Merge pull request #28575 from abhishek-gola:shape_inference_bug_fix

[BUG FIX] Incorrect shape assert bug fix in 5.x #28575

Closes: https://github.com/opencv/opencv/issues/28563

### 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 another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the 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.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/dnn/src/layers/reduce2_layer.cpp

@@ -122,7 +122,7 @@ public:
                     std::fill(shape_out.begin(), shape_out.end(), 1);
                     outs[0] = shape_out;
                 } else {
-                    outs[0] = MatShape(1, 1);
+                    outs[0] = MatShape::scalar();
                 }
             }
             return false;
@@ -142,7 +142,7 @@ public:
                 shape_output.push_back(shape_output_[i]);
             }
         }
-        if (shape_output.empty()) shape_output.push_back(1);
+        if (shape_output.empty()) shape_output = MatShape::scalar();
         outs[0] = shape_output;
         return false;
     }
@@ -471,7 +471,7 @@ public:
                     outShape = inpShape;
                     for (int i = 0; i < (int)outShape.size(); ++i) outShape[i] = 1;
                 } else {
-                    outShape.assign(1, 1);
+                    outShape = MatShape::scalar();
                 }
             }
         } else {
@@ -487,7 +487,7 @@ public:
                     outShape.push_back(tmp[i]);
                 }
             }
-            if (outShape.empty()) outShape.push_back(1);
+            if (outShape.empty()) outShape = MatShape::scalar();
             axes = norm_axes;
         }
 

modules/dnn/src/layers/reduce_layer.cpp

@@ -118,7 +118,7 @@ public:
                     for (auto i = 0; i < shape_output.size(); ++i)
                         shape_output[i] = 1;
                 } else {
-                    shape_output.push_back(1);
+                    shape_output = MatShape::scalar();
                 }
                 outputs.assign(1, shape_output);
             }
@@ -139,7 +139,7 @@ public:
                     shape_output.push_back(shape_output_[i]);
             }
             if (shape_output.empty())
-                shape_output.push_back(1);
+                shape_output = MatShape::scalar();
 
             outputs.assign(1, shape_output);
         }

modules/dnn/test/test_common.impl.hpp

@@ -79,11 +79,27 @@ void normAssert(
         cv::InputArray ref, cv::InputArray test, const char *comment /*= ""*/,
         double l1 /*= 0.00001*/, double lInf /*= 0.0001*/)
 {
-    double normL1 = cvtest::norm(ref, test, cv::NORM_L1) / ref.getMat().total();
-    EXPECT_LE(normL1, l1) << comment << "  |ref| = " << cvtest::norm(ref, cv::NORM_INF);
+    cv::Mat refMat = ref.getMat();
+    cv::Mat testMat = test.getMat();
+    const cv::MatShape refShape = refMat.shape();
+    const cv::MatShape testShape = testMat.shape();
+    const bool scalar1dCompatible =
+        (refShape.isScalar() && testShape.size() == 1 && testShape[0] == 1) ||
+        (testShape.isScalar() && refShape.size() == 1 && refShape[0] == 1);
+    if (scalar1dCompatible)
+    {
+        const cv::MatShape oneShape{1};
+        if (refShape.isScalar())
+            refMat = refMat.reshape(1, oneShape);
+        if (testShape.isScalar())
+            testMat = testMat.reshape(1, oneShape);
+    }
 
-    double normInf = cvtest::norm(ref, test, cv::NORM_INF);
-    EXPECT_LE(normInf, lInf) << comment << "  |ref| = " << cvtest::norm(ref, cv::NORM_INF);
+    double normL1 = cvtest::norm(refMat, testMat, cv::NORM_L1) / refMat.total();
+    EXPECT_LE(normL1, l1) << comment << "  |ref| = " << cvtest::norm(refMat, cv::NORM_INF);
+
+    double normInf = cvtest::norm(refMat, testMat, cv::NORM_INF);
+    EXPECT_LE(normInf, lInf) << comment << "  |ref| = " << cvtest::norm(refMat, cv::NORM_INF);
 }
 
 std::vector<cv::Rect2d> matToBoxes(const cv::Mat& m)

modules/dnn/test/test_onnx_importer.cpp

@@ -118,8 +118,12 @@ public:
             net.setInput(inps[i], inputNames[i]);
         Mat out = net.forward("");
 
-        // BUG: https://github.com/opencv/opencv/issues/28563
-        // EXPECT_EQ(shape(out), shape(ref));
+        MatShape outShape = shape(out);
+        MatShape refShape = shape(ref);
+        bool scalar1dCompatible =
+            (outShape.isScalar() && refShape.size() == 1 && refShape[0] == 1) ||
+            (refShape.isScalar() && outShape.size() == 1 && outShape[0] == 1);
+        EXPECT_TRUE(outShape == refShape || scalar1dCompatible);
 
         if (useSoftmax)
         {