Since the class pivoted away from the Medium articles style of teaching, this project will not be completed.

In Development: Triplet Loss Network in Keras (with TensorFlow backend)

A quick implementation of a triplet network with an online (batch-based) triplet loss (in Keras).

This was primarily written to support a series of Medium articles ("Building a Triplet Network in Keras") written as a tutorial for students in UMD's FIRE171 (and FIRE271) class who are working with similarity learning. These are the article subtitles:

1. Building the Embedding Network
2. [Customizing the Triplet Loss Function]
3. [Training the Model]
4. [Evaluating and Visualizing Results]

More implementation details are in the articles.

Data

The data used for training is a super small (~140 images) dataset of a few families of bees, collected from manual Google Images search. The dataset I used is provided in the release. I currently only have a training set (I need more time to collect validation and test set).

All images are resized and padded to 299x299 (padding with repeats, using the default numpy resize function).

Model

The model is simple: I chose to use InceptionV3 as the backbone here since it provides high accuracy while not being super large. Plus, for the purposes of the articles, there is already a prebuilt Keras implementation with weights pretrained on ImageNet. The last fully-connected layer is removed, and we add a few new fully-connected layers for our output embedding.

Loss Function

The version of triplet loss that is used is the online version (no prior triplet mining). This is implemented in TensorFlow. This is for a few reasons:

• higher accuracy with faster training time (see FaceNet paper)
• the training model and the inference model are the same
• we can care less about which images go into each batch
• no need to store anything about the triplets beforehand
• this is the version they are expected to use for their student projects

However, it poses some challenges/constraints:

• we need to make sure there's at least one positive pair in the batch
• the loss function itself is more complicated to write (we have to find pairs using the TensorFlow API only)

Training

Evaluation

Visualization