Added display-histogram.cpp

1 files changed, 74 insertions, 0 deletions

diff --git a/display-histogram.cpp b/display-histogram.cpp
new file mode 100644
index 0000000..6ebf93e
--- /dev/null
+++ b/display-histogram.cpp
@@ -0,0 +1,74 @@
+#include <opencv2/imgproc/imgproc.hpp>
+#include <opencv2/highgui/highgui.hpp>
+#include <iostream>
+
+using namespace cv;
+using namespace std;
+
+void showHistogram(Mat& img)
+{
+	int bins = 256;							// number of bins
+	int nc = img.channels();		// number of channels
+	vector<Mat> hist(nc);
+
+	for (int i = 0; i < hist.size(); i++)
+		hist[i] = Mat::zeros(1, bins, CV_32SC1);
+
+	for (int i = 0; i < img.rows; i++)
+	{
+		for (int j = 0; j < img.cols; j++)
+		{
+			for (int k = 0; k < nc; k++)
+			{
+				uchar val = nc == 1 ? img.at<uchar>(i,j) : img.at<Vec3b>(i,j)[k];
+				hist[k].at<int>(val) += 1;
+			}
+		}
+	}
+
+	int hmax[3] = {0,0,0};
+	for (int i = 0; i < nc; i++)
+	{
+		for (int j = 0; j < bins-1; j++)
+			hmax[i] = hist[i].at<int>(j) > hmax[i] ? hist[i].at<int>(j) : hmax[i];
+	}
+
+	const char* wname[3] = { "blue", "green", "red" };
+	Scalar colors[3] = { Scalar(255,0,0), Scalar(0,255,0), Scalar(0,0,255) };
+
+	vector<Mat> canvas(nc);
+
+	for (int i = 0; i < nc; i++)
+	{
+		canvas[i] = Mat::ones(125, bins, CV_8UC3);
+
+		for (int j = 0, rows = canvas[i].rows; j < bins-1; j++)
+		{
+			line(
+				canvas[i], 
+				Point(j, rows), 
+				Point(j, rows - (hist[i].at<int>(j) * rows/hmax[i])), 
+				nc == 1 ? Scalar(200,200,200) : colors[i], 
+				1, 8, 0
+			);
+		}
+
+		imshow(nc == 1 ? "value" : wname[i], canvas[i]);
+	}
+}
+
+int main()
+{
+	Mat src = imread("c:/users/nash/desktop/assets/lena.jpg");
+
+	if (src.empty())
+		return -1;
+
+	showHistogram(src);
+
+	imshow("src", src);
+	waitKey(0);
+
+	return 0;
+}
+