fixed invalid output of cv::dft when using DFT_ROWS + DFT_COMPLEX_OUTPUT (http://code.opencv.org/issues/3428)

modules/core/src/dxt.cpp

@@ -1473,6 +1473,47 @@ typedef IppStatus (CV_STDCALL* IppDFTGetSizeFunc)(int, int, IppHintAlgorithm, in
 typedef IppStatus (CV_STDCALL* IppDFTInitFunc)(int, int, IppHintAlgorithm, void*, uchar*);
 #endif
 
+namespace cv
+{
+static void complementComplexOutput(Mat& dst, int len, int dft_dims)
+{
+    int i, n = dst.cols;
+    size_t elem_size = dst.elemSize1();
+    if (elem_size == sizeof(float))
+    {
+        float* p0 = dst.ptr<float>();
+        size_t dstep = dst.step / sizeof(p0[0]);
+        for (i = 0; i < len; i++)
+        {
+            float* p = p0 + dstep*i;
+            float* q = dft_dims == 1 || i == 0 || i * 2 == len ? p : p0 + dstep*(len - i);
+
+            for (int j = 1; j < (n + 1) / 2; j++)
+            {
+                p[(n - j) * 2] = q[j * 2];
+                p[(n - j) * 2 + 1] = -q[j * 2 + 1];
+            }
+        }
+    }
+    else
+    {
+        double* p0 = dst.ptr<double>();
+        size_t dstep = dst.step / sizeof(p0[0]);
+        for (i = 0; i < len; i++)
+        {
+            double* p = p0 + dstep*i;
+            double* q = dft_dims == 1 || i == 0 || i * 2 == len ? p : p0 + dstep*(len - i);
+
+            for (int j = 1; j < (n + 1) / 2; j++)
+            {
+                p[(n - j) * 2] = q[j * 2];
+                p[(n - j) * 2 + 1] = -q[j * 2 + 1];
+            }
+        }
+    }
+}
+}
+
 void cv::dft( InputArray _src0, OutputArray _dst, int flags, int nonzero_rows )
 {
     static DFTFunc dft_tbl[6] =
@@ -1688,8 +1729,12 @@ void cv::dft( InputArray _src0, OutputArray _dst, int flags, int nonzero_rows )
                 memset( dptr0, 0, dst_full_len );
             }
 
-            if( stage != 1 )
+            if (stage != 1)
+            {
+                if (!inv && real_transform && dst.channels() == 2)
+                    complementComplexOutput(dst, nonzero_rows, 1);
                 break;
+            }
             src = dst;
         }
         else
@@ -1831,41 +1876,7 @@ void cv::dft( InputArray _src0, OutputArray _dst, int flags, int nonzero_rows )
             if( stage != 0 )
             {
                 if( !inv && real_transform && dst.channels() == 2 && len > 1 )
-                {
-                    int n = dst.cols;
-                    if( elem_size == (int)sizeof(float) )
-                    {
-                        float* p0 = (float*)dst.data;
-                        size_t dstep = dst.step/sizeof(p0[0]);
-                        for( i = 0; i < len; i++ )
-                        {
-                            float* p = p0 + dstep*i;
-                            float* q = i == 0 || i*2 == len ? p : p0 + dstep*(len-i);
-
-                            for( int j = 1; j < (n+1)/2; j++ )
-                            {
-                                p[(n-j)*2] = q[j*2];
-                                p[(n-j)*2+1] = -q[j*2+1];
-                            }
-                        }
-                    }
-                    else
-                    {
-                        double* p0 = (double*)dst.data;
-                        size_t dstep = dst.step/sizeof(p0[0]);
-                        for( i = 0; i < len; i++ )
-                        {
-                            double* p = p0 + dstep*i;
-                            double* q = i == 0 || i*2 == len ? p : p0 + dstep*(len-i);
-
-                            for( int j = 1; j < (n+1)/2; j++ )
-                            {
-                                p[(n-j)*2] = q[j*2];
-                                p[(n-j)*2+1] = -q[j*2+1];
-                            }
-                        }
-                    }
-                }
+                    complementComplexOutput(dst, len, 2);
                 break;
             }
             src = dst;

modules/core/test/test_dxt.cpp

@@ -866,3 +866,24 @@ protected:
 };
 
 TEST(Core_DFT, complex_output) { Core_DFTComplexOutputTest test; test.safe_run(); }
+
+TEST(Core_DFT, complex_output2)
+{
+    for (int i = 0; i < 100; i++)
+    {
+        int type = theRNG().uniform(0, 2) ? CV_64F : CV_32F;
+        int m = theRNG().uniform(1, 10);
+        int n = theRNG().uniform(1, 10);
+        Mat x(m, n, type), out;
+        randu(x, -1., 1.);
+        dft(x, out, DFT_ROWS | DFT_COMPLEX_OUTPUT);
+        double nrm = norm(out, NORM_INF);
+        double thresh = n*m * 2;
+        if (nrm > thresh)
+        {
+            cout << "x: " << x << endl;
+            cout << "out: " << out << endl;
+            ASSERT_LT(nrm, thresh);
+        }
+    }
+}