diff --git a/doc/features2d_detection_description.tex b/doc/features2d_detection_description.tex
index 07d554701bad90a8bc87db7c868be5d9d99c9a6a..60742f5fda94533255a293f71583d9eafb27a2ae 100644
--- a/doc/features2d_detection_description.tex
+++ b/doc/features2d_detection_description.tex
@@ -414,7 +414,10 @@ public:
     // detects keypoints using fast multi-scale Hessian detector
     void operator()(const Mat& img, const Mat& mask,
                     vector<KeyPoint>& keypoints) const;
-    // detects keypoints and computes the SURF descriptors for them
+    // detects keypoints and computes the SURF descriptors for them;
+    // output vector "descriptors" stores elements of descriptors and has size 
+    // equal descriptorSize()*keypoints.size() as each descriptor is 
+    // descriptorSize() elements of this vector.
     void operator()(const Mat& img, const Mat& mask,
                     vector<KeyPoint>& keypoints,
                     vector<float>& descriptors,