshow( "Original image", src1 ); 

    Mat gray;
    cvtColor(src1, gray, CV_BGR2GRAY);
    namedWindow( "Gray image", CV_WINDOW_AUTOSIZE );  
    imshow( "Gray image", gray );

    // know the number of channels the image has
    cout<<"original image channels: "<<src1.channels()<<"gray image channels: "<<gray.channels()<<endl; 

// ******************* READ the Pixel intensity *********************
    // single channel grey scale image (type 8UC1) and pixel coordinates x=5 and y=2
    // by convention, {row number = y} and {column number = x}
    // intensity.val[0] contains a value from 0 to 255
    Scalar intensity1 = gray.at<uchar>(2, 5);
    cout << "Intensity = " << endl << " " << intensity1.val[0] << endl << endl;

    // 3 channel image with BGR color (type 8UC3)
    // the values can be stored in "int" or in "uchar". Here int is used.
    Vec3b intensity2 = src1.at<Vec3b>(10,15);    
    int blue = intensity2.val[0];
    int green = intensity2.val[1];
    int red = intensity2.val[2];
    cout << "Intensity = " << endl << " " << blue << " " << green << " " << red << endl << endl;

// ******************* WRITE to Pixel intensity **********************
    // This is an example in OpenCV 2.4.6.0 documentation 
    Mat H(10, 10, CV_64F);
    for(int i = 0; i < H.rows; i++)
        for(int j = 0; j < H.cols; j++)
            H.at<double>(i,j)=1./(i+j+1);
    cout<<H<<endl<<endl;

    // Modify the pixels of the BGR image
    for (int i=100; i<src1.rows; i++)
    {
        for (int j=100; j<src1.cols; j++)
        {
                src1.at<Vec3b>(i,j)[0] = 0;
                src1.at<Vec3b>(i,j)[1] = 200;
                src1.at<Vec3b>(i,j)[2] = 0;            
        }
    }
    namedWindow( "Modify pixel", CV_WINDOW_AUTOSIZE );  
    imshow( "Modify pixel", src1 );

    waitKey(0);                                         
    return 0;
} 

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