fix Flatten layer

modules/dnn/src/layers/flatten_layer.cpp

@@ -100,7 +100,6 @@ public:
         {
             outputShapeVec.push_back(inputs[0][i]);
         }
-        CV_Assert(outputShapeVec.size() <= 4);
 
         outputs.resize(inputs.size(), outputShapeVec);
 

modules/dnn/src/onnx/onnx_importer.cpp

@@ -1781,20 +1781,67 @@ void ONNXImporter::parseSqueeze(LayerParams& layerParams, const opencv_onnx::Nod
     addLayer(layerParams, node_proto);
 }
 
-void ONNXImporter::parseFlatten(LayerParams& layerParams, const opencv_onnx::NodeProto& node_proto)
+void ONNXImporter::parseFlatten(LayerParams& layerParams, const opencv_onnx::NodeProto& node_proto_)
 {
+    opencv_onnx::NodeProto node_proto = node_proto_;
     CV_CheckEQ(node_proto.input_size(), 1, "");
+    int axis_ = layerParams.get<int>("axis", 1);
     if (constBlobs.find(node_proto.input(0)) != constBlobs.end())
     {
         Mat input = getBlob(node_proto, 0);
-        int axis = normalize_axis(layerParams.get<int>("axis", 1), input.dims);
+        int axis = normalize_axis(axis_, input.dims);
 
-        std::vector<int> out_size(&input.size[0], &input.size[0] + axis);
-        out_size.push_back(input.total(axis));
-        Mat output = input.reshape(1, out_size);
+        int out_size[2] = {1, 1};
+        for (int i = 0; i < axis; ++i)
+        {
+            out_size[0] *= input.size[i];
+        }
+        for (int i = axis; i < input.dims; ++i)
+        {
+            out_size[1] *= input.size[i];
+        }
+
+        Mat output = input.reshape(1, 2, out_size);
         addConstant(layerParams.name, output);
         return;
     }
+    IterShape_t shapeIt = outShapes.find(node_proto.input(0));
+    CV_Assert(shapeIt != outShapes.end());
+    MatShape inpShape = shapeIt->second;
+    int axis = normalize_axis(axis_, inpShape.size());
+
+    if (axis == 0 || axis == inpShape.size())
+    {
+        LayerParams reshapeLp;
+        reshapeLp.name = layerParams.name + "/reshape";
+        reshapeLp.type = "Reshape";
+        CV_Assert(layer_id.find(reshapeLp.name) == layer_id.end());
+
+        inpShape.insert(axis == 0 ? inpShape.begin() : inpShape.end(), 1);
+        reshapeLp.set("dim", DictValue::arrayInt(&inpShape[0], inpShape.size()));
+
+        opencv_onnx::NodeProto proto;
+        proto.add_input(node_proto.input(0));
+        proto.add_output(reshapeLp.name);
+        addLayer(reshapeLp, proto);
+        node_proto.set_input(0, reshapeLp.name);
+        axis += 1;
+    }
+
+    LayerParams first_pass;
+    first_pass.name = layerParams.name + "/flatten";
+    CV_Assert(layer_id.find(first_pass.name) == layer_id.end());
+    first_pass.type = "Flatten";
+    first_pass.set("axis", 0);
+    first_pass.set("end_axis", axis - 1);
+
+    opencv_onnx::NodeProto proto;
+    proto.add_input(node_proto.input(0));
+    proto.add_output(first_pass.name);
+    addLayer(first_pass, proto);
+
+    layerParams.set("axis", 1);
+    node_proto.set_input(0, first_pass.name);
     addLayer(layerParams, node_proto);
 }
 

modules/dnn/test/test_onnx_conformance_layer_filter__halide_denylist.inl.hpp

@@ -17,12 +17,6 @@
 "test_elu",
 "test_elu_default",
 "test_exp",
-"test_flatten_axis0",
-"test_flatten_axis2",
-"test_flatten_axis3",
-"test_flatten_negative_axis1",
-"test_flatten_negative_axis2",
-"test_flatten_negative_axis4",
 "test_leakyrelu",
 "test_leakyrelu_default",
 "test_logsoftmax_axis_1",

modules/dnn/test/test_onnx_conformance_layer_filter__openvino.inl.hpp

@@ -561,35 +561,23 @@ CASE(test_eyelike_with_dtype)
 CASE(test_eyelike_without_dtype)
     // no filter
 CASE(test_flatten_axis0)
-#if INF_ENGINE_VER_MAJOR_EQ(2021040000)
-    SKIP;
-#endif
+    // no filter
 CASE(test_flatten_axis1)
     // no filter
 CASE(test_flatten_axis2)
-#if INF_ENGINE_VER_MAJOR_EQ(2021040000)
-    SKIP;
-#endif
+    // no filter
 CASE(test_flatten_axis3)
-#if INF_ENGINE_VER_MAJOR_EQ(2021040000)
-    SKIP;
-#endif
+    // no filter
 CASE(test_flatten_default_axis)
     // no filter
 CASE(test_flatten_negative_axis1)
-#if INF_ENGINE_VER_MAJOR_EQ(2021040000)
-    SKIP;
-#endif
+    // no filter
 CASE(test_flatten_negative_axis2)
-#if INF_ENGINE_VER_MAJOR_EQ(2021040000)
-    SKIP;
-#endif
+    // no filter
 CASE(test_flatten_negative_axis3)
     // no filter
 CASE(test_flatten_negative_axis4)
-#if INF_ENGINE_VER_MAJOR_EQ(2021040000)
-    SKIP;
-#endif
+    // no filter
 CASE(test_floor)
     // no filter
 CASE(test_floor_example)

modules/dnn/test/test_onnx_conformance_layer_filter_opencv_all_denylist.inl.hpp

@@ -7,12 +7,6 @@
 "test_castlike_FLOAT_to_STRING_expanded",
 "test_castlike_STRING_to_FLOAT_expanded",
 "test_concat_1d_axis_negative_1",
-"test_flatten_axis0",
-"test_flatten_axis2",
-"test_flatten_axis3",
-"test_flatten_negative_axis1",
-"test_flatten_negative_axis2",
-"test_flatten_negative_axis4",
 "test_logsoftmax_default_axis",
 "test_maxpool_2d_dilations",
 "test_maxpool_2d_same_lower",