add API to reinterpret Mat type

modules/core/include/opencv2/core/mat.hpp

@@ -371,6 +371,7 @@ public:
     void release() const;
     void clear() const;
     void setTo(const _InputArray& value, const _InputArray & mask = _InputArray()) const;
+    Mat reinterpret( int type ) const;
 
     void assign(const UMat& u) const;
     void assign(const Mat& m) const;
@@ -1322,6 +1323,15 @@ public:
      */
     Mat reshape(int cn, const std::vector<int>& newshape) const;
 
+    /** @brief Reset the type of matrix.
+
+    The methods reset the data type of matrix. If the new type and the old type of the matrix
+    have the same element size, the current buffer can be reused. The method needs to consider whether the
+    current mat is a submatrix or has any references.
+    @param type New data type.
+     */
+    Mat reinterpret( int type ) const;
+
     /** @brief Transposes a matrix.
 
     The method performs matrix transposition by means of matrix expressions. It does not perform the

modules/core/src/matrix.cpp

@@ -1261,6 +1261,16 @@ Mat Mat::reshape(int _cn, const std::vector<int>& _newshape) const
     return reshape(_cn, (int)_newshape.size(), &_newshape[0]);
 }
 
+Mat Mat::reinterpret(int type) const
+{
+    type = CV_MAT_TYPE(type);
+    CV_Assert(CV_ELEM_SIZE(this->type()) == CV_ELEM_SIZE(type));
+    Mat m = *this;
+    m.flags = (m.flags & ~CV_MAT_TYPE_MASK) | type;
+    m.updateContinuityFlag();
+    return m;
+}
+
 Mat Mat::diag(const Mat& d)
 {
     CV_Assert( d.cols == 1 || d.rows == 1 );

modules/core/src/matrix_wrap.cpp

@@ -1656,6 +1656,12 @@ void _OutputArray::create(int d, const int* sizes, int mtype, int i,
     CV_Error(Error::StsNotImplemented, "Unknown/unsupported array type");
 }
 
+Mat _OutputArray::reinterpret(int mtype) const
+{
+    mtype = CV_MAT_TYPE(mtype);
+    return getMat().reinterpret(mtype);
+}
+
 void _OutputArray::createSameSize(const _InputArray& arr, int mtype) const
 {
     int arrsz[CV_MAX_DIM], d = arr.sizend(arrsz);

modules/core/test/test_mat.cpp

@@ -1303,6 +1303,42 @@ TEST(Core_Mat, reshape_ndims_4)
     }
 }
 
+TEST(Core_Mat, reinterpret_Mat_8UC3_8SC3)
+{
+    cv::Mat A(8, 16, CV_8UC3, cv::Scalar(1, 2, 3));
+    cv::Mat B = A.reinterpret(CV_8SC3);
+
+    EXPECT_EQ(A.data, B.data);
+    EXPECT_EQ(B.type(), CV_8SC3);
+}
+
+TEST(Core_Mat, reinterpret_Mat_8UC4_32FC1)
+{
+    cv::Mat A(8, 16, CV_8UC4, cv::Scalar(1, 2, 3, 4));
+    cv::Mat B = A.reinterpret(CV_32FC1);
+
+    EXPECT_EQ(A.data, B.data);
+    EXPECT_EQ(B.type(), CV_32FC1);
+}
+
+TEST(Core_Mat, reinterpret_OutputArray_8UC3_8SC3) {
+    cv::Mat A(8, 16, CV_8UC3, cv::Scalar(1, 2, 3));
+    cv::OutputArray C(A);
+    cv::Mat B = C.reinterpret(CV_8SC3);
+
+    EXPECT_EQ(A.data, B.data);
+    EXPECT_EQ(B.type(), CV_8SC3);
+}
+
+TEST(Core_Mat, reinterpret_OutputArray_8UC4_32FC1) {
+    cv::Mat A(8, 16, CV_8UC4, cv::Scalar(1, 2, 3, 4));
+    cv::OutputArray C(A);
+    cv::Mat B = C.reinterpret(CV_32FC1);
+
+    EXPECT_EQ(A.data, B.data);
+    EXPECT_EQ(B.type(), CV_32FC1);
+}
+
 TEST(Core_Mat, push_back)
 {
     Mat a = (Mat_<float>(1,2) << 3.4884074f, 1.4159607f);