some improvements on tutorials

samples/cpp/tutorial_code/ImgTrans/HoughCircle_Demo.cpp

@@ -21,7 +21,7 @@ namespace
     const std::string usage = "Usage : tutorial_HoughCircle_Demo <path_to_input_image>\n";
 
     // initial and max values of the parameters of interests.
-    const int cannyThresholdInitialValue = 200;
+    const int cannyThresholdInitialValue = 100;
     const int accumulatorThresholdInitialValue = 50;
     const int maxAccumulatorThreshold = 200;
     const int maxCannyThreshold = 255;
@@ -55,15 +55,13 @@ int main(int argc, char** argv)
 {
     Mat src, src_gray;
 
-    if (argc < 2)
-    {
-        std::cerr<<"No input image specified\n";
-        std::cout<<usage;
-        return -1;
-    }
-
     // Read the image
-    src = imread( argv[1], IMREAD_COLOR );
+    String imageName("../data/stuff.jpg"); // by default
+    if (argc > 1)
+    {
+       imageName = argv[1];
+    }
+    src = imread( imageName, IMREAD_COLOR );
 
     if( src.empty() )
     {