Keras 2 : examples : 生成深層学習 – CycleGAN (翻訳/解説)

翻訳 : (株)クラスキャット セールスインフォメーション
作成日時 : 07/05/2022 (keras 2.9.0)

* 本ページは、Keras の以下のドキュメントを翻訳した上で適宜、補足説明したものです：

• Code examples : Generative Deep Learning : CycleGAN (Author: A_K_Nain)

* サンプルコードの動作確認はしておりますが、必要な場合には適宜、追加改変しています。
* ご自由にリンクを張って頂いてかまいませんが、sales-info@classcat.com までご一報いただけると嬉しいです。

 

 

 

Keras 2 : examples : 生成深層学習 – CycleGAN

Description : CycleGAN の実装

 
画像-to-画像変換 (= translation) 問題を解くことを目標としたモデルです。画像-to-画像変換問題のゴールは、整列された画像ペアの訓練セットを利用して、入力画像と出力画像の間のマッピングを学習することです。けれども、ペアになったサンプルを得ることは常に実行可能ではありません。CycleGAN は cycle-consistent 敵対的ネットワークを使用して、ペアになった入力-出力画像を必要とすることなくこのマッピングを学習しようとします。

• Paper
• Original implementation

 

セットアップ

import os
import numpy as np
import matplotlib.pyplot as plt

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

import tensorflow_addons as tfa
import tensorflow_datasets as tfds

tfds.disable_progress_bar()
autotune = tf.data.AUTOTUNE

 

データセットの準備

この例では、horse to zebra データセットを使用していきます。

# Load the horse-zebra dataset using tensorflow-datasets.
dataset, _ = tfds.load("cycle_gan/horse2zebra", with_info=True, as_supervised=True)
train_horses, train_zebras = dataset["trainA"], dataset["trainB"]
test_horses, test_zebras = dataset["testA"], dataset["testB"]

# Define the standard image size.
orig_img_size = (286, 286)
# Size of the random crops to be used during training.
input_img_size = (256, 256, 3)
# Weights initializer for the layers.
kernel_init = keras.initializers.RandomNormal(mean=0.0, stddev=0.02)
# Gamma initializer for instance normalization.
gamma_init = keras.initializers.RandomNormal(mean=0.0, stddev=0.02)

buffer_size = 256
batch_size = 1


def normalize_img(img):
    img = tf.cast(img, dtype=tf.float32)
    # Map values in the range [-1, 1]
    return (img / 127.5) - 1.0


def preprocess_train_image(img, label):
    # Random flip
    img = tf.image.random_flip_left_right(img)
    # Resize to the original size first
    img = tf.image.resize(img, [*orig_img_size])
    # Random crop to 256X256
    img = tf.image.random_crop(img, size=[*input_img_size])
    # Normalize the pixel values in the range [-1, 1]
    img = normalize_img(img)
    return img


def preprocess_test_image(img, label):
    # Only resizing and normalization for the test images.
    img = tf.image.resize(img, [input_img_size[0], input_img_size[1]])
    img = normalize_img(img)
    return img

 

Dataset オブジェクトの作成

# Apply the preprocessing operations to the training data
train_horses = (
    train_horses.map(preprocess_train_image, num_parallel_calls=autotune)
    .cache()
    .shuffle(buffer_size)
    .batch(batch_size)
)
train_zebras = (
    train_zebras.map(preprocess_train_image, num_parallel_calls=autotune)
    .cache()
    .shuffle(buffer_size)
    .batch(batch_size)
)

# Apply the preprocessing operations to the test data
test_horses = (
    test_horses.map(preprocess_test_image, num_parallel_calls=autotune)
    .cache()
    .shuffle(buffer_size)
    .batch(batch_size)
)
test_zebras = (
    test_zebras.map(preprocess_test_image, num_parallel_calls=autotune)
    .cache()
    .shuffle(buffer_size)
    .batch(batch_size)
)

 

幾つかのサンプルの可視化

_, ax = plt.subplots(4, 2, figsize=(10, 15))
for i, samples in enumerate(zip(train_horses.take(4), train_zebras.take(4))):
    horse = (((samples[0][0] * 127.5) + 127.5).numpy()).astype(np.uint8)
    zebra = (((samples[1][0] * 127.5) + 127.5).numpy()).astype(np.uint8)
    ax[i, 0].imshow(horse)
    ax[i, 1].imshow(zebra)
plt.show()

 

CycleGAN generators と discriminators で使用されるビルディング・ブロック

class ReflectionPadding2D(layers.Layer):
    """Implements Reflection Padding as a layer.

    Args:
        padding(tuple): Amount of padding for the
        spatial dimensions.

    Returns:
        A padded tensor with the same type as the input tensor.
    """

    def __init__(self, padding=(1, 1), **kwargs):
        self.padding = tuple(padding)
        super(ReflectionPadding2D, self).__init__(**kwargs)

    def call(self, input_tensor, mask=None):
        padding_width, padding_height = self.padding
        padding_tensor = [
            [0, 0],
            [padding_height, padding_height],
            [padding_width, padding_width],
            [0, 0],
        ]
        return tf.pad(input_tensor, padding_tensor, mode="REFLECT")


def residual_block(
    x,
    activation,
    kernel_initializer=kernel_init,
    kernel_size=(3, 3),
    strides=(1, 1),
    padding="valid",
    gamma_initializer=gamma_init,
    use_bias=False,
):
    dim = x.shape[-1]
    input_tensor = x

    x = ReflectionPadding2D()(input_tensor)
    x = layers.Conv2D(
        dim,
        kernel_size,
        strides=strides,
        kernel_initializer=kernel_initializer,
        padding=padding,
        use_bias=use_bias,
    )(x)
    x = tfa.layers.InstanceNormalization(gamma_initializer=gamma_initializer)(x)
    x = activation(x)

    x = ReflectionPadding2D()(x)
    x = layers.Conv2D(
        dim,
        kernel_size,
        strides=strides,
        kernel_initializer=kernel_initializer,
        padding=padding,
        use_bias=use_bias,
    )(x)
    x = tfa.layers.InstanceNormalization(gamma_initializer=gamma_initializer)(x)
    x = layers.add([input_tensor, x])
    return x


def downsample(
    x,
    filters,
    activation,
    kernel_initializer=kernel_init,
    kernel_size=(3, 3),
    strides=(2, 2),
    padding="same",
    gamma_initializer=gamma_init,
    use_bias=False,
):
    x = layers.Conv2D(
        filters,
        kernel_size,
        strides=strides,
        kernel_initializer=kernel_initializer,
        padding=padding,
        use_bias=use_bias,
    )(x)
    x = tfa.layers.InstanceNormalization(gamma_initializer=gamma_initializer)(x)
    if activation:
        x = activation(x)
    return x


def upsample(
    x,
    filters,
    activation,
    kernel_size=(3, 3),
    strides=(2, 2),
    padding="same",
    kernel_initializer=kernel_init,
    gamma_initializer=gamma_init,
    use_bias=False,
):
    x = layers.Conv2DTranspose(
        filters,
        kernel_size,
        strides=strides,
        padding=padding,
        kernel_initializer=kernel_initializer,
        use_bias=use_bias,
    )(x)
    x = tfa.layers.InstanceNormalization(gamma_initializer=gamma_initializer)(x)
    if activation:
        x = activation(x)
    return x

 

generators の構築

generator はダウンサンプリング・ブロック、9 つの残差ブロックとアップサンプリング・ブロックから構成されます。generator の構造は以下です :

c7s1-64 ==> Conv block with `relu` activation, filter size of 7
d128 ====|
         |-> 2 downsampling blocks
d256 ====|
R256 ====|
R256     |
R256     |
R256     |
R256     |-> 9 residual blocks
R256     |
R256     |
R256     |
R256 ====|
u128 ====|
         |-> 2 upsampling blocks
u64  ====|
c7s1-3 => Last conv block with `tanh` activation, filter size of 7.

def get_resnet_generator(
    filters=64,
    num_downsampling_blocks=2,
    num_residual_blocks=9,
    num_upsample_blocks=2,
    gamma_initializer=gamma_init,
    name=None,
):
    img_input = layers.Input(shape=input_img_size, name=name + "_img_input")
    x = ReflectionPadding2D(padding=(3, 3))(img_input)
    x = layers.Conv2D(filters, (7, 7), kernel_initializer=kernel_init, use_bias=False)(
        x
    )
    x = tfa.layers.InstanceNormalization(gamma_initializer=gamma_initializer)(x)
    x = layers.Activation("relu")(x)

    # Downsampling
    for _ in range(num_downsampling_blocks):
        filters *= 2
        x = downsample(x, filters=filters, activation=layers.Activation("relu"))

    # Residual blocks
    for _ in range(num_residual_blocks):
        x = residual_block(x, activation=layers.Activation("relu"))

    # Upsampling
    for _ in range(num_upsample_blocks):
        filters //= 2
        x = upsample(x, filters, activation=layers.Activation("relu"))

    # Final block
    x = ReflectionPadding2D(padding=(3, 3))(x)
    x = layers.Conv2D(3, (7, 7), padding="valid")(x)
    x = layers.Activation("tanh")(x)

    model = keras.models.Model(img_input, x, name=name)
    return model

 

discriminators の構築

discriminators は次のアーキテクチャを実装します : C64->C128->C256->C512

def get_discriminator(
    filters=64, kernel_initializer=kernel_init, num_downsampling=3, name=None
):
    img_input = layers.Input(shape=input_img_size, name=name + "_img_input")
    x = layers.Conv2D(
        filters,
        (4, 4),
        strides=(2, 2),
        padding="same",
        kernel_initializer=kernel_initializer,
    )(img_input)
    x = layers.LeakyReLU(0.2)(x)

    num_filters = filters
    for num_downsample_block in range(3):
        num_filters *= 2
        if num_downsample_block < 2:
            x = downsample(
                x,
                filters=num_filters,
                activation=layers.LeakyReLU(0.2),
                kernel_size=(4, 4),
                strides=(2, 2),
            )
        else:
            x = downsample(
                x,
                filters=num_filters,
                activation=layers.LeakyReLU(0.2),
                kernel_size=(4, 4),
                strides=(1, 1),
            )

    x = layers.Conv2D(
        1, (4, 4), strides=(1, 1), padding="same", kernel_initializer=kernel_initializer
    )(x)

    model = keras.models.Model(inputs=img_input, outputs=x, name=name)
    return model


# Get the generators
gen_G = get_resnet_generator(name="generator_G")
gen_F = get_resnet_generator(name="generator_F")

# Get the discriminators
disc_X = get_discriminator(name="discriminator_X")
disc_Y = get_discriminator(name="discriminator_Y")

 

CycleGAN モデルの構築

fit() による訓練のために Model クラスの train_step() ステップをオーバーライドします。

class CycleGan(keras.Model):
    def __init__(
        self,
        generator_G,
        generator_F,
        discriminator_X,
        discriminator_Y,
        lambda_cycle=10.0,
        lambda_identity=0.5,
    ):
        super(CycleGan, self).__init__()
        self.gen_G = generator_G
        self.gen_F = generator_F
        self.disc_X = discriminator_X
        self.disc_Y = discriminator_Y
        self.lambda_cycle = lambda_cycle
        self.lambda_identity = lambda_identity

    def compile(
        self,
        gen_G_optimizer,
        gen_F_optimizer,
        disc_X_optimizer,
        disc_Y_optimizer,
        gen_loss_fn,
        disc_loss_fn,
    ):
        super(CycleGan, self).compile()
        self.gen_G_optimizer = gen_G_optimizer
        self.gen_F_optimizer = gen_F_optimizer
        self.disc_X_optimizer = disc_X_optimizer
        self.disc_Y_optimizer = disc_Y_optimizer
        self.generator_loss_fn = gen_loss_fn
        self.discriminator_loss_fn = disc_loss_fn
        self.cycle_loss_fn = keras.losses.MeanAbsoluteError()
        self.identity_loss_fn = keras.losses.MeanAbsoluteError()

    def train_step(self, batch_data):
        # x is Horse and y is zebra
        real_x, real_y = batch_data

        # For CycleGAN, we need to calculate different
        # kinds of losses for the generators and discriminators.
        # We will perform the following steps here:
        #
        # 1. Pass real images through the generators and get the generated images
        # 2. Pass the generated images back to the generators to check if we
        #    we can predict the original image from the generated image.
        # 3. Do an identity mapping of the real images using the generators.
        # 4. Pass the generated images in 1) to the corresponding discriminators.
        # 5. Calculate the generators total loss (adverserial + cycle + identity)
        # 6. Calculate the discriminators loss
        # 7. Update the weights of the generators
        # 8. Update the weights of the discriminators
        # 9. Return the losses in a dictionary

        with tf.GradientTape(persistent=True) as tape:
            # Horse to fake zebra
            fake_y = self.gen_G(real_x, training=True)
            # Zebra to fake horse -> y2x
            fake_x = self.gen_F(real_y, training=True)

            # Cycle (Horse to fake zebra to fake horse): x -> y -> x
            cycled_x = self.gen_F(fake_y, training=True)
            # Cycle (Zebra to fake horse to fake zebra) y -> x -> y
            cycled_y = self.gen_G(fake_x, training=True)

            # Identity mapping
            same_x = self.gen_F(real_x, training=True)
            same_y = self.gen_G(real_y, training=True)

            # Discriminator output
            disc_real_x = self.disc_X(real_x, training=True)
            disc_fake_x = self.disc_X(fake_x, training=True)

            disc_real_y = self.disc_Y(real_y, training=True)
            disc_fake_y = self.disc_Y(fake_y, training=True)

            # Generator adverserial loss
            gen_G_loss = self.generator_loss_fn(disc_fake_y)
            gen_F_loss = self.generator_loss_fn(disc_fake_x)

            # Generator cycle loss
            cycle_loss_G = self.cycle_loss_fn(real_y, cycled_y) * self.lambda_cycle
            cycle_loss_F = self.cycle_loss_fn(real_x, cycled_x) * self.lambda_cycle

            # Generator identity loss
            id_loss_G = (
                self.identity_loss_fn(real_y, same_y)
                * self.lambda_cycle
                * self.lambda_identity
            )
            id_loss_F = (
                self.identity_loss_fn(real_x, same_x)
                * self.lambda_cycle
                * self.lambda_identity
            )

            # Total generator loss
            total_loss_G = gen_G_loss + cycle_loss_G + id_loss_G
            total_loss_F = gen_F_loss + cycle_loss_F + id_loss_F

            # Discriminator loss
            disc_X_loss = self.discriminator_loss_fn(disc_real_x, disc_fake_x)
            disc_Y_loss = self.discriminator_loss_fn(disc_real_y, disc_fake_y)

        # Get the gradients for the generators
        grads_G = tape.gradient(total_loss_G, self.gen_G.trainable_variables)
        grads_F = tape.gradient(total_loss_F, self.gen_F.trainable_variables)

        # Get the gradients for the discriminators
        disc_X_grads = tape.gradient(disc_X_loss, self.disc_X.trainable_variables)
        disc_Y_grads = tape.gradient(disc_Y_loss, self.disc_Y.trainable_variables)

        # Update the weights of the generators
        self.gen_G_optimizer.apply_gradients(
            zip(grads_G, self.gen_G.trainable_variables)
        )
        self.gen_F_optimizer.apply_gradients(
            zip(grads_F, self.gen_F.trainable_variables)
        )

        # Update the weights of the discriminators
        self.disc_X_optimizer.apply_gradients(
            zip(disc_X_grads, self.disc_X.trainable_variables)
        )
        self.disc_Y_optimizer.apply_gradients(
            zip(disc_Y_grads, self.disc_Y.trainable_variables)
        )

        return {
            "G_loss": total_loss_G,
            "F_loss": total_loss_F,
            "D_X_loss": disc_X_loss,
            "D_Y_loss": disc_Y_loss,
        }

 

生成画像を定期的にセーブするコールバックの作成

class GANMonitor(keras.callbacks.Callback):
    """A callback to generate and save images after each epoch"""

    def __init__(self, num_img=4):
        self.num_img = num_img

    def on_epoch_end(self, epoch, logs=None):
        _, ax = plt.subplots(4, 2, figsize=(12, 12))
        for i, img in enumerate(test_horses.take(self.num_img)):
            prediction = self.model.gen_G(img)[0].numpy()
            prediction = (prediction * 127.5 + 127.5).astype(np.uint8)
            img = (img[0] * 127.5 + 127.5).numpy().astype(np.uint8)

            ax[i, 0].imshow(img)
            ax[i, 1].imshow(prediction)
            ax[i, 0].set_title("Input image")
            ax[i, 1].set_title("Translated image")
            ax[i, 0].axis("off")
            ax[i, 1].axis("off")

            prediction = keras.preprocessing.image.array_to_img(prediction)
            prediction.save(
                "generated_img_{i}_{epoch}.png".format(i=i, epoch=epoch + 1)
            )
        plt.show()
        plt.close()

 

end-to-end モデルの訓練

# Loss function for evaluating adversarial loss
adv_loss_fn = keras.losses.MeanSquaredError()

# Define the loss function for the generators
def generator_loss_fn(fake):
    fake_loss = adv_loss_fn(tf.ones_like(fake), fake)
    return fake_loss


# Define the loss function for the discriminators
def discriminator_loss_fn(real, fake):
    real_loss = adv_loss_fn(tf.ones_like(real), real)
    fake_loss = adv_loss_fn(tf.zeros_like(fake), fake)
    return (real_loss + fake_loss) * 0.5


# Create cycle gan model
cycle_gan_model = CycleGan(
    generator_G=gen_G, generator_F=gen_F, discriminator_X=disc_X, discriminator_Y=disc_Y
)

# Compile the model
cycle_gan_model.compile(
    gen_G_optimizer=keras.optimizers.Adam(learning_rate=2e-4, beta_1=0.5),
    gen_F_optimizer=keras.optimizers.Adam(learning_rate=2e-4, beta_1=0.5),
    disc_X_optimizer=keras.optimizers.Adam(learning_rate=2e-4, beta_1=0.5),
    disc_Y_optimizer=keras.optimizers.Adam(learning_rate=2e-4, beta_1=0.5),
    gen_loss_fn=generator_loss_fn,
    disc_loss_fn=discriminator_loss_fn,
)
# Callbacks
plotter = GANMonitor()
checkpoint_filepath = "./model_checkpoints/cyclegan_checkpoints.{epoch:03d}"
model_checkpoint_callback = keras.callbacks.ModelCheckpoint(
    filepath=checkpoint_filepath
)

# Here we will train the model for just one epoch as each epoch takes around
# 7 minutes on a single P100 backed machine.
cycle_gan_model.fit(
    tf.data.Dataset.zip((train_horses, train_zebras)),
    epochs=1,
    callbacks=[plotter, model_checkpoint_callback],
)

1067/1067 [==============================] - ETA: 0s - G_loss: 4.4794 - F_loss: 4.1048 - D_X_loss: 0.1584 - D_Y_loss: 0.1233

1067/1067 [==============================] - 390s 366ms/step - G_loss: 4.4783 - F_loss: 4.1035 - D_X_loss: 0.1584 - D_Y_loss: 0.1232

<tensorflow.python.keras.callbacks.History at 0x7f4184326e90>

モデルのパフォーマンスをテストします。

Hugging Face ハブ にホストされている訓練済みモデルを使用して、Hugging Face Spaces でデモを試すことができます。

# This model was trained for 90 epochs. We will be loading those weights
# here. Once the weights are loaded, we will take a few samples from the test
# data and check the model's performance.

!curl -LO https://github.com/AakashKumarNain/CycleGAN_TF2/releases/download/v1.0/saved_checkpoints.zip
!unzip -qq saved_checkpoints.zip

# Load the checkpoints
weight_file = "./saved_checkpoints/cyclegan_checkpoints.090"
cycle_gan_model.load_weights(weight_file).expect_partial()
print("Weights loaded successfully")

_, ax = plt.subplots(4, 2, figsize=(10, 15))
for i, img in enumerate(test_horses.take(4)):
    prediction = cycle_gan_model.gen_G(img, training=False)[0].numpy()
    prediction = (prediction * 127.5 + 127.5).astype(np.uint8)
    img = (img[0] * 127.5 + 127.5).numpy().astype(np.uint8)

    ax[i, 0].imshow(img)
    ax[i, 1].imshow(prediction)
    ax[i, 0].set_title("Input image")
    ax[i, 0].set_title("Input image")
    ax[i, 1].set_title("Translated image")
    ax[i, 0].axis("off")
    ax[i, 1].axis("off")

    prediction = keras.preprocessing.image.array_to_img(prediction)
    prediction.save("predicted_img_{i}.png".format(i=i))
plt.tight_layout()
plt.show()

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   634  100   634    0     0   2874      0 --:--:-- --:--:-- --:--:--  2881
100  273M  100  273M    0     0  1736k      0  0:02:41  0:02:41 --:--:-- 2049k

Weights loaded successfully

以上