118 lines
6.2 KiB
Python
118 lines
6.2 KiB
Python
# ------------------------------------------------------------------------------------------------
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# Deformable DETR
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# Copyright (c) 2020 SenseTime. All Rights Reserved.
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# Licensed under the Apache License, Version 2.0 [see LICENSE for details]
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# ------------------------------------------------------------------------------------------------
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# Modified from https://github.com/chengdazhi/Deformable-Convolution-V2-PyTorch/tree/pytorch_1.0.0
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# ------------------------------------------------------------------------------------------------
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from __future__ import absolute_import
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from __future__ import print_function
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from __future__ import division
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import warnings
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import math
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import torch
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from torch import nn
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import torch.nn.functional as F
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from torch.nn.init import xavier_uniform_, constant_
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from ..functions import MSDeformAttnFunction
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def _is_power_of_2(n):
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if (not isinstance(n, int)) or (n < 0):
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raise ValueError("invalid input for _is_power_of_2: {} (type: {})".format(n, type(n)))
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return (n & (n-1) == 0) and n != 0
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class MSDeformAttn(nn.Module):
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def __init__(self, d_model=256, n_levels=4, n_heads=8, n_points=4):
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"""
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Multi-Scale Deformable Attention Module
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:param d_model hidden dimension
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:param n_levels number of feature levels
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:param n_heads number of attention heads
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:param n_points number of sampling points per attention head per feature level
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"""
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super().__init__()
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if d_model % n_heads != 0:
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raise ValueError('d_model must be divisible by n_heads, but got {} and {}'.format(d_model, n_heads))
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_d_per_head = d_model // n_heads
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# you'd better set _d_per_head to a power of 2 which is more efficient in our CUDA implementation
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if not _is_power_of_2(_d_per_head):
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warnings.warn("You'd better set d_model in MSDeformAttn to make the dimension of each attention head a power of 2 "
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"which is more efficient in our CUDA implementation.")
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self.im2col_step = 64
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self.d_model = d_model
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self.n_levels = n_levels
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self.n_heads = n_heads
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self.n_points = n_points
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self.sampling_offsets = nn.Linear(d_model, n_heads * n_levels * n_points * 2)
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self.attention_weights = nn.Linear(d_model, n_heads * n_levels * n_points)
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self.value_proj = nn.Linear(d_model, d_model)
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self.output_proj = nn.Linear(d_model, d_model)
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self._reset_parameters()
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def _reset_parameters(self):
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constant_(self.sampling_offsets.weight.data, 0.)
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thetas = torch.arange(self.n_heads, dtype=torch.float32) * (2.0 * math.pi / self.n_heads)
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grid_init = torch.stack([thetas.cos(), thetas.sin()], -1)
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grid_init = (grid_init / grid_init.abs().max(-1, keepdim=True)[0]).view(self.n_heads, 1, 1, 2).repeat(1, self.n_levels, self.n_points, 1)
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for i in range(self.n_points):
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grid_init[:, :, i, :] *= i + 1
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with torch.no_grad():
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self.sampling_offsets.bias = nn.Parameter(grid_init.view(-1))
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constant_(self.attention_weights.weight.data, 0.)
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constant_(self.attention_weights.bias.data, 0.)
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xavier_uniform_(self.value_proj.weight.data)
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constant_(self.value_proj.bias.data, 0.)
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xavier_uniform_(self.output_proj.weight.data)
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constant_(self.output_proj.bias.data, 0.)
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def forward(self, query, reference_points, input_flatten, input_spatial_shapes, input_level_start_index, input_padding_mask=None):
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"""
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:param query (N, Length_{query}, C)
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:param reference_points (N, Length_{query}, n_levels, 2), range in [0, 1], top-left (0,0), bottom-right (1, 1), including padding area
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or (N, Length_{query}, n_levels, 4), add additional (w, h) to form reference boxes
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:param input_flatten (N, \sum_{l=0}^{L-1} H_l \cdot W_l, C)
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:param input_spatial_shapes (n_levels, 2), [(H_0, W_0), (H_1, W_1), ..., (H_{L-1}, W_{L-1})]
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:param input_level_start_index (n_levels, ), [0, H_0*W_0, H_0*W_0+H_1*W_1, H_0*W_0+H_1*W_1+H_2*W_2, ..., H_0*W_0+H_1*W_1+...+H_{L-1}*W_{L-1}]
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:param input_padding_mask (N, \sum_{l=0}^{L-1} H_l \cdot W_l), True for padding elements, False for non-padding elements
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:return output (N, Length_{query}, C)
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"""
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N, Len_q, _ = query.shape
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N, Len_in, _ = input_flatten.shape
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assert (input_spatial_shapes[:, 0] * input_spatial_shapes[:, 1]).sum() == Len_in
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value = self.value_proj(input_flatten)
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if input_padding_mask is not None:
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value = value.masked_fill(input_padding_mask[..., None], float(0))
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value = value.view(N, Len_in, self.n_heads, self.d_model // self.n_heads)
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sampling_offsets = self.sampling_offsets(query).view(N, Len_q, self.n_heads, self.n_levels, self.n_points, 2)
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attention_weights = self.attention_weights(query).view(N, Len_q, self.n_heads, self.n_levels * self.n_points)
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attention_weights = F.softmax(attention_weights, -1).view(N, Len_q, self.n_heads, self.n_levels, self.n_points)
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# N, Len_q, n_heads, n_levels, n_points, 2
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if reference_points.shape[-1] == 2:
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offset_normalizer = torch.stack([input_spatial_shapes[..., 1], input_spatial_shapes[..., 0]], -1)
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# print("shape122", offset_normalizer.shape)
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# print(sampling_offsets.shape)
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sampling_locations = reference_points[:, :, None, :, None, :] \
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+ sampling_offsets / offset_normalizer[None, None, None, :, None, :]
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elif reference_points.shape[-1] == 4:
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sampling_locations = reference_points[:, :, None, :, None, :2] \
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+ sampling_offsets / self.n_points * reference_points[:, :, None, :, None, 2:] * 0.5
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else:
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raise ValueError(
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'Last dim of reference_points must be 2 or 4, but get {} instead.'.format(reference_points.shape[-1]))
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output = MSDeformAttnFunction.apply(
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value, input_spatial_shapes, input_level_start_index, sampling_locations, attention_weights, self.im2col_step)
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output = self.output_proj(output)
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return output
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