Next-Frame Video Prediction with Convolutional LSTMs

import numpy as np
import matplotlib.pyplot as plt

import keras
from keras import layers

import io
import imageio
from IPython.display import Image, display
from ipywidgets import widgets, Layout, HBox

# Download and load the dataset.
fpath = keras.utils.get_file(
    "moving_mnist.npy",
    "http://www.cs.toronto.edu/~nitish/unsupervised_video/mnist_test_seq.npy",
)
dataset = np.load(fpath)

# Swap the axes representing the number of frames and number of data samples.
dataset = np.swapaxes(dataset, 0, 1)
# We'll pick out 1000 of the 10000 total examples and use those.
dataset = dataset[:1000, ...]
# Add a channel dimension since the images are grayscale.
dataset = np.expand_dims(dataset, axis=-1)

# Split into train and validation sets using indexing to optimize memory.
indexes = np.arange(dataset.shape[0])
np.random.shuffle(indexes)
train_index = indexes[: int(0.9 * dataset.shape[0])]
val_index = indexes[int(0.9 * dataset.shape[0]) :]
train_dataset = dataset[train_index]
val_dataset = dataset[val_index]

# Normalize the data to the 0-1 range.
train_dataset = train_dataset / 255
val_dataset = val_dataset / 255


# We'll define a helper function to shift the frames, where
# `x` is frames 0 to n - 1, and `y` is frames 1 to n.
def create_shifted_frames(data):
    x = data[:, 0 : data.shape[1] - 1, :, :]
    y = data[:, 1 : data.shape[1], :, :]
    return x, y


# Apply the processing function to the datasets.
x_train, y_train = create_shifted_frames(train_dataset)
x_val, y_val = create_shifted_frames(val_dataset)

# Inspect the dataset.
print("Training Dataset Shapes: " + str(x_train.shape) + ", " + str(y_train.shape))
print("Validation Dataset Shapes: " + str(x_val.shape) + ", " + str(y_val.shape))

# Construct a figure on which we will visualize the images.
fig, axes = plt.subplots(4, 5, figsize=(10, 8))

# Plot each of the sequential images for one random data example.
data_choice = np.random.choice(range(len(train_dataset)), size=1)[0]
for idx, ax in enumerate(axes.flat):
    ax.imshow(np.squeeze(train_dataset[data_choice][idx]), cmap="gray")
    ax.set_title(f"Frame {idx + 1}")
    ax.axis("off")

# Print information and display the figure.
print(f"Displaying frames for example {data_choice}.")
plt.show()

# Construct the input layer with no definite frame size.
inp = layers.Input(shape=(None, *x_train.shape[2:]))

# We will construct 3 `ConvLSTM2D` layers with batch normalization,
# followed by a `Conv3D` layer for the spatiotemporal outputs.
x = layers.ConvLSTM2D(
    filters=64,
    kernel_size=(5, 5),
    padding="same",
    return_sequences=True,
    activation="relu",
)(inp)
x = layers.BatchNormalization()(x)
x = layers.ConvLSTM2D(
    filters=64,
    kernel_size=(3, 3),
    padding="same",
    return_sequences=True,
    activation="relu",
)(x)
x = layers.BatchNormalization()(x)
x = layers.ConvLSTM2D(
    filters=64,
    kernel_size=(1, 1),
    padding="same",
    return_sequences=True,
    activation="relu",
)(x)
x = layers.Conv3D(
    filters=1, kernel_size=(3, 3, 3), activation="sigmoid", padding="same"
)(x)

# Next, we will build the complete model and compile it.
model = keras.models.Model(inp, x)
model.compile(
    loss=keras.losses.binary_crossentropy,
    optimizer=keras.optimizers.Adam(),
)

# Define some callbacks to improve training.
early_stopping = keras.callbacks.EarlyStopping(monitor="val_loss", patience=10)
reduce_lr = keras.callbacks.ReduceLROnPlateau(monitor="val_loss", patience=5)

# Define modifiable training hyperparameters.
epochs = 20
batch_size = 5

# Fit the model to the training data.
model.fit(
    x_train,
    y_train,
    batch_size=batch_size,
    epochs=epochs,
    validation_data=(x_val, y_val),
    callbacks=[early_stopping, reduce_lr],
)

# Select a random example from the validation dataset.
example = val_dataset[np.random.choice(range(len(val_dataset)), size=1)[0]]

# Pick the first/last ten frames from the example.
frames = example[:10, ...]
original_frames = example[10:, ...]

# Predict a new set of 10 frames.
for _ in range(10):
    # Extract the model's prediction and post-process it.
    new_prediction = model.predict(np.expand_dims(frames, axis=0))
    new_prediction = np.squeeze(new_prediction, axis=0)
    predicted_frame = np.expand_dims(new_prediction[-1, ...], axis=0)

    # Extend the set of prediction frames.
    frames = np.concatenate((frames, predicted_frame), axis=0)

# Construct a figure for the original and new frames.
fig, axes = plt.subplots(2, 10, figsize=(20, 4))

# Plot the original frames.
for idx, ax in enumerate(axes[0]):
    ax.imshow(np.squeeze(original_frames[idx]), cmap="gray")
    ax.set_title(f"Frame {idx + 11}")
    ax.axis("off")

# Plot the new frames.
new_frames = frames[10:, ...]
for idx, ax in enumerate(axes[1]):
    ax.imshow(np.squeeze(new_frames[idx]), cmap="gray")
    ax.set_title(f"Frame {idx + 11}")
    ax.axis("off")

# Display the figure.
plt.show()

# Select a few random examples from the dataset.
examples = val_dataset[np.random.choice(range(len(val_dataset)), size=5)]

# Iterate over the examples and predict the frames.
predicted_videos = []
for example in examples:
    # Pick the first/last ten frames from the example.
    frames = example[:10, ...]
    original_frames = example[10:, ...]
    new_predictions = np.zeros(shape=(10, *frames[0].shape))

    # Predict a new set of 10 frames.
    for i in range(10):
        # Extract the model's prediction and post-process it.
        frames = example[: 10 + i + 1, ...]
        new_prediction = model.predict(np.expand_dims(frames, axis=0))
        new_prediction = np.squeeze(new_prediction, axis=0)
        predicted_frame = np.expand_dims(new_prediction[-1, ...], axis=0)

        # Extend the set of prediction frames.
        new_predictions[i] = predicted_frame

    # Create and save GIFs for each of the ground truth/prediction images.
    for frame_set in [original_frames, new_predictions]:
        # Construct a GIF from the selected video frames.
        current_frames = np.squeeze(frame_set)
        current_frames = current_frames[..., np.newaxis] * np.ones(3)
        current_frames = (current_frames * 255).astype(np.uint8)
        current_frames = list(current_frames)

        # Construct a GIF from the frames.
        with io.BytesIO() as gif:
            imageio.mimsave(gif, current_frames, "GIF", duration=200)
            predicted_videos.append(gif.getvalue())

# Display the videos.
print(" Truth\tPrediction")
for i in range(0, len(predicted_videos), 2):
    # Construct and display an `HBox` with the ground truth and prediction.
    box = HBox(
        [
            widgets.Image(value=predicted_videos[i]),
            widgets.Image(value=predicted_videos[i + 1]),
        ]
    )
    display(box)