Program reads a picture file called boy.jpg in the current folder and displays it. After 1 second it will change to grey scale.

view_picture.cpp

#include<highgui.h>
#include<cv.h>

using namespace cv;

int main()
{
        Mat A,B;
        A=imread("boy.jpg");                        //Read the image file
        namedWindow("Boy", CV_WINDOW_AUTOSIZE );    //Create a new window to show  the image. Name the window as "boy"
        cvtColor(A,B,CV_BGR2GRAY);                  //To convert bgr (blue green red) to greyscale and store it in B
        imshow("Boy",A);                            //Display it in the window named Boy
        cvWaitKey(1000);                            //Delay of 1 second
        imshow("Boy",B);                            //Display Second Image
        cvWaitKey(1000);
}