In [0]:
#@title Licensed under the Apache License, Version 2.0
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
|
|
|
|
As first introduced in the FaceNet paper, TripletLoss is a loss function that trains a neural network to closely embed features of the same class while maximizing the distance between embeddings of different classes. To do this an anchor is chosen along with one negative and one positive sample.
The loss function is described as a Euclidean distance function:
Where A is our anchor input, P is the positive sample input, N is the negative sample input, and alpha is some margin we use to specify when a triplet has become too "easy" and we no longer want to adjust the weights from it.
As shown in the paper, the best results are from triplets known as "Semi-Hard". These are defined as triplets where the negative is farther from the anchor than the positive, but still produces a positive loss. To efficiently find these triplets we utilize online learning and only train from the Semi-Hard examples in each batch.
In [0]:
import io
import numpy as np
In [0]:
import tensorflow as tf
import tensorflow_addons as tfa
import tensorflow_datasets as tfds
In [0]:
def _normalize_img(img, label):
img = tf.cast(img, tf.float32) / 255.
return (img, label)
train_dataset, test_dataset = tfds.load(name="mnist", split=['train', 'test'], as_supervised=True)
# Build your input pipelines
train_dataset = train_dataset.shuffle(1024).batch(32)
train_dataset = train_dataset.map(_normalize_img)
test_dataset = test_dataset.batch(32)
test_dataset = test_dataset.map(_normalize_img)
In [0]:
model = tf.keras.Sequential([
tf.keras.layers.Conv2D(filters=64, kernel_size=2, padding='same', activation='relu', input_shape=(28,28,1)),
tf.keras.layers.MaxPooling2D(pool_size=2),
tf.keras.layers.Dropout(0.3),
tf.keras.layers.Conv2D(filters=32, kernel_size=2, padding='same', activation='relu'),
tf.keras.layers.MaxPooling2D(pool_size=2),
tf.keras.layers.Dropout(0.3),
tf.keras.layers.Flatten(),
tf.keras.layers.Dense(256, activation=None), # No activation on final dense layer
tf.keras.layers.Lambda(lambda x: tf.math.l2_normalize(x, axis=1)) # L2 normalize embeddings
])
In [0]:
# Compile the model
model.compile(
optimizer=tf.keras.optimizers.Adam(0.001),
loss=tfa.losses.TripletSemiHardLoss())
In [0]:
# Train the network
history = model.fit(
train_dataset,
epochs=5)
In [0]:
# Evaluate the network
results = model.predict(test_dataset)
In [0]:
# Save test embeddings for visualization in projector
np.savetxt("vecs.tsv", results, delimiter='\t')
out_m = io.open('meta.tsv', 'w', encoding='utf-8')
for img, labels in tfds.as_numpy(test_dataset):
[out_m.write(str(x) + "\n") for x in labels]
out_m.close()
try:
from google.colab import files
files.download('vecs.tsv')
files.download('meta.tsv')
except:
pass
The vector and metadata files can be loaded and visualized here: https://projector.tensorflow.org/
You can see the results of our embedded test data when visualized with UMAP: