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model.py

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+# --------------------------------------------------------
+# References:
+# MAE: https://github.com/facebookresearch/mae
+# timm: https://github.com/rwightman/pytorch-image-models/tree/master/timm
+# DeiT: https://github.com/facebookresearch/deit
+# --------------------------------------------------------
+
+from functools import partial
+import numpy as np
+import torch
+import torch.nn as nn
+import torch.nn.functional as F
+from timm.models.vision_transformer import PatchEmbed, Block
+from huggingface_hub import PyTorchModelHubMixin
+
+
+def get_2d_sincos_pos_embed(embed_dim, grid_size, cls_token=False):
+    """
+    grid_size: int of the grid height and width
+    return:
+    pos_embed: [grid_size*grid_size, embed_dim] or [1+grid_size*grid_size, embed_dim] (w/ or w/o cls_token)
+    """
+    grid_h = np.arange(grid_size, dtype=np.float32)
+    grid_w = np.arange(grid_size, dtype=np.float32)
+    grid = np.meshgrid(grid_w, grid_h)  # here w goes first
+    grid = np.stack(grid, axis=0)
+
+    grid = grid.reshape([2, 1, grid_size, grid_size])
+    pos_embed = get_2d_sincos_pos_embed_from_grid(embed_dim, grid)
+    if cls_token:
+        pos_embed = np.concatenate([np.zeros([1, embed_dim]), pos_embed], axis=0)
+    return pos_embed
+
+def get_2d_sincos_pos_embed_from_grid(embed_dim, grid):
+    assert embed_dim % 2 == 0
+
+    # use half of dimensions to encode grid_h
+    emb_h = get_1d_sincos_pos_embed_from_grid(embed_dim // 2, grid[0])  # (H*W, D/2)
+    emb_w = get_1d_sincos_pos_embed_from_grid(embed_dim // 2, grid[1])  # (H*W, D/2)
+
+    emb = np.concatenate([emb_h, emb_w], axis=1) # (H*W, D)
+    return emb
+
+
+def get_1d_sincos_pos_embed_from_grid(embed_dim, pos):
+    """
+    embed_dim: output dimension for each position
+    pos: a list of positions to be encoded: size (M,)
+    out: (M, D)
+    """
+    assert embed_dim % 2 == 0
+    omega = np.arange(embed_dim // 2, dtype=np.float32)
+    omega /= embed_dim / 2.
+    omega = 1. / 10000**omega  # (D/2,)
+
+    pos = pos.reshape(-1)  # (M,)
+    out = np.einsum('m,d->md', pos, omega)  # (M, D/2), outer product
+
+    emb_sin = np.sin(out) # (M, D/2)
+    emb_cos = np.cos(out) # (M, D/2)
+
+    emb = np.concatenate([emb_sin, emb_cos], axis=1)  # (M, D)
+    return emb
+
+
+################################################################################
+# Upsample Block Modules
+################################################################################
+class LayerNorm(nn.Module):
+    def __init__(self, normalized_shape, eps=1e-6, data_format="channels_last"):
+        super().__init__()
+        self.weight = nn.Parameter(torch.ones(normalized_shape))
+        self.bias = nn.Parameter(torch.zeros(normalized_shape))
+        self.eps = eps
+        self.data_format = data_format
+        if self.data_format not in ["channels_last", "channels_first"]:
+            raise NotImplementedError
+        self.normalized_shape = (normalized_shape,)
+
+    def forward(self, x):
+        if self.data_format == "channels_last":
+            return F.layer_norm(x, self.normalized_shape, self.weight, self.bias, self.eps)
+        elif self.data_format == "channels_first":
+            u = x.mean(1, keepdim=True)
+            s = (x - u).pow(2).mean(1, keepdim=True)
+            x = (x - u) / torch.sqrt(s + self.eps)
+            x = self.weight[:, None, None] * x + self.bias[:, None, None]
+            return x
+
+class ResidualBlock(torch.nn.Module):
+    """
+    Utilized in upsample block
+    """
+    def __init__(self, channels):
+        super(ResidualBlock, self).__init__()
+        self.conv1 = nn.Conv2d(channels, channels, kernel_size=3, stride=1, padding=1)
+        self.conv2 = nn.Conv2d(channels, channels, kernel_size=3, stride=1, padding=1)
+        self.relu = nn.ReLU()
+
+    def forward(self, x):
+        """
+        x: tensor of shape (B,C,H,W)
+        """
+        residual = x
+        out = self.relu(self.conv1(x))
+        out = self.conv2(out) * 0.5
+        out = out + residual
+
+        return out
+
+
+class UpsampleBlock(nn.Module):
+    def __init__(self, in_channels, out_channels):
+        super(UpsampleBlock, self).__init__()
+
+        self.up_conv = nn.ConvTranspose2d(in_channels, in_channels, kernel_size=4, stride=2, padding=1)
+        self.up_norm = LayerNorm(in_channels, eps=1e-6, data_format="channels_first")
+
+        self.res_block = ResidualBlock(in_channels)
+        self.res_norm = LayerNorm(in_channels, eps=1e-6, data_format="channels_first")
+
+        self.proj_out = nn.Conv2d(in_channels, out_channels, kernel_size=3, stride=1, padding=1)
+
+        self.apply(self._init_weights)
+
+    def _init_weights(self, m):
+        if isinstance(m, nn.Linear):
+            torch.nn.init.xavier_uniform_(m.weight)
+            if isinstance(m, nn.Linear) and m.bias is not None:
+                nn.init.constant_(m.bias, 0)
+
+        elif isinstance(m, nn.Conv2d):
+            nn.init.constant_(m.bias, 0)
+            nn.init.xavier_uniform_(m.weight)
+
+        elif isinstance(m, nn.LayerNorm):
+            nn.init.constant_(m.bias, 0)
+            nn.init.constant_(m.weight, 1.0)
+
+    def forward(self, x):
+        ## upsample 2x
+        x = self.up_conv(x)
+        x = self.up_norm(x)
+        x = torch.nn.functional.leaky_relu(x)
+
+        # residual block
+        x = self.res_block(x)
+        x = self.res_norm(x)
+
+        out = self.proj_out(x)
+
+        return x, out
+
+################################################################################
+
+class MaskedAutoencoderViT(nn.Module, PyTorchModelHubMixin):
+    """ Masked Autoencoder with VisionTransformer backbone
+    """
+    def __init__(self, img_size=224, patch_size=16, in_chans=3,
+                 embed_dim=1024, depth=24, num_heads=16,
+                 decoder_embed_dim=512, decoder_depth=8, decoder_num_heads=16,
+                 mlp_ratio=4., norm_layer=nn.LayerNorm, norm_pix_loss=False, 
+                 proj_ratio=4):
+        super().__init__()
+
+        self.in_c = in_chans
+
+        ######################################################
+        # create upsample block layers
+        ms_dim = self.in_c*proj_ratio
+        self.proj_up_conv = nn.Conv2d(self.in_c, ms_dim, kernel_size=1, stride=1, padding=0)
+        self.proj_up_norm = LayerNorm(ms_dim, eps=1e-6, data_format="channels_first")
+        
+        self.up_block = UpsampleBlock(ms_dim, self.in_c)
+
+        ######################################################
+        # MAE encoder specifics
+        self.patch_embed = PatchEmbed(img_size, patch_size, in_chans, embed_dim)
+        num_patches = self.patch_embed.num_patches
+
+        self.cls_token = nn.Parameter(torch.zeros(1, 1, embed_dim))
+        self.pos_embed = nn.Parameter(torch.zeros(1, num_patches + 1, embed_dim), requires_grad=False)  # fixed sin-cos embedding
+
+        self.blocks = nn.ModuleList([
+            Block(embed_dim, num_heads, mlp_ratio, qkv_bias=True, norm_layer=norm_layer)
+            for i in range(depth)])
+        self.norm = norm_layer(embed_dim)
+
+        ######################################################
+        # MAE decoder specifics
+        self.decoder_embed = nn.Linear(embed_dim, decoder_embed_dim, bias=True)
+
+        self.mask_token = nn.Parameter(torch.zeros(1, 1, decoder_embed_dim))
+
+        self.decoder_pos_embed = nn.Parameter(torch.zeros(1, num_patches + 1, decoder_embed_dim), requires_grad=False)  # fixed sin-cos embedding
+
+        self.decoder_blocks = nn.ModuleList([
+            Block(decoder_embed_dim, decoder_num_heads, mlp_ratio, qkv_bias=True, norm_layer=norm_layer)
+            for i in range(decoder_depth)])
+
+        self.decoder_norm = norm_layer(decoder_embed_dim)
+        self.decoder_pred = nn.Linear(decoder_embed_dim, patch_size**2 * in_chans, bias=True) # decoder to patch
+        
+
+        self.norm_pix_loss = norm_pix_loss
+
+        self.initialize_weights()
+
+    def initialize_weights(self):
+        # initialization
+        # initialize (and freeze) pos_embed by sin-cos embedding
+        pos_embed = get_2d_sincos_pos_embed(self.pos_embed.shape[-1], int(self.patch_embed.num_patches**.5), cls_token=True)
+        self.pos_embed.data.copy_(torch.from_numpy(pos_embed).float().unsqueeze(0))
+
+        decoder_pos_embed = get_2d_sincos_pos_embed(self.decoder_pos_embed.shape[-1], int(self.patch_embed.num_patches**.5), cls_token=True)
+        self.decoder_pos_embed.data.copy_(torch.from_numpy(decoder_pos_embed).float().unsqueeze(0))
+
+        # initialize patch_embed like nn.Linear (instead of nn.Conv2d)
+        w = self.patch_embed.proj.weight.data
+        torch.nn.init.xavier_uniform_(w.view([w.shape[0], -1]))
+
+        # timm's trunc_normal_(std=.02) is effectively normal_(std=0.02) as cutoff is too big (2.)
+        torch.nn.init.normal_(self.cls_token, std=.02)
+        torch.nn.init.normal_(self.mask_token, std=.02)
+
+        # initialize nn.Linear and nn.LayerNorm
+        self.apply(self._init_weights)
+
+    def _init_weights(self, m):
+        if isinstance(m, nn.Linear):
+            # we use xavier_uniform following official JAX ViT:
+            torch.nn.init.xavier_uniform_(m.weight)
+            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 patchify(self, imgs, p, c):
+        """
+        imgs: (N, C, H, W)
+        p: Patch embed patch size
+        c: Number of channels
+        x: (N, L, patch_size**2 *C)
+        """
+        # p = self.patch_embed.patch_size[0]
+        assert imgs.shape[2] == imgs.shape[3] and imgs.shape[2] % p == 0
+
+        # c = self.in_c
+        h = w = imgs.shape[2] // p
+        x = imgs.reshape(shape=(imgs.shape[0], c, h, p, w, p))
+        x = torch.einsum('nchpwq->nhwpqc', x)
+        x = x.reshape(shape=(imgs.shape[0], h * w, p**2 * c))
+        return x
+
+    def unpatchify(self, x, p, c):
+        """
+        x: (N, L, patch_size**2 *C)
+        p: Patch embed patch size
+        c: Number of channels
+        imgs: (N, C, H, W)
+        """
+        h = w = int(x.shape[1]**.5)
+        assert h * w == x.shape[1]
+        
+        x = x.reshape(shape=(x.shape[0], h, w, p, p, c))
+        x = torch.einsum('nhwpqc->nchpwq', x)
+        imgs = x.reshape(shape=(x.shape[0], c, h * p, h * p))
+        return imgs
+
+    def random_masking(self, x, mask_ratio):
+        """
+        Perform per-sample random masking by per-sample shuffling.
+        Per-sample shuffling is done by argsort random noise.
+        x: [N, L, D], sequence
+        """
+        N, L, D = x.shape  # batch, length, dim
+        len_keep = int(L * (1 - mask_ratio))
+        
+        noise = torch.rand(N, L, device=x.device)  # noise in [0, 1]
+        
+        # sort noise for each sample
+        ids_shuffle = torch.argsort(noise, dim=1)  # ascend: small is keep, large is remove
+        ids_restore = torch.argsort(ids_shuffle, dim=1)
+
+        # keep the first subset
+        ids_keep = ids_shuffle[:, :len_keep]
+        x_masked = torch.gather(x, dim=1, index=ids_keep.unsqueeze(-1).repeat(1, 1, D))
+
+        # generate the binary mask: 0 is keep, 1 is remove
+        mask = torch.ones([N, L], device=x.device)
+        mask[:, :len_keep] = 0
+        # unshuffle to get the binary mask
+        mask = torch.gather(mask, dim=1, index=ids_restore)
+
+        return x_masked, mask, ids_restore
+
+    def forward_encoder(self, x, mask_ratio):
+        # embed patches
+        x = self.patch_embed(x)
+
+        # add pos embed w/o cls token
+        x = x + self.pos_embed[:, 1:, :]
+
+        # masking: length -> length * mask_ratio
+        x, mask, ids_restore = self.random_masking(x, mask_ratio)
+
+        # append cls token
+        cls_token = self.cls_token + self.pos_embed[:, :1, :]
+        cls_tokens = cls_token.expand(x.shape[0], -1, -1)
+        x = torch.cat((cls_tokens, x), dim=1)
+
+        # apply Transformer blocks
+        for blk in self.blocks:
+            x = blk(x)
+        x = self.norm(x)
+
+        return x, mask, ids_restore
+
+    def forward_decoder(self, x, ids_restore):
+        # embed tokens
+        x = self.decoder_embed(x)
+
+        # append mask tokens to sequence
+        mask_tokens = self.mask_token.repeat(x.shape[0], ids_restore.shape[1] + 1 - x.shape[1], 1)
+        x_ = torch.cat([x[:, 1:, :], mask_tokens], dim=1)  # no cls token
+        x_ = torch.gather(x_, dim=1, index=ids_restore.unsqueeze(-1).repeat(1, 1, x.shape[2]))  # unshuffle
+        x = torch.cat([x[:, :1, :], x_], dim=1)  # append cls token
+
+        # add pos embed
+        x = x + self.decoder_pos_embed
+
+        # apply Transformer blocks
+        for blk in self.decoder_blocks:
+            x = blk(x)
+        x = self.decoder_norm(x)
+
+        # predictor projection
+        x = self.decoder_pred(x)
+
+        # remove cls token
+        x = x[:, 1:, :]
+
+        return x
+
+    def forward_loss(self, imgs, pred, mask):
+        """
+        imgs: [N, 3, H, W]
+        pred: [N, L, p*p*3]
+        mask: [N, L], 0 is keep, 1 is remove, 
+        """
+        target = self.patchify(imgs, self.patch_embed.patch_size[0], self.in_c)
+
+        if self.norm_pix_loss:
+            mean = target.mean(dim=-1, keepdim=True)
+            var = target.var(dim=-1, keepdim=True)
+            target = (target - mean) / (var + 1.e-6)**.5
+
+        loss = (pred - target) ** 2
+        loss = loss.mean(dim=-1)  # [N, L], mean loss per patch
+
+        loss = (loss * mask).sum() / mask.sum()  # mean loss on removed patches
+        return loss
+
+    def forward_multiscale(self, x):
+        """ 
+        x: (N, L, p*p*3) 
+        """
+        x = self.unpatchify(x, self.patch_embed.patch_size[0], self.in_c)
+
+        x = self.proj_up_conv(x)
+        x = F.gelu(x)
+        x = self.proj_up_norm(x)
+
+        _, x = self.up_block(x)
+
+        return x
+
+    def forward(self, imgs, imgs_up, mask_ratio=0.75):
+        latent, mask, ids_restore = self.forward_encoder(imgs, mask_ratio)
+        pred = self.forward_decoder(latent, ids_restore)  # [N, L, p*p*3]
+        pred_ms = self.forward_multiscale(pred)
+
+        loss = self.forward_loss(imgs, pred, mask)  # MSE loss
+        ms_loss = F.l1_loss(pred_ms, imgs_up) # compute multiscale loss (L1 loss)
+
+        return loss, ms_loss, pred, mask