diff --git a/app/src/main/cpp/camera2/OpenCVHdr.h b/app/src/main/cpp/camera2/OpenCVHdr.h
index f79ef57c..dc246719 100644
--- a/app/src/main/cpp/camera2/OpenCVHdr.h
+++ b/app/src/main/cpp/camera2/OpenCVHdr.h
@@ -9,6 +9,7 @@
 using namespace std;
 using namespace cv;
 
+// https://zhuanlan.zhihu.com/p/38176640
 
 void Debevec(vector<Mat>exposureImages, vector<float>exposureTimes, Mat& output);
 void Robertson(vector<Mat>exposureImages, vector<float>exposureTimes, Mat& output);