时间:2025-07-22 作者:游乐小编
本文介绍了Swin Transformer模型的代码复现情况。作者完成了BackBone代码迁移,ImageNet 1k预训练模型可用且精度对齐,模型代码和ImageNet 22k预训练模型将更新到PPIM项目。文中展示了模型组网代码,包括窗口划分、注意力机制等模块,还提供了预设模型及精度验证结果,Swin-T在验证集上top1准确率达81.19%。
论文:Swin Transformer: Hierarchical Vision Transformer using Shifted Windows
最新项目:microsoft/Swin-Transformer
才疏学浅,只会写写代码,就不班门弄斧解读这论文了
具体详解可以参考 @长风破浪会有时 大佬发布的项目 Swin Transformer,之前大佬写的 RepVGG 和 ReXNet 模型解析太强了
模型精度细节:
# 安装 PPIM!pip install ppim登录后复制
import numpy as npimport paddleimport paddle.nn as nnimport paddle.vision.transforms as Tfrom ppim.models.vit import Mlpfrom ppim.models.common import to_2tuplefrom ppim.models.common import DropPath, Identityfrom ppim.models.common import trunc_normal_, zeros_, ones_登录后复制
def window_partition(x, window_size): """ Args: x: (B, H, W, C) window_size (int): window size Returns: windows: (num_windows*B, window_size, window_size, C) """ B, H, W, C = x.shape x = x.reshape((B, H // window_size, window_size, W // window_size, window_size, C)) windows = x.transpose((0, 1, 3, 2, 4, 5)).reshape( (-1, window_size, window_size, C)) return windowsdef window_reverse(windows, window_size, H, W): """ Args: windows: (num_windows*B, window_size, window_size, C) window_size (int): Window size H (int): Height of image W (int): Width of image Returns: x: (B, H, W, C) """ B = int(windows.shape[0] / (H * W / window_size / window_size)) x = windows.reshape( (B, H // window_size, W // window_size, window_size, window_size, -1)) x = x.transpose((0, 1, 3, 2, 4, 5)).reshape((B, H, W, -1)) return xclass WindowAttention(nn.Layer): r""" Window based multi-head self attention (W-MSA) module with relative position bias. It supports both of shifted and non-shifted window. Args: dim (int): Number of input channels. window_size (tuple[int]): The height and width of the window. num_heads (int): Number of attention heads. qkv_bias (bool, optional): If True, add a learnable bias to query, key, value. Default: True qk_scale (float | None, optional): Override default qk scale of head_dim ** -0.5 if set attn_drop (float, optional): Dropout ratio of attention weight. Default: 0.0 proj_drop (float, optional): Dropout ratio of output. Default: 0.0 """ def __init__(self, dim, window_size, num_heads, qkv_bias=True, qk_scale=None, attn_drop=0., proj_drop=0.): super().__init__() self.dim = dim self.window_size = window_size # Wh, Ww self.num_heads = num_heads head_dim = dim // num_heads self.scale = qk_scale or head_dim ** -0.5 # define a parameter table of relative position bias self.relative_position_bias_table = self.create_parameter( shape=((2 * window_size[0] - 1) * (2 * window_size[1] - 1), num_heads), default_initializer=zeros_ ) # 2*Wh-1 * 2*Ww-1, nH self.add_parameter("relative_position_bias_table", self.relative_position_bias_table) # get pair-wise relative position index for each token inside the window coords_h = paddle.arange(self.window_size[0]) coords_w = paddle.arange(self.window_size[1]) coords = paddle.stack(paddle.meshgrid( [coords_h, coords_w])) # 2, Wh, Ww coords_flatten = paddle.flatten(coords, 1) # 2, Wh*Ww relative_coords = coords_flatten.unsqueeze(-1) - \ coords_flatten.unsqueeze(1) # 2, Wh*Ww, Wh*Ww relative_coords = relative_coords.transpose( (1, 2, 0)) # Wh*Ww, Wh*Ww, 2 relative_coords[:, :, 0] += self.window_size[0] - \ 1 # shift to start from 0 relative_coords[:, :, 1] += self.window_size[1] - 1 relative_coords[:, :, 0] *= 2 * self.window_size[1] - 1 relative_position_index = relative_coords.sum(-1) # Wh*Ww, Wh*Ww self.register_buffer("relative_position_index", relative_position_index) self.qkv = nn.Linear(dim, dim * 3, bias_attr=qkv_bias) self.attn_drop = nn.Dropout(attn_drop) self.proj = nn.Linear(dim, dim) self.proj_drop = nn.Dropout(proj_drop) trunc_normal_(self.relative_position_bias_table) self.softmax = nn.Softmax(axis=-1) def forward(self, x, mask=None): """ Args: x: input features with shape of (num_windows*B, N, C) mask: (0/-inf) mask with shape of (num_windows, Wh*Ww, Wh*Ww) or None """ B_, N, C = x.shape qkv = self.qkv(x).reshape((B_, N, 3, self.num_heads, C // self.num_heads)).transpose((2, 0, 3, 1, 4)) q, k, v = qkv[0], qkv[1], qkv[2] q = q * self.scale attn = q.matmul(k.transpose((0, 1, 3, 2))) relative_position_bias = paddle.index_select( self.relative_position_bias_table, self.relative_position_index.reshape((-1,)), axis=0).reshape( (self.window_size[0] * self.window_size[1], self.window_size[0] * self.window_size[1], -1)) relative_position_bias = relative_position_bias.transpose((2, 0, 1)) attn = attn + relative_position_bias.unsqueeze(0) if mask is not None: nW = mask.shape[0] attn = attn.reshape( (B_ // nW, nW, self.num_heads, N, N) ) + mask.unsqueeze(1).unsqueeze(0) attn = attn.reshape((-1, self.num_heads, N, N)) attn = self.softmax(attn) else: attn = self.softmax(attn) attn = self.attn_drop(attn) x = (attn.matmul(v)).transpose((0, 2, 1, 3)).reshape((B_, N, C)) x = self.proj(x) x = self.proj_drop(x) return xclass SwinTransformerBlock(nn.Layer): r""" Swin Transformer Block. Args: dim (int): Number of input channels. input_resolution (tuple[int]): Input resulotion. num_heads (int): Number of attention heads. window_size (int): Window size. shift_size (int): Shift size for SW-MSA. mlp_ratio (float): Ratio of mlp hidden dim to embedding dim. qkv_bias (bool, optional): If True, add a learnable bias to query, key, value. Default: True qk_scale (float | None, optional): Override default qk scale of head_dim ** -0.5 if set. drop (float, optional): Dropout rate. Default: 0.0 attn_drop (float, optional): Attention dropout rate. Default: 0.0 drop_path (float, optional): Stochastic depth rate. Default: 0.0 act_layer (nn.Layer, optional): Activation layer. Default: nn.GELU norm_layer (nn.Layer, optional): Normalization layer. Default: nn.LayerNorm """ def __init__(self, dim, input_resolution, num_heads, window_size=7, shift_size=0, mlp_ratio=4., qkv_bias=True, qk_scale=None, drop=0., attn_drop=0., drop_path=0., act_layer=nn.GELU, norm_layer=nn.LayerNorm): super().__init__() self.dim = dim self.input_resolution = input_resolution self.num_heads = num_heads self.window_size = window_size self.shift_size = shift_size self.mlp_ratio = mlp_ratio if min(self.input_resolution) <= self.window_size: # if window size is larger than input resolution, we don't partition windows self.shift_size = 0 self.window_size = min(self.input_resolution) assert 0 <= self.shift_size < self.window_size, "shift_size must in 0-window_size" self.norm1 = norm_layer(dim) self.attn = WindowAttention( dim, window_size=to_2tuple(self.window_size), num_heads=num_heads, qkv_bias=qkv_bias, qk_scale=qk_scale, attn_drop=attn_drop, proj_drop=drop) self.drop_path = DropPath(drop_path) if drop_path > 0. else Identity() self.norm2 = norm_layer(dim) mlp_hidden_dim = int(dim * mlp_ratio) self.mlp = Mlp(in_features=dim, hidden_features=mlp_hidden_dim, act_layer=act_layer, drop=drop) if self.shift_size > 0: # calculate attention mask for SW-MSA H, W = self.input_resolution img_mask = paddle.zeros((1, H, W, 1)) # 1 H W 1 h_slices = (slice(0, -self.window_size), slice(-self.window_size, -self.shift_size), slice(-self.shift_size, None)) w_slices = (slice(0, -self.window_size), slice(-self.window_size, -self.shift_size), slice(-self.shift_size, None)) cnt = 0 for h in h_slices: for w in w_slices: img_mask[:, h, w, :] = cnt cnt += 1 # nW, window_size, window_size, 1 mask_windows = window_partition(img_mask, self.window_size) mask_windows = mask_windows.reshape((-1, self.window_size * self.window_size)) attn_mask = mask_windows.unsqueeze(1) - mask_windows.unsqueeze(2) _h = paddle.full_like(attn_mask, -100.0, dtype='float32') _z = paddle.full_like(attn_mask, 0.0, dtype='float32') attn_mask = paddle.where(attn_mask != 0, _h, _z) else: attn_mask = None self.register_buffer("attn_mask", attn_mask) def forward(self, x): H, W = self.input_resolution B, L, C = x.shape assert L == H * W, "input feature has wrong size" shortcut = x x = self.norm1(x) x = x.reshape((B, H, W, C)) # cyclic shift if self.shift_size > 0: shifted_x = paddle.roll( x, shifts=(-self.shift_size, -self.shift_size), axis=(1, 2)) else: shifted_x = x # partition windows # nW*B, window_size, window_size, C x_windows = window_partition(shifted_x, self.window_size) # nW*B, window_size*window_size, C x_windows = x_windows.reshape( (-1, self.window_size * self.window_size, C)) # W-MSA/SW-MSA # nW*B, window_size*window_size, C attn_windows = self.attn(x_windows, mask=self.attn_mask) # merge windows attn_windows = attn_windows.reshape( (-1, self.window_size, self.window_size, C)) shifted_x = window_reverse( attn_windows, self.window_size, H, W) # B H' W' C # reverse cyclic shift if self.shift_size > 0: x = paddle.roll(shifted_x, shifts=( self.shift_size, self.shift_size), axis=(1, 2)) else: x = shifted_x x = x.reshape((B, H * W, C)) # FFN x = shortcut + self.drop_path(x) x = x + self.drop_path(self.mlp(self.norm2(x))) return xclass PatchMerging(nn.Layer): r""" Patch Merging Layer. Args: input_resolution (tuple[int]): Resolution of input feature. dim (int): Number of input channels. norm_layer (nn.Layer, optional): Normalization layer. Default: nn.LayerNorm """ def __init__(self, input_resolution, dim, norm_layer=nn.LayerNorm): super().__init__() self.input_resolution = input_resolution self.dim = dim self.reduction = nn.Linear(4 * dim, 2 * dim, bias_attr=False) self.norm = norm_layer(4 * dim) def forward(self, x): """ x: B, H*W, C """ H, W = self.input_resolution B, L, C = x.shape assert L == H * W, "input feature has wrong size" assert H % 2 == 0 and W % 2 == 0, f"x size ({H}*{W}) are not even." x = x.reshape((B, H, W, C)) x0 = x[:, 0::2, 0::2, :] # B H/2 W/2 C x1 = x[:, 1::2, 0::2, :] # B H/2 W/2 C x2 = x[:, 0::2, 1::2, :] # B H/2 W/2 C x3 = x[:, 1::2, 1::2, :] # B H/2 W/2 C x = paddle.concat([x0, x1, x2, x3], -1) # B H/2 W/2 4*C x = x.reshape((B, -1, 4 * C)) # B H/2*W/2 4*C x = self.norm(x) x = self.reduction(x) return xclass BasicLayer(nn.Layer): """ A basic Swin Transformer layer for one stage. Args: dim (int): Number of input channels. input_resolution (tuple[int]): Input resolution. depth (int): Number of blocks. num_heads (int): Number of attention heads. window_size (int): Local window size. mlp_ratio (float): Ratio of mlp hidden dim to embedding dim. qkv_bias (bool, optional): If True, add a learnable bias to query, key, value. Default: True qk_scale (float | None, optional): Override default qk scale of head_dim ** -0.5 if set. drop (float, optional): Dropout rate. Default: 0.0 attn_drop (float, optional): Attention dropout rate. Default: 0.0 drop_path (float | tuple[float], optional): Stochastic depth rate. Default: 0.0 norm_layer (nn.Layer, optional): Normalization layer. Default: nn.LayerNorm downsample (nn.Layer | None, optional): Downsample layer at the end of the layer. Default: None """ def __init__(self, dim, input_resolution, depth, num_heads, window_size, mlp_ratio=4., qkv_bias=True, qk_scale=None, drop=0., attn_drop=0., drop_path=0., norm_layer=nn.LayerNorm, downsample=None): super().__init__() self.dim = dim self.input_resolution = input_resolution self.depth = depth # build blocks self.blocks = nn.LayerList([ SwinTransformerBlock(dim=dim, input_resolution=input_resolution, num_heads=num_heads, window_size=window_size, shift_size=0 if ( i % 2 == 0) else window_size // 2, mlp_ratio=mlp_ratio, qkv_bias=qkv_bias, qk_scale=qk_scale, drop=drop, attn_drop=attn_drop, drop_path=drop_path[i] if isinstance( drop_path, np.ndarray) else drop_path, norm_layer=norm_layer) for i in range(depth)]) # patch merging layer if downsample is not None: self.downsample = downsample( input_resolution, dim=dim, norm_layer=norm_layer) else: self.downsample = None def forward(self, x): for blk in self.blocks: x = blk(x) if self.downsample is not None: x = self.downsample(x) return xclass PatchEmbed(nn.Layer): r""" Image to Patch Embedding Args: img_size (int): Image size. Default: 224. patch_size (int): Patch token size. Default: 4. in_chans (int): Number of input image channels. Default: 3. embed_dim (int): Number of linear projection output channels. Default: 96. norm_layer (nn.Layer, optional): Normalization layer. Default: None """ def __init__(self, img_size=224, patch_size=4, in_chans=3, embed_dim=96, norm_layer=None): super().__init__() img_size = to_2tuple(img_size) patch_size = to_2tuple(patch_size) patches_resolution = [img_size[0] // patch_size[0], img_size[1] // patch_size[1]] self.img_size = img_size self.patch_size = patch_size self.patches_resolution = patches_resolution self.num_patches = patches_resolution[0] * patches_resolution[1] self.in_chans = in_chans self.embed_dim = embed_dim self.proj = nn.Conv2D(in_chans, embed_dim, kernel_size=patch_size, stride=patch_size) if norm_layer is not None: self.norm = norm_layer(embed_dim) else: self.norm = None def forward(self, x): B, C, H, W = x.shape # FIXME look at relaxing size constraints assert H == self.img_size[0] and W == self.img_size[1], \ f"Input image size ({H}*{W}) doesn't match model ({self.img_size[0]}*{self.img_size[1]})." x = self.proj(x).flatten(2).transpose((0, 2, 1)) # B Ph*Pw C if self.norm is not None: x = self.norm(x) return xclass SwinTransformer(nn.Layer): r""" Swin Transformer A Paddle impl of : `Swin Transformer: Hierarchical Vision Transformer using Shifted Windows` - https://arxiv.org/pdf/2103.14030 Args: img_size (int | tuple(int)): Input image size. Default 224 patch_size (int | tuple(int)): Patch size. Default: 4 in_chans (int): Number of input image channels. Default: 3 class_dim (int): Number of classes for classification head. Default: 1000 embed_dim (int): Patch embedding dimension. Default: 96 depths (tuple(int)): Depth of each Swin Transformer layer. num_heads (tuple(int)): Number of attention heads in different layers. window_size (int): Window size. Default: 7 mlp_ratio (float): Ratio of mlp hidden dim to embedding dim. Default: 4 qkv_bias (bool): If True, add a learnable bias to query, key, value. Default: True qk_scale (float): Override default qk scale of head_dim ** -0.5 if set. Default: None drop_rate (float): Dropout rate. Default: 0 attn_drop_rate (float): Attention dropout rate. Default: 0 drop_path_rate (float): Stochastic depth rate. Default: 0.1 norm_layer (nn.Layer): Normalization layer. Default: nn.LayerNorm. ape (bool): If True, add absolute position embedding to the patch embedding. Default: False patch_norm (bool): If True, add normalization after patch embedding. Default: True """ def __init__(self, img_size=224, patch_size=4, in_chans=3, embed_dim=96, depths=[2, 2, 6, 2], num_heads=[3, 6, 12, 24], window_size=7, mlp_ratio=4., qkv_bias=True, qk_scale=None, drop_rate=0., attn_drop_rate=0., drop_path_rate=0.1, norm_layer=nn.LayerNorm, ape=False, patch_norm=True, class_dim=1000, with_pool=True, **kwargs): super().__init__() self.class_dim = class_dim self.with_pool = with_pool self.num_layers = len(depths) self.embed_dim = embed_dim self.ape = ape self.patch_norm = patch_norm self.num_features = int(embed_dim * 2 ** (self.num_layers - 1)) self.mlp_ratio = mlp_ratio # split image into non-overlapping patches self.patch_embed = PatchEmbed( img_size=img_size, patch_size=patch_size, in_chans=in_chans, embed_dim=embed_dim, norm_layer=norm_layer if self.patch_norm else None) num_patches = self.patch_embed.num_patches patches_resolution = self.patch_embed.patches_resolution self.patches_resolution = patches_resolution # absolute position embedding if self.ape: self.absolute_pos_embed = self.create_parameter( shape=(1, num_patches, embed_dim), default_initializer=zeros_ ) self.add_parameter("absolute_pos_embed", self.absolute_pos_embed) trunc_normal_(self.absolute_pos_embed) self.pos_drop = nn.Dropout(p=drop_rate) # stochastic depth dpr = np.linspace(0, drop_path_rate, sum(depths)) # build layers self.layers = nn.LayerList() for i_layer in range(self.num_layers): layer = BasicLayer(dim=int(embed_dim * 2 ** i_layer), input_resolution=(patches_resolution[0] // (2 ** i_layer), patches_resolution[1] // (2 ** i_layer)), depth=depths[i_layer], num_heads=num_heads[i_layer], window_size=window_size, mlp_ratio=self.mlp_ratio, qkv_bias=qkv_bias, qk_scale=qk_scale, drop=drop_rate, attn_drop=attn_drop_rate, drop_path=dpr[sum(depths[:i_layer]):sum( depths[:i_layer + 1])], norm_layer=norm_layer, downsample=PatchMerging if ( i_layer < self.num_layers - 1) else None ) self.layers.append(layer) self.norm = norm_layer(self.num_features) if with_pool: self.avgpool = nn.AdaptiveAvgPool1D(1) if class_dim > 0: self.head = nn.Linear(self.num_features, class_dim) self.apply(self._init_weights) def _init_weights(self, m): if isinstance(m, nn.Linear): trunc_normal_(m.weight) if isinstance(m, nn.Linear) and m.bias is not None: zeros_(m.bias) elif isinstance(m, nn.LayerNorm): zeros_(m.bias) ones_(m.weight) def forward_features(self, x): x = self.patch_embed(x) if self.ape: x = x + self.absolute_pos_embed x = self.pos_drop(x) for layer in self.layers: x = layer(x) x = self.norm(x) # B L C return x.transpose((0, 2, 1)) # B C 1 def forward(self, x): x = self.forward_features(x) if self.with_pool: x = self.avgpool(x) if self.class_dim > 0: x = paddle.flatten(x, 1) x = self.head(x) return x登录后复制
def get_transforms(resize, crop): transforms = [T.Resize(resize, interpolation='bicubic')] if crop: transforms.append(T.CenterCrop(crop)) transforms.append(T.ToTensor()) transforms.append(T.Normalize( mean=[0.485, 0.456, 0.406], std=[0.229, 0.224, 0.225])) transforms = T.Compose(transforms) return transformstransforms_224 = get_transforms(256, 224)transforms_384 = get_transforms((384, 384), None)登录后复制
def swin_ti(pretrained=False, **kwargs): model = SwinTransformer(**kwargs) if pretrained: model.set_dict(paddle.load('data/data80934/swin_tiny_patch2_window7_224.pdparams')) return model, transforms_224def swin_s(pretrained=False, **kwargs): model = SwinTransformer( depths=[2, 2, 18, 2], num_heads=[3, 6, 12, 24] ** kwargs ) if pretrained: model.set_dict(paddle.load('data/data80934/swin_small_patch2_window7_224.pdparams')) return model, transforms_224def swin_b(pretrained=False, **kwargs): model = SwinTransformer( embed_dim=128, depths=[2, 2, 18, 2], num_heads=[4, 8, 16, 32] ** kwargs ) if pretrained: model.set_dict(paddle.load('data/data80934/swin_base_patch2_window7_224.pdparams')) return model, transforms_224def swin_b_384(pretrained=False, **kwargs): model = SwinTransformer( img_size=384, embed_dim=128, depths=[2, 2, 18, 2], num_heads=[4, 8, 16, 32], window_size=12, **kwargs ) if pretrained: model.set_dict(paddle.load('data/data80934/swin_base_patch2_window12_384.pdparams')) return model, transforms_384登录后复制
# 解压数据集!mkdir ~/data/ILSVRC2012!tar -xf ~/data/data68594/ILSVRC2012_img_val.tar -C ~/data/ILSVRC2012登录后复制
import osimport cv2import numpy as npimport paddle# from ppim import pit_b_distilledfrom PIL import Image# 构建数据集class ILSVRC2012(paddle.io.Dataset): def __init__(self, root, label_list, transform, backend='pil'): self.transform = transform self.root = root self.label_list = label_list self.backend = backend self.load_datas() def load_datas(self): self.imgs = [] self.labels = [] with open(self.label_list, 'r') as f: for line in f: img, label = line[:-1].split(' ') self.imgs.append(os.path.join(self.root, img)) self.labels.append(int(label)) def __getitem__(self, idx): label = self.labels[idx] image = self.imgs[idx] if self.backend=='cv2': image = cv2.imread(image) else: image = Image.open(image).convert('RGB') image = self.transform(image) return image.astype('float32'), np.array(label).astype('int64') def __len__(self): return len(self.imgs)# 配置模型model, val_transforms = swin_ti(pretrained=True)model = paddle.Model(model)model.prepare(metrics=paddle.metric.Accuracy(topk=(1, 5)))# 配置数据集val_dataset = ILSVRC2012('data/ILSVRC2012', transform=val_transforms, label_list='data/data68594/val_list.txt')# 模型验证model.evaluate(val_dataset, batch_size=512)登录后复制
Eval begin...The loss value printed in the log is the current batch, and the metric is the average value of previous step.登录后复制
/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/paddle/fluid/layers/utils.py:77: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated, and in 3.8 it will stop working return (isinstance(seq, collections.Sequence) and登录后复制
step 10/98 - acc_top1: 0.8164 - acc_top5: 0.9547 - 7s/stepstep 20/98 - acc_top1: 0.8155 - acc_top5: 0.9549 - 7s/stepstep 30/98 - acc_top1: 0.8113 - acc_top5: 0.9542 - 7s/stepstep 40/98 - acc_top1: 0.8113 - acc_top5: 0.9543 - 7s/stepstep 50/98 - acc_top1: 0.8115 - acc_top5: 0.9547 - 7s/stepstep 60/98 - acc_top1: 0.8115 - acc_top5: 0.9547 - 7s/stepstep 70/98 - acc_top1: 0.8107 - acc_top5: 0.9550 - 7s/stepstep 80/98 - acc_top1: 0.8116 - acc_top5: 0.9549 - 7s/stepstep 90/98 - acc_top1: 0.8113 - acc_top5: 0.9549 - 6s/stepstep 98/98 - acc_top1: 0.8119 - acc_top5: 0.9551 - 6s/stepEval samples: 50000登录后复制
{'acc_top1': 0.81186, 'acc_top5': 0.9551}登录后复制
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