Keras实现swinunetr网络

Swin Transformer是一种基于Transformer的神经网络结构，它在图像分类和目标检测等计算机视觉任务中表现出色。Swin Transformer的特点是具有高度可扩展性和高效性。

在Keras中实现Swin Transformer网络，需要安装Keras和TensorFlow库，然后按照以下步骤进行操作：

1. 导入必要的库

import tensorflow as tf
from tensorflow import keras
from tensorflow.keras import layers

2. 定义Swin Transformer网络结构

def SwinTransformer(input_shape=(224, 224, 3), num_classes=1000):
    # 输入层
    inputs = keras.Input(shape=input_shape)

    # Patch Embedding层
    x = layers.Conv2D(filters=96, kernel_size=7, strides=4, padding='same')(inputs)
    x = layers.BatchNormalization()(x)
    x = layers.Activation('relu')(x)
    x = layers.MaxPooling2D(pool_size=(3, 3), strides=2, padding='same')(x)

    # Swin Transformer块
    x = SwinTransformerBlock(x, hidden_dim=96, num_heads=3, window_size=7, shift_size=2, name='block1')
    x = SwinTransformerBlock(x, hidden_dim=192, num_heads=6, window_size=7, shift_size=2, name='block2')
    x = SwinTransformerBlock(x, hidden_dim=384, num_heads=12, window_size=7, shift_size=2, name='block3')
    x = SwinTransformerBlock(x, hidden_dim=768, num_heads=24, window_size=7, shift_size=2, name='block4')
    x = SwinTransformerBlock(x, hidden_dim=1536, num_heads=32, window_size=7, shift_size=2, name='block5')

    # Layer Norm层
    x = layers.LayerNormalization()(x)

    # 全局平均池化层
    x = layers.GlobalAveragePooling2D()(x)

    # Dropout层
    x = layers.Dropout(0.2)(x)

    # 输出层
    outputs = layers.Dense(num_classes, activation='softmax')(x)

    # 构建模型
    model = keras.Model(inputs=inputs, outputs=outputs, name='swin_transformer')
    return model

其中，Swin Transformer块的实现可以参考以下代码：

def SwinTransformerBlock(inputs, hidden_dim, num_heads, window_size, shift_size, name):
    # 输入层
    x = inputs

    # Shift层
    x = ShiftLayer(window_size=window_size, shift_size=shift_size, name=name+'_shift')(x)

    # Layer Norm层
    x = layers.LayerNormalization()(x)

    # Multi-Head Attention层
    x = MultiHeadAttention(hidden_dim=hidden_dim, num_heads=num_heads, name=name+'_mha')(x)

    # Layer Norm层
    x = layers.LayerNormalization()(x)

    # MLP层
    x = MLP(hidden_dim=hidden_dim, name=name+'_mlp')(x)

    # Residual连接
    x = layers.Add()([inputs, x])

    return x

其中，Shift层、Multi-Head Attention层和MLP层的实现可以参考以下代码：

class ShiftLayer(layers.Layer):
    def __init__(self, window_size, shift_size, **kwargs):
        super(ShiftLayer, self).__init__(**kwargs)
        self.window_size = window_size
        self.shift_size = shift_size

    def call(self, inputs):
        # 得到输入张量的形状和空间维度
        shape = tf.shape(inputs)
        batch_size, height, width, channels = shape[0], shape[1], shape[2], shape[3]

        # 将输入张量分割为不同的块
        x = tf.reshape(inputs, [batch_size, height // self.window_size, self.window_size, width // self.window_size, self.window_size, channels])
        x = tf.transpose(x, [0, 1, 3, 2, 4, 5])
        x = tf.reshape(x, [batch_size, height // self.window_size, width // self.window_size, self.window_size * self.window_size * channels])

        # Shift操作
        x = tf.roll(x, shift=(-self.shift_size, -self.shift_size), axis=(1, 2))

        # 将块重新组合成张量
        x = tf.reshape(x, [batch_size, height // self.window_size, width // self.window_size, self.window_size, self.window_size, channels])
        x = tf.transpose(x, [0, 1, 3, 2, 4, 5])
        x = tf.reshape(x, [batch_size, height, width, channels])

        return x

class MultiHeadAttention(layers.Layer):
    def __init__(self, hidden_dim, num_heads, **kwargs):
        super(MultiHeadAttention, self).__init__(**kwargs)
        self.hidden_dim = hidden_dim
        self.num_heads = num_heads

        assert hidden_dim % num_heads == 0

        self.depth = hidden_dim // num_heads

        self.query_dense = layers.Dense(hidden_dim)
        self.key_dense = layers.Dense(hidden_dim)
        self.value_dense = layers.Dense(hidden_dim)

        self.combine_heads = layers.Dense(hidden_dim)

    def call(self, inputs):
        # 得到输入张量的形状和空间维度
        shape = tf.shape(inputs)
        batch_size, height, width, channels = shape[0], shape[1], shape[2], shape[3]

        # 计算Query、Key和Value张量
        query = self.query_dense(inputs)
        key = self.key_dense(inputs)
        value = self.value_dense(inputs)

        # 按通道数分割Query、Key和Value张量，并重塑形状
        query = tf.reshape(query, [batch_size, height, width, self.num_heads, self.depth])
        key = tf.reshape(key, [batch_size, height, width, self.num_heads, self.depth])
        value = tf.reshape(value, [batch_size, height, width, self.num_heads, self.depth])

        # 计算Attention分数
        attention_scores = tf.matmul(query, key, transpose_b=True)
        attention_scores = attention_scores / tf.math.sqrt(tf.cast(self.depth, tf.float32))

        # 计算Attention权重
        attention_weights = tf.nn.softmax(attention_scores, axis=-1)

        # 计算加权的Value张量
        attention_output = tf.matmul(attention_weights, value)

        # 重塑形状并合并通道数
        attention_output = tf.reshape(attention_output, [batch_size, height, width, self.hidden_dim])
        attention_output = self.combine_heads(attention_output)

        return attention_output

def MLP(hidden_dim, **kwargs):
    return keras.Sequential([
        layers.Dense(hidden_dim * 4, activation='gelu'),
        layers.Dense(hidden_dim)
    ], **kwargs)

3. 编译和训练模型

# 编译模型
model = SwinTransformer(num_classes=1000)
model.compile(optimizer='adam', loss='categorical_crossentropy', metrics=['accuracy'])

# 训练模型
model.fit(train_dataset, epochs=10, validation_data=val_dataset)

以上代码中，train_dataset和val_dataset是训练集和验证集的数据集对象，需要根据实际情况进行定义。

希望这个实现Swin Transformer网络的Keras代码能够对您有所帮助！