Add pad to size utility.

PiperOrigin-RevId: 532121341

dm_pix/_src/augment.py

@@ -20,7 +20,7 @@
 """
 
 import functools
-from typing import Callable, Optional, Sequence, Tuple, Union
+from typing import Any, Callable, Optional, Sequence, Tuple, Union
 
 import chex
 from dm_pix._src import color_conversion
@@ -291,6 +291,61 @@ def center_crop(
   )
 
 
+def pad_to_size(
+    image: chex.Array,
+    target_height: int,
+    target_width: int,
+    *,
+    mode: str = "constant",
+    pad_kwargs: Optional[Any] = None,
+    channel_axis: int = -1,
+) -> chex.Array:
+  """Pads an image to the given size keeping the original image centered.
+
+  For different padding methods and kwargs please see:
+  https://jax.readthedocs.io/en/latest/_autosummary/jax.numpy.pad.html
+
+  In case of odd size difference along any dimension the bottom/right side gets
+  the extra padding pixel.
+
+  Target size can be smaller than original size which results in a no-op for
+  such dimension.
+
+  Args:
+    image: a JAX array representing an image. Assumes that the image is either
+      ...HWC or ...CHW.
+    target_height: target height to pad the image to.
+    target_width: target width to pad the image to.
+    mode: Mode for padding the images, see jax.numpy.pad for details. Default is
+      `constant`.
+    pad_kwargs: Keyword arguments to pass jax.numpy.pad, see documentation for
+      options.
+    channel_axis: the index of the channel axis.
+
+  Returns:
+    The padded image(s).
+  """
+  chex.assert_rank(image, {3, 4})
+  batch, height, width, _ = _get_dimension_values(
+      image=image, channel_axis=channel_axis
+  )
+  delta_width = max(target_width - width, 0)
+  delta_height = max(target_height - height, 0)
+  if delta_width == 0 and delta_height == 0:
+    return image
+
+  left = delta_width // 2
+  right = max(target_width - (left + width), 0)
+  top = delta_height // 2
+  bottom = max(target_height - (top + height), 0)
+
+  pad_width = ((top, bottom), (left, right), (0, 0))
+  if batch:
+    pad_width = ((0, 0), *pad_width)
+
+  return jnp.pad(image, pad_width=pad_width, mode=mode, **pad_kwargs or {})
+
+
 def flip_left_right(
     image: chex.Array,
     *,

dm_pix/_src/augment_test.py

@@ -376,6 +376,29 @@ def test_center_crop(self, images_list, height, width):
     )
     self._test_fn(images_list, jax_fn=center_crop, reference_fn=reference)
 
+  @parameterized.product(
+      images_list=(_RAND_FLOATS_IN_RANGE, _RAND_FLOATS_OUT_OF_RANGE),
+      target_height=(156, 131, 200, 251),
+      target_width=(156, 111, 200, 251),
+  )
+  def test_pad_to_size(self, images_list, target_height, target_width):
+    pad_fn = functools.partial(
+        augment.pad_to_size,
+        target_height=target_height,
+        target_width=target_width,
+        mode="constant",
+        pad_kwargs={"constant_values": 0},
+    )
+    # We have to rely on `resize_with_crop_or_pad` as there are no pad to size
+    # equivalents.
+    reference_fn = functools.partial(
+        tf.image.resize_with_crop_or_pad,
+        target_height=target_height,
+        target_width=target_width,
+    )
+
+    self._test_fn(images_list, jax_fn=pad_fn, reference_fn=reference_fn)
+
 
 class TestMatchReference(_ImageAugmentationTest):
 
@@ -487,6 +510,30 @@ def test_center_crop_size_bigger_than_original(
     self.assertEqual(output.shape[1], expected_height)
     self.assertEqual(output.shape[2], expected_width)
 
+  @parameterized.product(
+      images_list=(_RAND_FLOATS_IN_RANGE, _RAND_FLOATS_OUT_OF_RANGE),
+      target_height=(55, 84),
+      target_width=(55, 84),
+      expected_height=(131, 131),
+      expected_width=(111, 111),
+  )
+  def test_pad_to_size_when_target_size_smaller_than_original(
+      self,
+      images_list,
+      target_height,
+      target_width,
+      expected_height,
+      expected_width,
+  ):
+    output = augment.pad_to_size(
+        image=jnp.array(images_list),
+        target_height=target_height,
+        target_width=target_width,
+    )
+
+    self.assertEqual(output.shape[1], expected_height)
+    self.assertEqual(output.shape[2], expected_width)
+
 
 if __name__ == "__main__":
   jax.config.update("jax_default_matmul_precision", "float32")

docs/api.rst

@@ -16,6 +16,7 @@ Augmentations
     flip_left_right
     flip_up_down
     gaussian_blur
+    pad_to_size
     random_brightness
     random_contrast
     random_crop
@@ -84,6 +85,12 @@ gaussian_blur
 
 .. autofunction:: gaussian_blur
 
+pad_to_size
+~~~~~~~~~~~~~
+
+.. autofunction:: pad_to_size
+
+
 random_brightness
 ~~~~~~~~~~~~~~~~~