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/brisk.cpp

@@ -54,7 +54,7 @@ namespace cv
 class BRISK_Impl CV_FINAL : public BRISK
 {
 public:
-    explicit BRISK_Impl(int thresh=30, int octaves=3, float patternScale=1.0f);
+    explicit BRISK_Impl(int _threshold=30, int _octaves=3, float _patternScale=1.0f);
     // custom setup
     explicit BRISK_Impl(const std::vector<float> &radiusList, const std::vector<int> &numberList,
         float dMax=5.85f, float dMin=8.2f, const std::vector<int> indexChange=std::vector<int>());
@@ -65,6 +65,9 @@ public:
 
     virtual ~BRISK_Impl();
 
+    void read( const FileNode& fn) CV_OVERRIDE;
+    void write( FileStorage& fs) const CV_OVERRIDE;
+
     int descriptorSize() const CV_OVERRIDE
     {
         return strings_;
@@ -99,6 +102,35 @@ public:
     {
         return octaves;
     }
+    virtual void setPatternScale(float _patternScale) CV_OVERRIDE
+    {
+      patternScale = _patternScale;
+      std::vector<float> rList;
+      std::vector<int> nList;
+
+      // this is the standard pattern found to be suitable also
+      rList.resize(5);
+      nList.resize(5);
+      const double f = 0.85 * patternScale;
+
+      rList[0] = (float)(f * 0.);
+      rList[1] = (float)(f * 2.9);
+      rList[2] = (float)(f * 4.9);
+      rList[3] = (float)(f * 7.4);
+      rList[4] = (float)(f * 10.8);
+
+      nList[0] = 1;
+      nList[1] = 10;
+      nList[2] = 14;
+      nList[3] = 15;
+      nList[4] = 20;
+
+      generateKernel(rList, nList, (float)(5.85 * patternScale), (float)(8.2 * patternScale));
+    }
+    virtual float getPatternScale() const  CV_OVERRIDE
+    {
+      return patternScale;
+    }
 
     // call this to generate the kernel:
     // circle of radius r (pixels), with n points;
@@ -122,6 +154,7 @@ protected:
     // Feature parameters
     CV_PROP_RW int threshold;
     CV_PROP_RW int octaves;
+    CV_PROP_RW float patternScale;
 
     // some helper structures for the Brisk pattern representation
     struct BriskPatternPoint{
@@ -309,32 +342,12 @@ const float BriskScaleSpace::safetyFactor_ = 1.0f;
 const float BriskScaleSpace::basicSize_ = 12.0f;
 
 // constructors
-BRISK_Impl::BRISK_Impl(int thresh, int octaves_in, float patternScale)
+BRISK_Impl::BRISK_Impl(int _threshold, int _octaves, float _patternScale)
 {
-  threshold = thresh;
-  octaves = octaves_in;
+  threshold = _threshold;
+  octaves = _octaves;
 
-  std::vector<float> rList;
-  std::vector<int> nList;
-
-  // this is the standard pattern found to be suitable also
-  rList.resize(5);
-  nList.resize(5);
-  const double f = 0.85 * patternScale;
-
-  rList[0] = (float)(f * 0.);
-  rList[1] = (float)(f * 2.9);
-  rList[2] = (float)(f * 4.9);
-  rList[3] = (float)(f * 7.4);
-  rList[4] = (float)(f * 10.8);
-
-  nList[0] = 1;
-  nList[1] = 10;
-  nList[2] = 14;
-  nList[3] = 15;
-  nList[4] = 20;
-
-  generateKernel(rList, nList, (float)(5.85 * patternScale), (float)(8.2 * patternScale));
+  setPatternScale(_patternScale);
 }
 
 BRISK_Impl::BRISK_Impl(const std::vector<float> &radiusList,
@@ -359,6 +372,31 @@ BRISK_Impl::BRISK_Impl(int thresh,
   octaves = octaves_in;
 }
 
+void BRISK_Impl::read( const FileNode& fn)
+{
+  // if node is empty, keep previous value
+  if (!fn["threshold"].empty())
+    fn["threshold"] >> threshold;
+  if (!fn["octaves"].empty())
+    fn["octaves"] >> octaves;
+  if (!fn["patternScale"].empty())
+  {
+    float _patternScale;
+    fn["patternScale"] >> _patternScale;
+    setPatternScale(_patternScale);
+  }
+}
+void BRISK_Impl::write( FileStorage& fs) const
+{
+  if(fs.isOpened())
+  {
+    fs << "name" << getDefaultName();
+    fs << "threshold" << threshold;
+    fs << "octaves" << octaves;
+    fs << "patternScale" << patternScale;
+  }
+}
+
 void
 BRISK_Impl::generateKernel(const std::vector<float> &radiusList,
                            const std::vector<int> &numberList,