test1.cpp

#include<iostream>
#include<opencv2/highgui/highgui.hpp>
#include<opencv2/imgproc/imgproc.hpp>
 
using namespace std;
using namespace cv;
 
int main()
{
    Mat image = imread("rust1.jpg", CV_LOAD_IMAGE_GRAYSCALE);
 
    // allcoate memory for no of pixels for each intensity value
    int histogram[256];
 
    // initialize all intensity values to 0
    for(int i = 0; i < 255; i++)
    {
        histogram[i] = 0;
    }
 
    // calculate the no of pixels for each intensity values
    for(int y = 0; y < image.rows; y++)
        for(int x = 0; x < image.cols; x++)
            histogram[(int)image.at<uchar>(y,x)]++;
 
    for(int i = 0; i < 256; i++)
        cout<<histogram[i]<<" ";
 
    // draw the histograms
    int hist_w = 512; int hist_h = 400;
    int bin_w = cvRound((double) hist_w/256);
 
    Mat histImage(hist_h, hist_w, CV_8UC1, Scalar(255, 255, 255));
 
    // find the maximum intensity element from histogram
    int max = histogram[0];
    for(int i = 1; i < 256; i++){
        if(max < histogram[i]){
            max = histogram[i];
        }
    }
 
    // normalize the histogram between 0 and histImage.rows
 
    for(int i = 0; i < 255; i++){
        histogram[i] = ((double)histogram[i]/max)*histImage.rows;
    }
 
 
    // draw the intensity line for histogram
    for(int i = 0; i < 255; i++)
    {
        line(histImage, Point(bin_w*(i), hist_h),
                              Point(bin_w*(i), hist_h - histogram[i]),
             Scalar(0,0,0), 1, 8, 0);
    }
 
    // display histogram
    namedWindow("Intensity Histogram", CV_WINDOW_AUTOSIZE);
    imshow("Intensity Histogram", histImage);
 
    namedWindow("Image", CV_WINDOW_AUTOSIZE);
    imshow("Image", image);
    waitKey();
    return 0;
}