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Image captioning with visual attention

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Given an image like the example below, our goal is to generate a caption such as "a surfer riding on a wave".

Man Surfing

Image Source; License: Public Domain

To accomplish this, you'll use an attention-based model, which enables us to see what parts of the image the model focuses on as it generates a caption.

Prediction

The model architecture is similar to Show, Attend and Tell: Neural Image Caption Generation with Visual Attention.

This notebook is an end-to-end example. When you run the notebook, it downloads the MS-COCO dataset, preprocesses and caches a subset of images using Inception V3, trains an encoder-decoder model, and generates captions on new images using the trained model.

In this example, you will train a model on a relatively small amount of data—the first 30,000 captions for about 20,000 images (because there are multiple captions per image in the dataset).

import tensorflow as tf

# You'll generate plots of attention in order to see which parts of an image
# our model focuses on during captioning
import matplotlib.pyplot as plt

import collections
import random
import numpy as np
import os
import time
import json
from PIL import Image

Download and prepare the MS-COCO dataset

You will use the MS-COCO dataset to train our model. The dataset contains over 82,000 images, each of which has at least 5 different caption annotations. The code below downloads and extracts the dataset automatically.

# Download caption annotation files
annotation_folder = '/annotations/'
if not os.path.exists(os.path.abspath('.') + annotation_folder):
  annotation_zip = tf.keras.utils.get_file('captions.zip',
                                           cache_subdir=os.path.abspath('.'),
                                           origin='http://images.cocodataset.org/annotations/annotations_trainval2014.zip',
                                           extract=True)
  annotation_file = os.path.dirname(annotation_zip)+'/annotations/captions_train2014.json'
  os.remove(annotation_zip)

# Download image files
image_folder = '/train2014/'
if not os.path.exists(os.path.abspath('.') + image_folder):
  image_zip = tf.keras.utils.get_file('train2014.zip',
                                      cache_subdir=os.path.abspath('.'),
                                      origin='http://images.cocodataset.org/zips/train2014.zip',
                                      extract=True)
  PATH = os.path.dirname(image_zip) + image_folder
  os.remove(image_zip)
else:
  PATH = os.path.abspath('.') + image_folder
Downloading data from http://images.cocodataset.org/annotations/annotations_trainval2014.zip
252878848/252872794 [==============================] - 16s 0us/step
Downloading data from http://images.cocodataset.org/zips/train2014.zip
13510574080/13510573713 [==============================] - 774s 0us/step

Optional: limit the size of the training set

To speed up training for this tutorial, you'll use a subset of 30,000 captions and their corresponding images to train our model. Choosing to use more data would result in improved captioning quality.

with open(annotation_file, 'r') as f:
    annotations = json.load(f)
# Group all captions together having the same image ID.
image_path_to_caption = collections.defaultdict(list)
for val in annotations['annotations']:
  caption = f"<start> {val['caption']} <end>"
  image_path = PATH + 'COCO_train2014_' + '%012d.jpg' % (val['image_id'])
  image_path_to_caption[image_path].append(caption)
image_paths = list(image_path_to_caption.keys())
random.shuffle(image_paths)

# Select the first 6000 image_paths from the shuffled set.
# Approximately each image id has 5 captions associated with it, so that will
# lead to 30,000 examples.
train_image_paths = image_paths[:6000]
print(len(train_image_paths))
6000
train_captions = []
img_name_vector = []

for image_path in train_image_paths:
  caption_list = image_path_to_caption[image_path]
  train_captions.extend(caption_list)
  img_name_vector.extend([image_path] * len(caption_list))
print(train_captions[0])
Image.open(img_name_vector[0])
<start> A laptop sitting on a desk open to a webpage. <end>

png

Preprocess the images using InceptionV3

Next, you will use InceptionV3 (which is pretrained on Imagenet) to classify each image. You will extract features from the last convolutional layer.

First, you will convert the images into InceptionV3's expected format by:

  • Resizing the image to 299px by 299px
  • Preprocess the images using the preprocess_input method to normalize the image so that it contains pixels in the range of -1 to 1, which matches the format of the images used to train InceptionV3.
def load_image(image_path):
    img = tf.io.read_file(image_path)
    img = tf.image.decode_jpeg(img, channels=3)
    img = tf.image.resize(img, (299, 299))
    img = tf.keras.applications.inception_v3.preprocess_input(img)
    return img, image_path

Initialize InceptionV3 and load the pretrained Imagenet weights

Now you'll create a tf.keras model where the output layer is the last convolutional layer in the InceptionV3 architecture. The shape of the output of this layer is 8x8x2048. You use the last convolutional layer because you are using attention in this example. You don't perform this initialization during training because it could become a bottleneck.

  • You forward each image through the network and store the resulting vector in a dictionary (image_name --> feature_vector).
  • After all the images are passed through the network, you save the dictionary to disk.
image_model = tf.keras.applications.InceptionV3(include_top=False,
                                                weights='imagenet')
new_input = image_model.input
hidden_layer = image_model.layers[-1].output

image_features_extract_model = tf.keras.Model(new_input, hidden_layer)
Downloading data from https://storage.googleapis.com/tensorflow/keras-applications/inception_v3/inception_v3_weights_tf_dim_ordering_tf_kernels_notop.h5
87916544/87910968 [==============================] - 3s 0us/step

Caching the features extracted from InceptionV3

You will pre-process each image with InceptionV3 and cache the output to disk. Caching the output in RAM would be faster but also memory intensive, requiring 8 * 8 * 2048 floats per image. At the time of writing, this exceeds the memory limitations of Colab (currently 12GB of memory).

Performance could be improved with a more sophisticated caching strategy (for example, by sharding the images to reduce random access disk I/O), but that would require more code.

The caching will take about 10 minutes to run in Colab with a GPU. If you'd like to see a progress bar, you can:

  1. install tqdm:

    !pip install -q tqdm

  2. Import tqdm:

    from tqdm import tqdm

  3. Change the following line:

    for img, path in image_dataset:

    to:

    for img, path in tqdm(image_dataset):

# Get unique images
encode_train = sorted(set(img_name_vector))

# Feel free to change batch_size according to your system configuration
image_dataset = tf.data.Dataset.from_tensor_slices(encode_train)
image_dataset = image_dataset.map(
  load_image, num_parallel_calls=tf.data.AUTOTUNE).batch(16)

for img, path in image_dataset:
  batch_features = image_features_extract_model(img)
  batch_features = tf.reshape(batch_features,
                              (batch_features.shape[0], -1, batch_features.shape[3]))

  for bf, p in zip(batch_features, path):
    path_of_feature = p.numpy().decode("utf-8")
    np.save(path_of_feature, bf.numpy())

Preprocess and tokenize the captions

  • First, you'll tokenize the captions (for example, by splitting on spaces). This gives us a vocabulary of all of the unique words in the data (for example, "surfing", "football", and so on).
  • Next, you'll limit the vocabulary size to the top 5,000 words (to save memory). You'll replace all other words with the token "UNK" (unknown).
  • You then create word-to-index and index-to-word mappings.
  • Finally, you pad all sequences to be the same length as the longest one.
# Find the maximum length of any caption in our dataset
def calc_max_length(tensor):
    return max(len(t) for t in tensor)
# Choose the top 5000 words from the vocabulary
top_k = 5000
tokenizer = tf.keras.preprocessing.text.Tokenizer(num_words=top_k,
                                                  oov_token="<unk>",
                                                  filters='!"#$%&()*+.,-/:;=?@[\]^_`{|}~ ')
tokenizer.fit_on_texts(train_captions)
tokenizer.word_index['<pad>'] = 0
tokenizer.index_word[0] = '<pad>'
# Create the tokenized vectors
train_seqs = tokenizer.texts_to_sequences(train_captions)
# Pad each vector to the max_length of the captions
# If you do not provide a max_length value, pad_sequences calculates it automatically
cap_vector = tf.keras.preprocessing.sequence.pad_sequences(train_seqs, padding='post')
# Calculates the max_length, which is used to store the attention weights
max_length = calc_max_length(train_seqs)

Split the data into training and testing

img_to_cap_vector = collections.defaultdict(list)
for img, cap in zip(img_name_vector, cap_vector):
  img_to_cap_vector[img].append(cap)

# Create training and validation sets using an 80-20 split randomly.
img_keys = list(img_to_cap_vector.keys())
random.shuffle(img_keys)

slice_index = int(len(img_keys)*0.8)
img_name_train_keys, img_name_val_keys = img_keys[:slice_index], img_keys[slice_index:]

img_name_train = []
cap_train = []
for imgt in img_name_train_keys:
  capt_len = len(img_to_cap_vector[imgt])
  img_name_train.extend([imgt] * capt_len)
  cap_train.extend(img_to_cap_vector[imgt])

img_name_val = []
cap_val = []
for imgv in img_name_val_keys:
  capv_len = len(img_to_cap_vector[imgv])
  img_name_val.extend([imgv] * capv_len)
  cap_val.extend(img_to_cap_vector[imgv])
len(img_name_train), len(cap_train), len(img_name_val), len(cap_val)
(24011, 24011, 6003, 6003)

Create a tf.data dataset for training

Our images and captions are ready! Next, let's create a tf.data dataset to use for training our model.

# Feel free to change these parameters according to your system's configuration

BATCH_SIZE = 64
BUFFER_SIZE = 1000
embedding_dim = 256
units = 512
vocab_size = top_k + 1
num_steps = len(img_name_train) // BATCH_SIZE
# Shape of the vector extracted from InceptionV3 is (64, 2048)
# These two variables represent that vector shape
features_shape = 2048
attention_features_shape = 64
# Load the numpy files
def map_func(img_name, cap):
  img_tensor = np.load(img_name.decode('utf-8')+'.npy')
  return img_tensor, cap
dataset = tf.data.Dataset.from_tensor_slices((img_name_train, cap_train))

# Use map to load the numpy files in parallel
dataset = dataset.map(lambda item1, item2: tf.numpy_function(
          map_func, [item1, item2], [tf.float32, tf.int32]),
          num_parallel_calls=tf.data.AUTOTUNE)

# Shuffle and batch
dataset = dataset.shuffle(BUFFER_SIZE).batch(BATCH_SIZE)
dataset = dataset.prefetch(buffer_size=tf.data.AUTOTUNE)

Model

Fun fact: the decoder below is identical to the one in the example for Neural Machine Translation with Attention.

The model architecture is inspired by the Show, Attend and Tell paper.

  • In this example, you extract the features from the lower convolutional layer of InceptionV3 giving us a vector of shape (8, 8, 2048).
  • You squash that to a shape of (64, 2048).
  • This vector is then passed through the CNN Encoder (which consists of a single Fully connected layer).
  • The RNN (here GRU) attends over the image to predict the next word.
class BahdanauAttention(tf.keras.Model):
  def __init__(self, units):
    super(BahdanauAttention, self).__init__()
    self.W1 = tf.keras.layers.Dense(units)
    self.W2 = tf.keras.layers.Dense(units)
    self.V = tf.keras.layers.Dense(1)

  def call(self, features, hidden):
    # features(CNN_encoder output) shape == (batch_size, 64, embedding_dim)

    # hidden shape == (batch_size, hidden_size)
    # hidden_with_time_axis shape == (batch_size, 1, hidden_size)
    hidden_with_time_axis = tf.expand_dims(hidden, 1)

    # attention_hidden_layer shape == (batch_size, 64, units)
    attention_hidden_layer = (tf.nn.tanh(self.W1(features) +
                                         self.W2(hidden_with_time_axis)))

    # score shape == (batch_size, 64, 1)
    # This gives you an unnormalized score for each image feature.
    score = self.V(attention_hidden_layer)

    # attention_weights shape == (batch_size, 64, 1)
    attention_weights = tf.nn.softmax(score, axis=1)

    # context_vector shape after sum == (batch_size, hidden_size)
    context_vector = attention_weights * features
    context_vector = tf.reduce_sum(context_vector, axis=1)

    return context_vector, attention_weights
class CNN_Encoder(tf.keras.Model):
    # Since you have already extracted the features and dumped it
    # This encoder passes those features through a Fully connected layer
    def __init__(self, embedding_dim):
        super(CNN_Encoder, self).__init__()
        # shape after fc == (batch_size, 64, embedding_dim)
        self.fc = tf.keras.layers.Dense(embedding_dim)

    def call(self, x):
        x = self.fc(x)
        x = tf.nn.relu(x)
        return x
class RNN_Decoder(tf.keras.Model):
  def __init__(self, embedding_dim, units, vocab_size):
    super(RNN_Decoder, self).__init__()
    self.units = units

    self.embedding = tf.keras.layers.Embedding(vocab_size, embedding_dim)
    self.gru = tf.keras.layers.GRU(self.units,
                                   return_sequences=True,
                                   return_state=True,
                                   recurrent_initializer='glorot_uniform')
    self.fc1 = tf.keras.layers.Dense(self.units)
    self.fc2 = tf.keras.layers.Dense(vocab_size)

    self.attention = BahdanauAttention(self.units)

  def call(self, x, features, hidden):
    # defining attention as a separate model
    context_vector, attention_weights = self.attention(features, hidden)

    # x shape after passing through embedding == (batch_size, 1, embedding_dim)
    x = self.embedding(x)

    # x shape after concatenation == (batch_size, 1, embedding_dim + hidden_size)
    x = tf.concat([tf.expand_dims(context_vector, 1), x], axis=-1)

    # passing the concatenated vector to the GRU
    output, state = self.gru(x)

    # shape == (batch_size, max_length, hidden_size)
    x = self.fc1(output)

    # x shape == (batch_size * max_length, hidden_size)
    x = tf.reshape(x, (-1, x.shape[2]))

    # output shape == (batch_size * max_length, vocab)
    x = self.fc2(x)

    return x, state, attention_weights

  def reset_state(self, batch_size):
    return tf.zeros((batch_size, self.units))
encoder = CNN_Encoder(embedding_dim)
decoder = RNN_Decoder(embedding_dim, units, vocab_size)
optimizer = tf.keras.optimizers.Adam()
loss_object = tf.keras.losses.SparseCategoricalCrossentropy(
    from_logits=True, reduction='none')


def loss_function(real, pred):
  mask = tf.math.logical_not(tf.math.equal(real, 0))
  loss_ = loss_object(real, pred)

  mask = tf.cast(mask, dtype=loss_.dtype)
  loss_ *= mask

  return tf.reduce_mean(loss_)

Checkpoint

checkpoint_path = "./checkpoints/train"
ckpt = tf.train.Checkpoint(encoder=encoder,
                           decoder=decoder,
                           optimizer=optimizer)
ckpt_manager = tf.train.CheckpointManager(ckpt, checkpoint_path, max_to_keep=5)
start_epoch = 0
if ckpt_manager.latest_checkpoint:
  start_epoch = int(ckpt_manager.latest_checkpoint.split('-')[-1])
  # restoring the latest checkpoint in checkpoint_path
  ckpt.restore(ckpt_manager.latest_checkpoint)

Training

  • You extract the features stored in the respective .npy files and then pass those features through the encoder.
  • The encoder output, hidden state(initialized to 0) and the decoder input (which is the start token) is passed to the decoder.
  • The decoder returns the predictions and the decoder hidden state.
  • The decoder hidden state is then passed back into the model and the predictions are used to calculate the loss.
  • Use teacher forcing to decide the next input to the decoder.
  • Teacher forcing is the technique where the target word is passed as the next input to the decoder.
  • The final step is to calculate the gradients and apply it to the optimizer and backpropagate.
# adding this in a separate cell because if you run the training cell
# many times, the loss_plot array will be reset
loss_plot = []
@tf.function
def train_step(img_tensor, target):
  loss = 0

  # initializing the hidden state for each batch
  # because the captions are not related from image to image
  hidden = decoder.reset_state(batch_size=target.shape[0])

  dec_input = tf.expand_dims([tokenizer.word_index['<start>']] * target.shape[0], 1)

  with tf.GradientTape() as tape:
      features = encoder(img_tensor)

      for i in range(1, target.shape[1]):
          # passing the features through the decoder
          predictions, hidden, _ = decoder(dec_input, features, hidden)

          loss += loss_function(target[:, i], predictions)

          # using teacher forcing
          dec_input = tf.expand_dims(target[:, i], 1)

  total_loss = (loss / int(target.shape[1]))

  trainable_variables = encoder.trainable_variables + decoder.trainable_variables

  gradients = tape.gradient(loss, trainable_variables)

  optimizer.apply_gradients(zip(gradients, trainable_variables))

  return loss, total_loss
EPOCHS = 20

for epoch in range(start_epoch, EPOCHS):
    start = time.time()
    total_loss = 0

    for (batch, (img_tensor, target)) in enumerate(dataset):
        batch_loss, t_loss = train_step(img_tensor, target)
        total_loss += t_loss

        if batch % 100 == 0:
            average_batch_loss = batch_loss.numpy()/int(target.shape[1])
            print(f'Epoch {epoch+1} Batch {batch} Loss {average_batch_loss:.4f}')
    # storing the epoch end loss value to plot later
    loss_plot.append(total_loss / num_steps)

    if epoch % 5 == 0:
      ckpt_manager.save()

    print(f'Epoch {epoch+1} Loss {total_loss/num_steps:.6f}')
    print(f'Time taken for 1 epoch {time.time()-start:.2f} sec\n')
Epoch 1 Batch 0 Loss 2.0436
Epoch 1 Batch 100 Loss 1.2139
Epoch 1 Batch 200 Loss 1.0171
Epoch 1 Batch 300 Loss 0.9492
Epoch 1 Loss 1.094750
Time taken for 1 epoch 115.99 sec

Epoch 2 Batch 0 Loss 0.9204
Epoch 2 Batch 100 Loss 0.7476
Epoch 2 Batch 200 Loss 0.8300
Epoch 2 Batch 300 Loss 0.8252
Epoch 2 Loss 0.834296
Time taken for 1 epoch 45.89 sec

Epoch 3 Batch 0 Loss 0.7721
Epoch 3 Batch 100 Loss 0.7509
Epoch 3 Batch 200 Loss 0.8069
Epoch 3 Batch 300 Loss 0.7527
Epoch 3 Loss 0.752264
Time taken for 1 epoch 45.67 sec

Epoch 4 Batch 0 Loss 0.7364
Epoch 4 Batch 100 Loss 0.6961
Epoch 4 Batch 200 Loss 0.7111
Epoch 4 Batch 300 Loss 0.7302
Epoch 4 Loss 0.697394
Time taken for 1 epoch 47.18 sec

Epoch 5 Batch 0 Loss 0.6719
Epoch 5 Batch 100 Loss 0.6485
Epoch 5 Batch 200 Loss 0.6410
Epoch 5 Batch 300 Loss 0.5863
Epoch 5 Loss 0.656725
Time taken for 1 epoch 46.51 sec

Epoch 6 Batch 0 Loss 0.6303
Epoch 6 Batch 100 Loss 0.6145
Epoch 6 Batch 200 Loss 0.6173
Epoch 6 Batch 300 Loss 0.5613
Epoch 6 Loss 0.617368
Time taken for 1 epoch 45.54 sec

Epoch 7 Batch 0 Loss 0.5689
Epoch 7 Batch 100 Loss 0.5396
Epoch 7 Batch 200 Loss 0.6018
Epoch 7 Batch 300 Loss 0.6358
Epoch 7 Loss 0.584526
Time taken for 1 epoch 45.98 sec

Epoch 8 Batch 0 Loss 0.5883
Epoch 8 Batch 100 Loss 0.5473
Epoch 8 Batch 200 Loss 0.5676
Epoch 8 Batch 300 Loss 0.5417
Epoch 8 Loss 0.554602
Time taken for 1 epoch 45.03 sec

Epoch 9 Batch 0 Loss 0.5423
Epoch 9 Batch 100 Loss 0.5331
Epoch 9 Batch 200 Loss 0.5054
Epoch 9 Batch 300 Loss 0.4515
Epoch 9 Loss 0.525291
Time taken for 1 epoch 44.87 sec

Epoch 10 Batch 0 Loss 0.5095
Epoch 10 Batch 100 Loss 0.5017
Epoch 10 Batch 200 Loss 0.4781
Epoch 10 Batch 300 Loss 0.4704
Epoch 10 Loss 0.497998
Time taken for 1 epoch 45.22 sec

Epoch 11 Batch 0 Loss 0.4385
Epoch 11 Batch 100 Loss 0.4621
Epoch 11 Batch 200 Loss 0.5013
Epoch 11 Batch 300 Loss 0.5085
Epoch 11 Loss 0.473056
Time taken for 1 epoch 47.45 sec

Epoch 12 Batch 0 Loss 0.4842
Epoch 12 Batch 100 Loss 0.4583
Epoch 12 Batch 200 Loss 0.4253
Epoch 12 Batch 300 Loss 0.4387
Epoch 12 Loss 0.448735
Time taken for 1 epoch 47.58 sec

Epoch 13 Batch 0 Loss 0.4350
Epoch 13 Batch 100 Loss 0.4013
Epoch 13 Batch 200 Loss 0.4413
Epoch 13 Batch 300 Loss 0.4178
Epoch 13 Loss 0.425068
Time taken for 1 epoch 46.99 sec

Epoch 14 Batch 0 Loss 0.4234
Epoch 14 Batch 100 Loss 0.4112
Epoch 14 Batch 200 Loss 0.4164
Epoch 14 Batch 300 Loss 0.3829
Epoch 14 Loss 0.404426
Time taken for 1 epoch 46.81 sec

Epoch 15 Batch 0 Loss 0.3797
Epoch 15 Batch 100 Loss 0.3471
Epoch 15 Batch 200 Loss 0.3635
Epoch 15 Batch 300 Loss 0.3502
Epoch 15 Loss 0.384106
Time taken for 1 epoch 46.46 sec

Epoch 16 Batch 0 Loss 0.3790
Epoch 16 Batch 100 Loss 0.3795
Epoch 16 Batch 200 Loss 0.3778
Epoch 16 Batch 300 Loss 0.3371
Epoch 16 Loss 0.365713
Time taken for 1 epoch 44.86 sec

Epoch 17 Batch 0 Loss 0.3997
Epoch 17 Batch 100 Loss 0.3389
Epoch 17 Batch 200 Loss 0.3373
Epoch 17 Batch 300 Loss 0.3326
Epoch 17 Loss 0.349113
Time taken for 1 epoch 43.83 sec

Epoch 18 Batch 0 Loss 0.3439
Epoch 18 Batch 100 Loss 0.3746
Epoch 18 Batch 200 Loss 0.3828
Epoch 18 Batch 300 Loss 0.3210
Epoch 18 Loss 0.331469
Time taken for 1 epoch 45.52 sec

Epoch 19 Batch 0 Loss 0.3199
Epoch 19 Batch 100 Loss 0.3233
Epoch 19 Batch 200 Loss 0.2991
Epoch 19 Batch 300 Loss 0.3366
Epoch 19 Loss 0.315025
Time taken for 1 epoch 45.93 sec

Epoch 20 Batch 0 Loss 0.3088
Epoch 20 Batch 100 Loss 0.2845
Epoch 20 Batch 200 Loss 0.3127
Epoch 20 Batch 300 Loss 0.3254
Epoch 20 Loss 0.301194
Time taken for 1 epoch 45.48 sec
plt.plot(loss_plot)
plt.xlabel('Epochs')
plt.ylabel('Loss')
plt.title('Loss Plot')
plt.show()

png

Caption!

  • The evaluate function is similar to the training loop, except you don't use teacher forcing here. The input to the decoder at each time step is its previous predictions along with the hidden state and the encoder output.
  • Stop predicting when the model predicts the end token.
  • And store the attention weights for every time step.
def evaluate(image):
    attention_plot = np.zeros((max_length, attention_features_shape))

    hidden = decoder.reset_state(batch_size=1)

    temp_input = tf.expand_dims(load_image(image)[0], 0)
    img_tensor_val = image_features_extract_model(temp_input)
    img_tensor_val = tf.reshape(img_tensor_val, (img_tensor_val.shape[0],
                                                 -1,
                                                 img_tensor_val.shape[3]))

    features = encoder(img_tensor_val)

    dec_input = tf.expand_dims([tokenizer.word_index['<start>']], 0)
    result = []

    for i in range(max_length):
        predictions, hidden, attention_weights = decoder(dec_input,
                                                         features,
                                                         hidden)

        attention_plot[i] = tf.reshape(attention_weights, (-1, )).numpy()

        predicted_id = tf.random.categorical(predictions, 1)[0][0].numpy()
        result.append(tokenizer.index_word[predicted_id])

        if tokenizer.index_word[predicted_id] == '<end>':
            return result, attention_plot

        dec_input = tf.expand_dims([predicted_id], 0)

    attention_plot = attention_plot[:len(result), :]
    return result, attention_plot
def plot_attention(image, result, attention_plot):
    temp_image = np.array(Image.open(image))

    fig = plt.figure(figsize=(10, 10))

    len_result = len(result)
    for i in range(len_result):
        temp_att = np.resize(attention_plot[i], (8, 8))
        grid_size = max(np.ceil(len_result/2), 2)
        ax = fig.add_subplot(grid_size, grid_size, i+1)
        ax.set_title(result[i])
        img = ax.imshow(temp_image)
        ax.imshow(temp_att, cmap='gray', alpha=0.6, extent=img.get_extent())

    plt.tight_layout()
    plt.show()
# captions on the validation set
rid = np.random.randint(0, len(img_name_val))
image = img_name_val[rid]
real_caption = ' '.join([tokenizer.index_word[i]
                        for i in cap_val[rid] if i not in [0]])
result, attention_plot = evaluate(image)

print('Real Caption:', real_caption)
print('Prediction Caption:', ' '.join(result))
plot_attention(image, result, attention_plot)
Real Caption: <start> an image of a man with other men on skiis <end>
Prediction Caption: a small skiers standing on a snow around a woman in the snow <end>
/home/kbuilder/.local/lib/python3.6/site-packages/ipykernel_launcher.py:10: MatplotlibDeprecationWarning: Passing non-integers as three-element position specification is deprecated since 3.3 and will be removed two minor releases later.
  # Remove the CWD from sys.path while we load stuff.

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Try it on your own images

For fun, below we've provided a method you can use to caption your own images with the model we've just trained. Keep in mind, it was trained on a relatively small amount of data, and your images may be different from the training data (so be prepared for weird results!)

image_url = 'https://tensorflow.org/images/surf.jpg'
image_extension = image_url[-4:]
image_path = tf.keras.utils.get_file('image'+image_extension, origin=image_url)

result, attention_plot = evaluate(image_path)
print('Prediction Caption:', ' '.join(result))
plot_attention(image_path, result, attention_plot)
# opening the image
Image.open(image_path)
Downloading data from https://tensorflow.org/images/surf.jpg
65536/64400 [==============================] - 0s 4us/step
Prediction Caption: a man rides a wave on a sunny day <end>
/home/kbuilder/.local/lib/python3.6/site-packages/ipykernel_launcher.py:10: MatplotlibDeprecationWarning: Passing non-integers as three-element position specification is deprecated since 3.3 and will be removed two minor releases later.
  # Remove the CWD from sys.path while we load stuff.

png

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Next steps

Congrats! You've just trained an image captioning model with attention. Next, take a look at this example Neural Machine Translation with Attention. It uses a similar architecture to translate between Spanish and English sentences. You can also experiment with training the code in this notebook on a different dataset.