add int to int and cleanup

Author: pmeier

test/test_transforms.py

@@ -23,6 +23,20 @@
     os.path.dirname(os.path.abspath(__file__)), 'assets', 'grace_hopper_517x606.jpg')
 
 
+def cycle_over(objs):
+    objs = list(objs)
+    for idx, obj in enumerate(objs):
+        yield obj, objs[:idx] + objs[idx + 1:]
+
+def int_dtypes():
+    yield from iter(
+        (torch.uint8, torch.int8, torch.int16, torch.short, torch.int32, torch.int, torch.int64, torch.long,)
+    )
+
+def float_dtypes():
+    yield from iter((torch.float32, torch.float, torch.float64, torch.double))
+
+
 class Tester(unittest.TestCase):
 
     def test_crop(self):
@@ -510,54 +524,99 @@ def test_to_tensor(self):
         output = trans(img)
         self.assertTrue(np.allclose(input_data.numpy(), output.numpy()))
 
-    def test_convert_image_dtype(self):
-        def cycle_over(objs):
-            objs = list(objs)
-            for idx, obj in enumerate(objs):
-                yield obj, objs[:idx] + objs[idx + 1:]
-
-        # dtype_max_value = {
-        #     dtype: 1.0
-        #     for dtype in (torch.float32, torch.float, torch.float64, torch.double)#, torch.bool,)
-        #     # torch.float16 and torch.half are disabled for now since they do not support torch.max
-        #     # See https://github.com/pytorch/pytorch/issues/28623#issuecomment-611379051
-        #     # (torch.float32, torch.float, torch.float64, torch.double, torch.float16, torch.half, torch.bool, )
-        # }
-        dtype_max_value = {}
-        dtype_max_value.update(
-            {
-                dtype: torch.iinfo(dtype).max
-                for dtype in (
-                    torch.uint8,
-                    torch.int8,
-                    torch.int16,
-                    torch.short,
-                    torch.int32,
-                    torch.int,
-                    torch.int64,
-                    torch.long,
-                )
-            }
-        )
+    def test_convert_image_dtype_float_to_float(self):
+        for input_dtype, output_dtypes in cycle_over(float_dtypes()):
+            input_image = torch.tensor((0.0, 1.0), dtype=input_dtype)
+            for output_dtype in output_dtypes:
+                with self.subTest(input_dtype=input_dtype, output_dtype=output_dtype):
+                    transform = transforms.ConvertImageDtype(output_dtype)
+                    output_image = transform(input_image)
+
+                    actual_min, actual_max = output_image.tolist()
+                    desired_min, desired_max = 0.0, 1.0
+
+                    self.assertAlmostEqual(actual_min, desired_min)
+                    self.assertAlmostEqual(actual_max, desired_max)
+
+    def test_convert_image_dtype_float_to_int(self):
+        for input_dtype in float_dtypes():
+            input_image = torch.tensor((0.0, 1.0), dtype=input_dtype)
+            for output_dtype in int_dtypes():
+                with self.subTest(input_dtype=input_dtype, output_dtype=output_dtype):
+                    transform = transforms.ConvertImageDtype(output_dtype)
+
+                    if (input_dtype == torch.float32 and output_dtype in (torch.int32, torch.int64)) or (
+                            input_dtype == torch.float64 and output_dtype == torch.int64
+                    ):
+                        with self.assertRaises(RuntimeError):
+                            transform(input_image)
+                    else:
+                        output_image = transform(input_image)
 
-        for input_dtype, output_dtypes in cycle_over(dtype_max_value.keys()):
-            input_image = torch.ones(1, dtype=input_dtype) * dtype_max_value[input_dtype]
+                        actual_min, actual_max = output_image.tolist()
+                        desired_min, desired_max = 0, torch.iinfo(output_dtype).max
 
+                        self.assertEqual(actual_min, desired_min)
+                        self.assertEqual(actual_max, desired_max)
+
+    def test_convert_image_dtype_int_to_float(self):
+        for input_dtype in int_dtypes():
+            input_image = torch.tensor((0, torch.iinfo(input_dtype).max), dtype=input_dtype)
+            for output_dtype in float_dtypes():
+                with self.subTest(input_dtype=input_dtype, output_dtype=output_dtype):
+                    transform = transforms.ConvertImageDtype(output_dtype)
+                    output_image = transform(input_image)
+
+                    actual_min, actual_max = output_image.tolist()
+                    desired_min, desired_max = 0.0, 1.0
+
+                    self.assertAlmostEqual(actual_min, desired_min)
+                    self.assertGreaterEqual(actual_min, desired_min)
+                    self.assertAlmostEqual(actual_max, desired_max)
+                    self.assertLessEqual(actual_max, desired_max)
+
+    def test_convert_image_dtype_int_to_int(self):
+        for input_dtype, output_dtypes in cycle_over(int_dtypes()):
+            input_max = torch.iinfo(input_dtype).max
+            input_image = torch.tensor((0, input_max), dtype=input_dtype)
             for output_dtype in output_dtypes:
+                output_max = torch.iinfo(output_dtype).max
+
                 with self.subTest(input_dtype=input_dtype, output_dtype=output_dtype):
                     transform = transforms.ConvertImageDtype(output_dtype)
                     output_image = transform(input_image)
 
-                    actual = output_image.dtype
-                    desired = output_dtype
-                    self.assertEqual(actual, desired)
+                    actual_min, actual_max = output_image.tolist()
+                    desired_min, desired_max = 0, output_max
 
-                    actual = torch.max(output_image).item()
-                    desired = dtype_max_value[output_dtype]
-                    if output_dtype.is_floating_point:
-                        self.assertAlmostEqual(actual, desired)
+                    # see https://github.com/pytorch/vision/pull/2078#issuecomment-641036236 for details
+                    if input_max >= output_max:
+                        error_term = 0
                     else:
-                        self.assertEqual(actual, desired)
+                        error_term = 1 - (torch.iinfo(output_dtype).max + 1) // (torch.iinfo(input_dtype).max + 1)
+
+                    self.assertEqual(actual_min, desired_min)
+                    self.assertEqual(actual_max, desired_max + error_term)
+
+    def test_convert_image_dtype_int_to_int_consistency(self):
+        for input_dtype, output_dtypes in cycle_over(int_dtypes()):
+            input_max = torch.iinfo(input_dtype).max
+            input_image = torch.tensor((0, input_max), dtype=input_dtype)
+            for output_dtype in output_dtypes:
+                output_max = torch.iinfo(output_dtype).max
+                if output_max <= input_max:
+                    continue
+
+                with self.subTest(input_dtype=input_dtype, output_dtype=output_dtype):
+                    transform = transforms.ConvertImageDtype(output_dtype)
+                    inverse_transfrom = transforms.ConvertImageDtype(input_dtype)
+                    output_image = inverse_transfrom(transform(input_image))
+
+                    actual_min, actual_max = output_image.tolist()
+                    desired_min, desired_max = 0, input_max
+
+                    self.assertEqual(actual_min, desired_min)
+                    self.assertEqual(actual_max, desired_max)
 
     @unittest.skipIf(accimage is None, 'accimage not available')
     def test_accimage_to_tensor(self):

torchvision/transforms/functional.py

@@ -113,9 +113,7 @@ def pil_to_tensor(pic):
     return img
 
 
-def convert_image_dtype(
-    image: torch.Tensor, dtype: torch.dtype = torch.float
-) -> torch.Tensor:
+def convert_image_dtype(image: torch.Tensor, dtype: torch.dtype = torch.float) -> torch.Tensor:
     """Convert a tensor image to the given ``dtype`` and scale the values accordingly
 
     Args:
@@ -125,28 +123,42 @@ def convert_image_dtype(
     Returns:
         (torch.Tensor): Converted image
 
+    .. note::
+
+        When converting from a smaller to a larger integer ``dtype`` the maximum values are **not** mapped exactly.
+        If converted back and forth, this mismatch has no effect.
+
     Raises:
-        TypeError: When trying to cast :class:`torch.float32` to :class:`torch.int32`
-            or :class:`torch.int64` as well as for trying to cast
-            :class:`torch.float64` to :class:`torch.int64`. These conversions are
-            unsafe since the floating point ``dtype`` cannot store consecutive XXX. which might lead to overflow errors
+        RuntimeError: When trying to cast :class:`torch.float32` to :class:`torch.int32` or :class:`torch.int64` as
+            well as for trying to cast :class:`torch.float64` to :class:`torch.int64`. These conversions might lead to
+            overflow errors since the floating point ``dtype`` cannot store consecutive integers over the whole range
+            of the integer ``dtype``.
     """
-    def float_to_float(image: torch.Tensor, dtype: torch.dtype) -> torch.Tensor:
-        return image.to(dtype)
-
-    def float_to_int(image: torch.Tensor, dtype: torch.dtype, eps=1e-3) -> torch.Tensor:
-        if (image.dtype == torch.float32 and dtype in (torch.int32, torch.int64)) or (image.dtype == torch.float64 and dtype == torch.int64):
-            msg = (f"The cast from {image.dtype} to {dtype} cannot be performed safely, " 
-                   f"since {image.dtype} cannot ")
-            raise TypeError(msg)
-        return image.mul(torch.iinfo(dtype).max + 1 - eps).to(dtype)
+    if image.dtype == dtype:
+        return image
 
-    def int_to_float(image: torch.Tensor, dtype: torch.dtype) -> torch.Tensor:
-        max = torch.iinfo(image.dtype).max
-        image = image.to(dtype)
-        return image / max
+    if image.dtype.is_floating_point:
+        # float to float
+        if dtype.is_floating_point:
+            return image.to(dtype)
+
+        # float to int
+        if (image.dtype == torch.float32 and dtype in (torch.int32, torch.int64)) or (
+            image.dtype == torch.float64 and dtype == torch.int64
+        ):
+            msg = f"The cast from {image.dtype} to {dtype} cannot be performed safely."
+            raise RuntimeError(msg)
 
-    def int_to_int(image: torch.Tensor, dtype: torch.dtype) -> torch.Tensor:
+        eps = 1e-3
+        return image.mul(torch.iinfo(dtype).max + 1 - eps).to(dtype)
+    else:
+        # int to float
+        if dtype.is_floating_point:
+            max = torch.iinfo(image.dtype).max
+            image = image.to(dtype)
+            return image / max
+
+        # int to int
         input_max = torch.iinfo(image.dtype).max
         output_max = torch.iinfo(dtype).max
 
@@ -157,21 +169,7 @@ def int_to_int(image: torch.Tensor, dtype: torch.dtype) -> torch.Tensor:
         else:
             factor = (output_max + 1) // (input_max + 1)
             image = image.to(dtype)
-            return (image + 1) * factor - 1
-
-    if image.dtype == dtype:
-        return image
-
-    if image.dtype.is_floating_point:
-        if dtype.is_floating_point:
-            return float_to_float(image, dtype)
-        else:
-            return float_to_int(image, dtype)
-    else:
-        if dtype.is_floating_point:
-            return int_to_float(image, dtype)
-        else:
-            return int_to_int(image, dtype)
+            return image * factor
 
 
 def to_pil_image(pic, mode=None):

torchvision/transforms/transforms.py

@@ -121,7 +121,18 @@ class ConvertImageDtype(object):
     Args:
         dtype (torch.dtype): Desired data type of the output
 
+    .. note::
+
+        When converting from a smaller to a larger integer ``dtype`` the maximum values are **not** mapped exactly.
+        If converted back and forth, this mismatch has no effect.
+
+    Raises:
+        RuntimeError: When trying to cast :class:`torch.float32` to :class:`torch.int32` or :class:`torch.int64` as
+            well as for trying to cast :class:`torch.float64` to :class:`torch.int64`. These conversions might lead to
+            overflow errors since the floating point ``dtype`` cannot store consecutive integers over the whole range
+            of the integer ``dtype``.
     """
+
     def __init__(self, dtype: torch.dtype) -> None:
         self.dtype = dtype