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sam3/model/vitdet.py
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879
sam3/model/vitdet.py
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# Copyright (c) Meta Platforms, Inc. and affiliates. All Rights Reserved
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"""
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ViTDet backbone adapted from Detectron2.
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This module implements Vision Transformer (ViT) backbone for object detection.
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Rope embedding code adopted from:
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1. https://github.com/meta-llama/codellama/blob/main/llama/model.py
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2. https://github.com/naver-ai/rope-vit
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3. https://github.com/lucidrains/rotary-embedding-torch
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"""
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import math
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from functools import partial
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from typing import Callable, List, Optional, Tuple, Union
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import torch
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import torch.nn as nn
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import torch.nn.functional as F
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import torch.utils.checkpoint as checkpoint
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try:
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from timm.layers import DropPath, Mlp, trunc_normal_
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except ModuleNotFoundError:
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# compatibility for older timm versions
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from timm.models.layers import DropPath, Mlp, trunc_normal_
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from torch import Tensor
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from .model_misc import LayerScale
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def init_t_xy(
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end_x: int, end_y: int, scale: float = 1.0, offset: int = 0
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) -> Tuple[torch.Tensor, torch.Tensor]:
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t = torch.arange(end_x * end_y, dtype=torch.float32)
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t_x = (t % end_x).float()
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t_y = torch.div(t, end_x, rounding_mode="floor").float()
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return t_x * scale + offset, t_y * scale + offset
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def compute_axial_cis(
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dim: int,
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end_x: int,
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end_y: int,
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theta: float = 10000.0,
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scale_pos: float = 1.0,
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offset: int = 0,
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) -> torch.Tensor:
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freqs_x = 1.0 / (theta ** (torch.arange(0, dim, 4)[: (dim // 4)].float() / dim))
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freqs_y = 1.0 / (theta ** (torch.arange(0, dim, 4)[: (dim // 4)].float() / dim))
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t_x, t_y = init_t_xy(end_x, end_y, scale_pos, offset)
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freqs_x = torch.outer(t_x, freqs_x)
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freqs_y = torch.outer(t_y, freqs_y)
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freqs_cis_x = torch.polar(torch.ones_like(freqs_x), freqs_x)
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freqs_cis_y = torch.polar(torch.ones_like(freqs_y), freqs_y)
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return torch.cat([freqs_cis_x, freqs_cis_y], dim=-1)
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def reshape_for_broadcast(freqs_cis: torch.Tensor, x: torch.Tensor) -> torch.Tensor:
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ndim = x.ndim
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assert 0 <= 1 < ndim
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assert freqs_cis.shape == (x.shape[-2], x.shape[-1])
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shape = [d if i >= ndim - 2 else 1 for i, d in enumerate(x.shape)]
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return freqs_cis.view(*shape)
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def apply_rotary_enc(
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xq: torch.Tensor,
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xk: torch.Tensor,
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freqs_cis: torch.Tensor,
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repeat_freqs_k: bool = False,
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) -> Tuple[torch.Tensor, torch.Tensor]:
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xq_ = torch.view_as_complex(xq.float().reshape(*xq.shape[:-1], -1, 2))
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xk_ = (
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torch.view_as_complex(xk.float().reshape(*xk.shape[:-1], -1, 2))
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if xk.shape[-2] != 0
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else None
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)
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freqs_cis = reshape_for_broadcast(freqs_cis, xq_)
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xq_out = torch.view_as_real(xq_ * freqs_cis).flatten(3)
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if xk_ is None:
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# no keys to rotate, due to dropout
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return xq_out.type_as(xq).to(xq.device), xk
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# repeat freqs along seq_len dim to match k seq_len
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if repeat_freqs_k:
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r = xk_.shape[-2] // xq_.shape[-2]
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freqs_cis = freqs_cis.repeat(*([1] * (freqs_cis.ndim - 2)), r, 1)
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xk_out = torch.view_as_real(xk_ * freqs_cis).flatten(3)
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return xq_out.type_as(xq).to(xq.device), xk_out.type_as(xk).to(xk.device)
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def window_partition(x: Tensor, window_size: int) -> Tuple[Tensor, Tuple[int, int]]:
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"""
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Partition into non-overlapping windows with padding if needed.
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Args:
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x (tensor): input tokens with [B, H, W, C].
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window_size (int): window size.
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Returns:
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windows: windows after partition with [B * num_windows, window_size, window_size, C].
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(Hp, Wp): padded height and width before partition
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"""
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B, H, W, C = x.shape
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pad_h = (window_size - H % window_size) % window_size
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pad_w = (window_size - W % window_size) % window_size
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if pad_h > 0 or pad_w > 0:
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x = F.pad(x, (0, 0, 0, pad_w, 0, pad_h))
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Hp, Wp = H + pad_h, W + pad_w
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x = x.view(B, Hp // window_size, window_size, Wp // window_size, window_size, C)
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windows = x.permute(0, 1, 3, 2, 4, 5).reshape(-1, window_size, window_size, C)
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return windows, (Hp, Wp)
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def window_unpartition(
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windows: Tensor, window_size: int, pad_hw: Tuple[int, int], hw: Tuple[int, int]
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) -> Tensor:
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"""
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Window unpartition into original sequences and removing padding.
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Args:
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x (tensor): input tokens with [B * num_windows, window_size, window_size, C].
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window_size (int): window size.
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pad_hw (Tuple): padded height and width (Hp, Wp).
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hw (Tuple): original height and width (H, W) before padding.
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Returns:
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x: unpartitioned sequences with [B, H, W, C].
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"""
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Hp, Wp = pad_hw
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H, W = hw
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B = windows.shape[0] // (Hp * Wp // window_size // window_size)
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x = windows.reshape(
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B, Hp // window_size, Wp // window_size, window_size, window_size, -1
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)
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x = x.permute(0, 1, 3, 2, 4, 5).reshape(B, Hp, Wp, -1)
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if Hp > H or Wp > W:
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x = x[:, :H, :W, :]
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return x
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def get_rel_pos(q_size: int, k_size: int, rel_pos: Tensor) -> Tensor:
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"""
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Get relative positional embeddings according to the relative positions of
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query and key sizes.
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Args:
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q_size (int): size of query q.
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k_size (int): size of key k.
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rel_pos (Tensor): relative position embeddings (L, C).
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Returns:
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Extracted positional embeddings according to relative positions.
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"""
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max_rel_dist = int(2 * max(q_size, k_size) - 1)
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# Interpolate rel pos if needed.
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if rel_pos.shape[0] != max_rel_dist:
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# Interpolate rel pos.
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rel_pos_resized = F.interpolate(
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rel_pos.reshape(1, rel_pos.shape[0], -1).permute(0, 2, 1),
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size=max_rel_dist,
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mode="linear",
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align_corners=False,
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)
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rel_pos_resized = rel_pos_resized.reshape(-1, max_rel_dist).permute(1, 0)
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else:
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rel_pos_resized = rel_pos
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# Scale the coords with short length if shapes for q and k are different.
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q_coords = torch.arange(q_size)[:, None] * max(k_size / q_size, 1.0)
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k_coords = torch.arange(k_size)[None, :] * max(q_size / k_size, 1.0)
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relative_coords = (q_coords - k_coords) + (k_size - 1) * max(q_size / k_size, 1.0)
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return rel_pos_resized[relative_coords.long()]
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def get_abs_pos(
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abs_pos: Tensor,
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has_cls_token: bool,
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hw: Tuple[int, int],
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retain_cls_token: bool = False,
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tiling: bool = False,
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) -> Tensor:
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"""
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Calculate absolute positional embeddings. If needed, resize embeddings and remove cls_token
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dimension for the original embeddings.
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Args:
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abs_pos (Tensor): absolute positional embeddings with (1, num_position, C).
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has_cls_token (bool): If true, has 1 embedding in abs_pos for cls token.
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hw (Tuple): size of input image tokens.
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retain_cls_token: whether to retain the cls_token
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tiling: whether to tile the embeddings, *instead* of interpolation (a la abs_win)
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Returns:
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Absolute positional embeddings after processing with shape (1, H, W, C),
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if retain_cls_token is False, otherwise (1, 1+H*W, C)
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"""
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if retain_cls_token:
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assert has_cls_token
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h, w = hw
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if has_cls_token:
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cls_pos = abs_pos[:, :1]
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abs_pos = abs_pos[:, 1:]
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xy_num = abs_pos.shape[1]
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size = int(math.sqrt(xy_num))
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assert size * size == xy_num
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if size != h or size != w:
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new_abs_pos = abs_pos.reshape(1, size, size, -1).permute(0, 3, 1, 2)
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if tiling:
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new_abs_pos = new_abs_pos.tile(
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[1, 1] + [x // y + 1 for x, y in zip((h, w), new_abs_pos.shape[2:])]
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)[:, :, :h, :w]
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else:
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new_abs_pos = F.interpolate(
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new_abs_pos,
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size=(h, w),
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mode="bicubic",
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align_corners=False,
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)
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if not retain_cls_token:
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return new_abs_pos.permute(0, 2, 3, 1)
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else:
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# add cls_token back, flatten spatial dims
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assert has_cls_token
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return torch.cat(
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[cls_pos, new_abs_pos.permute(0, 2, 3, 1).reshape(1, h * w, -1)],
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dim=1,
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)
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else:
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if not retain_cls_token:
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return abs_pos.reshape(1, h, w, -1)
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else:
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assert has_cls_token
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return torch.cat([cls_pos, abs_pos], dim=1)
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def concat_rel_pos(
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q: Tensor,
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k: Tensor,
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q_hw: Tuple[int, int],
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k_hw: Tuple[int, int],
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rel_pos_h: Tensor,
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rel_pos_w: Tensor,
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rescale: bool = False,
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relative_coords: Optional[Tensor] = None,
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) -> Tuple[Tensor, Tensor]:
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"""
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Concatenate rel pos coeffs to the q & k tensors, so that qk^T is now
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effectively including rel pos biases.
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Args:
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q (Tensor): q tensor with shape (B, L_q, C).
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k (Tensor): k tensor with shape (B, L_k, C).
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q_hw, k_hw: These are spatial size of q & k tensors.
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rel_pos_h, rel_pos_w: These are relative pos embeddings/params of height, width.
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rescale (bool): whether to rescale. e.g. for use when using sdpa, pytorch will
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scale by the wrong factor due to the concat.
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Returns:
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q, k: But, padded so that qk^T accounts for rel pos biases
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"""
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q_h, q_w = q_hw
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k_h, k_w = k_hw
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assert (q_h == q_w) and (k_h == k_w), "only square inputs supported"
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if relative_coords is not None:
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Rh = rel_pos_h[relative_coords]
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Rw = rel_pos_w[relative_coords]
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else:
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Rh = get_rel_pos(q_h, k_h, rel_pos_h)
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Rw = get_rel_pos(q_w, k_w, rel_pos_w)
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B, _, dim = q.shape
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r_q = q.reshape(B, q_h, q_w, dim)
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old_scale = dim**0.5
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new_scale = (dim + k_h + k_w) ** 0.5 if rescale else old_scale # for sdpa
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# attn will be divided by new_scale, but we want to divide q by old_scale
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scale_ratio = new_scale / old_scale
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rel_h = torch.einsum("bhwc,hkc->bhwk", r_q, Rh) * new_scale # (B, q_h, q_w, k_h)
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rel_w = torch.einsum("bhwc,wkc->bhwk", r_q, Rw) * new_scale # (B, q_h, q_w, k_w)
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eye_h = torch.eye(k_h, dtype=q.dtype, device=q.device)
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eye_w = torch.eye(k_w, dtype=q.dtype, device=q.device)
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eye_h = eye_h.view(1, k_h, 1, k_h).expand([B, k_h, k_w, k_h])
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eye_w = eye_w.view(1, 1, k_w, k_w).expand([B, k_h, k_w, k_w])
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q = torch.cat([r_q * scale_ratio, rel_h, rel_w], dim=-1).view(B, q_h * q_w, -1)
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k = torch.cat([k.view(B, k_h, k_w, -1), eye_h, eye_w], dim=-1).view(
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B, k_h * k_w, -1
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)
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return q, k
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class PatchEmbed(nn.Module):
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"""
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Image to Patch Embedding.
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"""
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def __init__(
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self,
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kernel_size: Tuple[int, int] = (16, 16),
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stride: Tuple[int, int] = (16, 16),
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padding: Tuple[int, int] = (0, 0),
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in_chans: int = 3,
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embed_dim: int = 768,
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bias: bool = True,
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):
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"""
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Args:
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kernel_size (Tuple): kernel size of the projection layer.
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stride (Tuple): stride of the projection layer.
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padding (Tuple): padding size of the projection layer.
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in_chans (int): Number of input image channels.
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embed_dim (int): embed_dim (int): Patch embedding dimension.
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"""
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super().__init__()
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self.proj = nn.Conv2d(
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in_chans,
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embed_dim,
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kernel_size=kernel_size,
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stride=stride,
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padding=padding,
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bias=bias,
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)
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def forward(self, x: Tensor) -> Tensor:
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x = self.proj(x)
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# B C H W -> B H W C
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x = x.permute(0, 2, 3, 1)
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return x
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class Attention(nn.Module):
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"""Multi-head Attention block with relative position embeddings and 2d-rope."""
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def __init__(
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self,
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dim: int,
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num_heads: int = 8,
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qkv_bias: bool = True,
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use_rel_pos: bool = False,
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rel_pos_zero_init: bool = True,
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input_size: Optional[Tuple[int, int]] = None,
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cls_token: bool = False,
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use_rope: bool = False,
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rope_theta: float = 10000.0,
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rope_pt_size: Optional[Tuple[int, int]] = None,
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rope_interp: bool = False,
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):
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"""
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Args:
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dim (int): Number of input channels.
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num_heads (int): Number of attention heads.
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qkv_bias (bool: If True, add a learnable bias to query, key, value.
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rel_pos (bool): If True, add relative positional embeddings to the attention map.
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rel_pos_zero_init (bool): If True, zero initialize relative positional parameters.
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input_size (int or None): Input resolution for calculating the relative positional
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parameter size or rope size.
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attn_type: Type of attention operation, e.g. "vanilla", "vanilla-xformer".
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cls_token: whether a cls_token is present.
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use_rope: whether to use rope 2d (indep of use_rel_pos, as it can be used together)
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rope_theta: control frequencies of rope
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rope_pt_size: size of rope in previous stage of training, needed for interpolation or tiling
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rope_interp: whether to interpolate (or extrapolate) rope to match input size
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"""
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super().__init__()
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self.num_heads = num_heads
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self.head_dim = dim // num_heads
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self.scale = self.head_dim**-0.5
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self.cls_token = cls_token
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self.qkv = nn.Linear(dim, dim * 3, bias=qkv_bias)
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self.proj = nn.Linear(dim, dim)
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# rel_pos embeddings and rope
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self.use_rel_pos = use_rel_pos
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self.input_size = input_size
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self.use_rope = use_rope
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self.rope_theta = rope_theta
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self.rope_pt_size = rope_pt_size
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self.rope_interp = rope_interp
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# init rel_pos embeddings and rope
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self._setup_rel_pos(rel_pos_zero_init)
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self._setup_rope_freqs()
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def _setup_rel_pos(self, rel_pos_zero_init: bool = True) -> None:
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if not self.use_rel_pos:
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self.rel_pos_h = None
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self.rel_pos_w = None
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return
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assert self.input_size is not None
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assert self.cls_token is False, "not supported"
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# initialize relative positional embeddings
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self.rel_pos_h = nn.Parameter(
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torch.zeros(2 * self.input_size[0] - 1, self.head_dim)
|
||||
)
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self.rel_pos_w = nn.Parameter(
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torch.zeros(2 * self.input_size[1] - 1, self.head_dim)
|
||||
)
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||||
|
||||
if not rel_pos_zero_init:
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trunc_normal_(self.rel_pos_h, std=0.02)
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trunc_normal_(self.rel_pos_w, std=0.02)
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||||
|
||||
# Precompute the relative coords
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H, W = self.input_size
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||||
q_coords = torch.arange(H)[:, None]
|
||||
k_coords = torch.arange(W)[None, :]
|
||||
relative_coords = (q_coords - k_coords) + (H - 1)
|
||||
self.register_buffer("relative_coords", relative_coords.long())
|
||||
|
||||
def _setup_rope_freqs(self) -> None:
|
||||
if not self.use_rope:
|
||||
self.freqs_cis = None
|
||||
return
|
||||
|
||||
assert self.input_size is not None
|
||||
# determine rope input size
|
||||
if self.rope_pt_size is None:
|
||||
self.rope_pt_size = self.input_size
|
||||
|
||||
# initialize 2d rope freqs
|
||||
self.compute_cis = partial(
|
||||
compute_axial_cis,
|
||||
dim=self.head_dim,
|
||||
theta=self.rope_theta,
|
||||
)
|
||||
|
||||
# interpolate rope
|
||||
scale_pos = 1.0
|
||||
if self.rope_interp:
|
||||
scale_pos = self.rope_pt_size[0] / self.input_size[0]
|
||||
# get scaled freqs_cis
|
||||
freqs_cis = self.compute_cis(
|
||||
end_x=self.input_size[0],
|
||||
end_y=self.input_size[1],
|
||||
scale_pos=scale_pos,
|
||||
)
|
||||
if self.cls_token:
|
||||
t = torch.zeros(
|
||||
self.head_dim // 2,
|
||||
dtype=torch.float32,
|
||||
device=freqs_cis.device,
|
||||
)
|
||||
cls_freqs_cis = torch.polar(torch.ones_like(t), t)[None, :]
|
||||
freqs_cis = torch.cat([cls_freqs_cis, freqs_cis], dim=0)
|
||||
|
||||
self.register_buffer("freqs_cis", freqs_cis)
|
||||
|
||||
def _apply_rope(self, q, k) -> Tuple[Tensor, Tensor]:
|
||||
if not self.use_rope:
|
||||
return q, k
|
||||
|
||||
assert self.freqs_cis is not None
|
||||
return apply_rotary_enc(q, k, freqs_cis=self.freqs_cis)
|
||||
|
||||
def forward(self, x: Tensor) -> Tensor:
|
||||
s = 1 if self.cls_token else 0 # used to exclude cls_token
|
||||
if x.ndim == 4:
|
||||
B, H, W, _ = x.shape
|
||||
assert s == 0 # no cls_token
|
||||
L = H * W
|
||||
ndim = 4
|
||||
else:
|
||||
assert x.ndim == 3
|
||||
B, L, _ = x.shape
|
||||
ndim = 3
|
||||
H = W = math.sqrt(L - s)
|
||||
|
||||
# qkv with shape (3, B, nHead, L, C)
|
||||
qkv = self.qkv(x).reshape(B, L, 3, self.num_heads, -1)
|
||||
# q, k, v with shape (B, nHead, L, C)
|
||||
q, k, v = qkv.permute(2, 0, 3, 1, 4).unbind(0)
|
||||
|
||||
# handle rope and rel pos embeddings
|
||||
q, k = self._apply_rope(q, k)
|
||||
if self.use_rel_pos:
|
||||
q, k = concat_rel_pos(
|
||||
q.flatten(0, 1),
|
||||
k.flatten(0, 1),
|
||||
(H, W),
|
||||
x.shape[1:3],
|
||||
self.rel_pos_h,
|
||||
self.rel_pos_w,
|
||||
rescale=True,
|
||||
relative_coords=self.relative_coords,
|
||||
)
|
||||
|
||||
# sdpa expects [B, nheads, H*W, C] so we transpose back
|
||||
q = q.reshape(B, self.num_heads, H * W, -1)
|
||||
k = k.reshape(B, self.num_heads, H * W, -1)
|
||||
|
||||
x = F.scaled_dot_product_attention(q, k, v)
|
||||
|
||||
if ndim == 4:
|
||||
x = (
|
||||
x.view(B, self.num_heads, H, W, -1)
|
||||
.permute(0, 2, 3, 1, 4)
|
||||
.reshape(B, H, W, -1)
|
||||
)
|
||||
else:
|
||||
x = x.view(B, self.num_heads, L, -1).permute(0, 2, 1, 3).reshape(B, L, -1)
|
||||
|
||||
x = self.proj(x)
|
||||
|
||||
return x
|
||||
|
||||
|
||||
class Block(nn.Module):
|
||||
"""Transformer blocks with support of window attention"""
|
||||
|
||||
def __init__(
|
||||
self,
|
||||
dim: int,
|
||||
num_heads: int,
|
||||
mlp_ratio: float = 4.0,
|
||||
qkv_bias: bool = True,
|
||||
drop_path: float = 0.0,
|
||||
norm_layer: Callable[..., nn.Module] = nn.LayerNorm,
|
||||
act_layer: Callable[..., nn.Module] = nn.GELU,
|
||||
use_rel_pos: bool = False,
|
||||
rel_pos_zero_init: bool = True,
|
||||
window_size: int = 0,
|
||||
input_size: Optional[Tuple[int, int]] = None,
|
||||
use_rope: bool = False,
|
||||
rope_pt_size: Optional[Tuple[int, int]] = None,
|
||||
rope_tiled: bool = False,
|
||||
rope_interp: bool = False,
|
||||
use_ve_rope: bool = False,
|
||||
cls_token: bool = False,
|
||||
dropout: float = 0.0,
|
||||
init_values: Optional[float] = None,
|
||||
):
|
||||
"""
|
||||
Args:
|
||||
dim (int): Number of input channels.
|
||||
num_heads (int): Number of attention heads in each ViT block.
|
||||
mlp_ratio (float): Ratio of mlp hidden dim to embedding dim.
|
||||
qkv_bias (bool): If True, add a learnable bias to query, key, value.
|
||||
drop_path (float): Stochastic depth rate.
|
||||
norm_layer (nn.Module): Normalization layer.
|
||||
act_layer (nn.Module): Activation layer.
|
||||
use_rel_pos (bool): If True, add relative positional embeddings to the attention map.
|
||||
rel_pos_zero_init (bool): If True, zero initialize relative positional parameters.
|
||||
window_size (int): Window size for window attention blocks. If it equals 0, then not
|
||||
use window attention.
|
||||
input_size (int or None): Input resolution for calculating the relative positional
|
||||
parameter size.
|
||||
dropout (float): Dropout rate.
|
||||
cls_token: whether a cls_token is present.
|
||||
use_rope: whether to use rope 2d (indep of use_rel_pos, as it can be used together)
|
||||
rope_pt_size: size of rope in previous stage of training, needed for interpolation or tiling
|
||||
rope_interp: whether to interpolate (or extrapolate) rope to match target input size,
|
||||
expected to specify source size as rope_pt_size.
|
||||
"""
|
||||
super().__init__()
|
||||
self.norm1 = norm_layer(dim)
|
||||
self.attn = Attention(
|
||||
dim,
|
||||
num_heads=num_heads,
|
||||
qkv_bias=qkv_bias,
|
||||
use_rel_pos=use_rel_pos,
|
||||
rel_pos_zero_init=rel_pos_zero_init,
|
||||
input_size=input_size if window_size == 0 else (window_size, window_size),
|
||||
use_rope=use_rope,
|
||||
rope_pt_size=rope_pt_size,
|
||||
rope_interp=rope_interp,
|
||||
cls_token=cls_token,
|
||||
)
|
||||
self.ls1 = (
|
||||
LayerScale(dim, init_values=init_values) if init_values else nn.Identity()
|
||||
)
|
||||
self.drop_path = DropPath(drop_path) if drop_path > 0.0 else nn.Identity()
|
||||
|
||||
self.norm2 = norm_layer(dim)
|
||||
self.mlp = Mlp(
|
||||
in_features=dim,
|
||||
hidden_features=int(dim * mlp_ratio),
|
||||
act_layer=act_layer,
|
||||
drop=(dropout, 0.0),
|
||||
)
|
||||
self.ls2 = (
|
||||
LayerScale(dim, init_values=init_values) if init_values else nn.Identity()
|
||||
)
|
||||
self.dropout = nn.Dropout(dropout)
|
||||
self.window_size = window_size
|
||||
|
||||
def forward(self, x: Tensor) -> Tensor:
|
||||
shortcut = x
|
||||
x = self.norm1(x)
|
||||
# Window partition
|
||||
if self.window_size > 0:
|
||||
H, W = x.shape[1], x.shape[2]
|
||||
x, pad_hw = window_partition(x, self.window_size)
|
||||
|
||||
x = self.ls1(self.attn(x))
|
||||
# Reverse window partition
|
||||
if self.window_size > 0:
|
||||
x = window_unpartition(x, self.window_size, pad_hw, (H, W))
|
||||
|
||||
x = shortcut + self.dropout(self.drop_path(x))
|
||||
x = x + self.dropout(self.drop_path(self.ls2(self.mlp(self.norm2(x)))))
|
||||
|
||||
return x
|
||||
|
||||
|
||||
class ViT(nn.Module):
|
||||
"""
|
||||
This module implements Vision Transformer (ViT) backbone in :paper:`vitdet`.
|
||||
"Exploring Plain Vision Transformer Backbones for Object Detection",
|
||||
https://arxiv.org/abs/2203.16527
|
||||
"""
|
||||
|
||||
def __init__(
|
||||
self,
|
||||
img_size: int = 1024,
|
||||
patch_size: int = 16,
|
||||
in_chans: int = 3,
|
||||
embed_dim: int = 768,
|
||||
depth: int = 12,
|
||||
num_heads: int = 12,
|
||||
mlp_ratio: float = 4.0,
|
||||
qkv_bias: bool = True,
|
||||
drop_path_rate: float = 0.0,
|
||||
norm_layer: Union[Callable[..., nn.Module], str] = "LayerNorm",
|
||||
act_layer: Callable[..., nn.Module] = nn.GELU,
|
||||
use_abs_pos: bool = True,
|
||||
tile_abs_pos: bool = True,
|
||||
rel_pos_blocks: Union[Tuple[int, ...], bool] = (2, 5, 8, 11),
|
||||
rel_pos_zero_init: bool = True,
|
||||
window_size: int = 14,
|
||||
global_att_blocks: Tuple[int, ...] = (2, 5, 8, 11),
|
||||
use_rope: bool = False,
|
||||
rope_pt_size: Optional[int] = None,
|
||||
use_interp_rope: bool = False,
|
||||
pretrain_img_size: int = 224,
|
||||
pretrain_use_cls_token: bool = True,
|
||||
retain_cls_token: bool = True,
|
||||
dropout: float = 0.0,
|
||||
return_interm_layers: bool = False,
|
||||
init_values: Optional[float] = None, # for layerscale
|
||||
ln_pre: bool = False,
|
||||
ln_post: bool = False,
|
||||
bias_patch_embed: bool = True,
|
||||
compile_mode: Optional[str] = None,
|
||||
use_act_checkpoint: bool = True,
|
||||
):
|
||||
"""
|
||||
Args:
|
||||
img_size (int): Input image size. Only relevant for rel pos or rope.
|
||||
patch_size (int): Patch size.
|
||||
in_chans (int): Number of input image channels.
|
||||
embed_dim (int): Patch embedding dimension.
|
||||
depth (int): Depth of ViT.
|
||||
num_heads (int): Number of attention heads in each ViT block.
|
||||
mlp_ratio (float): Ratio of mlp hidden dim to embedding dim.
|
||||
qkv_bias (bool): If True, add a learnable bias to query, key, value.
|
||||
drop_path_rate (float): Stochastic depth rate.
|
||||
norm_layer (nn.Module): Normalization layer.
|
||||
act_layer (nn.Module): Activation layer.
|
||||
use_abs_pos (bool): If True, use absolute positional embeddings.
|
||||
tile_abs_pos (bool): If True, tile absolute positional embeddings instead of interpolation.
|
||||
rel_pos_blocks (list): Blocks which have rel pos embeddings.
|
||||
rel_pos_zero_init (bool): If True, zero initialize relative positional parameters.
|
||||
window_size (int): Window size for window attention blocks.
|
||||
global_att_blocks (list): Indexes for blocks using global attention (other blocks use window attention).
|
||||
use_rope (bool): whether to use rope 2d (indep of rel_pos_blocks, as it can be used together).
|
||||
rope_pt_size (int): size of rope in previous stage of training, needed for interpolation or tiling.
|
||||
use_interp_rope: whether to interpolate (or extrapolate) rope to match target input size,
|
||||
expected to specify source size as rope_pt_size.
|
||||
use_act_checkpoint (bool): If True, use activation checkpointing.
|
||||
pretrain_img_size (int): input image size for pretraining models.
|
||||
pretrain_use_cls_token (bool): If True, pretraining models use class token.
|
||||
retain_cls_token: whether cls_token should be retained.
|
||||
dropout (float): Dropout rate. Applied in residual blocks of attn, mlp and inside the mlp.
|
||||
|
||||
return_interm_layers (bool): Whether to return intermediate layers (all global attention blocks).
|
||||
init_values: layer scale init, None for no layer scale.
|
||||
|
||||
ln_pre (bool): If True, apply layer norm before transformer blocks.
|
||||
ln_post (bool): If True, apply layer norm after transformer blocks.
|
||||
bias_patch_embed (bool): bias in conv for patch embed?
|
||||
compile_mode (str): mode to compile the forward
|
||||
"""
|
||||
super().__init__()
|
||||
self.pretrain_use_cls_token = pretrain_use_cls_token
|
||||
|
||||
window_block_indexes = [i for i in range(depth) if i not in global_att_blocks]
|
||||
self.full_attn_ids = list(global_att_blocks)
|
||||
self.rel_pos_blocks = [False] * depth
|
||||
if isinstance(rel_pos_blocks, bool) and rel_pos_blocks:
|
||||
self.rel_pos_blocks = [True] * depth
|
||||
else:
|
||||
for i in rel_pos_blocks:
|
||||
self.rel_pos_blocks[i] = True
|
||||
|
||||
self.retain_cls_token = retain_cls_token
|
||||
if self.retain_cls_token:
|
||||
assert pretrain_use_cls_token
|
||||
assert (
|
||||
len(window_block_indexes) == 0
|
||||
), "windowing not supported with cls token"
|
||||
|
||||
assert sum(self.rel_pos_blocks) == 0, "rel pos not supported with cls token"
|
||||
|
||||
scale = embed_dim**-0.5
|
||||
self.class_embedding = nn.Parameter(scale * torch.randn(1, 1, embed_dim))
|
||||
|
||||
if isinstance(norm_layer, str):
|
||||
norm_layer = partial(getattr(nn, norm_layer), eps=1e-5)
|
||||
|
||||
self.patch_embed = PatchEmbed(
|
||||
kernel_size=(patch_size, patch_size),
|
||||
stride=(patch_size, patch_size),
|
||||
in_chans=in_chans,
|
||||
embed_dim=embed_dim,
|
||||
bias=bias_patch_embed,
|
||||
)
|
||||
|
||||
# Handle absolute positional embedding
|
||||
self.tile_abs_pos = tile_abs_pos
|
||||
self.use_abs_pos = use_abs_pos
|
||||
if self.tile_abs_pos:
|
||||
assert self.use_abs_pos
|
||||
|
||||
if self.use_abs_pos:
|
||||
# Initialize absolute positional embedding with pretrain image size.
|
||||
num_patches = (pretrain_img_size // patch_size) * (
|
||||
pretrain_img_size // patch_size
|
||||
)
|
||||
num_positions = (num_patches + 1) if pretrain_use_cls_token else num_patches
|
||||
self.pos_embed = nn.Parameter(torch.zeros(1, num_positions, embed_dim))
|
||||
else:
|
||||
self.pos_embed = None
|
||||
|
||||
# stochastic depth decay rule
|
||||
dpr = [x.item() for x in torch.linspace(0, drop_path_rate, depth)]
|
||||
|
||||
self.blocks = nn.ModuleList()
|
||||
cur_stage = 1
|
||||
for i in range(depth):
|
||||
block = Block(
|
||||
dim=embed_dim,
|
||||
num_heads=num_heads,
|
||||
mlp_ratio=mlp_ratio,
|
||||
qkv_bias=qkv_bias,
|
||||
drop_path=dpr[i],
|
||||
norm_layer=norm_layer,
|
||||
act_layer=act_layer,
|
||||
use_rel_pos=self.rel_pos_blocks[i],
|
||||
rel_pos_zero_init=rel_pos_zero_init,
|
||||
window_size=window_size if i in window_block_indexes else 0,
|
||||
input_size=(img_size // patch_size, img_size // patch_size),
|
||||
use_rope=use_rope,
|
||||
rope_pt_size=(
|
||||
(window_size, window_size)
|
||||
if rope_pt_size is None
|
||||
else (rope_pt_size, rope_pt_size)
|
||||
),
|
||||
rope_interp=use_interp_rope,
|
||||
cls_token=self.retain_cls_token,
|
||||
dropout=dropout,
|
||||
init_values=init_values,
|
||||
)
|
||||
|
||||
if i not in window_block_indexes:
|
||||
cur_stage += 1
|
||||
|
||||
self.use_act_checkpoint = use_act_checkpoint
|
||||
|
||||
self.blocks.append(block)
|
||||
|
||||
self.return_interm_layers = return_interm_layers
|
||||
self.channel_list = (
|
||||
[embed_dim] * len(self.full_attn_ids)
|
||||
if return_interm_layers
|
||||
else [embed_dim]
|
||||
)
|
||||
|
||||
if self.pos_embed is not None:
|
||||
trunc_normal_(self.pos_embed, std=0.02)
|
||||
|
||||
self.ln_pre = norm_layer(embed_dim) if ln_pre else nn.Identity()
|
||||
self.ln_post = norm_layer(embed_dim) if ln_post else nn.Identity()
|
||||
|
||||
self.apply(self._init_weights)
|
||||
|
||||
if compile_mode is not None:
|
||||
self.forward = torch.compile(
|
||||
self.forward, mode=compile_mode, fullgraph=True
|
||||
)
|
||||
if self.use_act_checkpoint and self.training:
|
||||
torch._dynamo.config.optimize_ddp = False
|
||||
|
||||
def _init_weights(self, m: nn.Module) -> None:
|
||||
if isinstance(m, nn.Linear):
|
||||
trunc_normal_(m.weight, std=0.02)
|
||||
if isinstance(m, nn.Linear) and m.bias is not None:
|
||||
nn.init.constant_(m.bias, 0)
|
||||
elif isinstance(m, nn.LayerNorm):
|
||||
nn.init.constant_(m.bias, 0)
|
||||
nn.init.constant_(m.weight, 1.0)
|
||||
|
||||
def forward(self, x: torch.Tensor) -> List[torch.Tensor]:
|
||||
x = self.patch_embed(x)
|
||||
h, w = x.shape[1], x.shape[2]
|
||||
|
||||
s = 0
|
||||
if self.retain_cls_token:
|
||||
# If cls_token is retained, we don't
|
||||
# maintain spatial shape
|
||||
x = torch.cat([self.class_embedding, x.flatten(1, 2)], dim=1)
|
||||
s = 1
|
||||
|
||||
if self.pos_embed is not None:
|
||||
x = x + get_abs_pos(
|
||||
self.pos_embed,
|
||||
self.pretrain_use_cls_token,
|
||||
(h, w),
|
||||
self.retain_cls_token,
|
||||
tiling=self.tile_abs_pos,
|
||||
)
|
||||
|
||||
x = self.ln_pre(x)
|
||||
|
||||
outputs = []
|
||||
for i, blk in enumerate(self.blocks):
|
||||
if self.use_act_checkpoint and self.training:
|
||||
x = checkpoint.checkpoint(blk, x, use_reentrant=False)
|
||||
else:
|
||||
x = blk(x)
|
||||
if (i == self.full_attn_ids[-1]) or (
|
||||
self.return_interm_layers and i in self.full_attn_ids
|
||||
):
|
||||
if i == self.full_attn_ids[-1]:
|
||||
x = self.ln_post(x)
|
||||
|
||||
feats = x[:, s:]
|
||||
if feats.ndim == 4:
|
||||
feats = feats.permute(0, 3, 1, 2)
|
||||
else:
|
||||
assert feats.ndim == 3
|
||||
h = w = math.sqrt(feats.shape[1])
|
||||
feats = feats.reshape(
|
||||
feats.shape[0], h, w, feats.shape[-1]
|
||||
).permute(0, 3, 1, 2)
|
||||
|
||||
outputs.append(feats)
|
||||
|
||||
return outputs
|
||||
|
||||
def get_layer_id(self, layer_name: str) -> int:
|
||||
# https://github.com/microsoft/unilm/blob/master/beit/optim_factory.py#L33
|
||||
num_layers = self.get_num_layers()
|
||||
|
||||
if layer_name.find("rel_pos") != -1:
|
||||
return num_layers + 1
|
||||
elif layer_name.find("ln_pre") != -1:
|
||||
return 0
|
||||
elif layer_name.find("pos_embed") != -1 or layer_name.find("cls_token") != -1:
|
||||
return 0
|
||||
elif layer_name.find("patch_embed") != -1:
|
||||
return 0
|
||||
elif layer_name.find("blocks") != -1:
|
||||
return int(layer_name.split("blocks")[1].split(".")[1]) + 1
|
||||
else:
|
||||
return num_layers + 1
|
||||
|
||||
def get_num_layers(self) -> int:
|
||||
return len(self.blocks)
|
||||
Reference in New Issue
Block a user