introduce heuristic for simple tensor handling of transforms v2 (#7170)

test/test_prototype_transforms.py

 import itertools
+import re
 
 import numpy as np
 
 import PIL.Image
-
 import pytest
 import torch
 
 import torchvision.prototype.transforms.utils
-from common_utils import assert_equal, cpu_and_gpu
+from common_utils import cpu_and_gpu
 from prototype_common_utils import (
+    assert_equal,
     DEFAULT_EXTRA_DIMS,
     make_bounding_box,
     make_bounding_boxes,
@@ -25,7 +26,7 @@ from prototype_common_utils import (
 )
 from torchvision.ops.boxes import box_iou
 from torchvision.prototype import datapoints, transforms
-from torchvision.prototype.transforms.utils import check_type
+from torchvision.prototype.transforms.utils import check_type, is_simple_tensor
 from torchvision.transforms.functional import InterpolationMode, pil_to_tensor, to_pil_image
 
 BATCH_EXTRA_DIMS = [extra_dims for extra_dims in DEFAULT_EXTRA_DIMS if extra_dims]
@@ -222,6 +223,67 @@ class TestSmoke:
         transform(input)
 
 
+@pytest.mark.parametrize(
+    "flat_inputs",
+    itertools.permutations(
+        [
+            next(make_vanilla_tensor_images()),
+            next(make_vanilla_tensor_images()),
+            next(make_pil_images()),
+            make_image(),
+            next(make_videos()),
+        ],
+        3,
+    ),
+)
+def test_simple_tensor_heuristic(flat_inputs):
+    def split_on_simple_tensor(to_split):
+        # This takes a sequence that is structurally aligned with `flat_inputs` and splits its items into three parts:
+        # 1. The first simple tensor. If none is present, this will be `None`
+        # 2. A list of the remaining simple tensors
+        # 3. A list of all other items
+        simple_tensors = []
+        others = []
+        # Splitting always happens on the original `flat_inputs` to avoid any erroneous type changes by the transform to
+        # affect the splitting.
+        for item, inpt in zip(to_split, flat_inputs):
+            (simple_tensors if is_simple_tensor(inpt) else others).append(item)
+        return simple_tensors[0] if simple_tensors else None, simple_tensors[1:], others
+
+    class CopyCloneTransform(transforms.Transform):
+        def _transform(self, inpt, params):
+            return inpt.clone() if isinstance(inpt, torch.Tensor) else inpt.copy()
+
+        @staticmethod
+        def was_applied(output, inpt):
+            identity = output is inpt
+            if identity:
+                return False
+
+            # Make sure nothing fishy is going on
+            assert_equal(output, inpt)
+            return True
+
+    first_simple_tensor_input, other_simple_tensor_inputs, other_inputs = split_on_simple_tensor(flat_inputs)
+
+    transform = CopyCloneTransform()
+    transformed_sample = transform(flat_inputs)
+
+    first_simple_tensor_output, other_simple_tensor_outputs, other_outputs = split_on_simple_tensor(transformed_sample)
+
+    if first_simple_tensor_input is not None:
+        if other_inputs:
+            assert not transform.was_applied(first_simple_tensor_output, first_simple_tensor_input)
+        else:
+            assert transform.was_applied(first_simple_tensor_output, first_simple_tensor_input)
+
+    for output, inpt in zip(other_simple_tensor_outputs, other_simple_tensor_inputs):
+        assert not transform.was_applied(output, inpt)
+
+    for input, output in zip(other_inputs, other_outputs):
+        assert transform.was_applied(output, input)
+
+
 @pytest.mark.parametrize("p", [0.0, 1.0])
 class TestRandomHorizontalFlip:
     def input_expected_image_tensor(self, p, dtype=torch.float32):
@@ -1755,22 +1817,27 @@ class TestRandomResize:
         )
 
 
-@pytest.mark.parametrize(
+class TestToDtype:
+    @pytest.mark.parametrize(
         ("dtype", "expected_dtypes"),
         [
             (
                 torch.float64,
-            {torch.Tensor: torch.float64, datapoints.Image: torch.float64, datapoints.BoundingBox: torch.float64},
+                {
+                    datapoints.Video: torch.float64,
+                    datapoints.Image: torch.float64,
+                    datapoints.BoundingBox: torch.float64,
+                },
             ),
             (
-            {torch.Tensor: torch.int32, datapoints.Image: torch.float32, datapoints.BoundingBox: torch.float64},
-            {torch.Tensor: torch.int32, datapoints.Image: torch.float32, datapoints.BoundingBox: torch.float64},
+                {datapoints.Video: torch.int32, datapoints.Image: torch.float32, datapoints.BoundingBox: torch.float64},
+                {datapoints.Video: torch.int32, datapoints.Image: torch.float32, datapoints.BoundingBox: torch.float64},
             ),
         ],
-)
-def test_to_dtype(dtype, expected_dtypes):
+    )
+    def test_call(self, dtype, expected_dtypes):
         sample = dict(
-        plain_tensor=torch.testing.make_tensor(5, dtype=torch.int64, device="cpu"),
+            video=make_video(dtype=torch.int64),
             image=make_image(dtype=torch.uint8),
             bounding_box=make_bounding_box(format=datapoints.BoundingBoxFormat.XYXY, dtype=torch.float32),
             str="str",
@@ -1792,23 +1859,35 @@ def test_to_dtype(dtype, expected_dtypes):
             else:
                 assert transformed_value is value
 
+    @pytest.mark.filterwarnings("error")
+    def test_plain_tensor_call(self):
+        tensor = torch.empty((), dtype=torch.float32)
+        transform = transforms.ToDtype({torch.Tensor: torch.float64})
 
-@pytest.mark.parametrize(
+        assert transform(tensor).dtype is torch.float64
+
+    @pytest.mark.parametrize("other_type", [datapoints.Image, datapoints.Video])
+    def test_plain_tensor_warning(self, other_type):
+        with pytest.warns(UserWarning, match=re.escape("`torch.Tensor` will *not* be transformed")):
+            transforms.ToDtype(dtype={torch.Tensor: torch.float32, other_type: torch.float64})
+
+
+class TestPermuteDimensions:
+    @pytest.mark.parametrize(
         ("dims", "inverse_dims"),
         [
             (
-            {torch.Tensor: (1, 2, 0), datapoints.Image: (2, 1, 0), datapoints.Video: None},
-            {torch.Tensor: (2, 0, 1), datapoints.Image: (2, 1, 0), datapoints.Video: None},
+                {datapoints.Image: (2, 1, 0), datapoints.Video: None},
+                {datapoints.Image: (2, 1, 0), datapoints.Video: None},
             ),
             (
-            {torch.Tensor: (1, 2, 0), datapoints.Image: (2, 1, 0), datapoints.Video: (1, 2, 3, 0)},
-            {torch.Tensor: (2, 0, 1), datapoints.Image: (2, 1, 0), datapoints.Video: (3, 0, 1, 2)},
+                {datapoints.Image: (2, 1, 0), datapoints.Video: (1, 2, 3, 0)},
+                {datapoints.Image: (2, 1, 0), datapoints.Video: (3, 0, 1, 2)},
             ),
         ],
-)
-def test_permute_dimensions(dims, inverse_dims):
+    )
+    def test_call(self, dims, inverse_dims):
         sample = dict(
-        plain_tensor=torch.testing.make_tensor((3, 28, 28), dtype=torch.uint8, device="cpu"),
             image=make_image(),
             bounding_box=make_bounding_box(format=datapoints.BoundingBoxFormat.XYXY),
             video=make_video(),
@@ -1832,17 +1911,29 @@ def test_permute_dimensions(dims, inverse_dims):
             else:
                 assert transformed_value is value
 
+    @pytest.mark.filterwarnings("error")
+    def test_plain_tensor_call(self):
+        tensor = torch.empty((2, 3, 4))
+        transform = transforms.PermuteDimensions(dims=(1, 2, 0))
 
-@pytest.mark.parametrize(
+        assert transform(tensor).shape == (3, 4, 2)
+
+    @pytest.mark.parametrize("other_type", [datapoints.Image, datapoints.Video])
+    def test_plain_tensor_warning(self, other_type):
+        with pytest.warns(UserWarning, match=re.escape("`torch.Tensor` will *not* be transformed")):
+            transforms.PermuteDimensions(dims={torch.Tensor: (0, 1), other_type: (1, 0)})
+
+
+class TestTransposeDimensions:
+    @pytest.mark.parametrize(
         "dims",
         [
             (-1, -2),
-        {torch.Tensor: (-1, -2), datapoints.Image: (1, 2), datapoints.Video: None},
+            {datapoints.Image: (1, 2), datapoints.Video: None},
         ],
-)
-def test_transpose_dimensions(dims):
+    )
+    def test_call(self, dims):
         sample = dict(
-        plain_tensor=torch.testing.make_tensor((3, 28, 28), dtype=torch.uint8, device="cpu"),
             image=make_image(),
             bounding_box=make_bounding_box(format=datapoints.BoundingBoxFormat.XYXY),
             video=make_video(),
@@ -1867,6 +1958,18 @@ def test_transpose_dimensions(dims):
             else:
                 assert transformed_value is value
 
+    @pytest.mark.filterwarnings("error")
+    def test_plain_tensor_call(self):
+        tensor = torch.empty((2, 3, 4))
+        transform = transforms.TransposeDimensions(dims=(0, 2))
+
+        assert transform(tensor).shape == (4, 3, 2)
+
+    @pytest.mark.parametrize("other_type", [datapoints.Image, datapoints.Video])
+    def test_plain_tensor_warning(self, other_type):
+        with pytest.warns(UserWarning, match=re.escape("`torch.Tensor` will *not* be transformed")):
+            transforms.TransposeDimensions(dims={torch.Tensor: (0, 1), other_type: (1, 0)})
+
 
 class TestUniformTemporalSubsample:
     @pytest.mark.parametrize(

torchvision/prototype/transforms/_misc.py

+import warnings
 from typing import Any, Callable, Dict, List, Optional, Sequence, Tuple, Type, Union
 
 import PIL.Image
@@ -155,6 +156,12 @@ class ToDtype(Transform):
         super().__init__()
         if not isinstance(dtype, dict):
             dtype = _get_defaultdict(dtype)
+        if torch.Tensor in dtype and any(cls in dtype for cls in [datapoints.Image, datapoints.Video]):
+            warnings.warn(
+                "Got `dtype` values for `torch.Tensor` and either `datapoints.Image` or `datapoints.Video`. "
+                "Note that a plain `torch.Tensor` will *not* be transformed by this (or any other transformation) "
+                "in case a `datapoints.Image` or `datapoints.Video` is present in the input."
+            )
         self.dtype = dtype
 
     def _transform(self, inpt: Any, params: Dict[str, Any]) -> Any:
@@ -171,6 +178,12 @@ class PermuteDimensions(Transform):
         super().__init__()
         if not isinstance(dims, dict):
             dims = _get_defaultdict(dims)
+        if torch.Tensor in dims and any(cls in dims for cls in [datapoints.Image, datapoints.Video]):
+            warnings.warn(
+                "Got `dims` values for `torch.Tensor` and either `datapoints.Image` or `datapoints.Video`. "
+                "Note that a plain `torch.Tensor` will *not* be transformed by this (or any other transformation) "
+                "in case a `datapoints.Image` or `datapoints.Video` is present in the input."
+            )
         self.dims = dims
 
     def _transform(
@@ -189,6 +202,12 @@ class TransposeDimensions(Transform):
         super().__init__()
         if not isinstance(dims, dict):
             dims = _get_defaultdict(dims)
+        if torch.Tensor in dims and any(cls in dims for cls in [datapoints.Image, datapoints.Video]):
+            warnings.warn(
+                "Got `dims` values for `torch.Tensor` and either `datapoints.Image` or `datapoints.Video`. "
+                "Note that a plain `torch.Tensor` will *not* be transformed by this (or any other transformation) "
+                "in case a `datapoints.Image` or `datapoints.Video` is present in the input."
+            )
         self.dims = dims
 
     def _transform(

torchvision/prototype/transforms/_transform.py

@@ -7,7 +7,8 @@ import PIL.Image
 import torch
 from torch import nn
 from torch.utils._pytree import tree_flatten, tree_unflatten
-from torchvision.prototype.transforms.utils import check_type
+from torchvision.prototype import datapoints
+from torchvision.prototype.transforms.utils import check_type, has_any, is_simple_tensor
 from torchvision.utils import _log_api_usage_once
 
 
@@ -37,9 +38,35 @@ class Transform(nn.Module):
 
         params = self._get_params(flat_inputs)
 
-        flat_outputs = [
-            self._transform(inpt, params) if check_type(inpt, self._transformed_types) else inpt for inpt in flat_inputs
-        ]
+        # Below is a heuristic on how to deal with simple tensor inputs:
+        # 1. Simple tensors, i.e. tensors that are not a datapoint, are passed through if there is an explicit image
+        #    (`datapoints.Image` or `PIL.Image.Image`) or video (`datapoints.Video`) in the sample.
+        # 2. If there is no explicit image or video in the sample, only the first encountered simple tensor is
+        #    transformed as image, while the rest is passed through. The order is defined by the returned `flat_inputs`
+        #    of `tree_flatten`, which recurses depth-first through the input.
+        #
+        # This heuristic stems from two requirements:
+        # 1. We need to keep BC for single input simple tensors and treat them as images.
+        # 2. We don't want to treat all simple tensors as images, because some datasets like `CelebA` or `Widerface`
+        #    return supplemental numerical data as tensors that cannot be transformed as images.
+        #
+        # The heuristic should work well for most people in practice. The only case where it doesn't is if someone
+        # tries to transform multiple simple tensors at the same time, expecting them all to be treated as images.
+        # However, this case wasn't supported by transforms v1 either, so there is no BC concern.
+        flat_outputs = []
+        transform_simple_tensor = not has_any(flat_inputs, datapoints.Image, datapoints.Video, PIL.Image.Image)
+        for inpt in flat_inputs:
+            needs_transform = True
+
+            if not check_type(inpt, self._transformed_types):
+                needs_transform = False
+            elif is_simple_tensor(inpt):
+                if transform_simple_tensor:
+                    transform_simple_tensor = False
+                else:
+                    needs_transform = False
+
+            flat_outputs.append(self._transform(inpt, params) if needs_transform else inpt)
 
         return tree_unflatten(flat_outputs, spec)