added docstrings and license header

official/vision/beta/projects/panoptic_maskrcnn/modeling/layers/paste_masks.py

+# Copyright 2021 The TensorFlow Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Contains definition for bilinear grid sampling and mask pasting layers."""
+
+from typing import List
+
 import tensorflow as tf
 
 
 class BilinearGridSampler(tf.keras.layers.Layer):
-  def __init__(self, align_corners, **kwargs):
+  """ Bilinear Grid Sampling layer."""
+
+  def __init__(self, align_corners: bool = False, **kwargs):
+    """Generates panoptic segmentation masks.
+
+    Args:
+      align_corners: A `bool` bool, if True, the centers of the 4 corner
+        pixels of the input and output tensors are aligned, preserving the
+        values at the corner pixels.
+    """    
     super(BilinearGridSampler, self).__init__(**kwargs)
     self.align_corners = align_corners
 
@@ -25,7 +52,7 @@ class BilinearGridSampler(tf.keras.layers.Layer):
             tf.greater_equal(y_coord, 0)),
         tf.logical_and(
             tf.less(x_coord, self._width),
-            tf.less(y_coord, self._width)))
+            tf.less(y_coord, self._height)))
 
   def _get_pixel(self, features, x_coord, y_coord):
     x_coord = tf.cast(x_coord, dtype=tf.int32)
@@ -97,8 +124,18 @@ class BilinearGridSampler(tf.keras.layers.Layer):
 
 
 class PasteMasks(tf.keras.layers.Layer):
-
-  def __init__(self, output_size, grid_sampler, **kwargs):
+  """Layer to paste instance masks."""
+
+  def __init__(self, output_size: List[int], 
+      grid_sampler, **kwargs):
+    """Generates panoptic segmentation masks.
+
+    Args:
+      output_size: A `List` of integers that represent the height and width of
+        the output mask.
+      grid_sampler: A grid sampling layer. Currently only `BilinearGridSampler`
+        is supported.
+    """
     super(PasteMasks, self).__init__(**kwargs)
     self._output_size = output_size
     self._grid_sampler = grid_sampler