Přenos stylu pomocí VGG19 a TensorFlow

				
					import tensorflow as tf
import matplotlib.pyplot as plt
import numpy as np
from tensorflow.keras.applications.vgg19 import preprocess_input
from tensorflow.keras.models import Model
from tensorflow.keras.applications.vgg19 import VGG19
from IPython.display import clear_output

# Load images
def load_image(image_path):
    img = tf.io.read_file(image_path)
    img = tf.image.decode_image(img, channels=3)
    img = tf.image.convert_image_dtype(img, tf.float32)
    img = img[tf.newaxis, :] # Add batch dimension
    img = preprocess_input(img*255) # Preprocess image
    return img

# Display an image
def display_image(image, title=None):
    if len(image.shape) > 3:
        image = tf.squeeze(image, axis=0)

    plt.imshow(image)
    if title:
        plt.title(title)
    plt.axis("off")
    plt.show()

# Content and style layers
content_layers = ['block5_conv2']
style_layers = ['block1_conv1', 'block2_conv1', 'block3_conv1', 'block4_conv1', 'block5_conv1']
num_content_layers = len(content_layers)
num_style_layers = len(style_layers)

# Load images
content_image = load_image('path_to_content_image.jpg')
style_image = load_image('path_to_style_image.jpg')

# Create a vgg model
def vgg_model(layer_names):
    vgg = VGG19(include_top=False, weights='imagenet')
    vgg.trainable = False
    outputs = [vgg.get_layer(name).output for name in layer_names]
    model = Model([vgg.input], outputs)
    return model

# Create a model with access to intermediate layers
style_extractor = vgg_model(style_layers)
style_outputs = style_extractor(style_image*255)

# Calculate style
def gram_matrix(input_tensor):
    result = tf.linalg.einsum('bijc,bijd->bcd', input_tensor, input_tensor)
    input_shape = tf.shape(input_tensor)
    num_locations = tf.cast(input_shape[1]*input_shape[2], tf.float32)
    return result/(num_locations)

# Style and content models
class StyleContentModel(Model):
    def __init__(self, style_layers, content_layers):
        super(StyleContentModel, self).__init__()
        self.vgg = vgg_model(style_layers + content_layers)
        self.style_layers = style_layers
        self.content_layers = content_layers
        self.num_style_layers = len(style_layers)
        self.vgg.trainable = False

    def call(self, inputs):
        inputs = inputs*255.0
        preprocessed_input = preprocess_input(inputs)
        outputs = self.vgg(preprocessed_input)
        style_outputs, content_outputs = (outputs[:self.num_style_layers], outputs[self.num_style_layers:])
        style_outputs = [gram_matrix(style_output) for style_output in style_outputs]
        content_dict = {content_name:value for content_name, value in zip(self.content_layers, content_outputs)}
        style_dict = {style_name:value for style_name, value in zip(self.style_layers, style_outputs)}
        return {'content':content_dict, 'style':style_dict}

# Instantiate extractor
extractor = StyleContentModel(style_layers, content_layers)
results = extractor(tf.constant(content_image))

# Define style and content targets
style_targets = extractor(style_image)['style']
content_targets = extractor(content_image)['content']

# Initialize image to optimize
image = tf.Variable(content_image)

# Set weight of total variational loss
total_variation_weight = 1e8
style_weight = 1e-2
content_weight = 1e4

# Define a function to calculate loss
def style_content_loss(outputs):
    style_outputs = outputs['style']
    content_outputs = outputs['content']
    style_loss = tf.add_n([tf.reduce_mean((style_outputs[name]-style_targets[name])**2)
                           for name in style_outputs.keys()])
    content_loss = tf.add_n([tf.reduce_mean((content_outputs[name]-content_targets[name])**2)
                             for name in content_outputs.keys()])
    style_loss *= style_weight / num_style_layers
    content_loss *= content_weight / num_content_layers
    loss = style_loss + content_loss
    return loss

# Create a tf.function for performance
@tf.function()
def train_step(image):
    with tf.GradientTape() as tape:
        outputs = extractor(image)
        loss = style_content_loss(outputs)
        loss += total_variation_weight*tf.image.total_variation(image)

    grad = tape.gradient(loss, image)
    opt.apply_gradients([(grad, image)])
    image.assign(tf.clip_by_value(image, 0.0, 1.0))

# Use Adam optimizer
opt = tf.optimizers.Adam(learning_rate=0.02, beta_1=0.99, epsilon=1e-1)

# Perform optimization
epochs = 10
steps_per_epoch = 100

step = 0
for n in range(epochs):
    for m in range(steps_per_epoch):
        step += 1
        train_step(image)
        print(".", end='')
    clear_output(wait=True)
    display_image(image.read_value())
    print("Train step: {}".format(step))