Use only inference engine dnn backend for VehicleLicensePlateDetector.

Emgu.CV.Example/XamarinForms/Core/App.cs

@@ -263,7 +263,7 @@ namespace Emgu.CV.XamarinForms
                 p.IsVisible = true;
                 p.Title = "Preferred DNN backend & target";
 
-                foreach (String option in GetDnnBackends())
+                foreach (String option in GetDnnBackends(DnnBackendType.InferenceEngineOnly))
                 {
                     p.Items.Add(option);
                 }
@@ -356,7 +356,13 @@ namespace Emgu.CV.XamarinForms
             }
         }
 
-        private String[] GetDnnBackends()
+        private enum DnnBackendType
+        {
+            Default,
+            InferenceEngineOnly
+        }
+
+        private String[] GetDnnBackends(DnnBackendType backendType = DnnBackendType.Default)
         {
             var openCVConfigDict = CvInvoke.ConfigDict;
             bool haveDNN = (openCVConfigDict["HAVE_OPENCV_DNN"] != 0);
@@ -367,6 +373,11 @@ namespace Emgu.CV.XamarinForms
                 List<String> dnnBackendsText = new List<string>();
                 foreach (var dnnBackend in dnnBackends)
                 {
+                    if (backendType == DnnBackendType.InferenceEngineOnly &&
+                        !((dnnBackend.Backend == Dnn.Backend.InferenceEngine)
+                        || (dnnBackend.Backend == Dnn.Backend.InferenceEngineNgraph)
+                        || (dnnBackend.Backend == Dnn.Backend.InferenceEngineNnBuilder2019)))
+                        continue;
                     dnnBackendsText.Add(String.Format("{0};{1}", dnnBackend.Backend, dnnBackend.Target));
                 }
 

Emgu.CV.Models/Dnn/VehicleLicensePlateDetector.cs

@@ -263,7 +263,7 @@ namespace Emgu.CV.Models
             Object initOptions = null)
 #endif
         {
-            Dnn.Backend backend = Dnn.Backend.OpenCV;
+            Dnn.Backend backend = Dnn.Backend.InferenceEngine;
             Dnn.Target target = Target.Cpu;
             if (initOptions != null && ((initOptions as String) != null))
             {
@@ -277,7 +277,7 @@ namespace Emgu.CV.Models
                         Enum.TryParse(targetStr, true, out target)))
                     {
                         //If failed to part either backend or target, use the following default
-                        backend = Dnn.Backend.OpenCV;
+                        backend = Dnn.Backend.InferenceEngine;
                         target = Target.Cpu;
                     }
                 }