Add ability to read thresh and nms_threshold from YOLO layer in YOLOV3 cfg file.

Currently the thresh is hard-coded to be 0.2 and nms_threshold as 0.4.

modules/dnn/src/darknet/darknet_io.cpp

@@ -371,7 +371,7 @@ namespace cv {
                     fused_layer_names.push_back(last_layer);
                 }
 
-                void setYolo(int classes, const std::vector<int>& mask, const std::vector<float>& anchors)
+                void setYolo(int classes, const std::vector<int>& mask, const std::vector<float>& anchors, float thresh, float nms_threshold)
                 {
                     cv::dnn::LayerParams region_param;
                     region_param.name = "Region-name";
@@ -382,6 +382,8 @@ namespace cv {
                     region_param.set<int>("classes", classes);
                     region_param.set<int>("anchors", numAnchors);
                     region_param.set<bool>("logistic", true);
+                    region_param.set<float>("thresh", thresh);
+                    region_param.set<float>("nms_threshold", nms_threshold);
 
                     std::vector<float> usedAnchors(numAnchors * 2);
                     for (int i = 0; i < numAnchors; ++i)
@@ -646,6 +648,8 @@ namespace cv {
                     {
                         int classes = getParam<int>(layer_params, "classes", -1);
                         int num_of_anchors = getParam<int>(layer_params, "num", -1);
+                        float thresh = getParam<float>(layer_params, "thresh", 0.2);
+                        float nms_threshold = getParam<float>(layer_params, "nms_threshold", 0.4);
 
                         std::string anchors_values = getParam<std::string>(layer_params, "anchors", std::string());
                         CV_Assert(!anchors_values.empty());
@@ -658,7 +662,7 @@ namespace cv {
                         CV_Assert(classes > 0 && num_of_anchors > 0 && (num_of_anchors * 2) == anchors_vec.size());
 
                         setParams.setPermute(false);
-                        setParams.setYolo(classes, mask_vec, anchors_vec);
+                        setParams.setYolo(classes, mask_vec, anchors_vec, thresh, nms_threshold);
                     }
                     else {
                         CV_Error(cv::Error::StsParseError, "Unknown layer type: " + layer_type);