Shortcuts

Source code for mmpretrain.models.utils.position_encoding

# Copyright (c) OpenMMLab. All rights reserved.
import math
from functools import partial
from typing import Optional, Sequence, Union

import torch
import torch.nn as nn
from mmengine.model import BaseModule
from mmengine.utils import digit_version

from ..utils import to_2tuple

# After pytorch v1.10.0, use torch.meshgrid without indexing
# will raise extra warning. For more details,
# refers to https://github.com/pytorch/pytorch/issues/50276
if digit_version(torch.__version__) >= digit_version('1.10.0'):
    torch_meshgrid = partial(torch.meshgrid, indexing='ij')
else:
    torch_meshgrid = torch.meshgrid


[docs]class ConditionalPositionEncoding(BaseModule): """The Conditional Position Encoding (CPE) module. The CPE is the implementation of 'Conditional Positional Encodings for Vision Transformers <https://arxiv.org/abs/2102.10882>'_. Args: in_channels (int): Number of input channels. embed_dims (int): The feature dimension. Default: 768. stride (int): Stride of conv layer. Default: 1. """ def __init__(self, in_channels, embed_dims=768, stride=1, init_cfg=None): super(ConditionalPositionEncoding, self).__init__(init_cfg=init_cfg) self.proj = nn.Conv2d( in_channels, embed_dims, kernel_size=3, stride=stride, padding=1, bias=True, groups=embed_dims) self.stride = stride def forward(self, x, hw_shape): B, N, C = x.shape H, W = hw_shape feat_token = x # convert (B, N, C) to (B, C, H, W) cnn_feat = feat_token.transpose(1, 2).view(B, C, H, W).contiguous() if self.stride == 1: x = self.proj(cnn_feat) + cnn_feat else: x = self.proj(cnn_feat) x = x.flatten(2).transpose(1, 2) return x
class PositionEncodingFourier(BaseModule): """The Position Encoding Fourier (PEF) module. The PEF is adopted from EdgeNeXt <https://arxiv.org/abs/2206.10589>'_. Args: in_channels (int): Number of input channels. Default: 32 embed_dims (int): The feature dimension. Default: 768. temperature (int): Temperature. Default: 10000. dtype (torch.dtype): The data type. Default: torch.float32. init_cfg (dict): The config dict for initializing the module. Default: None. """ def __init__(self, in_channels=32, embed_dims=768, temperature=10000, dtype=torch.float32, init_cfg=None): super(PositionEncodingFourier, self).__init__(init_cfg=init_cfg) self.proj = nn.Conv2d(in_channels * 2, embed_dims, kernel_size=1) self.scale = 2 * math.pi self.in_channels = in_channels self.embed_dims = embed_dims self.dtype = dtype if digit_version(torch.__version__) < digit_version('1.8.0'): floor_div = torch.floor_divide else: floor_div = partial(torch.div, rounding_mode='floor') dim_t = torch.arange(in_channels, dtype=self.dtype) self.dim_t = temperature**(2 * floor_div(dim_t, 2) / in_channels) def forward(self, bhw_shape): B, H, W = bhw_shape mask = torch.zeros(B, H, W).bool().to(self.proj.weight.device) not_mask = ~mask eps = 1e-6 y_embed = not_mask.cumsum(1, dtype=self.dtype) x_embed = not_mask.cumsum(2, dtype=self.dtype) y_embed = y_embed / (y_embed[:, -1:, :] + eps) * self.scale x_embed = x_embed / (x_embed[:, :, -1:] + eps) * self.scale dim_t = self.dim_t.to(mask.device) pos_x = x_embed[:, :, :, None] / dim_t pos_y = y_embed[:, :, :, None] / dim_t pos_x = torch.stack( (pos_x[:, :, :, 0::2].sin(), pos_x[:, :, :, 1::2].cos()), dim=4).flatten(3) pos_y = torch.stack( (pos_y[:, :, :, 0::2].sin(), pos_y[:, :, :, 1::2].cos()), dim=4).flatten(3) pos = torch.cat((pos_y, pos_x), dim=3).permute(0, 3, 1, 2) pos = self.proj(pos) return pos def build_2d_sincos_position_embedding( patches_resolution: Union[int, Sequence[int]], embed_dims: int, temperature: Optional[int] = 10000., cls_token: Optional[bool] = False) -> torch.Tensor: """The function is to build position embedding for model to obtain the position information of the image patches. Args: patches_resolution (Union[int, Sequence[int]]): The resolution of each patch. embed_dims (int): The dimension of the embedding vector. temperature (int, optional): The temperature parameter. Defaults to 10000. cls_token (bool, optional): Whether to concatenate class token. Defaults to False. Returns: torch.Tensor: The position embedding vector. """ if isinstance(patches_resolution, int): patches_resolution = (patches_resolution, patches_resolution) h, w = patches_resolution grid_w = torch.arange(w, dtype=torch.float32) grid_h = torch.arange(h, dtype=torch.float32) grid_w, grid_h = torch_meshgrid(grid_w, grid_h) assert embed_dims % 4 == 0, \ 'Embed dimension must be divisible by 4.' pos_dim = embed_dims // 4 omega = torch.arange(pos_dim, dtype=torch.float32) / pos_dim omega = 1. / (temperature**omega) out_w = torch.einsum('m,d->md', [grid_w.flatten(), omega]) out_h = torch.einsum('m,d->md', [grid_h.flatten(), omega]) pos_emb = torch.cat( [ torch.sin(out_w), torch.cos(out_w), torch.sin(out_h), torch.cos(out_h) ], dim=1, )[None, :, :] if cls_token: cls_token_pe = torch.zeros([1, 1, embed_dims], dtype=torch.float32) pos_emb = torch.cat([cls_token_pe, pos_emb], dim=1) return pos_emb class RotaryEmbeddingFast(BaseModule): """Implements 2D rotary embedding (RoPE) for image tokens. Position encoding is implemented with sin and cos functions, .. math:: Pos_{cos} = cos(\frac{t}{\theta^{\frac{2i}{d}}} \\ Pos_{sin} = sin(\frac{t}{\theta^{\frac{2i}{d}}} Args: embed_dims (int): The feature dimension for each head. patch_resolution (int | tuple): The resolution of the image, in format (H, W). theta (float): The hyperparameter for position coding. Defaults to 10000. init_cfg (dict, optional): Initialization config dict. Defaults to None. """ def __init__(self, embed_dims, patch_resolution, theta=10000., init_cfg=None): super(RotaryEmbeddingFast, self).__init__(init_cfg=init_cfg) self.half_dim = embed_dims // 2 self.patch_resolution = to_2tuple(patch_resolution) self.theta = theta freqs_cos, freqs_sin = self.compute_position_embedding() self.register_buffer('freqs_cos', freqs_cos) self.register_buffer('freqs_sin', freqs_sin) def compute_position_embedding(self): frequency = self.theta**( torch.arange(0, self.half_dim, 2).float() / self.half_dim) frequency = 1. / frequency h, w = self.patch_resolution th = torch.arange(h) / h * self.half_dim tw = torch.arange(w) / w * self.half_dim position_h = (th[:, None] @ frequency[None, :]).repeat(1, 2) position_w = (tw[:, None] @ frequency[None, :]).repeat(1, 2) height = position_h[:, None, :].expand(h, w, self.half_dim) width = position_w[None, :, :].expand(h, w, self.half_dim) position = torch.cat((height, width), dim=-1) freqs_cos = position.cos().view(-1, position.shape[-1]) freqs_sin = position.sin().view(-1, position.shape[-1]) return freqs_cos, freqs_sin def forward(self, x, patch_resolution): # Check whether the patch resolution is the predefined size patch_resolution = to_2tuple(patch_resolution) if patch_resolution != self.patch_resolution: self.patch_resolution = patch_resolution freqs_cos, freqs_sin = self.compute_position_embedding() self.register_buffer('freqs_cos', freqs_cos.to(x.device)) self.register_buffer('freqs_sin', freqs_sin.to(x.device)) batch, num_heads, num_patches, dim = x.shape inputs = x x = x.reshape(batch, num_heads, num_patches, -1, 2) x1, x2 = x.unbind(dim=-1) x = torch.stack((-x2, x1), dim=-1) x = x.reshape(batch, num_heads, num_patches, dim) return inputs * self.freqs_cos + x * self.freqs_sin
Read the Docs v: dev
Versions
latest
stable
mmcls-1.x
mmcls-0.x
dev
Downloads
epub
On Read the Docs
Project Home
Builds

Free document hosting provided by Read the Docs.