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

using namespace cv;
using namespace std;

void on_trackbar(int pos, void* userdata);

int main(int argc, char* argv[]) {
	Mat src;

	if (argc < 2)
		src = imread("../../resources/images/neutrophils.png", IMREAD_GRAYSCALE);
	else
		src = imread(argv[1], IMREAD_GRAYSCALE);

	if (src.empty()) {
		cerr << "Image load failed!" << endl;
		return -1;
	}

	namedWindow("dst");
	createTrackbar("Threshold", "dst", 0, 255, on_trackbar, (void*)&src);
	setTrackbarPos("Threshold", "dst", 128);

	cv::waitKey();
	cv::destroyAllWindows();
}

void on_trackbar(int pos, void* userdata) {
	Mat src = *(Mat*)userdata;

	Mat hist;
	int channels[] = { 0 };
	int dims = 1;
	const int histSize[] = { 256 };
	float graylevel[] = { 0, 256 };
	const float* ranges[] = { graylevel };

	calcHist(&src, 1, channels, noArray(), hist, dims, histSize, ranges);
	double histMax;
	minMaxLoc(hist, 0, &histMax);
	Mat imgHist(100, 256, CV_8UC1, Scalar(255));
	for (int i = 0; i < 256; i++) {
		line(imgHist, Point(i, 100), Point(i, 100 - cvRound(hist.at<float>(i, 0) * 100 / histMax)), Scalar(0));
	}
	line(imgHist, Point(pos, 0), Point(pos, 100), 0, 1, LINE_AA);

	Mat dst;
	threshold(src, dst, pos, 255, THRESH_BINARY);

	imshow("dst", dst);
	imshow("hist", imgHist);
}