Shortest triplet network with tf 2.0

You will need tensorflow 2.0 in order to run this script

Importing libraries and loading MNIST dataset

import tensorflow as tf
from tensorflow import keras
import tensorflow_addons as tfa


(x_train, y_train), (x_test, y_test) = keras.datasets.mnist.load_data()
x_train = x_train / 255.0

Creating a model using the Sequential API

new_model = tf.keras.Sequential([
        keras.layers.Reshape(
            target_shape=[28, 28, 1],
            input_shape=(28, 28)),
        keras.layers.Conv2D(2, 5, padding='same', activation=tf.nn.relu),
        keras.layers.MaxPooling2D((2, 2), (2, 2), padding='same'),
        keras.layers.Conv2D(4, 5, padding='same', activation=tf.nn.relu),
        keras.layers.MaxPooling2D((2, 2), (2, 2), padding='same'),
        keras.layers.Flatten(),
        keras.layers.Dense(64, activation=tf.nn.relu)])

Compile the model using triplet_semihard_loss from tensorflow_addons

opt = keras.optimizers.Adam(learning_rate=1e-3)
new_model.compile(optimizer=opt, loss=tfa.losses.triplet_semihard_loss)

Fit and save the model!

new_model.fit(x_train, y_train, batch_size=64, epochs=20)
new_model.save("model.h5")

Let's now test the model by comparing it to a untrained network

_, (x_test, y_test) = keras.datasets.mnist.load_data()
x_test = x_test / 255.0

trainedNet = tf.keras.models.load_model("model.h5")
untrainedNet = tf.keras.Sequential([
        keras.layers.Reshape(
            target_shape=[28, 28, 1],
            input_shape=(28, 28)),
        keras.layers.Conv2D(2, 5, padding='same', activation=tf.nn.relu),
        keras.layers.MaxPooling2D((2, 2), (2, 2), padding='same'),
        keras.layers.Conv2D(4, 5, padding='same', activation=tf.nn.relu),
        keras.layers.MaxPooling2D((2, 2), (2, 2), padding='same'),
        keras.layers.Flatten(),
        keras.layers.Dense(64, activation=tf.nn.relu)])


good_embeddings = trainedNet(x_test)
bad_embeddings = untrainedNet(x_test)

Let's apply PCA to both our embeddings and visualize the results.

no_of_components = 2
pca = PCA(n_components=no_of_components)

trained_compoments = pca.fit_transform(good_embeddings)
untrained_components = pca.fit_transform(bad_embeddings)

test_class_labels = np.unique(np.array(y_test))

epochs = 20
step = 10
fig = plt.figure(figsize=(16, 8))
for label in test_class_labels:
    decomposed_embeddings_class = trained_compoments[y_test == label]
    decomposed_gray_class = untrained_components[y_test == label]

    plt.subplot(1, 2, 1)
    plt.scatter(decomposed_gray_class[::step, 1], decomposed_gray_class[::step, 0], label=str(label))
    plt.title('before training (embeddings)')
    plt.legend()

    plt.subplot(1, 2, 2)
    plt.scatter(decomposed_embeddings_class[::step, 1], decomposed_embeddings_class[::step, 0], label=str(label))
    plt.title('after @%d epochs' % epochs)
    plt.legend()

plt.show()