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