Transfer Learning

Introduction

Transfer learning allows you to leverage pre-trained models trained on large datasets (like ImageNet) to solve new tasks with less data and compute.

Instead of training a model from scratch, you reuse learned features, which:

✅ Reduces training time.
✅ Improves model performance on smaller datasets.
✅ Requires fewer computational resources.

Why Use Transfer Learning?

• Training deep networks from scratch requires large labeled datasets and high compute.
• Pre-trained models capture generic patterns (edges, textures) useful for many tasks.
• Transfer learning is widely used in computer vision and NLP applications.

Approaches to Transfer Learning

1️⃣ Feature Extraction: Use the pre-trained model as a fixed feature extractor, replacing the top layer(s) with your classifier.
2️⃣ Fine-Tuning: Unfreeze some deeper layers and retrain them on your dataset to adapt learned features.

Example: Transfer Learning for Image Classification with Keras

We will use MobileNetV2, a lightweight pre-trained CNN, to classify images on a custom dataset.

1️⃣ Install and Import Libraries

pip install tensorflow

import tensorflow as tf
from tensorflow.keras.applications import MobileNetV2
from tensorflow.keras.layers import Dense, GlobalAveragePooling2D
from tensorflow.keras.models import Model
from tensorflow.keras.preprocessing.image import ImageDataGenerator

2️⃣ Load and Prepare Data

Prepare your dataset using ImageDataGenerator for augmentation and rescaling.

train_datagen = ImageDataGenerator(rescale=1./255, validation_split=0.2)

train_generator = train_datagen.flow_from_directory(
    'path_to_dataset',
    target_size=(224, 224),
    batch_size=32,
    class_mode='categorical',
    subset='training'
)

val_generator = train_datagen.flow_from_directory(
    'path_to_dataset',
    target_size=(224, 224),
    batch_size=32,
    class_mode='categorical',
    subset='validation'
)

3️⃣ Load Pre-Trained Model

base_model = MobileNetV2(weights='imagenet', include_top=False, input_shape=(224, 224, 3))

# Freeze base model layers
base_model.trainable = False

# Add custom top layers
x = base_model.output
x = GlobalAveragePooling2D()(x)
outputs = Dense(train_generator.num_classes, activation='softmax')(x)

model = Model(inputs=base_model.input, outputs=outputs)

4️⃣ Compile and Train the Model

model.compile(optimizer='adam', loss='categorical_crossentropy', metrics=['accuracy'])

history = model.fit(
    train_generator,
    epochs=10,
    validation_data=val_generator
)

5️⃣ Fine-Tuning (Optional)

After initial training, you can unfreeze some layers and continue training with a low learning rate for fine-tuning.

base_model.trainable = True

model.compile(optimizer=tf.keras.optimizers.Adam(1e-5),
              loss='categorical_crossentropy',
              metrics=['accuracy'])

history_finetune = model.fit(
    train_generator,
    epochs=5,
    validation_data=val_generator
)

Conclusion

✅ Transfer learning allows efficient use of pre-trained models for new tasks.
✅ It helps you build performant models even with limited data and compute.
✅ You can implement feature extraction and fine-tuning using Keras easily.

What’s Next?

✅ Experiment with other pre-trained models like ResNet, Inception, or EfficientNet.
✅ Apply transfer learning for NLP tasks using models like BERT.
✅ Integrate transfer learning into your pipelines for real-world projects.

Join our SuperML Community to share your transfer learning projects and continue growing as a deep learning practitioner.

Happy Learning! 🚀