Support batch input for median_filter2d (tensorflow#288)

tensorflow_addons/image/filters.py

@@ -21,20 +21,6 @@
 from tensorflow_addons.utils import keras_utils
 
 
-@tf.function
-def _normalize(li, ma):
-    one = tf.convert_to_tensor(1.0)
-    two = tf.convert_to_tensor(255.0)
-
-    def func1():
-        return li
-
-    def func2():
-        return tf.math.truediv(li, two)
-
-    return tf.cond(tf.math.greater(ma, one), func2, func1)
-
-
 def _pad(image, filter_shape, mode="CONSTANT", constant_values=0):
     """Explicitly pad a 4-D image.
 
@@ -142,80 +128,84 @@ def mean_filter2d(image,
 
 
 @tf.function
-def median_filter2d(image, filter_shape=(3, 3), name=None):
-    """This method performs Median Filtering on image. Filter shape can be user
-    given.
+def median_filter2d(image,
+                    filter_shape=(3, 3),
+                    padding="REFLECT",
+                    constant_values=0,
+                    name=None):
+    """Perform median filtering on image(s).
 
-    This method takes both kind of images where pixel values lie between 0 to
-    255 and where it lies between 0.0 and 1.0
     Args:
-        image: A 3D `Tensor` of type `float32` or 'int32' or 'float64' or
-               'int64 and of shape`[rows, columns, channels]`
-
-        filter_shape: Optional Argument. A tuple of 2 integers (R,C).
-               R is the first value is the number of rows in the filter and
-               C is the second value in the filter is the number of columns
-               in the filter. This creates a filter of shape (R,C) or RxC
-               filter. Default value = (3,3)
-        name: The name of the op.
-
-     Returns:
-         A 3D median filtered image tensor of shape [rows,columns,channels] and
-         type 'int32'. Pixel value of returned tensor ranges between 0 to 255
+      image: Either a 3-D `Tensor` of shape `[height, width, channels]`,
+        or a 4-D `Tensor` of shape `[batch_size, height, width, channels]`.
+      filter_shape: An `integer` or `tuple`/`list` of 2 integers, specifying
+        the height and width of the 2-D median filter. Can be a single integer
+        to specify the same value for all spatial dimensions.
+      padding: A `string`, one of "REFLECT", "CONSTANT", or "SYMMETRIC".
+        The type of padding algorithm to use, which is compatible with
+        `mode` argument in `tf.pad`. For more details, please refer to
+        https://www.tensorflow.org/api_docs/python/tf/pad.
+      constant_values: A `scalar`, the pad value to use in "CONSTANT"
+        padding mode.
+      name: A name for this operation (optional).
+    Returns:
+      3-D or 4-D `Tensor` of the same dtype as input.
+    Raises:
+      ValueError: If `image` is not 3 or 4-dimensional,
+        if `padding` is other than "REFLECT", "CONSTANT" or "SYMMETRIC",
+        or if `filter_shape` is invalid.
     """
-
     with tf.name_scope(name or "median_filter2d"):
-        if not isinstance(filter_shape, tuple):
-            raise TypeError('Filter shape must be a tuple')
-        if len(filter_shape) != 2:
-            raise ValueError('Filter shape must be a tuple of 2 integers. '
-                             'Got %s values in tuple' % len(filter_shape))
-        filter_shapex = filter_shape[0]
-        filter_shapey = filter_shape[1]
-        if not isinstance(filter_shapex, int) or not isinstance(
-                filter_shapey, int):
-            raise TypeError('Size of the filter must be Integers')
-        (row, col, ch) = (image.shape[0], image.shape[1], image.shape[2])
-        if row != None and col != None and ch != None:
-            (row, col, ch) = (int(row), int(col), int(ch))
-        else:
-            raise TypeError('All the Dimensions of the input image '
-                            'tensor must be Integers.')
-        if row < filter_shapex or col < filter_shapey:
+        image = tf.convert_to_tensor(image, name="image")
+
+        rank = image.shape.rank
+        if rank != 3 and rank != 4:
+            raise ValueError("image should be either 3 or 4-dimensional.")
+
+        if padding not in ["REFLECT", "CONSTANT", "SYMMETRIC"]:
             raise ValueError(
-                'Number of Pixels in each dimension of the image should be \
-                more than the filter size. Got filter_shape (%sx' %
-                filter_shape[0] + '%s).' % filter_shape[1] +
-                ' Image Shape (%s)' % image.shape)
-        if filter_shapex % 2 == 0 or filter_shapey % 2 == 0:
-            raise ValueError('Filter size should be odd. Got filter_shape '
-                             '(%sx%s)' % (filter_shape[0], filter_shape[1]))
-        image = tf.cast(image, tf.float32)
-        tf_i = tf.reshape(image, [row * col * ch])
-        ma = tf.math.reduce_max(tf_i)
-        image = _normalize(image, ma)
-
-        # k and l is the Zero-padding size
-
-        listi = []
-        for a in range(ch):
-            img = image[:, :, a:a + 1]
-            img = tf.reshape(img, [1, row, col, 1])
-            slic = tf.image.extract_patches(
-                img, [1, filter_shapex, filter_shapey, 1], [1, 1, 1, 1],
-                [1, 1, 1, 1],
-                padding='SAME')
-            mid = int(filter_shapex * filter_shapey / 2 + 1)
-            top = tf.nn.top_k(slic, mid, sorted=True)
-            li = tf.slice(top[0], [0, 0, 0, mid - 1], [-1, -1, -1, 1])
-            li = tf.reshape(li, [row, col, 1])
-            listi.append(li)
-        y = tf.concat(listi[0], 2)
-
-        for i in range(len(listi) - 1):
-            y = tf.concat([y, listi[i + 1]], 2)
-
-        y *= 255
-        y = tf.cast(y, tf.int32)
-
-        return y
+                "padding should be one of \"REFLECT\", \"CONSTANT\", or "
+                "\"SYMMETRIC\".")
+
+        filter_shape = keras_utils.conv_utils.normalize_tuple(
+            filter_shape, 2, "filter_shape")
+
+        # Expand to a 4-D tensor
+        if rank == 3:
+            image = tf.expand_dims(image, axis=0)
+
+        # Explicitly pad the image
+        image = _pad(
+            image, filter_shape, mode=padding, constant_values=constant_values)
+
+        floor = (filter_shape[0] * filter_shape[1] + 1) // 2
+        ceil = (filter_shape[0] * filter_shape[1]) // 2 + 1
+
+        def _median_filter2d_single_channel(x):
+            x = tf.expand_dims(x, axis=-1)
+            patches = tf.image.extract_patches(
+                x,
+                sizes=[1, filter_shape[0], filter_shape[1], 1],
+                strides=[1, 1, 1, 1],
+                rates=[1, 1, 1, 1],
+                padding="VALID")
+
+            # Note the returned median is casted back to the original type
+            # Take [5, 6, 7, 8] for example, the median is (6 + 7) / 2 = 3.5
+            # It turns out to be int(6.5) = 6 if the original type is int
+            top = tf.nn.top_k(patches, k=ceil).values
+            median = (top[:, :, :, floor - 1] + top[:, :, :, ceil - 1]) / 2
+            return tf.dtypes.cast(median, x.dtype)
+
+        output = tf.map_fn(
+            _median_filter2d_single_channel,
+            elems=tf.transpose(image, [3, 0, 1, 2]),
+            dtype=image.dtype)
+        output = tf.transpose(output, [1, 2, 3, 0])
+
+        # Squeeze out the first axis to make sure
+        # output has the same dimension with image.
+        if rank == 3:
+            output = tf.squeeze(output, axis=0)
+
+        return output