Merge remote-tracking branch 'upstream/3.4' into merge-3.4

modules/stitching/include/opencv2/stitching/detail/matchers.hpp

@@ -137,6 +137,21 @@ private:
     Ptr<Feature2D> surf;
 };
 
+
+/** @brief SIFT features finder.
+
+@sa detail::FeaturesFinder, SIFT
+*/
+class CV_EXPORTS SiftFeaturesFinder : public FeaturesFinder
+{
+public:
+    SiftFeaturesFinder();
+
+private:
+    void find(InputArray image, ImageFeatures &features) CV_OVERRIDE;
+    Ptr<Feature2D> sift;
+};
+
 /** @brief ORB features finder. :
 
 @sa detail::FeaturesFinder, ORB

modules/stitching/src/matchers.cpp

@@ -51,6 +51,7 @@ using namespace cv::cuda;
 #ifdef HAVE_OPENCV_XFEATURES2D
 #include "opencv2/xfeatures2d.hpp"
 using xfeatures2d::SURF;
+using xfeatures2d::SIFT;
 #endif
 
 #ifdef HAVE_OPENCV_CUDAIMGPROC
@@ -475,6 +476,35 @@ void SurfFeaturesFinder::find(InputArray image, ImageFeatures &features)
     }
 }
 
+SiftFeaturesFinder::SiftFeaturesFinder()
+{
+#ifdef HAVE_OPENCV_XFEATURES2D
+    Ptr<SIFT> sift_ = SIFT::create();
+    if( !sift_ )
+        CV_Error( Error::StsNotImplemented, "OpenCV was built without SIFT support" );
+    sift = sift_;
+#else
+    CV_Error( Error::StsNotImplemented, "OpenCV was built without SIFT support" );
+#endif
+}
+
+void SiftFeaturesFinder::find(InputArray image, ImageFeatures &features)
+{
+    UMat gray_image;
+    CV_Assert((image.type() == CV_8UC3) || (image.type() == CV_8UC1));
+    if(image.type() == CV_8UC3)
+    {
+        cvtColor(image, gray_image, COLOR_BGR2GRAY);
+    }
+    else
+    {
+        gray_image = image.getUMat();
+    }
+    UMat descriptors;
+    sift->detectAndCompute(gray_image, Mat(), features.keypoints, descriptors);
+    features.descriptors = descriptors.reshape(1, (int)features.keypoints.size());
+}
+
 OrbFeaturesFinder::OrbFeaturesFinder(Size _grid_size, int n_features, float scaleFactor, int nlevels)
 {
     grid_size = _grid_size;