Merge pull request #20367 from augustinmanecy:features2d-rw

**Merge with contrib**: https://github.com/opencv/opencv_contrib/pull/3003

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or other license that is incompatible with OpenCV
- [x] The PR is proposed to proper branch
- [ ] There is reference to original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake

modules/features2d/src/sift.dispatch.cpp

@@ -111,6 +111,24 @@ public:
     void findScaleSpaceExtrema( const std::vector<Mat>& gauss_pyr, const std::vector<Mat>& dog_pyr,
                                std::vector<KeyPoint>& keypoints ) const;
 
+    void read( const FileNode& fn) CV_OVERRIDE;
+    void write( FileStorage& fs) const CV_OVERRIDE;
+
+    void setNFeatures(int maxFeatures) CV_OVERRIDE { nfeatures = maxFeatures; }
+    int getNFeatures() const CV_OVERRIDE { return nfeatures; }
+
+    void setNOctaveLayers(int nOctaveLayers_) CV_OVERRIDE { nOctaveLayers = nOctaveLayers_; }
+    int getNOctaveLayers() const CV_OVERRIDE { return nOctaveLayers; }
+
+    void setContrastThreshold(double contrastThreshold_) CV_OVERRIDE  { contrastThreshold = contrastThreshold_; }
+    double getContrastThreshold() const CV_OVERRIDE { return contrastThreshold; }
+
+    void setEdgeThreshold(double edgeThreshold_) CV_OVERRIDE  { edgeThreshold = edgeThreshold_; }
+    double getEdgeThreshold() const CV_OVERRIDE { return edgeThreshold; }
+
+    void setSigma(double sigma_) CV_OVERRIDE  { sigma = sigma_; }
+    double getSigma() const CV_OVERRIDE { return sigma; }
+
 protected:
     CV_PROP_RW int nfeatures;
     CV_PROP_RW int nOctaveLayers;
@@ -554,4 +572,34 @@ void SIFT_Impl::detectAndCompute(InputArray _image, InputArray _mask,
     }
 }
 
+void SIFT_Impl::read( const FileNode& fn)
+{
+  // if node is empty, keep previous value
+  if (!fn["nfeatures"].empty())
+    fn["nfeatures"] >> nfeatures;
+  if (!fn["nOctaveLayers"].empty())
+    fn["nOctaveLayers"] >> nOctaveLayers;
+  if (!fn["contrastThreshold"].empty())
+    fn["contrastThreshold"] >> contrastThreshold;
+  if (!fn["edgeThreshold"].empty())
+    fn["edgeThreshold"] >> edgeThreshold;
+  if (!fn["sigma"].empty())
+    fn["sigma"] >> sigma;
+  if (!fn["descriptorType"].empty())
+    fn["descriptorType"] >> descriptor_type;
+}
+void SIFT_Impl::write( FileStorage& fs) const
+{
+  if(fs.isOpened())
+  {
+    fs << "name" << getDefaultName();
+    fs << "nfeatures" << nfeatures;
+    fs << "nOctaveLayers" << nOctaveLayers;
+    fs << "contrastThreshold" << contrastThreshold;
+    fs << "edgeThreshold" << edgeThreshold;
+    fs << "sigma" << sigma;
+    fs << "descriptorType" << descriptor_type;
+  }
+}
+
 }