[ONNX] Export ROIAlign with aligned=True (#2613)

* Add support for export ROIAlign

* Fix for feedback

* flake8

test/test_onnx.py

@@ -66,6 +66,7 @@ class ONNXExporterTester(unittest.TestCase):
         # compute onnxruntime output prediction
         ort_inputs = dict((ort_session.get_inputs()[i].name, inpt) for i, inpt in enumerate(inputs))
         ort_outs = ort_session.run(None, ort_inputs)
+
         for i in range(0, len(outputs)):
             try:
                 torch.testing.assert_allclose(outputs[i], ort_outs[i], rtol=1e-03, atol=1e-05)
@@ -121,6 +122,34 @@ class ONNXExporterTester(unittest.TestCase):
         model = ops.RoIAlign((5, 5), 1, 2)
         self.run_model(model, [(x, single_roi)])
 
+    def test_roi_align_aligned(self):
+        x = torch.rand(1, 1, 10, 10, dtype=torch.float32)
+        single_roi = torch.tensor([[0, 1.5, 1.5, 3, 3]], dtype=torch.float32)
+        model = ops.RoIAlign((5, 5), 1, 2, aligned=True)
+        self.run_model(model, [(x, single_roi)])
+
+        x = torch.rand(1, 1, 10, 10, dtype=torch.float32)
+        single_roi = torch.tensor([[0, 0.2, 0.3, 4.5, 3.5]], dtype=torch.float32)
+        model = ops.RoIAlign((5, 5), 0.5, 3, aligned=True)
+        self.run_model(model, [(x, single_roi)])
+
+        x = torch.rand(1, 1, 10, 10, dtype=torch.float32)
+        single_roi = torch.tensor([[0, 0.2, 0.3, 4.5, 3.5]], dtype=torch.float32)
+        model = ops.RoIAlign((5, 5), 1.8, 2, aligned=True)
+        self.run_model(model, [(x, single_roi)])
+
+        x = torch.rand(1, 1, 10, 10, dtype=torch.float32)
+        single_roi = torch.tensor([[0, 0.2, 0.3, 4.5, 3.5]], dtype=torch.float32)
+        model = ops.RoIAlign((2, 2), 2.5, 0, aligned=True)
+        self.run_model(model, [(x, single_roi)])
+
+    @unittest.skip  # Issue in exporting ROIAlign with aligned = True for malformed boxes
+    def test_roi_align_malformed_boxes(self):
+        x = torch.randn(1, 1, 10, 10, dtype=torch.float32)
+        single_roi = torch.tensor([[0, 2, 0.3, 1.5, 1.5]], dtype=torch.float32)
+        model = ops.RoIAlign((5, 5), 1, 1, aligned=True)
+        self.run_model(model, [(x, single_roi)])
+
     def test_roi_pool(self):
         x = torch.rand(1, 1, 10, 10, dtype=torch.float32)
         rois = torch.tensor([[0, 0, 0, 4, 4]], dtype=torch.float32)

torchvision/ops/_register_onnx_ops.py

 import sys
 import torch
+import warnings
 
 _onnx_opset_version = 11
 
@@ -20,11 +21,14 @@ def _register_custom_op():
 
     @parse_args('v', 'v', 'f', 'i', 'i', 'i', 'i')
     def roi_align(g, input, rois, spatial_scale, pooled_height, pooled_width, sampling_ratio, aligned):
-        if(aligned):
-            raise RuntimeError('Unsupported: ONNX export of roi_align with aligned')
         batch_indices = _cast_Long(g, squeeze(g, select(g, rois, 1, g.op('Constant',
                                    value_t=torch.tensor([0], dtype=torch.long))), 1), False)
         rois = select(g, rois, 1, g.op('Constant', value_t=torch.tensor([1, 2, 3, 4], dtype=torch.long)))
+        if aligned:
+            warnings.warn("ONNX export of ROIAlign with aligned=True does not match PyTorch when using malformed boxes,"
+                          " ONNX forces ROIs to be 1x1 or larger.")
+            scale = torch.tensor(0.5 / spatial_scale).to(dtype=torch.float)
+            rois = g.op("Sub", rois, scale)
         return g.op('RoiAlign', input, rois, batch_indices, spatial_scale_f=spatial_scale,
                     output_height_i=pooled_height, output_width_i=pooled_width, sampling_ratio_i=sampling_ratio)