int* computeHistogram(char* fname) {
	int* h = (int*)calloc(256, sizeof(int));
	Mat src = imread(fname, CV_LOAD_IMAGE_GRAYSCALE);
	for (int i = 0; i < src.rows; i++) {
		for (int j = 0; j < src.cols; j++) {
			h[src.at<uchar>(i, j)]++;
			//*(h + src.at<uchar>(i, j)) += 1;
		}
	}
	return h;
}
	//historgram
void createHistogram() {
	char fname[MAX_PATH];
	Mat src;
	Mat dst;
	int h[256] = { 0 };
	if (openFileDlg(fname)) {
		src = imread(fname, CV_LOAD_IMAGE_GRAYSCALE);
		int height = src.rows;
		int width = src.cols;
		int level;
		//dst = Mat(height, width, CV_8UC1);
		for (int i = 0; i < height; i++) {
			for (int j = 0; j < width; j++) {
				level = src.at<uchar>(i, j);
				h[level]++;
			}
		}
	}
	imshow("image", src);
	showHistogram("Histogram", h, 256, 256);
	waitKey();
}
void showHistogram(const std::string& name, int* hist, const int  hist_cols, const int hist_height)
{
	Mat imgHist(hist_height, hist_cols, CV_8UC3, CV_RGB(255, 255, 255)); // constructs a white image

																		 //computes histogram maximum
	int max_hist = 0;
	for (int i = 0; i < hist_cols; i++)
		if (hist[i] > max_hist)
			max_hist = hist[i];
	double scale = 1.0;
	scale = (double)hist_height / max_hist;
	int baseline = hist_height - 1;

	for (int x = 0; x < hist_cols; x++) {
		Point p1 = Point(x, baseline);
		Point p2 = Point(x, baseline - cvRound(hist[x] * scale));
		line(imgHist, p1, p2, CV_RGB(255, 0, 255)); // histogram bins colored in magenta
	}

	imshow(name, imgHist);
}