Merge pull request #12827 from hrnr:stitching_4

[evolution] Stitching for OpenCV 4.0

* stitching: wrap Stitcher::create for bindings

* provide method for consistent stitcher usage across languages

* samples: add python stitching sample

* port cpp stitching sample to python

* stitching: consolidate Stitcher create methods

* remove Stitcher::createDefault, it returns Stitcher, not Ptr<Stitcher> -> inconsistent API
* deprecate cv::createStitcher and cv::createStitcherScans in favor of Stitcher::create

* stitching: avoid anonymous enum in Stitcher

* ORIG_RESOL should be double
* add documentatiton

* stitching: improve documentation in Stitcher

* stitching: expose estimator in Stitcher

* remove ABI hack

* stitching: drop try_use_gpu flag

* OCL will be used automatically through T-API in OCL-enable paths
* CUDA won't be used unless user sets CUDA-enabled classes manually

* stitching: drop FeaturesFinder

* use Feature2D instead of FeaturesFinder
* interoperability with features2d module
* detach from dependency on xfeatures2d

* features2d: fix compute and detect to work with UMat vectors

* correctly pass UMats as UMats to allow OCL paths
* support vector of UMats as output arg

* stitching: use nearest interpolation for resizing masks

* fix warnings

samples/cpp/stitching.cpp

@@ -8,7 +8,6 @@
 using namespace std;
 using namespace cv;
 
-bool try_use_gpu = false;
 bool divide_images = false;
 Stitcher::Mode mode = Stitcher::PANORAMA;
 vector<Mat> imgs;
@@ -24,7 +23,7 @@ int main(int argc, char* argv[])
 
     //![stitching]
     Mat pano;
-    Ptr<Stitcher> stitcher = Stitcher::create(mode, try_use_gpu);
+    Ptr<Stitcher> stitcher = Stitcher::create(mode);
     Stitcher::Status status = stitcher->stitch(imgs, pano);
 
     if (status != Stitcher::OK)
@@ -47,9 +46,6 @@ void printUsage(char** argv)
          "Flags:\n"
          "  --d3\n"
          "      internally creates three chunks of each image to increase stitching success\n"
-         "  --try_use_gpu (yes|no)\n"
-         "      Try to use GPU. The default value is 'no'. All default values\n"
-         "      are for CPU mode.\n"
          "  --mode (panorama|scans)\n"
          "      Determines configuration of stitcher. The default is 'panorama',\n"
          "      mode suitable for creating photo panoramas. Option 'scans' is suitable\n"
@@ -75,19 +71,6 @@ int parseCmdArgs(int argc, char** argv)
             printUsage(argv);
             return EXIT_FAILURE;
         }
-        else if (string(argv[i]) == "--try_use_gpu")
-        {
-            if (string(argv[i + 1]) == "no")
-                try_use_gpu = false;
-            else if (string(argv[i + 1]) == "yes")
-                try_use_gpu = true;
-            else
-            {
-                cout << "Bad --try_use_gpu flag value\n";
-                return EXIT_FAILURE;
-            }
-            i++;
-        }
         else if (string(argv[i]) == "--d3")
         {
             divide_images = true;

samples/cpp/stitching_detailed.cpp

@@ -17,6 +17,10 @@
 #include "opencv2/stitching/detail/warpers.hpp"
 #include "opencv2/stitching/warpers.hpp"
 
+#ifdef HAVE_OPENCV_XFEATURES2D
+#include "opencv2/xfeatures2d/nonfree.hpp"
+#endif
+
 #define ENABLE_LOG 1
 #define LOG(msg) std::cout << msg
 #define LOGLN(msg) std::cout << msg << std::endl
@@ -374,23 +378,20 @@ int main(int argc, char* argv[])
     int64 t = getTickCount();
 #endif
 
-    Ptr<FeaturesFinder> finder;
-    if (features_type == "surf")
+    Ptr<Feature2D> finder;
+    if (features_type == "orb")
     {
-#ifdef HAVE_OPENCV_XFEATURES2D
-        if (try_cuda && cuda::getCudaEnabledDeviceCount() > 0)
-            finder = makePtr<SurfFeaturesFinderGpu>();
-        else
-#endif
-            finder = makePtr<SurfFeaturesFinder>();
+        finder = ORB::create();
     }
-    else if (features_type == "orb")
+#ifdef HAVE_OPENCV_XFEATURES2D
+    else if (features_type == "surf")
     {
-        finder = makePtr<OrbFeaturesFinder>();
+        finder = xfeatures2d::SURF::create();
     }
     else if (features_type == "sift") {
-        finder = makePtr<SiftFeaturesFinder>();
+        finder = xfeatures2d::SIFT::create();
     }
+#endif
     else
     {
         cout << "Unknown 2D features type: '" << features_type << "'.\n";
@@ -435,7 +436,7 @@ int main(int argc, char* argv[])
             is_seam_scale_set = true;
         }
 
-        (*finder)(img, features[i]);
+        computeImageFeatures(finder, img, features[i]);
         features[i].img_idx = i;
         LOGLN("Features in image #" << i+1 << ": " << features[i].keypoints.size());
 
@@ -443,7 +444,6 @@ int main(int argc, char* argv[])
         images[i] = img.clone();
     }
 
-    finder->collectGarbage();
     full_img.release();
     img.release();