diff --git a/doc/tutorials/dnn/dnn_yolo/dnn_yolo.markdown b/doc/tutorials/dnn/dnn_yolo/dnn_yolo.markdown
index a5eb0a9a32..e9f446db36 100644
--- a/doc/tutorials/dnn/dnn_yolo/dnn_yolo.markdown
+++ b/doc/tutorials/dnn/dnn_yolo/dnn_yolo.markdown
@@ -37,7 +37,7 @@ Execute with image or video file:
 
 @code{.bash}
 
-$ example_dnn_object_detection --config=[PATH-TO-DARKNET]/cfg/yolo.cfg --model=[PATH-TO-DARKNET]/yolo.weights --classes=object_detection_classes_pascal_voc.txt --width=416 --height=416 --scale=0.00392 --input[PATH-TO-IMAGE-OR-VIDEO-FILE]
+$ example_dnn_object_detection --config=[PATH-TO-DARKNET]/cfg/yolo.cfg --model=[PATH-TO-DARKNET]/yolo.weights --classes=object_detection_classes_pascal_voc.txt --width=416 --height=416 --scale=0.00392 --input=[PATH-TO-IMAGE-OR-VIDEO-FILE]
 
 @endcode
 
diff --git a/modules/core/test/test_utils.cpp b/modules/core/test/test_utils.cpp
index 6e352333d9..2a1503a33c 100644
--- a/modules/core/test/test_utils.cpp
+++ b/modules/core/test/test_utils.cpp
@@ -261,4 +261,26 @@ TEST(AutoBuffer, allocate_test)
     EXPECT_EQ(6u, abuf.size());
 }
 
+TEST(CommandLineParser, testScalar)
+{
+    static const char * const keys3 =
+            "{ s0 | 3 4 5 | default scalar }"
+            "{ s1 |       | single value scalar }"
+            "{ s2 |       | two values scalar (default with zeros) }"
+            "{ s3 |       | three values scalar }"
+            "{ s4 |       | four values scalar }"
+            "{ s5 |       | five values scalar }";
+
+    const char* argv[] = {"<bin>", "--s1=1.1", "--s3=1.1 2.2 3",
+                          "--s4=-4.2 1 0 3", "--s5=5 -4 3 2 1"};
+    const int argc = 5;
+    CommandLineParser parser(argc, argv, keys3);
+    EXPECT_EQ(parser.get<Scalar>("s0"), Scalar(3, 4, 5));
+    EXPECT_EQ(parser.get<Scalar>("s1"), Scalar(1.1));
+    EXPECT_EQ(parser.get<Scalar>("s2"), Scalar(0));
+    EXPECT_EQ(parser.get<Scalar>("s3"), Scalar(1.1, 2.2, 3));
+    EXPECT_EQ(parser.get<Scalar>("s4"), Scalar(-4.2, 1, 0, 3));
+    EXPECT_EQ(parser.get<Scalar>("s5"), Scalar(5, -4, 3, 2));
+}
+
 }} // namespace
diff --git a/modules/dnn/include/opencv2/dnn/all_layers.hpp b/modules/dnn/include/opencv2/dnn/all_layers.hpp
index 34f56169b9..e6c8e9f297 100644
--- a/modules/dnn/include/opencv2/dnn/all_layers.hpp
+++ b/modules/dnn/include/opencv2/dnn/all_layers.hpp
@@ -153,7 +153,7 @@ CV__DNN_EXPERIMENTAL_NS_BEGIN
         */
 
         int inputNameToIndex(String inputName);
-        int outputNameToIndex(String outputName);
+        int outputNameToIndex(const String& outputName);
     };
 
     /** @brief Classical recurrent layer
diff --git a/modules/dnn/include/opencv2/dnn/dnn.hpp b/modules/dnn/include/opencv2/dnn/dnn.hpp
index 5605cc0749..4812bd02d3 100644
--- a/modules/dnn/include/opencv2/dnn/dnn.hpp
+++ b/modules/dnn/include/opencv2/dnn/dnn.hpp
@@ -222,7 +222,7 @@ CV__DNN_EXPERIMENTAL_NS_BEGIN
         /** @brief Returns index of output blob in output array.
          *  @see inputNameToIndex()
          */
-        CV_WRAP virtual int outputNameToIndex(String outputName);
+        CV_WRAP virtual int outputNameToIndex(const String& outputName);
 
         /**
          * @brief Ask layer if it support specific backend for doing computations.
@@ -704,7 +704,7 @@ CV__DNN_EXPERIMENTAL_NS_BEGIN
       * @ref readNetFromTorch or @ref readNetFromDarknet. An order of @p model and @p config
       * arguments does not matter.
       */
-     CV_EXPORTS_W Net readNet(String model, String config = "", String framework = "");
+     CV_EXPORTS_W Net readNet(const String& model, const String& config = "", const String& framework = "");
 
     /** @brief Loads blob which was serialized as torch.Tensor object of Torch7 framework.
      *  @warning This function has the same limitations as readNetFromTorch().
diff --git a/modules/dnn/src/dnn.cpp b/modules/dnn/src/dnn.cpp
index 63fa22d04a..d08e646b96 100644
--- a/modules/dnn/src/dnn.cpp
+++ b/modules/dnn/src/dnn.cpp
@@ -398,7 +398,7 @@ struct DataLayer : public Layer
     void forward(std::vector<Mat*>&, std::vector<Mat>&, std::vector<Mat> &) {}
     void forward(InputArrayOfArrays inputs, OutputArrayOfArrays outputs, OutputArrayOfArrays internals) {}
 
-    int outputNameToIndex(String tgtName)
+    int outputNameToIndex(const String& tgtName)
     {
         int idx = (int)(std::find(outNames.begin(), outNames.end(), tgtName) - outNames.begin());
         return (idx < (int)outNames.size()) ? idx : -1;
@@ -2513,7 +2513,7 @@ int Layer::inputNameToIndex(String)
     return -1;
 }
 
-int Layer::outputNameToIndex(String)
+int Layer::outputNameToIndex(const String&)
 {
     return -1;
 }
@@ -2805,9 +2805,11 @@ BackendWrapper::BackendWrapper(const Ptr<BackendWrapper>& base, const MatShape&
 
 BackendWrapper::~BackendWrapper() {}
 
-Net readNet(String model, String config, String framework)
+Net readNet(const String& _model, const String& _config, const String& _framework)
 {
-    framework = framework.toLowerCase();
+    String framework = _framework.toLowerCase();
+    String model = _model;
+    String config = _config;
     const std::string modelExt = model.substr(model.rfind('.') + 1);
     const std::string configExt = config.substr(config.rfind('.') + 1);
     if (framework == "caffe" || modelExt == "caffemodel" || configExt == "caffemodel" ||
diff --git a/modules/dnn/src/layers/recurrent_layers.cpp b/modules/dnn/src/layers/recurrent_layers.cpp
index 92e9e0e233..cfccc191b8 100644
--- a/modules/dnn/src/layers/recurrent_layers.cpp
+++ b/modules/dnn/src/layers/recurrent_layers.cpp
@@ -355,7 +355,7 @@ int LSTMLayer::inputNameToIndex(String inputName)
     return -1;
 }
 
-int LSTMLayer::outputNameToIndex(String outputName)
+int LSTMLayer::outputNameToIndex(const String& outputName)
 {
     if (outputName.toLowerCase() == "h")
         return 0;