Merge pull request #12 from Bobholamovic/dev_gdf

[Feature] Add eight change detection models

paddlers/models/cd/models/__init__.py

@@ -12,4 +12,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from .cdnet import CDNet
+from .bit import BIT
+from .cdnet import CDNet
+from .dsifn import DSIFN
+from .stanet import STANet
+from .snunet import SNUNet
+from .dsamnet import DSAMNet
+from .unet_ef import UNetEarlyFusion
+from .unet_siamconc import UNetSiamConc
+from .unet_siamdiff import UNetSiamDiff

paddlers/models/cd/models/backbones/__init__.py

@@ -0,0 +1,13 @@
+# Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.

paddlers/models/cd/models/backbones/resnet.py

@@ -0,0 +1,358 @@
+# Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Adapted from https://github.com/PaddlePaddle/Paddle/blob/release/2.2/python/paddle/vision/models/resnet.py
+## Original head information
+# Copyright (c) 2020 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import division
+from __future__ import print_function
+
+import paddle
+import paddle.nn as nn
+
+from paddle.utils.download import get_weights_path_from_url
+
+__all__ = []
+
+model_urls = {
+    'resnet18': ('https://paddle-hapi.bj.bcebos.com/models/resnet18.pdparams',
+                 'cf548f46534aa3560945be4b95cd11c4'),
+    'resnet34': ('https://paddle-hapi.bj.bcebos.com/models/resnet34.pdparams',
+                 '8d2275cf8706028345f78ac0e1d31969'),
+    'resnet50': ('https://paddle-hapi.bj.bcebos.com/models/resnet50.pdparams',
+                 'ca6f485ee1ab0492d38f323885b0ad80'),
+    'resnet101': ('https://paddle-hapi.bj.bcebos.com/models/resnet101.pdparams',
+                  '02f35f034ca3858e1e54d4036443c92d'),
+    'resnet152': ('https://paddle-hapi.bj.bcebos.com/models/resnet152.pdparams',
+                  '7ad16a2f1e7333859ff986138630fd7a'),
+}
+
+
+class BasicBlock(nn.Layer):
+    expansion = 1
+
+    def __init__(self,
+                 inplanes,
+                 planes,
+                 stride=1,
+                 downsample=None,
+                 groups=1,
+                 base_width=64,
+                 dilation=1,
+                 norm_layer=None):
+        super(BasicBlock, self).__init__()
+        if norm_layer is None:
+            norm_layer = nn.BatchNorm2D
+
+        if dilation > 1:
+            raise NotImplementedError(
+                "Dilation > 1 not supported in BasicBlock")
+
+        self.conv1 = nn.Conv2D(
+            inplanes, planes, 3, padding=1, stride=stride, bias_attr=False)
+        self.bn1 = norm_layer(planes)
+        self.relu = nn.ReLU()
+        self.conv2 = nn.Conv2D(planes, planes, 3, padding=1, bias_attr=False)
+        self.bn2 = norm_layer(planes)
+        self.downsample = downsample
+        self.stride = stride
+
+    def forward(self, x):
+        identity = x
+
+        out = self.conv1(x)
+        out = self.bn1(out)
+        out = self.relu(out)
+
+        out = self.conv2(out)
+        out = self.bn2(out)
+
+        if self.downsample is not None:
+            identity = self.downsample(x)
+
+        out += identity
+        out = self.relu(out)
+
+        return out
+
+
+class BottleneckBlock(nn.Layer):
+
+    expansion = 4
+
+    def __init__(self,
+                 inplanes,
+                 planes,
+                 stride=1,
+                 downsample=None,
+                 groups=1,
+                 base_width=64,
+                 dilation=1,
+                 norm_layer=None):
+        super(BottleneckBlock, self).__init__()
+        if norm_layer is None:
+            norm_layer = nn.BatchNorm2D
+        width = int(planes * (base_width / 64.)) * groups
+
+        self.conv1 = nn.Conv2D(inplanes, width, 1, bias_attr=False)
+        self.bn1 = norm_layer(width)
+
+        self.conv2 = nn.Conv2D(
+            width,
+            width,
+            3,
+            padding=dilation,
+            stride=stride,
+            groups=groups,
+            dilation=dilation,
+            bias_attr=False)
+        self.bn2 = norm_layer(width)
+
+        self.conv3 = nn.Conv2D(
+            width, planes * self.expansion, 1, bias_attr=False)
+        self.bn3 = norm_layer(planes * self.expansion)
+        self.relu = nn.ReLU()
+        self.downsample = downsample
+        self.stride = stride
+
+    def forward(self, x):
+        identity = x
+
+        out = self.conv1(x)
+        out = self.bn1(out)
+        out = self.relu(out)
+
+        out = self.conv2(out)
+        out = self.bn2(out)
+        out = self.relu(out)
+
+        out = self.conv3(out)
+        out = self.bn3(out)
+
+        if self.downsample is not None:
+            identity = self.downsample(x)
+
+        out += identity
+        out = self.relu(out)
+
+        return out
+
+
+class ResNet(nn.Layer):
+    """ResNet model from
+    `"Deep Residual Learning for Image Recognition" <https://arxiv.org/pdf/1512.03385.pdf>`_
+    Args:
+        Block (BasicBlock|BottleneckBlock): block module of model.
+        depth (int): layers of resnet, default: 50.
+        num_classes (int): output dim of last fc layer. If num_classes <=0, last fc layer 
+                            will not be defined. Default: 1000.
+        with_pool (bool): use pool before the last fc layer or not. Default: True.
+    Examples:
+        .. code-block:: python
+            from paddle.vision.models import ResNet
+            from paddle.vision.models.resnet import BottleneckBlock, BasicBlock
+            resnet50 = ResNet(BottleneckBlock, 50)
+            resnet18 = ResNet(BasicBlock, 18)
+    """
+
+    def __init__(self, block, depth, num_classes=1000, with_pool=True, strides=(1,1,2,2,2), norm_layer=None):
+        super(ResNet, self).__init__()
+        layer_cfg = {
+            18: [2, 2, 2, 2],
+            34: [3, 4, 6, 3],
+            50: [3, 4, 6, 3],
+            101: [3, 4, 23, 3],
+            152: [3, 8, 36, 3]
+        }
+        layers = layer_cfg[depth]
+        self.num_classes = num_classes
+        self.with_pool = with_pool
+        self._norm_layer = nn.BatchNorm2D if norm_layer is None else norm_layer
+
+        self.inplanes = 64
+        self.dilation = 1
+
+        self.conv1 = nn.Conv2D(
+            3,
+            self.inplanes,
+            kernel_size=7,
+            stride=strides[0],
+            padding=3,
+            bias_attr=False)
+        self.bn1 = self._norm_layer(self.inplanes)
+        self.relu = nn.ReLU()
+        self.maxpool = nn.MaxPool2D(kernel_size=3, stride=2, padding=1)
+        self.layer1 = self._make_layer(block, 64, layers[0], stride=strides[1])
+        self.layer2 = self._make_layer(block, 128, layers[1], stride=strides[2])
+        self.layer3 = self._make_layer(block, 256, layers[2], stride=strides[3])
+        self.layer4 = self._make_layer(block, 512, layers[3], stride=strides[4])
+        if with_pool:
+            self.avgpool = nn.AdaptiveAvgPool2D((1, 1))
+
+        if num_classes > 0:
+            self.fc = nn.Linear(512 * block.expansion, num_classes)
+
+    def _make_layer(self, block, planes, blocks, stride=1, dilate=False):
+        norm_layer = self._norm_layer
+        downsample = None
+        previous_dilation = self.dilation
+        if dilate:
+            self.dilation *= stride
+            stride = 1
+        if stride != 1 or self.inplanes != planes * block.expansion:
+            downsample = nn.Sequential(
+                nn.Conv2D(
+                    self.inplanes,
+                    planes * block.expansion,
+                    1,
+                    stride=stride,
+                    bias_attr=False),
+                norm_layer(planes * block.expansion), )
+
+        layers = []
+        layers.append(
+            block(self.inplanes, planes, stride, downsample, 1, 64,
+                  previous_dilation, norm_layer))
+        self.inplanes = planes * block.expansion
+        for _ in range(1, blocks):
+            layers.append(block(self.inplanes, planes, norm_layer=norm_layer))
+
+        return nn.Sequential(*layers)
+
+    def forward(self, x):
+        x = self.conv1(x)
+        x = self.bn1(x)
+        x = self.relu(x)
+        x = self.maxpool(x)
+        x = self.layer1(x)
+        x = self.layer2(x)
+        x = self.layer3(x)
+        x = self.layer4(x)
+
+        if self.with_pool:
+            x = self.avgpool(x)
+
+        if self.num_classes > 0:
+            x = paddle.flatten(x, 1)
+            x = self.fc(x)
+
+        return x
+
+
+def _resnet(arch, Block, depth, pretrained, **kwargs):
+    model = ResNet(Block, depth, **kwargs)
+    if pretrained:
+        assert arch in model_urls, "{} model do not have a pretrained model now, you should set pretrained=False".format(
+            arch)
+        weight_path = get_weights_path_from_url(model_urls[arch][0],
+                                                model_urls[arch][1])
+
+        param = paddle.load(weight_path)
+        model.set_dict(param)
+
+    return model
+
+
+def resnet18(pretrained=False, **kwargs):
+    """ResNet 18-layer model
+    
+    Args:
+        pretrained (bool): If True, returns a model pre-trained on ImageNet
+    Examples:
+        .. code-block:: python
+            from paddle.vision.models import resnet18
+            # build model
+            model = resnet18()
+            # build model and load imagenet pretrained weight
+            # model = resnet18(pretrained=True)
+    """
+    return _resnet('resnet18', BasicBlock, 18, pretrained, **kwargs)
+
+
+def resnet34(pretrained=False, **kwargs):
+    """ResNet 34-layer model
+    
+    Args:
+        pretrained (bool): If True, returns a model pre-trained on ImageNet
+    
+    Examples:
+        .. code-block:: python
+            from paddle.vision.models import resnet34
+            # build model
+            model = resnet34()
+            # build model and load imagenet pretrained weight
+            # model = resnet34(pretrained=True)
+    """
+    return _resnet('resnet34', BasicBlock, 34, pretrained, **kwargs)
+
+
+def resnet50(pretrained=False, **kwargs):
+    """ResNet 50-layer model
+    
+    Args:
+        pretrained (bool): If True, returns a model pre-trained on ImageNet
+    Examples:
+        .. code-block:: python
+            from paddle.vision.models import resnet50
+            # build model
+            model = resnet50()
+            # build model and load imagenet pretrained weight
+            # model = resnet50(pretrained=True)
+    """
+    return _resnet('resnet50', BottleneckBlock, 50, pretrained, **kwargs)
+
+
+def resnet101(pretrained=False, **kwargs):
+    """ResNet 101-layer model
+    
+    Args:
+        pretrained (bool): If True, returns a model pre-trained on ImageNet
+    Examples:
+        .. code-block:: python
+            from paddle.vision.models import resnet101
+            # build model
+            model = resnet101()
+            # build model and load imagenet pretrained weight
+            # model = resnet101(pretrained=True)
+    """
+    return _resnet('resnet101', BottleneckBlock, 101, pretrained, **kwargs)
+
+
+def resnet152(pretrained=False, **kwargs):
+    """ResNet 152-layer model
+    
+    Args:
+        pretrained (bool): If True, returns a model pre-trained on ImageNet
+    Examples:
+        .. code-block:: python
+            from paddle.vision.models import resnet152
+            # build model
+            model = resnet152()
+            # build model and load imagenet pretrained weight
+            # model = resnet152(pretrained=True)
+    """
+    return _resnet('resnet152', BottleneckBlock, 152, pretrained, **kwargs)

paddlers/models/cd/models/bit.py

@@ -0,0 +1,395 @@
+# Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import paddle
+import paddle.nn as nn
+import paddle.nn.functional as F
+from paddle.nn.initializer import Normal
+
+
+from .backbones import resnet
+from .layers import Conv3x3, Conv1x1, get_norm_layer, Identity
+from .param_init import KaimingInitMixin
+
+
+class BIT(nn.Layer):
+    """
+    The BIT implementation based on PaddlePaddle.
+
+    The original article refers to
+        H. Chen, et al., "Remote Sensing Image Change Detection With Transformers"
+        (https://arxiv.org/abs/2103.00208).
+
+    This implementation adopts pretrained encoders, as opposed to the original work where weights are randomly initialized.
+
+    Args:
+        in_channels (int): The number of bands of the input images.
+        num_classes (int): The number of target classes.
+        backbone (str, optional): The ResNet architecture that is used as the backbone. Currently, only 'resnet18' and 
+            'resnet34' are supported. Default: 'resnet18'.
+        n_stages (int, optional): The number of ResNet stages used in the backbone, which should be a value in {3,4,5}. 
+            Default: 4.
+        use_tokenizer (bool, optional): Use a tokenizer or not. Default: True.
+        token_len (int, optional): The length of input tokens. Default: 4.
+        pool_mode (str, optional): The pooling strategy to obtain input tokens when `use_tokenizer` is set to False. 'max'
+            for global max pooling and 'avg' for global average pooling. Default: 'max'.
+        pool_size (int, optional): The height and width of the pooled feature maps when `use_tokenizer` is set to False. 
+            Default: 2.
+        enc_with_pos (bool, optional): Whether to add leanred positional embedding to the input feature sequence of the 
+            encoder. Default: True.
+        enc_depth (int, optional): The number of attention blocks used in the encoder. Default: 1
+        enc_head_dim (int, optional): The embedding dimension of each encoder head. Default: 64.
+        dec_depth (int, optional): The number of attention blocks used in the decoder. Default: 8.
+        dec_head_dim (int, optional): The embedding dimension of each decoder head. Default: 8.
+
+    Raises:
+        ValueError: When an unsupported backbone type is specified, or the number of backbone stages is not 3, 4, or 5.
+    """
+    
+    def __init__(
+        self, in_channels, num_classes,
+        backbone='resnet18', n_stages=4, 
+        use_tokenizer=True, token_len=4, 
+        pool_mode='max', pool_size=2,
+        enc_with_pos=True, 
+        enc_depth=1, enc_head_dim=64, 
+        dec_depth=8, dec_head_dim=8,
+        **backbone_kwargs
+    ):
+        super().__init__()
+
+        # TODO: reduce hard-coded parameters
+        DIM = 32
+        MLP_DIM = 2*DIM
+        EBD_DIM = DIM
+
+        self.backbone = Backbone(in_channels, EBD_DIM, arch=backbone, n_stages=n_stages, **backbone_kwargs)
+
+        self.use_tokenizer = use_tokenizer
+        if not use_tokenizer:
+            # If a tokenzier is not to be used，then downsample the feature maps.
+            self.pool_size = pool_size
+            self.pool_mode = pool_mode
+            self.token_len = pool_size * pool_size
+        else:
+            self.conv_att = Conv1x1(32, token_len, bias=False)
+            self.token_len = token_len
+
+        self.enc_with_pos = enc_with_pos
+        if enc_with_pos:
+            self.enc_pos_embedding = self.create_parameter(
+                shape=(1,self.token_len*2,EBD_DIM), 
+                default_initializer=Normal()
+            )
+
+        self.enc_depth = enc_depth
+        self.dec_depth = dec_depth
+        self.enc_head_dim = enc_head_dim
+        self.dec_head_dim = dec_head_dim
+        
+        self.encoder = TransformerEncoder(
+            dim=DIM, 
+            depth=enc_depth, 
+            n_heads=8,
+            head_dim=enc_head_dim,
+            mlp_dim=MLP_DIM,
+            dropout_rate=0.
+        )
+        self.decoder = TransformerDecoder(
+            dim=DIM, 
+            depth=dec_depth,
+            n_heads=8, 
+            head_dim=dec_head_dim, 
+            mlp_dim=MLP_DIM, 
+            dropout_rate=0.,
+            apply_softmax=True
+        )
+
+        self.upsample = nn.Upsample(scale_factor=4, mode='bilinear')
+        self.conv_out = nn.Sequential(
+            Conv3x3(EBD_DIM, EBD_DIM, norm=True, act=True),
+            Conv3x3(EBD_DIM, num_classes)
+        )
+
+    def _get_semantic_tokens(self, x):
+        b, c = paddle.shape(x)[:2]
+        att_map = self.conv_att(x)
+        att_map = att_map.reshape((b,self.token_len,1,-1))
+        att_map = F.softmax(att_map, axis=-1)
+        x = x.reshape((b,1,c,-1))
+        tokens = (x*att_map).sum(-1)
+        return tokens
+
+    def _get_reshaped_tokens(self, x):
+        if self.pool_mode == 'max':
+            x = F.adaptive_max_pool2d(x, (self.pool_size, self.pool_size))
+        elif self.pool_mode == 'avg':
+            x = F.adaptive_avg_pool2d(x, (self.pool_size, self.pool_size))
+        else:
+            x = x
+        tokens = x.transpose((0,2,3,1)).flatten(1,2)
+        return tokens
+
+    def encode(self, x):
+        if self.enc_with_pos:
+            x += self.enc_pos_embedding
+        x = self.encoder(x)
+        return x
+
+    def decode(self, x, m):
+        b, c, h, w = paddle.shape(x)
+        x = x.transpose((0,2,3,1)).flatten(1,2)
+        x = self.decoder(x, m)
+        x = x.transpose((0,2,1)).reshape((b,c,h,w))
+        return x
+
+    def forward(self, t1, t2):
+        # Extract features via shared backbone.
+        x1 = self.backbone(t1)
+        x2 = self.backbone(t2)
+
+        # Tokenization
+        if self.use_tokenizer:
+            token1 = self._get_semantic_tokens(x1)
+            token2 = self._get_semantic_tokens(x2)
+        else:
+            token1 = self._get_reshaped_tokens(x1)
+            token2 = self._get_reshaped_tokens(x2)
+
+        # Transformer encoder forward
+        token = paddle.concat([token1, token2], axis=1)
+        token = self.encode(token)
+        token1, token2 = paddle.chunk(token, 2, axis=1)
+
+        # Transformer decoder forward
+        y1 = self.decode(x1, token1)
+        y2 = self.decode(x2, token2)
+
+        # Feature differencing
+        y = paddle.abs(y1 - y2)
+        y = self.upsample(y)
+
+        # Classifier forward
+        pred = self.conv_out(y)
+        return pred,
+
+    def init_weight(self):
+        # Use the default initialization method.
+        pass
+
+
+class Residual(nn.Layer):
+    def __init__(self, fn):
+        super().__init__()
+        self.fn = fn
+
+    def forward(self, x, **kwargs):
+        return self.fn(x, **kwargs) + x
+
+
+class Residual2(nn.Layer):
+    def __init__(self, fn):
+        super().__init__()
+        self.fn = fn
+
+    def forward(self, x1, x2, **kwargs):
+        return self.fn(x1, x2, **kwargs) + x1
+
+
+class PreNorm(nn.Layer):
+    def __init__(self, dim, fn):
+        super().__init__()
+        self.norm = nn.LayerNorm(dim)
+        self.fn = fn
+
+    def forward(self, x, **kwargs):
+        return self.fn(self.norm(x), **kwargs)
+
+
+class PreNorm2(nn.Layer):
+    def __init__(self, dim, fn):
+        super().__init__()
+        self.norm = nn.LayerNorm(dim)
+        self.fn = fn
+
+    def forward(self, x1, x2, **kwargs):
+        return self.fn(self.norm(x1), self.norm(x2), **kwargs)
+
+
+class FeedForward(nn.Sequential):
+    def __init__(self, dim, hidden_dim, dropout_rate=0.):
+        super().__init__(
+            nn.Linear(dim, hidden_dim),
+            nn.GELU(),
+            nn.Dropout(dropout_rate),
+            nn.Linear(hidden_dim, dim),
+            nn.Dropout(dropout_rate)
+        )
+
+
+class CrossAttention(nn.Layer):
+    def __init__(self, dim, n_heads=8, head_dim=64, dropout_rate=0., apply_softmax=True):
+        super().__init__()
+
+        inner_dim = head_dim * n_heads
+        self.n_heads = n_heads
+        self.scale = dim ** -0.5
+
+        self.apply_softmax = apply_softmax
+        
+        self.fc_q = nn.Linear(dim, inner_dim, bias_attr=False)
+        self.fc_k = nn.Linear(dim, inner_dim, bias_attr=False)
+        self.fc_v = nn.Linear(dim, inner_dim, bias_attr=False)
+
+        self.fc_out = nn.Sequential(
+            nn.Linear(inner_dim, dim),
+            nn.Dropout(dropout_rate)
+        )
+
+    def forward(self, x, ref):
+        b, n = paddle.shape(x)[:2]
+        h = self.n_heads
+
+        q = self.fc_q(x)
+        k = self.fc_k(ref)
+        v = self.fc_v(ref)
+
+        q = q.reshape((b,n,h,-1)).transpose((0,2,1,3))
+        k = k.reshape((b,paddle.shape(ref)[1],h,-1)).transpose((0,2,1,3))
+        v = v.reshape((b,paddle.shape(ref)[1],h,-1)).transpose((0,2,1,3))
+
+        mult = paddle.matmul(q, k, transpose_y=True) * self.scale
+
+        if self.apply_softmax:
+            mult = F.softmax(mult, axis=-1)
+
+        out = paddle.matmul(mult, v)
+        out = out.transpose((0,2,1,3)).flatten(2)
+        return self.fc_out(out)
+
+
+class SelfAttention(CrossAttention):
+    def forward(self, x):
+        return super().forward(x, x)
+
+
+class TransformerEncoder(nn.Layer):
+    def __init__(self, dim, depth, n_heads, head_dim, mlp_dim, dropout_rate):
+        super().__init__()
+        self.layers = nn.LayerList([])
+        for _ in range(depth):
+            self.layers.append(nn.LayerList([
+                Residual(PreNorm(dim, SelfAttention(dim, n_heads, head_dim, dropout_rate))),
+                Residual(PreNorm(dim, FeedForward(dim, mlp_dim, dropout_rate)))
+            ]))
+
+    def forward(self, x):
+        for att, ff in self.layers:
+            x = att(x)
+            x = ff(x)
+        return x
+
+
+class TransformerDecoder(nn.Layer):
+    def __init__(self, dim, depth, n_heads, head_dim, mlp_dim, dropout_rate, apply_softmax=True):
+        super().__init__()
+        self.layers = nn.LayerList([])
+        for _ in range(depth):
+            self.layers.append(nn.LayerList([
+                Residual2(PreNorm2(dim, CrossAttention(dim, n_heads, head_dim, dropout_rate, apply_softmax))),
+                Residual(PreNorm(dim, FeedForward(dim, mlp_dim, dropout_rate)))
+            ]))
+
+    def forward(self, x, m):
+        for att, ff in self.layers:
+            x = att(x, m)
+            x = ff(x)
+        return x
+
+
+class Backbone(nn.Layer, KaimingInitMixin):
+    def __init__(
+        self, 
+        in_ch, out_ch=32,
+        arch='resnet18',
+        pretrained=True,
+        n_stages=5
+    ):
+        super().__init__()
+
+        expand = 1
+        strides = (2,1,2,1,1)
+        if arch == 'resnet18':
+            self.resnet = resnet.resnet18(pretrained=pretrained, strides=strides, norm_layer=get_norm_layer())
+        elif arch == 'resnet34':
+            self.resnet = resnet.resnet34(pretrained=pretrained, strides=strides, norm_layer=get_norm_layer())
+        else:
+            raise ValueError
+
+        self.n_stages = n_stages
+
+        if self.n_stages == 5:
+            itm_ch = 512 * expand
+        elif self.n_stages == 4:
+            itm_ch = 256 * expand
+        elif self.n_stages == 3:
+            itm_ch = 128 * expand
+        else:
+            raise ValueError
+            
+        self.upsample = nn.Upsample(scale_factor=2)
+        self.conv_out = Conv3x3(itm_ch, out_ch)
+
+        self._trim_resnet()
+
+        if in_ch != 3:
+            self.resnet.conv1 = nn.Conv2D(
+                in_ch, 
+                64,
+                kernel_size=7,
+                stride=2,
+                padding=3,
+                bias_attr=False
+            )
+
+        if not pretrained:
+            self.init_weight()
+
+    def forward(self, x):
+        y = self.resnet.conv1(x)
+        y = self.resnet.bn1(y)
+        y = self.resnet.relu(y)
+        y = self.resnet.maxpool(y)
+
+        y = self.resnet.layer1(y)
+        y = self.resnet.layer2(y)
+        y = self.resnet.layer3(y)
+        y = self.resnet.layer4(y)
+
+        y = self.upsample(y)
+
+        return self.conv_out(y)
+
+    def _trim_resnet(self):
+        if self.n_stages > 5:
+            raise ValueError
+
+        if self.n_stages < 5:
+            self.resnet.layer4 = Identity()
+
+        if self.n_stages <= 3:
+            self.resnet.layer3 = Identity()
+
+        self.resnet.avgpool = Identity()
+        self.resnet.fc = Identity()

paddlers/models/cd/models/dsamnet.py

@@ -0,0 +1,96 @@
+# Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import paddle
+import paddle.nn as nn
+import paddle.nn.functional as F
+
+
+from .layers import make_norm, Conv3x3, CBAM
+from .stanet import Backbone, Decoder
+
+
+class DSAMNet(nn.Layer):
+    """
+    The DSAMNet implementation based on PaddlePaddle.
+
+    The original article refers to
+        Q. Shi, et al., "A Deeply Supervised Attention Metric-Based Network and an Open Aerial Image Dataset for Remote Sensing 
+        Change Detection"
+        (https://ieeexplore.ieee.org/document/9467555).
+
+    Note that this implementation differs from the original work in two aspects:
+    1. We do not use multiple dilation rates in layer 4 of the ResNet backbone.
+    2. A classification head is used in place of the original metric learning-based head to stablize the training process.
+
+    Args:
+        in_channels (int): The number of bands of the input images.
+        num_classes (int): The number of target classes.
+        ca_ratio (int, optional): The channel reduction ratio for the channel attention module. Default: 8.
+        sa_kernel (int, optional): The size of the convolutional kernel used in the spatial attention module. Default: 7.
+    """
+    
+    def __init__(self, in_channels, num_classes, ca_ratio=8, sa_kernel=7):
+        super().__init__()
+
+        WIDTH = 64
+
+        self.backbone = Backbone(in_ch=in_channels, arch='resnet18', strides=(1,1,2,2,1))
+        self.decoder = Decoder(WIDTH)
+
+        self.cbam1 = CBAM(64, ratio=ca_ratio, kernel_size=sa_kernel)
+        self.cbam2 = CBAM(64, ratio=ca_ratio, kernel_size=sa_kernel)
+
+        self.dsl2 = DSLayer(64, num_classes, 32, stride=2, output_padding=1)
+        self.dsl3 = DSLayer(128, num_classes, 32, stride=4, output_padding=3)
+
+        self.conv_out = nn.Sequential(
+            Conv3x3(WIDTH, WIDTH, norm=True, act=True),
+            Conv3x3(WIDTH, num_classes)
+        )
+
+        self.init_weight()
+
+    def forward(self, t1, t2):
+        f1 = self.backbone(t1)
+        f2 = self.backbone(t2)
+
+        y1 = self.decoder(f1)
+        y2 = self.decoder(f2)
+
+        y1 = self.cbam1(y1)
+        y2 = self.cbam2(y2)
+
+        out = paddle.abs(y1-y2)
+        out = F.interpolate(out, size=paddle.shape(t1)[2:], mode='bilinear', align_corners=True)
+        pred = self.conv_out(out)
+
+        ds2 = self.dsl2(paddle.abs(f1[0]-f2[0]))
+        ds3 = self.dsl3(paddle.abs(f1[1]-f2[1]))
+
+        return pred, ds2, ds3
+
+    def init_weight(self):
+        pass
+
+
+class DSLayer(nn.Sequential):
+    def __init__(self, in_ch, out_ch, itm_ch, **convd_kwargs):
+        super().__init__(
+            nn.Conv2DTranspose(in_ch, itm_ch, kernel_size=3, padding=1, **convd_kwargs),
+            make_norm(itm_ch),
+            nn.ReLU(),
+            nn.Dropout2D(p=0.2),
+            nn.Conv2DTranspose(itm_ch, out_ch, kernel_size=3, padding=1)
+        )

paddlers/models/cd/models/dsifn.py

@@ -0,0 +1,209 @@
+# Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import paddle
+import paddle.nn as nn
+import paddle.nn.functional as F
+from paddle.vision.models import vgg16
+
+
+from .layers import Conv1x1, make_norm, ChannelAttention, SpatialAttention
+
+
+class DSIFN(nn.Layer):
+    """
+    The DSIFN implementation based on PaddlePaddle.
+
+    The original article refers to
+        C. Zhang, et al., "A deeply supervised image fusion network for change detection in high resolution bi-temporal remote 
+        sensing images"
+        (https://www.sciencedirect.com/science/article/pii/S0924271620301532).
+
+    Note that in this implementation, there is a flexible number of target classes.
+
+    Args:
+        num_classes (int): The number of target classes.
+        use_dropout (bool, optional): A bool value that indicates whether to use dropout layers. When the model is trained 
+            on a relatively small dataset, the dropout layers help prevent overfitting. Default: False.
+    """
+
+    def __init__(self, num_classes, use_dropout=False):
+        super().__init__()
+
+        self.encoder1 = self.encoder2 = VGG16FeaturePicker()
+
+        self.sa1 = SpatialAttention()
+        self.sa2= SpatialAttention()
+        self.sa3 = SpatialAttention()
+        self.sa4 = SpatialAttention()
+        self.sa5 = SpatialAttention()
+
+        self.ca1 = ChannelAttention(in_ch=1024)
+        self.bn_ca1 = make_norm(1024)
+        self.o1_conv1 = conv2d_bn(1024, 512, use_dropout)
+        self.o1_conv2 = conv2d_bn(512, 512, use_dropout)
+        self.bn_sa1 = make_norm(512)
+        self.o1_conv3 = Conv1x1(512, num_classes)
+        self.trans_conv1 = nn.Conv2DTranspose(512, 512, kernel_size=2, stride=2)
+
+        self.ca2 = ChannelAttention(in_ch=1536)
+        self.bn_ca2 = make_norm(1536)
+        self.o2_conv1 = conv2d_bn(1536, 512, use_dropout)
+        self.o2_conv2 = conv2d_bn(512, 256, use_dropout)
+        self.o2_conv3 = conv2d_bn(256, 256, use_dropout)
+        self.bn_sa2 = make_norm(256)
+        self.o2_conv4 = Conv1x1(256, num_classes)
+        self.trans_conv2 = nn.Conv2DTranspose(256, 256, kernel_size=2, stride=2)
+
+        self.ca3 = ChannelAttention(in_ch=768)
+        self.o3_conv1 = conv2d_bn(768, 256, use_dropout)
+        self.o3_conv2 = conv2d_bn(256, 128, use_dropout)
+        self.o3_conv3 = conv2d_bn(128, 128, use_dropout)
+        self.bn_sa3 = make_norm(128)
+        self.o3_conv4 = Conv1x1(128, num_classes)
+        self.trans_conv3 = nn.Conv2DTranspose(128, 128, kernel_size=2, stride=2)
+
+        self.ca4 = ChannelAttention(in_ch=384)
+        self.o4_conv1 = conv2d_bn(384, 128, use_dropout)
+        self.o4_conv2 = conv2d_bn(128, 64, use_dropout)
+        self.o4_conv3 = conv2d_bn(64, 64, use_dropout)
+        self.bn_sa4 = make_norm(64)
+        self.o4_conv4 = Conv1x1(64, num_classes)
+        self.trans_conv4 = nn.Conv2DTranspose(64, 64, kernel_size=2, stride=2)
+
+        self.ca5 = ChannelAttention(in_ch=192)
+        self.o5_conv1 = conv2d_bn(192, 64, use_dropout)
+        self.o5_conv2 = conv2d_bn(64, 32, use_dropout)
+        self.o5_conv3 = conv2d_bn(32, 16, use_dropout)
+        self.bn_sa5 = make_norm(16)
+        self.o5_conv4 = Conv1x1(16, num_classes)
+
+        self.init_weight()
+
+    def forward(self, t1, t2):
+        # Extract bi-temporal features.
+        with paddle.no_grad():
+            self.encoder1.eval(), self.encoder2.eval()
+            t1_feats = self.encoder1(t1)
+            t2_feats = self.encoder2(t2)
+
+        t1_f_l3, t1_f_l8, t1_f_l15, t1_f_l22, t1_f_l29 = t1_feats
+        t2_f_l3, t2_f_l8, t2_f_l15, t2_f_l22, t2_f_l29,= t2_feats
+
+        # Multi-level decoding
+        x = paddle.concat([t1_f_l29, t2_f_l29], axis=1)
+        x = self.o1_conv1(x)
+        x = self.o1_conv2(x)
+        x = self.sa1(x) * x
+        x = self.bn_sa1(x)
+
+        out1 = F.interpolate(
+            self.o1_conv3(x), 
+            size=paddle.shape(t1)[2:], 
+            mode='bilinear', 
+            align_corners=True
+        )
+
+        x = self.trans_conv1(x)
+        x = paddle.concat([x, t1_f_l22, t2_f_l22], axis=1)
+        x = self.ca2(x)*x
+        x = self.o2_conv1(x)
+        x = self.o2_conv2(x)
+        x = self.o2_conv3(x)
+        x = self.sa2(x) *x
+        x = self.bn_sa2(x)
+
+        out2 = F.interpolate(
+            self.o2_conv4(x), 
+            size=paddle.shape(t1)[2:], 
+            mode='bilinear', 
+            align_corners=True
+        )
+
+        x = self.trans_conv2(x)
+        x = paddle.concat([x, t1_f_l15, t2_f_l15], axis=1)
+        x = self.ca3(x)*x
+        x = self.o3_conv1(x)
+        x = self.o3_conv2(x)
+        x = self.o3_conv3(x)
+        x = self.sa3(x) *x
+        x = self.bn_sa3(x)
+
+        out3 = F.interpolate(
+            self.o3_conv4(x), 
+            size=paddle.shape(t1)[2:], 
+            mode='bilinear', 
+            align_corners=True
+        )
+
+        x = self.trans_conv3(x)
+        x = paddle.concat([x, t1_f_l8, t2_f_l8], axis=1)
+        x = self.ca4(x)*x
+        x = self.o4_conv1(x)
+        x = self.o4_conv2(x)
+        x = self.o4_conv3(x)
+        x = self.sa4(x) *x
+        x = self.bn_sa4(x)
+
+        out4 = F.interpolate(
+            self.o4_conv4(x), 
+            size=paddle.shape(t1)[2:], 
+            mode='bilinear', 
+            align_corners=True
+        )
+
+        x = self.trans_conv4(x)
+        x = paddle.concat([x, t1_f_l3, t2_f_l3], axis=1)
+        x = self.ca5(x)*x
+        x = self.o5_conv1(x)
+        x = self.o5_conv2(x)
+        x = self.o5_conv3(x)
+        x = self.sa5(x) *x
+        x = self.bn_sa5(x)
+
+        out5 = self.o5_conv4(x)
+
+        return out5, out4, out3, out2, out1
+
+    def init_weight(self):
+        # Do nothing
+        pass
+
+
+class VGG16FeaturePicker(nn.Layer):
+    def __init__(self, indices=(3,8,15,22,29)):
+        super().__init__()
+        features = list(vgg16(pretrained=True).features)[:30]
+        self.features = nn.LayerList(features)
+        self.features.eval()
+        self.indices = set(indices)
+
+    def forward(self, x):
+        picked_feats = []
+        for idx, model in enumerate(self.features):
+            x = model(x)
+            if idx in self.indices:
+                picked_feats.append(x)
+        return picked_feats
+
+
+def conv2d_bn(in_ch, out_ch, with_dropout=True):
+    lst = [
+        nn.Conv2D(in_ch, out_ch, kernel_size=3, stride=1, padding=1),
+        nn.PReLU(),
+        make_norm(out_ch),
+    ]
+    if with_dropout:
+        lst.append(nn.Dropout(p=0.6))
+    return nn.Sequential(*lst)

paddlers/models/cd/models/layers/__init__.py

@@ -0,0 +1,16 @@
+# Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from .blocks import *
+from .attention import ChannelAttention, SpatialAttention, CBAM

paddlers/models/cd/models/layers/attention.py

@@ -0,0 +1,96 @@
+# Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import paddle
+import paddle.nn as nn
+import paddle.nn.functional as F
+
+
+from .blocks import Conv1x1, BasicConv
+
+
+class ChannelAttention(nn.Layer):
+    """
+    The channel attention module implementation based on PaddlePaddle.
+
+    The original article refers to 
+        Sanghyun Woo, et al., "CBAM: Convolutional Block Attention Module"
+        (https://arxiv.org/abs/1807.06521).
+
+    Args:
+        in_ch (int): The number of channels of the input features.
+        ratio (int, optional): The channel reduction ratio. Default: 8.
+    """
+
+    def __init__(self, in_ch, ratio=8):
+        super().__init__()
+        self.avg_pool = nn.AdaptiveAvgPool2D(1)
+        self.max_pool = nn.AdaptiveMaxPool2D(1)
+        self.fc1 = Conv1x1(in_ch, in_ch//ratio, bias=False, act=True)
+        self.fc2 = Conv1x1(in_ch//ratio, in_ch, bias=False)
+
+    def forward(self,x):
+        avg_out = self.fc2(self.fc1(self.avg_pool(x)))
+        max_out = self.fc2(self.fc1(self.max_pool(x)))
+        out = avg_out + max_out
+        return F.sigmoid(out)
+
+
+class SpatialAttention(nn.Layer):
+    """
+    The spatial attention module implementation based on PaddlePaddle.
+
+    The original article refers to 
+        Sanghyun Woo, et al., "CBAM: Convolutional Block Attention Module"
+        (https://arxiv.org/abs/1807.06521).
+
+    Args:
+        kernel_size (int, optional): The size of the convolutional kernel. Default: 7.
+    """
+
+    def __init__(self, kernel_size=7):
+        super().__init__()
+        self.conv = BasicConv(2, 1, kernel_size, bias=False)
+
+    def forward(self, x):
+        avg_out = paddle.mean(x, axis=1, keepdim=True)
+        max_out = paddle.max(x, axis=1, keepdim=True)
+        x = paddle.concat([avg_out, max_out], axis=1)
+        x = self.conv(x)
+        return F.sigmoid(x)
+
+
+class CBAM(nn.Layer):
+    """
+    The CBAM implementation based on PaddlePaddle.
+
+    The original article refers to 
+        Sanghyun Woo, et al., "CBAM: Convolutional Block Attention Module"
+        (https://arxiv.org/abs/1807.06521).
+
+    Args:
+        in_ch (int): The number of channels of the input features.
+        ratio (int, optional): The channel reduction ratio for the channel attention module. Default: 8.
+        kernel_size (int, optional): The size of the convolutional kernel used in the spatial attention module. Default: 7.
+    """
+    
+    def __init__(self, in_ch, ratio=8, kernel_size=7):
+        super().__init__()
+        self.ca = ChannelAttention(in_ch, ratio=ratio)
+        self.sa = SpatialAttention(kernel_size=kernel_size)
+
+    def forward(self, x):
+        y = self.ca(x) * x
+        y = self.sa(y) * y
+        return y

paddlers/models/cd/models/layers/blocks.py

@@ -0,0 +1,142 @@
+# Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import paddle.nn as nn
+
+
+__all__ = [
+    'BasicConv', 'Conv1x1', 'Conv3x3', 'Conv7x7', 
+    'MaxPool2x2', 'MaxUnPool2x2', 
+    'ConvTransposed3x3',
+    'Identity',
+    'get_norm_layer', 'get_act_layer', 
+    'make_norm', 'make_act'
+]
+
+
+def get_norm_layer():
+    # TODO: select appropriate norm layer.
+    return nn.BatchNorm2D
+
+
+def get_act_layer():
+    # TODO: select appropriate activation layer.
+    return nn.ReLU
+
+
+def make_norm(*args, **kwargs):
+    norm_layer = get_norm_layer()
+    return norm_layer(*args, **kwargs)
+
+
+def make_act(*args, **kwargs):
+    act_layer = get_act_layer()
+    return act_layer(*args, **kwargs)
+
+
+class BasicConv(nn.Layer):
+    def __init__(
+        self, in_ch, out_ch, 
+        kernel_size, pad_mode='constant', 
+        bias='auto', norm=False, act=False, 
+        **kwargs
+    ):
+        super().__init__()
+        seq = []
+        if kernel_size >= 2:
+            seq.append(nn.Pad2D(kernel_size//2, mode=pad_mode))
+        seq.append(
+            nn.Conv2D(
+                in_ch, out_ch, kernel_size,
+                stride=1, padding=0,
+                bias_attr=(False if norm else None) if bias=='auto' else bias,
+                **kwargs
+            )
+        )
+        if norm:
+            if norm is True:
+                norm = make_norm(out_ch)
+            seq.append(norm)
+        if act:
+            if act is True:
+                act = make_act()
+            seq.append(act)
+        self.seq = nn.Sequential(*seq)
+
+    def forward(self, x):
+        return self.seq(x)
+
+
+class Conv1x1(BasicConv):
+    def __init__(self, in_ch, out_ch, pad_mode='constant', bias='auto', norm=False, act=False, **kwargs):
+        super().__init__(in_ch, out_ch, 1, pad_mode=pad_mode, bias=bias, norm=norm, act=act, **kwargs)
+
+
+class Conv3x3(BasicConv):
+    def __init__(self, in_ch, out_ch, pad_mode='constant', bias='auto', norm=False, act=False, **kwargs):
+        super().__init__(in_ch, out_ch, 3, pad_mode=pad_mode, bias=bias, norm=norm, act=act, **kwargs)
+
+
+class Conv7x7(BasicConv):
+    def __init__(self, in_ch, out_ch, pad_mode='constant', bias='auto', norm=False, act=False, **kwargs):
+        super().__init__(in_ch, out_ch, 7, pad_mode=pad_mode, bias=bias, norm=norm, act=act, **kwargs)
+
+
+class MaxPool2x2(nn.MaxPool2D):
+    def __init__(self, **kwargs):
+        super().__init__(kernel_size=2, stride=(2,2), padding=(0,0), **kwargs)
+
+
+class MaxUnPool2x2(nn.MaxUnPool2D):
+    def __init__(self, **kwargs):
+        super().__init__(kernel_size=2, stride=(2,2), padding=(0,0), **kwargs)
+
+
+class ConvTransposed3x3(nn.Layer):
+    def __init__(
+        self, in_ch, out_ch,
+        bias='auto', norm=False, act=False, 
+        **kwargs
+    ):
+        super().__init__()
+        seq = []
+        seq.append(
+            nn.Conv2DTranspose(
+                in_ch, out_ch, 3,
+                stride=2, padding=1,
+                bias_attr=(False if norm else None) if bias=='auto' else bias,
+                **kwargs
+            )
+        )
+        if norm:
+            if norm is True:
+                norm = make_norm(out_ch)
+            seq.append(norm)
+        if act:
+            if act is True:
+                act = make_act()
+            seq.append(act)
+        self.seq = nn.Sequential(*seq)
+
+    def forward(self, x):
+        return self.seq(x)
+
+
+class Identity(nn.Layer):
+    """A placeholder identity operator that accepts exactly one argument."""
+    def __init__(self, *args, **kwargs):
+        super().__init__()
+    
+    def forward(self, x):
+        return x

paddlers/models/cd/models/param_init.py

@@ -0,0 +1,86 @@
+# Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import paddle.nn as nn
+import paddle.nn.functional as F
+
+
+def normal_init(param, *args, **kwargs):
+    """
+    Initialize parameters with a normal distribution.
+
+    Args:
+        param (Tensor): The tensor that needs to be initialized.
+
+    Returns:
+        The initialized parameters.
+    """
+    
+    return nn.initializer.Normal(*args, **kwargs)(param)
+
+
+def kaiming_normal_init(param, *args, **kwargs):
+    """
+    Initialize parameters with the Kaiming normal distribution.
+
+    For more information about the Kaiming initialization method, please refer to
+        https://arxiv.org/abs/1502.01852
+
+    Args:
+        param (Tensor): The tensor that needs to be initialized.
+
+    Returns:
+        The initialized parameters.
+    """
+
+    return nn.initializer.KaimingNormal(*args, **kwargs)(param)
+
+
+def constant_init(param, *args, **kwargs):
+    """
+    Initialize parameters with constants.
+
+    Args:
+        param (Tensor): The tensor that needs to be initialized.
+
+    Returns:
+        The initialized parameters.
+    """
+
+    return nn.initializer.Constant(*args, **kwargs)(param)
+
+
+class KaimingInitMixin:
+    """
+    A mix-in that provides the Kaiming initialization functionality.
+
+    Examples:
+
+        from paddlers.models.cd.models.param_init import KaimingInitMixin
+
+        class CustomNet(nn.Layer, KaimingInitMixin):
+            def __init__(self, num_channels, num_classes):
+                super().__init__()
+                self.conv = nn.Conv2D(num_channels, num_classes, 3, 1, 0, bias_attr=False)
+                self.bn = nn.BatchNorm2D(num_classes)
+                self.init_weight()
+    """
+
+    def init_weight(self):
+        for layer in self.sublayers():
+            if isinstance(layer, nn.Conv2D):
+                kaiming_normal_init(layer.weight)
+            elif isinstance(layer, (nn.BatchNorm, nn.SyncBatchNorm)):
+                constant_init(layer.weight, value=1)
+                constant_init(layer.bias, value=0)

paddlers/models/cd/models/snunet.py

@@ -0,0 +1,155 @@
+# Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+import paddle
+import paddle.nn as nn
+import paddle.nn.functional as F
+
+
+from .layers import Conv1x1, MaxPool2x2, make_norm, ChannelAttention
+from .param_init import KaimingInitMixin
+
+
+class SNUNet(nn.Layer, KaimingInitMixin):
+    """
+    The SNUNet implementation based on PaddlePaddle.
+
+    The original article refers to
+        S. Fang, et al., "SNUNet-CD: A Densely Connected Siamese Network for Change Detection of VHR Images"
+        (https://ieeexplore.ieee.org/document/9355573).
+
+    Note that bilinear interpolation is adopted as the upsampling method, which is different from the paper.
+
+    Args:
+        in_channels (int): The number of bands of the input images.
+        num_classes (int): The number of target classes.
+        width (int, optional): The output channels of the first convolutional layer. Default: 32.
+    """
+    
+    def __init__(self, in_channels, num_classes, width=32):
+        super().__init__()
+
+        filters = (width, width*2, width*4, width*8, width*16)
+
+        self.conv0_0 = ConvBlockNested(in_channels, filters[0], filters[0])
+        self.conv1_0 = ConvBlockNested(filters[0], filters[1], filters[1])
+        self.conv2_0 = ConvBlockNested(filters[1], filters[2], filters[2])
+        self.conv3_0 = ConvBlockNested(filters[2], filters[3], filters[3])
+        self.conv4_0 = ConvBlockNested(filters[3], filters[4], filters[4])
+        self.down1 = MaxPool2x2()
+        self.down2 = MaxPool2x2()
+        self.down3 = MaxPool2x2()
+        self.down4 = MaxPool2x2()
+        self.up1_0 = Up(filters[1])
+        self.up2_0 = Up(filters[2])
+        self.up3_0 = Up(filters[3])
+        self.up4_0 = Up(filters[4])
+
+        self.conv0_1 = ConvBlockNested(filters[0]*2+filters[1], filters[0], filters[0])
+        self.conv1_1 = ConvBlockNested(filters[1]*2+filters[2], filters[1], filters[1])
+        self.conv2_1 = ConvBlockNested(filters[2]*2+filters[3], filters[2], filters[2])
+        self.conv3_1 = ConvBlockNested(filters[3]*2+filters[4], filters[3], filters[3])
+        self.up1_1 = Up(filters[1])
+        self.up2_1 = Up(filters[2])
+        self.up3_1 = Up(filters[3])
+
+        self.conv0_2 = ConvBlockNested(filters[0]*3+filters[1], filters[0], filters[0])
+        self.conv1_2 = ConvBlockNested(filters[1]*3+filters[2], filters[1], filters[1])
+        self.conv2_2 = ConvBlockNested(filters[2]*3+filters[3], filters[2], filters[2])
+        self.up1_2 = Up(filters[1])
+        self.up2_2 = Up(filters[2])
+
+        self.conv0_3 = ConvBlockNested(filters[0]*4+filters[1], filters[0], filters[0])
+        self.conv1_3 = ConvBlockNested(filters[1]*4+filters[2], filters[1], filters[1])
+        self.up1_3 = Up(filters[1])
+
+        self.conv0_4 = ConvBlockNested(filters[0]*5+filters[1], filters[0], filters[0])
+
+        self.ca_intra = ChannelAttention(filters[0], ratio=4)
+        self.ca_inter = ChannelAttention(filters[0]*4, ratio=16)
+
+        self.conv_out = Conv1x1(filters[0]*4, num_classes)
+
+        self.init_weight()
+
+    def forward(self, t1, t2):
+        x0_0_t1 = self.conv0_0(t1)
+        x1_0_t1 = self.conv1_0(self.down1(x0_0_t1))
+        x2_0_t1 = self.conv2_0(self.down2(x1_0_t1))
+        x3_0_t1 = self.conv3_0(self.down3(x2_0_t1))
+
+        x0_0_t2 = self.conv0_0(t2)
+        x1_0_t2 = self.conv1_0(self.down1(x0_0_t2))
+        x2_0_t2 = self.conv2_0(self.down2(x1_0_t2))
+        x3_0_t2 = self.conv3_0(self.down3(x2_0_t2))
+        x4_0_t2 = self.conv4_0(self.down4(x3_0_t2))
+
+        x0_1 = self.conv0_1(paddle.concat([x0_0_t1, x0_0_t2, self.up1_0(x1_0_t2)], 1))
+        x1_1 = self.conv1_1(paddle.concat([x1_0_t1, x1_0_t2, self.up2_0(x2_0_t2)], 1))
+        x0_2 = self.conv0_2(paddle.concat([x0_0_t1, x0_0_t2, x0_1, self.up1_1(x1_1)], 1))
+
+        x2_1 = self.conv2_1(paddle.concat([x2_0_t1, x2_0_t2, self.up3_0(x3_0_t2)], 1))
+        x1_2 = self.conv1_2(paddle.concat([x1_0_t1, x1_0_t2, x1_1, self.up2_1(x2_1)], 1))
+        x0_3 = self.conv0_3(paddle.concat([x0_0_t1, x0_0_t2, x0_1, x0_2, self.up1_2(x1_2)], 1))
+
+        x3_1 = self.conv3_1(paddle.concat([x3_0_t1, x3_0_t2, self.up4_0(x4_0_t2)], 1))
+        x2_2 = self.conv2_2(paddle.concat([x2_0_t1, x2_0_t2, x2_1, self.up3_1(x3_1)], 1))
+        x1_3 = self.conv1_3(paddle.concat([x1_0_t1, x1_0_t2, x1_1, x1_2, self.up2_2(x2_2)], 1))
+        x0_4 = self.conv0_4(paddle.concat([x0_0_t1, x0_0_t2, x0_1, x0_2, x0_3, self.up1_3(x1_3)], 1))
+
+        out = paddle.concat([x0_1, x0_2, x0_3, x0_4], 1)
+
+        intra = paddle.sum(paddle.stack([x0_1, x0_2, x0_3, x0_4]), axis=0)
+        m_intra = self.ca_intra(intra)
+        out = self.ca_inter(out) * (out + paddle.tile(m_intra, (1,4,1,1)))
+
+        pred = self.conv_out(out)
+        return pred,
+
+
+class ConvBlockNested(nn.Layer):
+    def __init__(self, in_ch, out_ch, mid_ch):
+        super().__init__()
+        self.act = nn.ReLU()
+        self.conv1 = nn.Conv2D(in_ch, mid_ch, kernel_size=3, padding=1)
+        self.bn1 = make_norm(mid_ch)
+        self.conv2 = nn.Conv2D(mid_ch, out_ch, kernel_size=3, padding=1)
+        self.bn2 = make_norm(out_ch)
+
+    def forward(self, x):
+        x = self.conv1(x)
+        identity = x
+        x = self.bn1(x)
+        x = self.act(x)
+
+        x = self.conv2(x)
+        x = self.bn2(x)
+        output = self.act(x + identity)
+        return output
+
+
+class Up(nn.Layer):
+    def __init__(self, in_ch, use_conv=False):
+        super().__init__()
+        if use_conv:
+            self.up = nn.Conv2DTranspose(in_ch, in_ch, 2, stride=2)
+        else:
+            self.up = nn.Upsample(scale_factor=2,
+                                  mode='bilinear',
+                                  align_corners=True)
+
+    def forward(self, x):
+        x = self.up(x)
+        return x

paddlers/models/cd/models/stanet.py

@@ -0,0 +1,298 @@
+# Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import paddle
+import paddle.nn as nn
+import paddle.nn.functional as F
+
+
+from .backbones import resnet
+from .layers import Conv1x1, Conv3x3, get_norm_layer, Identity
+from .param_init import KaimingInitMixin
+
+
+class STANet(nn.Layer):
+    """
+    The STANet implementation based on PaddlePaddle.
+
+    The original article refers to
+        H. Chen and Z. Shi, "A Spatial-Temporal Attention-Based Method and a New Dataset for Remote Sensing Image Change Detection"
+        (https://www.mdpi.com/2072-4292/12/10/1662).
+
+    Note that this implementation differs from the original work in two aspects:
+    1. We do not use multiple dilation rates in layer 4 of the ResNet backbone.
+    2. A classification head is used in place of the original metric learning-based head to stablize the training process.
+
+    Args:
+        in_channels (int): The number of bands of the input images.
+        num_classes (int): The number of target classes.
+        att_type (str, optional): The attention module used in the model. Options are 'PAM' and 'BAM'. Default: 'BAM'.
+        ds_factor (int, optional): The downsampling factor of the attention modules. When `ds_factor` is set to values 
+            greater than 1, the input features will first be processed by an average pooling layer with the kernel size of 
+            `ds_factor`, before being used to calculate the attention scores. Default: 1.
+
+    Raises:
+        ValueError: When `att_type` has an illeagal value (unsupported attention type).
+    """
+    
+    def __init__(
+        self, 
+        in_channels, 
+        num_classes, 
+        att_type='BAM', 
+        ds_factor=1
+    ):
+        super().__init__()
+
+        WIDTH = 64
+
+        self.extract = build_feat_extractor(in_ch=in_channels, width=WIDTH)
+        self.attend = build_sta_module(in_ch=WIDTH, att_type=att_type, ds=ds_factor)
+        self.conv_out = nn.Sequential(
+            Conv3x3(WIDTH, WIDTH, norm=True, act=True),
+            Conv3x3(WIDTH, num_classes)
+        )
+
+        self.init_weight()
+
+    def forward(self, t1, t2):
+        f1 = self.extract(t1)
+        f2 = self.extract(t2)
+
+        f1, f2 = self.attend(f1, f2)
+
+        y = paddle.abs(f1- f2)
+        y = F.interpolate(y, size=paddle.shape(t1)[2:], mode='bilinear', align_corners=True)
+
+        pred = self.conv_out(y)
+        return pred,
+
+    def init_weight(self):
+        # Do nothing here as the encoder and decoder weights have already been initialized.
+        # Note however that currently self.attend and self.conv_out use the default initilization method.
+        pass
+
+
+def build_feat_extractor(in_ch, width):
+    return nn.Sequential(
+        Backbone(in_ch, 'resnet18'),
+        Decoder(width)
+    )
+
+
+def build_sta_module(in_ch, att_type, ds):
+    if att_type == 'BAM':
+        return Attention(BAM(in_ch, ds))
+    elif att_type == 'PAM':
+        return Attention(PAM(in_ch, ds))
+    else:
+        raise ValueError
+
+
+class Backbone(nn.Layer, KaimingInitMixin):
+    def __init__(self, in_ch, arch, pretrained=True, strides=(2,1,2,2,2)):
+        super().__init__()
+
+        if arch == 'resnet18':
+            self.resnet = resnet.resnet18(pretrained=pretrained, strides=strides, norm_layer=get_norm_layer())
+        elif arch == 'resnet34':
+            self.resnet = resnet.resnet34(pretrained=pretrained, strides=strides, norm_layer=get_norm_layer())
+        elif arch == 'resnet50':
+            self.resnet = resnet.resnet50(pretrained=pretrained, strides=strides, norm_layer=get_norm_layer())
+        else:
+            raise ValueError
+
+        self._trim_resnet()
+
+        if in_ch != 3:
+            self.resnet.conv1 = nn.Conv2D(
+                in_ch, 
+                64,
+                kernel_size=7,
+                stride=strides[0],
+                padding=3,
+                bias_attr=False
+            )
+
+        if not pretrained:
+            self.init_weight()
+
+    def forward(self, x):
+        x = self.resnet.conv1(x)
+        x = self.resnet.bn1(x)
+        x = self.resnet.relu(x)
+        x = self.resnet.maxpool(x)
+
+        x1 = self.resnet.layer1(x)
+        x2 = self.resnet.layer2(x1)
+        x3 = self.resnet.layer3(x2)
+        x4 = self.resnet.layer4(x3)
+
+        return x1, x2, x3, x4
+
+    def _trim_resnet(self):
+        self.resnet.avgpool = Identity()
+        self.resnet.fc = Identity()
+
+
+class Decoder(nn.Layer, KaimingInitMixin):
+    def __init__(self, f_ch):
+        super().__init__()
+        self.dr1 = Conv1x1(64, 96, norm=True, act=True)
+        self.dr2 = Conv1x1(128, 96, norm=True, act=True)
+        self.dr3 = Conv1x1(256, 96, norm=True, act=True)
+        self.dr4 = Conv1x1(512, 96, norm=True, act=True)
+        self.conv_out = nn.Sequential(
+            Conv3x3(384, 256, norm=True, act=True),
+            nn.Dropout(0.5),
+            Conv1x1(256, f_ch, norm=True, act=True)
+        )
+
+        self.init_weight()
+
+    def forward(self, feats):
+        f1 = self.dr1(feats[0])
+        f2 = self.dr2(feats[1])
+        f3 = self.dr3(feats[2])
+        f4 = self.dr4(feats[3])
+
+        f2 = F.interpolate(f2, size=paddle.shape(f1)[2:], mode='bilinear', align_corners=True)
+        f3 = F.interpolate(f3, size=paddle.shape(f1)[2:], mode='bilinear', align_corners=True)
+        f4 = F.interpolate(f4, size=paddle.shape(f1)[2:], mode='bilinear', align_corners=True)
+
+        x = paddle.concat([f1, f2, f3, f4], axis=1)
+        y = self.conv_out(x)
+
+        return y
+
+
+class BAM(nn.Layer):
+    def __init__(self, in_ch, ds):
+        super().__init__()
+
+        self.ds = ds
+        self.pool = nn.AvgPool2D(self.ds)
+
+        self.val_ch = in_ch
+        self.key_ch = in_ch // 8
+        self.conv_q = Conv1x1(in_ch, self.key_ch)
+        self.conv_k = Conv1x1(in_ch, self.key_ch)
+        self.conv_v = Conv1x1(in_ch, self.val_ch)
+
+        self.softmax = nn.Softmax(axis=-1)
+
+    def forward(self, x):
+        x = x.flatten(-2)
+        x_rs = self.pool(x)
+        
+        b, c, h, w = paddle.shape(x_rs)
+        query = self.conv_q(x_rs).reshape((b,-1,h*w)).transpose((0,2,1))
+        key = self.conv_k(x_rs).reshape((b,-1,h*w))
+        energy = paddle.bmm(query, key)
+        energy = (self.key_ch**(-0.5)) * energy
+
+        attention = self.softmax(energy)
+
+        value = self.conv_v(x_rs).reshape((b,-1,w*h))
+
+        out = paddle.bmm(value, attention.transpose((0,2,1)))
+        out = out.reshape((b,c,h,w))
+
+        out = F.interpolate(out, scale_factor=self.ds)
+        out = out + x
+        return out.reshape(out.shape[:-1]+[out.shape[-1]//2, 2])
+
+
+class PAMBlock(nn.Layer):
+    def __init__(self, in_ch, scale=1, ds=1):
+        super().__init__()
+
+        self.scale = scale
+        self.ds = ds
+        self.pool = nn.AvgPool2D(self.ds)
+
+        self.val_ch = in_ch
+        self.key_ch = in_ch // 8
+        self.conv_q = Conv1x1(in_ch, self.key_ch, norm=True)
+        self.conv_k = Conv1x1(in_ch, self.key_ch, norm=True)
+        self.conv_v = Conv1x1(in_ch, self.val_ch)
+
+    def forward(self, x):
+        x_rs = self.pool(x)
+
+        # Get query, key, and value.
+        query = self.conv_q(x_rs)
+        key = self.conv_k(x_rs)
+        value = self.conv_v(x_rs)
+        
+        # Split the whole image into subregions.
+        b, c, h, w = paddle.shape(x_rs)
+        query = self._split_subregions(query)
+        key = self._split_subregions(key)
+        value = self._split_subregions(value)
+        
+        # Perform subregion-wise attention.
+        out = self._attend(query, key, value)
+
+        # Stack subregions to reconstruct the whole image.
+        out = self._recons_whole(out, b, c, h, w)
+        out = F.interpolate(out, scale_factor=self.ds)
+        return out
+
+    def _attend(self, query, key, value):
+        energy = paddle.bmm(query.transpose((0,2,1)), key)  # batch matrix multiplication
+        energy = (self.key_ch**(-0.5)) * energy
+        attention = F.softmax(energy, axis=-1)
+        out = paddle.bmm(value, attention.transpose((0,2,1)))
+        return out
+
+    def _split_subregions(self, x):
+        b, c, h, w = paddle.shape(x)
+        assert h % self.scale == 0 and w % self.scale == 0
+        x = x.reshape((b, c, self.scale, h//self.scale, self.scale, w//self.scale))
+        x = x.transpose((0,2,4,1,3,5)).reshape((b*self.scale*self.scale, c, -1))
+        return x
+
+    def _recons_whole(self, x, b, c, h, w):
+        x = x.reshape((b, self.scale, self.scale, c, h//self.scale, w//self.scale))
+        x = x.transpose((0,3,1,4,2,5)).reshape((b, c, h, w))
+        return x
+
+
+class PAM(nn.Layer):
+    def __init__(self, in_ch, ds, scales=(1,2,4,8)):
+        super().__init__()
+
+        self.stages = nn.LayerList([
+            PAMBlock(in_ch, scale=s, ds=ds)
+            for s in scales
+        ])
+        self.conv_out = Conv1x1(in_ch*len(scales), in_ch, bias=False)
+
+    def forward(self, x):
+        x = x.flatten(-2)
+        res = [stage(x) for stage in self.stages]
+        out = self.conv_out(paddle.concat(res, axis=1))
+        return out.reshape(out.shape[:-1]+[out.shape[-1]//2, 2])
+
+
+class Attention(nn.Layer):
+    def __init__(self, att):
+        super().__init__()
+        self.att = att
+
+    def forward(self, x1, x2):
+        x = paddle.stack([x1, x2], axis=-1)
+        y = self.att(x)
+        return y[...,0], y[...,1]

paddlers/models/cd/models/unet_ef.py

@@ -0,0 +1,201 @@
+# Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import paddle
+import paddle.nn as nn
+import paddle.nn.functional as F
+
+
+from .layers import Conv3x3, MaxPool2x2, ConvTransposed3x3, Identity
+from .param_init import normal_init, constant_init
+
+
+class UNetEarlyFusion(nn.Layer):
+    """
+    The FC-EF implementation based on PaddlePaddle.
+
+    The original article refers to
+        Caye Daudt, R., et al. "Fully convolutional siamese networks for change detection"
+        (https://arxiv.org/abs/1810.08462).
+
+    Args:
+        in_channels (int): The number of bands of the input images.
+        num_classes (int): The number of target classes.
+        use_dropout (bool, optional): A bool value that indicates whether to use dropout layers. When the model is trained 
+            on a relatively small dataset, the dropout layers help prevent overfitting. Default: False.
+    """
+
+    def __init__(
+        self, 
+        in_channels, 
+        num_classes, 
+        use_dropout=False
+    ):
+        super().__init__()
+
+        C1, C2, C3, C4, C5 = 16, 32, 64, 128, 256
+
+        self.use_dropout = use_dropout
+
+        self.conv11 = Conv3x3(in_channels, C1, norm=True, act=True)
+        self.do11 = self._make_dropout()
+        self.conv12 = Conv3x3(C1, C1, norm=True, act=True)
+        self.do12 = self._make_dropout()
+        self.pool1 = MaxPool2x2()
+
+        self.conv21 = Conv3x3(C1, C2, norm=True, act=True)
+        self.do21 = self._make_dropout()
+        self.conv22 = Conv3x3(C2, C2, norm=True, act=True)
+        self.do22 = self._make_dropout()
+        self.pool2 = MaxPool2x2()
+
+        self.conv31 = Conv3x3(C2, C3, norm=True, act=True)
+        self.do31 = self._make_dropout()
+        self.conv32 = Conv3x3(C3, C3, norm=True, act=True)
+        self.do32 = self._make_dropout()
+        self.conv33 = Conv3x3(C3, C3, norm=True, act=True)
+        self.do33 = self._make_dropout()
+        self.pool3 = MaxPool2x2()
+
+        self.conv41 = Conv3x3(C3, C4, norm=True, act=True)
+        self.do41 = self._make_dropout()
+        self.conv42 = Conv3x3(C4, C4, norm=True, act=True)
+        self.do42 = self._make_dropout()
+        self.conv43 = Conv3x3(C4, C4, norm=True, act=True)
+        self.do43 = self._make_dropout()
+        self.pool4 = MaxPool2x2()
+
+        self.upconv4 = ConvTransposed3x3(C4, C4, output_padding=1)
+
+        self.conv43d = Conv3x3(C5, C4, norm=True, act=True)
+        self.do43d = self._make_dropout()
+        self.conv42d = Conv3x3(C4, C4, norm=True, act=True)
+        self.do42d = self._make_dropout()
+        self.conv41d = Conv3x3(C4, C3, norm=True, act=True)
+        self.do41d = self._make_dropout()
+
+        self.upconv3 = ConvTransposed3x3(C3, C3, output_padding=1)
+
+        self.conv33d = Conv3x3(C4, C3, norm=True, act=True)
+        self.do33d = self._make_dropout()
+        self.conv32d = Conv3x3(C3, C3, norm=True, act=True)
+        self.do32d = self._make_dropout()
+        self.conv31d = Conv3x3(C3, C2, norm=True, act=True)
+        self.do31d = self._make_dropout()
+
+        self.upconv2 = ConvTransposed3x3(C2, C2, output_padding=1)
+
+        self.conv22d = Conv3x3(C3, C2, norm=True, act=True)
+        self.do22d = self._make_dropout()
+        self.conv21d = Conv3x3(C2, C1, norm=True, act=True)
+        self.do21d = self._make_dropout()
+
+        self.upconv1 = ConvTransposed3x3(C1, C1, output_padding=1)
+
+        self.conv12d = Conv3x3(C2, C1, norm=True, act=True)
+        self.do12d = self._make_dropout()
+        self.conv11d = Conv3x3(C1, num_classes)
+
+        self.init_weight()
+
+    def forward(self, t1, t2):
+        x = paddle.concat([t1, t2], axis=1)
+
+        # Stage 1
+        x11 = self.do11(self.conv11(x))
+        x12 = self.do12(self.conv12(x11))
+        x1p = self.pool1(x12)
+
+        # Stage 2
+        x21 = self.do21(self.conv21(x1p))
+        x22 = self.do22(self.conv22(x21))
+        x2p = self.pool2(x22)
+
+        # Stage 3
+        x31 = self.do31(self.conv31(x2p))
+        x32 = self.do32(self.conv32(x31))
+        x33 = self.do33(self.conv33(x32))
+        x3p = self.pool3(x33)
+
+        # Stage 4
+        x41 = self.do41(self.conv41(x3p))
+        x42 = self.do42(self.conv42(x41))
+        x43 = self.do43(self.conv43(x42))
+        x4p = self.pool4(x43)
+
+        # Stage 4d
+        x4d = self.upconv4(x4p)
+        pad4 = (
+            0, 
+            paddle.shape(x43)[3]-paddle.shape(x4d)[3], 
+            0, 
+            paddle.shape(x43)[2]-paddle.shape(x4d)[2]
+        )
+        x4d = paddle.concat([F.pad(x4d, pad=pad4, mode='replicate'), x43], 1)
+        x43d = self.do43d(self.conv43d(x4d))
+        x42d = self.do42d(self.conv42d(x43d))
+        x41d = self.do41d(self.conv41d(x42d))
+
+        # Stage 3d
+        x3d = self.upconv3(x41d)
+        pad3 = (
+            0, 
+            paddle.shape(x33)[3]-paddle.shape(x3d)[3], 
+            0, 
+            paddle.shape(x33)[2]-paddle.shape(x3d)[2]
+        )
+        x3d = paddle.concat([F.pad(x3d, pad=pad3, mode='replicate'), x33], 1)
+        x33d = self.do33d(self.conv33d(x3d))
+        x32d = self.do32d(self.conv32d(x33d))
+        x31d = self.do31d(self.conv31d(x32d))
+
+        # Stage 2d
+        x2d = self.upconv2(x31d)
+        pad2 = (
+            0, 
+            paddle.shape(x22)[3]-paddle.shape(x2d)[3], 
+            0, 
+            paddle.shape(x22)[2]-paddle.shape(x2d)[2]
+        )
+        x2d = paddle.concat([F.pad(x2d, pad=pad2, mode='replicate'), x22], 1)
+        x22d = self.do22d(self.conv22d(x2d))
+        x21d = self.do21d(self.conv21d(x22d))
+
+        # Stage 1d
+        x1d = self.upconv1(x21d)
+        pad1 = (
+            0, 
+            paddle.shape(x12)[3]-paddle.shape(x1d)[3], 
+            0, 
+            paddle.shape(x12)[2]-paddle.shape(x1d)[2]
+        )
+        x1d = paddle.concat([F.pad(x1d, pad=pad1, mode='replicate'), x12], 1)
+        x12d = self.do12d(self.conv12d(x1d))
+        x11d = self.conv11d(x12d)
+
+        return x11d,
+
+    def init_weight(self):
+        for sublayer in self.sublayers():
+            if isinstance(sublayer, nn.Conv2D):
+                normal_init(sublayer.weight, std=0.001)
+            elif isinstance(sublayer, (nn.BatchNorm, nn.SyncBatchNorm)):
+                constant_init(sublayer.weight, value=1.0)
+                constant_init(sublayer.bias, value=0.0)
+
+    def _make_dropout(self):
+        if self.use_dropout:
+            return nn.Dropout2D(p=0.2)
+        else:
+            return Identity()

paddlers/models/cd/models/unet_siamconc.py

@@ -0,0 +1,224 @@
+# Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import paddle
+import paddle.nn as nn
+import paddle.nn.functional as F
+
+
+from .layers import Conv3x3, MaxPool2x2, ConvTransposed3x3, Identity
+from .param_init import normal_init, constant_init
+
+
+class UNetSiamConc(nn.Layer):
+    """
+    The FC-Siam-conc implementation based on PaddlePaddle.
+
+    The original article refers to
+        Caye Daudt, R., et al. "Fully convolutional siamese networks for change detection"
+        (https://arxiv.org/abs/1810.08462).
+
+    Args:
+        in_channels (int): The number of bands of the input images.
+        num_classes (int): The number of target classes.
+        use_dropout (bool, optional): A bool value that indicates whether to use dropout layers. When the model is trained 
+            on a relatively small dataset, the dropout layers help prevent overfitting. Default: False.
+    """
+    
+    def __init__(
+        self, 
+        in_channels, 
+        num_classes, 
+        use_dropout=False
+    ):
+        super().__init__()
+
+        C1, C2, C3, C4, C5 = 16, 32, 64, 128, 256
+
+        self.use_dropout = use_dropout
+
+        self.conv11 = Conv3x3(in_channels, C1, norm=True, act=True)
+        self.do11 = self._make_dropout()
+        self.conv12 = Conv3x3(C1, C1, norm=True, act=True)
+        self.do12 = self._make_dropout()
+        self.pool1 = MaxPool2x2()
+
+        self.conv21 = Conv3x3(C1, C2, norm=True, act=True)
+        self.do21 = self._make_dropout()
+        self.conv22 = Conv3x3(C2, C2, norm=True, act=True)
+        self.do22 = self._make_dropout()
+        self.pool2 = MaxPool2x2()
+
+        self.conv31 = Conv3x3(C2, C3, norm=True, act=True)
+        self.do31 = self._make_dropout()
+        self.conv32 = Conv3x3(C3, C3, norm=True, act=True)
+        self.do32 = self._make_dropout()
+        self.conv33 = Conv3x3(C3, C3, norm=True, act=True)
+        self.do33 = self._make_dropout()
+        self.pool3 = MaxPool2x2()
+
+        self.conv41 = Conv3x3(C3, C4, norm=True, act=True)
+        self.do41 = self._make_dropout()
+        self.conv42 = Conv3x3(C4, C4, norm=True, act=True)
+        self.do42 = self._make_dropout()
+        self.conv43 = Conv3x3(C4, C4, norm=True, act=True)
+        self.do43 = self._make_dropout()
+        self.pool4 = MaxPool2x2()
+
+        self.upconv4 = ConvTransposed3x3(C4, C4, output_padding=1)
+
+        self.conv43d = Conv3x3(C5+C4, C4, norm=True, act=True)
+        self.do43d = self._make_dropout()
+        self.conv42d = Conv3x3(C4, C4, norm=True, act=True)
+        self.do42d = self._make_dropout()
+        self.conv41d = Conv3x3(C4, C3, norm=True, act=True)
+        self.do41d = self._make_dropout()
+
+        self.upconv3 = ConvTransposed3x3(C3, C3, output_padding=1)
+
+        self.conv33d = Conv3x3(C4+C3, C3, norm=True, act=True)
+        self.do33d = self._make_dropout()
+        self.conv32d = Conv3x3(C3, C3, norm=True, act=True)
+        self.do32d = self._make_dropout()
+        self.conv31d = Conv3x3(C3, C2, norm=True, act=True)
+        self.do31d = self._make_dropout()
+
+        self.upconv2 = ConvTransposed3x3(C2, C2, output_padding=1)
+
+        self.conv22d = Conv3x3(C3+C2, C2, norm=True, act=True)
+        self.do22d = self._make_dropout()
+        self.conv21d = Conv3x3(C2, C1, norm=True, act=True)
+        self.do21d = self._make_dropout()
+
+        self.upconv1 = ConvTransposed3x3(C1, C1, output_padding=1)
+
+        self.conv12d = Conv3x3(C2+C1, C1, norm=True, act=True)
+        self.do12d = self._make_dropout()
+        self.conv11d = Conv3x3(C1, num_classes)
+
+        self.init_weight()
+
+    def forward(self, t1, t2):
+        # Encode t1
+        # Stage 1
+        x11 = self.do11(self.conv11(t1))
+        x12_1 = self.do12(self.conv12(x11))
+        x1p = self.pool1(x12_1)
+
+        # Stage 2
+        x21 = self.do21(self.conv21(x1p))
+        x22_1 = self.do22(self.conv22(x21))
+        x2p = self.pool2(x22_1)
+
+        # Stage 3
+        x31 = self.do31(self.conv31(x2p))
+        x32 = self.do32(self.conv32(x31))
+        x33_1 = self.do33(self.conv33(x32))
+        x3p = self.pool3(x33_1)
+
+        # Stage 4
+        x41 = self.do41(self.conv41(x3p))
+        x42 = self.do42(self.conv42(x41))
+        x43_1 = self.do43(self.conv43(x42))
+        x4p = self.pool4(x43_1)
+
+        # Encode t2
+        # Stage 1
+        x11 = self.do11(self.conv11(t2))
+        x12_2 = self.do12(self.conv12(x11))
+        x1p = self.pool1(x12_2)
+
+        # Stage 2
+        x21 = self.do21(self.conv21(x1p))
+        x22_2 = self.do22(self.conv22(x21))
+        x2p = self.pool2(x22_2)
+
+        # Stage 3
+        x31 = self.do31(self.conv31(x2p))
+        x32 = self.do32(self.conv32(x31))
+        x33_2 = self.do33(self.conv33(x32))
+        x3p = self.pool3(x33_2)
+
+        # Stage 4
+        x41 = self.do41(self.conv41(x3p))
+        x42 = self.do42(self.conv42(x41))
+        x43_2 = self.do43(self.conv43(x42))
+        x4p = self.pool4(x43_2)
+
+        # Decode
+        # Stage 4d
+        x4d = self.upconv4(x4p)
+        pad4 = (
+            0, 
+            paddle.shape(x43_1)[3]-paddle.shape(x4d)[3], 
+            0, 
+            paddle.shape(x43_1)[2]-paddle.shape(x4d)[2]
+        )
+        x4d = paddle.concat([F.pad(x4d, pad=pad4, mode='replicate'), x43_1, x43_2], 1)
+        x43d = self.do43d(self.conv43d(x4d))
+        x42d = self.do42d(self.conv42d(x43d))
+        x41d = self.do41d(self.conv41d(x42d))
+
+        # Stage 3d
+        x3d = self.upconv3(x41d)
+        pad3 = (
+            0, 
+            paddle.shape(x33_1)[3]-paddle.shape(x3d)[3], 
+            0, 
+            paddle.shape(x33_1)[2]-paddle.shape(x3d)[2]
+        )
+        x3d = paddle.concat([F.pad(x3d, pad=pad3, mode='replicate'), x33_1, x33_2], 1)
+        x33d = self.do33d(self.conv33d(x3d))
+        x32d = self.do32d(self.conv32d(x33d))
+        x31d = self.do31d(self.conv31d(x32d))
+
+        # Stage 2d
+        x2d = self.upconv2(x31d)
+        pad2 = (
+            0, 
+            paddle.shape(x22_1)[3]-paddle.shape(x2d)[3], 
+            0, 
+            paddle.shape(x22_1)[2]-paddle.shape(x2d)[2]
+        )
+        x2d = paddle.concat([F.pad(x2d, pad=pad2, mode='replicate'), x22_1, x22_2], 1)
+        x22d = self.do22d(self.conv22d(x2d))
+        x21d = self.do21d(self.conv21d(x22d))
+
+        # Stage 1d
+        x1d = self.upconv1(x21d)
+        pad1 = (
+            0, 
+            paddle.shape(x12_1)[3]-paddle.shape(x1d)[3], 
+            0, 
+            paddle.shape(x12_1)[2]-paddle.shape(x1d)[2]
+        )
+        x1d = paddle.concat([F.pad(x1d, pad=pad1, mode='replicate'), x12_1, x12_2], 1)
+        x12d = self.do12d(self.conv12d(x1d))
+        x11d = self.conv11d(x12d)
+
+        return x11d,
+
+    def init_weight(self):
+        for sublayer in self.sublayers():
+            if isinstance(sublayer, nn.Conv2D):
+                normal_init(sublayer.weight, std=0.001)
+            elif isinstance(sublayer, (nn.BatchNorm, nn.SyncBatchNorm)):
+                constant_init(sublayer.weight, value=1.0)
+                constant_init(sublayer.bias, value=0.0)
+
+    def _make_dropout(self):
+        if self.use_dropout:
+            return nn.Dropout2D(p=0.2)
+        else:
+            return Identity()

paddlers/models/cd/models/unet_siamdiff.py

@@ -0,0 +1,224 @@
+# Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import paddle
+import paddle.nn as nn
+import paddle.nn.functional as F
+
+
+from .layers import Conv3x3, MaxPool2x2, ConvTransposed3x3, Identity
+from .param_init import normal_init, constant_init
+
+
+class UNetSiamDiff(nn.Layer):
+    """
+    The FC-Siam-diff implementation based on PaddlePaddle.
+
+    The original article refers to
+        Caye Daudt, R., et al. "Fully convolutional siamese networks for change detection"
+        (https://arxiv.org/abs/1810.08462).
+
+    Args:
+        in_channels (int): The number of bands of the input images.
+        num_classes (int): The number of target classes.
+        use_dropout (bool, optional): A bool value that indicates whether to use dropout layers. When the model is trained 
+            on a relatively small dataset, the dropout layers help prevent overfitting. Default: False.
+    """
+    
+    def __init__(
+        self, 
+        in_channels, 
+        num_classes, 
+        use_dropout=False
+    ):
+        super().__init__()
+
+        C1, C2, C3, C4, C5 = 16, 32, 64, 128, 256
+
+        self.use_dropout = use_dropout
+
+        self.conv11 = Conv3x3(in_channels, C1, norm=True, act=True)
+        self.do11 = self._make_dropout()
+        self.conv12 = Conv3x3(C1, C1, norm=True, act=True)
+        self.do12 = self._make_dropout()
+        self.pool1 = MaxPool2x2()
+
+        self.conv21 = Conv3x3(C1, C2, norm=True, act=True)
+        self.do21 = self._make_dropout()
+        self.conv22 = Conv3x3(C2, C2, norm=True, act=True)
+        self.do22 = self._make_dropout()
+        self.pool2 = MaxPool2x2()
+
+        self.conv31 = Conv3x3(C2, C3, norm=True, act=True)
+        self.do31 = self._make_dropout()
+        self.conv32 = Conv3x3(C3, C3, norm=True, act=True)
+        self.do32 = self._make_dropout()
+        self.conv33 = Conv3x3(C3, C3, norm=True, act=True)
+        self.do33 = self._make_dropout()
+        self.pool3 = MaxPool2x2()
+
+        self.conv41 = Conv3x3(C3, C4, norm=True, act=True)
+        self.do41 = self._make_dropout()
+        self.conv42 = Conv3x3(C4, C4, norm=True, act=True)
+        self.do42 = self._make_dropout()
+        self.conv43 = Conv3x3(C4, C4, norm=True, act=True)
+        self.do43 = self._make_dropout()
+        self.pool4 = MaxPool2x2()
+
+        self.upconv4 = ConvTransposed3x3(C4, C4, output_padding=1)
+
+        self.conv43d = Conv3x3(C5, C4, norm=True, act=True)
+        self.do43d = self._make_dropout()
+        self.conv42d = Conv3x3(C4, C4, norm=True, act=True)
+        self.do42d = self._make_dropout()
+        self.conv41d = Conv3x3(C4, C3, norm=True, act=True)
+        self.do41d = self._make_dropout()
+
+        self.upconv3 = ConvTransposed3x3(C3, C3, output_padding=1)
+
+        self.conv33d = Conv3x3(C4, C3, norm=True, act=True)
+        self.do33d = self._make_dropout()
+        self.conv32d = Conv3x3(C3, C3, norm=True, act=True)
+        self.do32d = self._make_dropout()
+        self.conv31d = Conv3x3(C3, C2, norm=True, act=True)
+        self.do31d = self._make_dropout()
+
+        self.upconv2 = ConvTransposed3x3(C2, C2, output_padding=1)
+
+        self.conv22d = Conv3x3(C3, C2, norm=True, act=True)
+        self.do22d = self._make_dropout()
+        self.conv21d = Conv3x3(C2, C1, norm=True, act=True)
+        self.do21d = self._make_dropout()
+
+        self.upconv1 = ConvTransposed3x3(C1, C1, output_padding=1)
+
+        self.conv12d = Conv3x3(C2, C1, norm=True, act=True)
+        self.do12d = self._make_dropout()
+        self.conv11d = Conv3x3(C1, num_classes)
+
+        self.init_weight()
+
+    def forward(self, t1, t2):
+        # Encode t1
+        # Stage 1
+        x11 = self.do11(self.conv11(t1))
+        x12_1 = self.do12(self.conv12(x11))
+        x1p = self.pool1(x12_1)
+
+        # Stage 2
+        x21 = self.do21(self.conv21(x1p))
+        x22_1 = self.do22(self.conv22(x21))
+        x2p = self.pool2(x22_1)
+
+        # Stage 3
+        x31 = self.do31(self.conv31(x2p))
+        x32 = self.do32(self.conv32(x31))
+        x33_1 = self.do33(self.conv33(x32))
+        x3p = self.pool3(x33_1)
+
+        # Stage 4
+        x41 = self.do41(self.conv41(x3p))
+        x42 = self.do42(self.conv42(x41))
+        x43_1 = self.do43(self.conv43(x42))
+        x4p = self.pool4(x43_1)
+
+        # Encode t2
+        # Stage 1
+        x11 = self.do11(self.conv11(t2))
+        x12_2 = self.do12(self.conv12(x11))
+        x1p = self.pool1(x12_2)
+
+        # Stage 2
+        x21 = self.do21(self.conv21(x1p))
+        x22_2 = self.do22(self.conv22(x21))
+        x2p = self.pool2(x22_2)
+
+        # Stage 3
+        x31 = self.do31(self.conv31(x2p))
+        x32 = self.do32(self.conv32(x31))
+        x33_2 = self.do33(self.conv33(x32))
+        x3p = self.pool3(x33_2)
+
+        # Stage 4
+        x41 = self.do41(self.conv41(x3p))
+        x42 = self.do42(self.conv42(x41))
+        x43_2 = self.do43(self.conv43(x42))
+        x4p = self.pool4(x43_2)
+
+        # Decode
+        # Stage 4d
+        x4d = self.upconv4(x4p)
+        pad4 = (
+            0, 
+            paddle.shape(x43_1)[3]-paddle.shape(x4d)[3], 
+            0, 
+            paddle.shape(x43_1)[2]-paddle.shape(x4d)[2]
+        )
+        x4d = paddle.concat([F.pad(x4d, pad=pad4, mode='replicate'), paddle.abs(x43_1-x43_2)], 1)
+        x43d = self.do43d(self.conv43d(x4d))
+        x42d = self.do42d(self.conv42d(x43d))
+        x41d = self.do41d(self.conv41d(x42d))
+
+        # Stage 3d
+        x3d = self.upconv3(x41d)
+        pad3 = (
+            0, 
+            paddle.shape(x33_1)[3]-paddle.shape(x3d)[3], 
+            0, 
+            paddle.shape(x33_1)[2]-paddle.shape(x3d)[2]
+        )
+        x3d = paddle.concat([F.pad(x3d, pad=pad3, mode='replicate'), paddle.abs(x33_1-x33_2)], 1)
+        x33d = self.do33d(self.conv33d(x3d))
+        x32d = self.do32d(self.conv32d(x33d))
+        x31d = self.do31d(self.conv31d(x32d))
+
+        # Stage 2d
+        x2d = self.upconv2(x31d)
+        pad2 = (
+            0, 
+            paddle.shape(x22_1)[3]-paddle.shape(x2d)[3], 
+            0, 
+            paddle.shape(x22_1)[2]-paddle.shape(x2d)[2]
+        )
+        x2d = paddle.concat([F.pad(x2d, pad=pad2, mode='replicate'), paddle.abs(x22_1-x22_2)], 1)
+        x22d = self.do22d(self.conv22d(x2d))
+        x21d = self.do21d(self.conv21d(x22d))
+
+        # Stage 1d
+        x1d = self.upconv1(x21d)
+        pad1 = (
+            0, 
+            paddle.shape(x12_1)[3]-paddle.shape(x1d)[3], 
+            0, 
+            paddle.shape(x12_1)[2]-paddle.shape(x1d)[2]
+        )
+        x1d = paddle.concat([F.pad(x1d, pad=pad1, mode='replicate'), paddle.abs(x12_1-x12_2)], 1)
+        x12d = self.do12d(self.conv12d(x1d))
+        x11d = self.conv11d(x12d)
+
+        return x11d,
+
+    def init_weight(self):
+        for sublayer in self.sublayers():
+            if isinstance(sublayer, nn.Conv2D):
+                normal_init(sublayer.weight, std=0.001)
+            elif isinstance(sublayer, (nn.BatchNorm, nn.SyncBatchNorm)):
+                constant_init(sublayer.weight, value=1.0)
+                constant_init(sublayer.bias, value=0.0)
+
+    def _make_dropout(self):
+        if self.use_dropout:
+            return nn.Dropout2D(p=0.2)
+        else:
+            return Identity()

paddlers/tasks/changedetector.py

@@ -31,7 +31,7 @@ from paddlers.utils.checkpoint import seg_pretrain_weights_dict
 from paddlers.transforms import ImgDecoder, Resize
 import paddlers.models.cd as cd
 
-__all__ = ["CDNet"]
+__all__ = ["CDNet", "UNetEarlyFusion", "UNetSiamConc", "UNetSiamDiff", "STANet", "BIT", "SNUNet", "DSIFN", "DSAMNet"]
 
 
 class BaseChangeDetector(BaseModel):
@@ -663,3 +663,190 @@ class CDNet(BaseChangeDetector):
             num_classes=num_classes,
             use_mixed_loss=use_mixed_loss,
             **params)
+
+
+class UNetEarlyFusion(BaseChangeDetector):
+    def __init__(self,
+                 num_classes=2,
+                 use_mixed_loss=False,
+                 in_channels=6,
+                 use_dropout=False,
+                 **params):
+        params.update({
+            'in_channels': in_channels,
+            'use_dropout': use_dropout
+        })
+        super(UNetEarlyFusion, self).__init__(
+            model_name='UNetEarlyFusion',
+            num_classes=num_classes,
+            use_mixed_loss=use_mixed_loss,
+            **params)
+
+
+class UNetSiamConc(BaseChangeDetector):
+    def __init__(self,
+                 num_classes=2,
+                 use_mixed_loss=False,
+                 in_channels=3,
+                 use_dropout=False,
+                 **params):
+        params.update({
+            'in_channels': in_channels,
+            'use_dropout': use_dropout
+        })
+        super(UNetSiamConc, self).__init__(
+            model_name='UNetSiamConc',
+            num_classes=num_classes,
+            use_mixed_loss=use_mixed_loss,
+            **params)
+
+
+class UNetSiamDiff(BaseChangeDetector):
+    def __init__(self,
+                 num_classes=2,
+                 use_mixed_loss=False,
+                 in_channels=3,
+                 use_dropout=False,
+                 **params):
+        params.update({
+            'in_channels': in_channels,
+            'use_dropout': use_dropout
+        })
+        super(UNetSiamDiff, self).__init__(
+            model_name='UNetSiamDiff',
+            num_classes=num_classes,
+            use_mixed_loss=use_mixed_loss,
+            **params)
+
+
+class STANet(BaseChangeDetector):
+    def __init__(self,
+                 num_classes=2,
+                 use_mixed_loss=False,
+                 in_channels=3,
+                 att_type='BAM',
+                 ds_factor=1,
+                 **params):
+        params.update({
+            'in_channels': in_channels,
+            'att_type': att_type,
+            'ds_factor': ds_factor
+        })
+        super(STANet, self).__init__(
+            model_name='STANet',
+            num_classes=num_classes,
+            use_mixed_loss=use_mixed_loss,
+            **params)
+
+
+class BIT(BaseChangeDetector):
+    def __init__(self,
+                 num_classes=2,
+                 use_mixed_loss=False,
+                 in_channels=3,
+                 backbone='resnet18', 
+                 n_stages=4, 
+                 use_tokenizer=True, 
+                 token_len=4, 
+                 pool_mode='max', 
+                 pool_size=2,
+                 enc_with_pos=True, 
+                 enc_depth=1, 
+                 enc_head_dim=64, 
+                 dec_depth=8, 
+                 dec_head_dim=8,
+                 **params):
+        params.update({
+            'in_channels': in_channels,
+            'backbone': backbone,
+            'n_stages': n_stages,
+            'use_tokenizer': use_tokenizer,
+            'token_len': token_len,
+            'pool_mode': pool_mode,
+            'pool_size': pool_size,
+            'enc_with_pos': enc_with_pos,
+            'enc_depth': enc_depth,
+            'enc_head_dim': enc_head_dim,
+            'dec_depth': dec_depth,
+            'dec_head_dim': dec_head_dim
+        })
+        super(BIT, self).__init__(
+            model_name='BIT',
+            num_classes=num_classes,
+            use_mixed_loss=use_mixed_loss,
+            **params)
+
+
+class SNUNet(BaseChangeDetector):
+    def __init__(self,
+                 num_classes=2,
+                 use_mixed_loss=False,
+                 in_channels=3,
+                 width=32,
+                 **params):
+        params.update({
+            'in_channels': in_channels,
+            'width': width
+        })
+        super(SNUNet, self).__init__(
+            model_name='SNUNet',
+            num_classes=num_classes,
+            use_mixed_loss=use_mixed_loss,
+            **params)
+
+
+class DSIFN(BaseChangeDetector):
+    def __init__(self,
+                 num_classes=2,
+                 use_mixed_loss=None,
+                 use_dropout=False,
+                 **params):
+        params.update({
+            'use_dropout': use_dropout
+        })
+        super(DSIFN, self).__init__(
+            model_name='DSIFN',
+            num_classes=num_classes,
+            use_mixed_loss=use_mixed_loss,
+            **params)
+        # HACK: currently the only legal value of `use_mixed_loss` is None, in which case the loss specifications are
+        # constructed automatically.
+        assert use_mixed_loss is None
+        if use_mixed_loss is None:
+            self.losses = {
+                # XXX: make sure the shallow copy works correctly here.
+                'types': [paddleseg.models.CrossEntropyLoss()]*5,
+                'coef': [1.0]*5
+            }
+
+
+class DSAMNet(BaseChangeDetector):
+    def __init__(self,
+                 num_classes=2,
+                 use_mixed_loss=None,
+                 in_channels=3,
+                 ca_ratio=8,
+                 sa_kernel=7,
+                 **params):
+        params.update({
+            'in_channels': in_channels,
+            'ca_ratio': ca_ratio,
+            'sa_kernel': sa_kernel
+        })
+        super(DSAMNet, self).__init__(
+            model_name='DSAMNet',
+            num_classes=num_classes,
+            use_mixed_loss=use_mixed_loss,
+            **params)
+        # HACK: currently the only legal value of `use_mixed_loss` is None, in which case the loss specifications are
+        # constructed automatically.
+        assert use_mixed_loss is None
+        if use_mixed_loss is None:
+            self.losses = {
+                'types': [
+                    paddleseg.models.CrossEntropyLoss(), 
+                    paddleseg.models.DiceLoss(), 
+                    paddleseg.models.DiceLoss()
+                ],
+                'coef': [1.0, 0.05, 0.05]
+            }