Read & Display Image & Historgram in C++ using OpenCV

Code

#include <iostream>
#include "opencv2/opencv.hpp"
#include <algorithm>

using namespace cv;
using namespace std;

int
main()
{
  Mat gimage, cimage;
  // image = imread("/home/cl-1/4101/as6/tiff.tiff", CV_LOAD_COLOR);
  gimage = imread("photo.jpg", CV_LOAD_IMAGE_GRAYSCALE); // or use 0
  cimage = imread("tiff.tiff", CV_LOAD_IMAGE_COLOR);     // or use >0
  /*
  if(! gimage.data )                              // Check for invalid input
  */
  namedWindow("GDisplay window", WINDOW_NORMAL); // Create a window for display.
  imshow("GDisplay window", gimage);             // Show our image inside it.
  /*
  resizeWindow("GDisplay window",400,400);  //Resize a window
  */

  float count[256];
  for (int i = 0; i < 256; i++)
    count[i] = 0;

  for (int y = 0; y < gimage.rows; y++)
    for (int x = 0; x < gimage.cols; x++)
      count[(int)gimage.at<uchar>(y, x)]++;

  float maxi = 0;
  for (int i = 0; i < 256; i++) {
    maxi = max(maxi, count[i]);
  }

  float factor = 400 / maxi;
  Scalar col;
  col = Scalar(255, 255, 255);

  Mat hist = Mat::zeros(500, 400, gimage.type());
  for (int i = 0; i < 256; i++) {
    int length = factor * count[i];
    int yfirst = 450;
    int ysecond = 450 - length;
    int xshift = 50;
    line(hist, Point(xshift + i, yfirst), Point(xshift + i, ysecond), col);
  }

  namedWindow("Histogram", WINDOW_NORMAL);
  imshow("Histogram", hist);

  waitKey(0); // Wait for a keystroke in the window
  return 0;
}

Compile & Run

[duke@duke-pc a6]$ g++ as6.cpp  `pkg-config --cflags --libs opencv`

[duke@duke-pc a6]$ ./a.out