Canny with own gradient (#6664)

* example using the Canny algorithm with custom image gradient.

* Modified example to integrate new function canny with custom gradient

samples/cpp/edge.cpp

@@ -9,19 +9,34 @@ using namespace cv;
 using namespace std;
 
 int edgeThresh = 1;
-Mat image, gray, edge, cedge;
+int edgeThreshScharr=1;
+
+Mat image, gray, blurImage, edge1, edge2, cedge;
+
+const char* window_name1 = "Edge map : Canny default (Sobel gradient)";
+const char* window_name2 = "Edge map : Canny with custom gradient (Scharr)";
 
 // define a trackbar callback
 static void onTrackbar(int, void*)
 {
-    blur(gray, edge, Size(3,3));
+    blur(gray, blurImage, Size(3,3));
 
     // Run the edge detector on grayscale
-    Canny(edge, edge, edgeThresh, edgeThresh*3, 3);
+    Canny(blurImage, edge1, edgeThresh, edgeThresh*3, 3);
     cedge = Scalar::all(0);
 
-    image.copyTo(cedge, edge);
-    imshow("Edge map", cedge);
+    image.copyTo(cedge, edge1);
+    imshow(window_name1, cedge);
+
+    /// Canny detector with scharr
+    Mat dx,dy;
+    Scharr(blurImage,dx,CV_16S,1,0);
+    Scharr(blurImage,dy,CV_16S,0,1);
+    Canny( dx,dy, edge2, edgeThreshScharr, edgeThreshScharr*3 );
+    /// Using Canny's output as a mask, we display our result
+    cedge = Scalar::all(0);
+    image.copyTo(cedge, edge2);
+    imshow(window_name2, cedge);
 }
 
 static void help()
@@ -57,10 +72,12 @@ int main( int argc, const char** argv )
     cvtColor(image, gray, COLOR_BGR2GRAY);
 
     // Create a window
-    namedWindow("Edge map", 1);
+    namedWindow(window_name1, 1);
+    namedWindow(window_name2, 1);
 
     // create a toolbar
-    createTrackbar("Canny threshold", "Edge map", &edgeThresh, 100, onTrackbar);
+    createTrackbar("Canny threshold default", window_name1, &edgeThresh, 100, onTrackbar);
+    createTrackbar("Canny threshold Scharr", window_name2, &edgeThreshScharr, 400, onTrackbar);
 
     // Show the image
     onTrackbar(0, 0);