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segmentation/mmseg_custom/models/utils/positional_encoding.py

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+# Copyright (c) OpenMMLab. All rights reserved.
+import math
+
+import torch
+import torch.nn as nn
+from mmcv.cnn.bricks.transformer import POSITIONAL_ENCODING
+from mmcv.runner import BaseModule
+
+
+@POSITIONAL_ENCODING.register_module()
+class SinePositionalEncoding(BaseModule):
+    """Position encoding with sine and cosine functions.
+
+    See `End-to-End Object Detection with Transformers
+    <https://arxiv.org/pdf/2005.12872>`_ for details.
+
+    Args:
+        num_feats (int): The feature dimension for each position
+            along x-axis or y-axis. Note the final returned dimension
+            for each position is 2 times of this value.
+        temperature (int, optional): The temperature used for scaling
+            the position embedding. Defaults to 10000.
+        normalize (bool, optional): Whether to normalize the position
+            embedding. Defaults to False.
+        scale (float, optional): A scale factor that scales the position
+            embedding. The scale will be used only when `normalize` is True.
+            Defaults to 2*pi.
+        eps (float, optional): A value added to the denominator for
+            numerical stability. Defaults to 1e-6.
+        offset (float): offset add to embed when do the normalization.
+            Defaults to 0.
+        init_cfg (dict or list[dict], optional): Initialization config dict.
+            Default: None
+    """
+    def __init__(self,
+                 num_feats,
+                 temperature=10000,
+                 normalize=False,
+                 scale=2 * math.pi,
+                 eps=1e-6,
+                 offset=0.,
+                 init_cfg=None):
+        super(SinePositionalEncoding, self).__init__(init_cfg)
+        if normalize:
+            assert isinstance(scale, (float, int)), 'when normalize is set,' \
+                'scale should be provided and in float or int type, ' \
+                f'found {type(scale)}'
+        self.num_feats = num_feats
+        self.temperature = temperature
+        self.normalize = normalize
+        self.scale = scale
+        self.eps = eps
+        self.offset = offset
+
+    def forward(self, mask):
+        """Forward function for `SinePositionalEncoding`.
+
+        Args:
+            mask (Tensor): ByteTensor mask. Non-zero values representing
+                ignored positions, while zero values means valid positions
+                for this image. Shape [bs, h, w].
+
+        Returns:
+            pos (Tensor): Returned position embedding with shape
+                [bs, num_feats*2, h, w].
+        """
+        # For convenience of exporting to ONNX, it's required to convert
+        # `masks` from bool to int.
+        mask = mask.to(torch.int)
+        not_mask = 1 - mask  # logical_not
+        y_embed = not_mask.cumsum(1, dtype=torch.float32)
+        x_embed = not_mask.cumsum(2, dtype=torch.float32)
+        if self.normalize:
+            y_embed = (y_embed + self.offset) / \
+                      (y_embed[:, -1:, :] + self.eps) * self.scale
+            x_embed = (x_embed + self.offset) / \
+                      (x_embed[:, :, -1:] + self.eps) * self.scale
+        dim_t = torch.arange(
+            self.num_feats, dtype=torch.float32, device=mask.device)
+        dim_t = self.temperature**(2 * (dim_t // 2) / self.num_feats)
+        pos_x = x_embed[:, :, :, None] / dim_t
+        pos_y = y_embed[:, :, :, None] / dim_t
+        # use `view` instead of `flatten` for dynamically exporting to ONNX
+        B, H, W = mask.size()
+        pos_x = torch.stack(
+            (pos_x[:, :, :, 0::2].sin(), pos_x[:, :, :, 1::2].cos()),
+            dim=4).view(B, H, W, -1)
+        pos_y = torch.stack(
+            (pos_y[:, :, :, 0::2].sin(), pos_y[:, :, :, 1::2].cos()),
+            dim=4).view(B, H, W, -1)
+        pos = torch.cat((pos_y, pos_x), dim=3).permute(0, 3, 1, 2)
+        return pos
+
+    def __repr__(self):
+        """str: a string that describes the module"""
+        repr_str = self.__class__.__name__
+        repr_str += f'(num_feats={self.num_feats}, '
+        repr_str += f'temperature={self.temperature}, '
+        repr_str += f'normalize={self.normalize}, '
+        repr_str += f'scale={self.scale}, '
+        repr_str += f'eps={self.eps})'
+        return repr_str
+
+
+@POSITIONAL_ENCODING.register_module()
+class LearnedPositionalEncoding(BaseModule):
+    """Position embedding with learnable embedding weights.
+
+    Args:
+        num_feats (int): The feature dimension for each position
+            along x-axis or y-axis. The final returned dimension for
+            each position is 2 times of this value.
+        row_num_embed (int, optional): The dictionary size of row embeddings.
+            Default 50.
+        col_num_embed (int, optional): The dictionary size of col embeddings.
+            Default 50.
+        init_cfg (dict or list[dict], optional): Initialization config dict.
+    """
+    def __init__(self,
+                 num_feats,
+                 row_num_embed=50,
+                 col_num_embed=50,
+                 init_cfg=dict(type='Uniform', layer='Embedding')):
+        super(LearnedPositionalEncoding, self).__init__(init_cfg)
+        self.row_embed = nn.Embedding(row_num_embed, num_feats)
+        self.col_embed = nn.Embedding(col_num_embed, num_feats)
+        self.num_feats = num_feats
+        self.row_num_embed = row_num_embed
+        self.col_num_embed = col_num_embed
+
+    def forward(self, mask):
+        """Forward function for `LearnedPositionalEncoding`.
+
+        Args:
+            mask (Tensor): ByteTensor mask. Non-zero values representing
+                ignored positions, while zero values means valid positions
+                for this image. Shape [bs, h, w].
+
+        Returns:
+            pos (Tensor): Returned position embedding with shape
+                [bs, num_feats*2, h, w].
+        """
+        h, w = mask.shape[-2:]
+        x = torch.arange(w, device=mask.device)
+        y = torch.arange(h, device=mask.device)
+        x_embed = self.col_embed(x)
+        y_embed = self.row_embed(y)
+        pos = torch.cat(
+            (x_embed.unsqueeze(0).repeat(h, 1, 1), y_embed.unsqueeze(1).repeat(
+                1, w, 1)),
+            dim=-1).permute(2, 0,
+                            1).unsqueeze(0).repeat(mask.shape[0], 1, 1, 1)
+        return pos
+
+    def __repr__(self):
+        """str: a string that describes the module"""
+        repr_str = self.__class__.__name__
+        repr_str += f'(num_feats={self.num_feats}, '
+        repr_str += f'row_num_embed={self.row_num_embed}, '
+        repr_str += f'col_num_embed={self.col_num_embed})'
+        return repr_str