use more accurate reshape

modules/core/src/matrix.cpp

@@ -2691,17 +2691,17 @@ double cv::kmeans( InputArray _data, int K,
                    int flags, OutputArray _centers )
 {
     const int SPP_TRIALS = 3;
-    Mat data = _data.getMat();
-    bool isrow = data.rows == 1 && data.channels() > 1;
-    int N = !isrow ? data.rows : data.cols;
-    int dims = (!isrow ? data.cols : 1)*data.channels();
-    int type = data.depth();
+    Mat data0 = _data.getMat();
+    bool isrow = data0.rows == 1 && data0.channels() > 1;
+    int N = !isrow ? data0.rows : data0.cols;
+    int dims = (!isrow ? data0.cols : 1)*data0.channels();
+    int type = data0.depth();
 
     attempts = std::max(attempts, 1);
-    CV_Assert( data.dims <= 2 && type == CV_32F && K > 0 );
+    CV_Assert( data0.dims <= 2 && type == CV_32F && K > 0 );
     CV_Assert( N >= K );
 
-    data = data.reshape(1, N);
+    Mat data(N, dims, CV_32F, data0.data, isrow ? dims * sizeof(float) : static_cast<size_t>(data0.step));
 
     _bestLabels.create(N, 1, CV_32S, -1, true);