Transfer learning and fine tuning

Transfer learning consists of taking features learned on one problem, and leveraging them on a new, similar problem. For instance, features from a model that has learned to identify racoons may be useful to kick-start a model meant to identify tanukis.

1. Take layers from a previously trained model.
2. Freeze them, so as to avoid destroying any of the information they contain during future training rounds.
3. Add some new, trainable layers on top of the frozen layers. They will learn to turn the old features into predictions on a new dataset.
4. Train the new layers on your dataset.

Layers & models have three weight attributes:

• weights is the list of all weights variables of the layer.
• trainable_weights is the list of those that are meant to be updated (via gradient descent) to minimize the loss during training.
• non_trainable_weights is the list of those that aren't meant to be trained. Typically they are updated by the model during the forward pass.