Testing a SAR-based ship classifier with different loss functions

This code explores the impact of various loss functions on the accuracy of SAR ship classification. It trains a convolutional neural network (CNN) with six different loss functions and compares their performance.

Key Features:

• Compares CrossEntropy, L1, MSE, BCEWithLogitsLoss, Kullback-Leibler Divergence and Focal Loss
• Uses PyTorch for deep learning
• Trains on the Fusar dataset (tiff images), and OpenSARShip (png images) dataset
• Evaluates accuracy on a test set
• Supports GPU acceleration

Loss Functions in SAR Ship Classification:

This section briefly explains and presents formulas for the loss functions used in the paper:

1. CrossEntropyLoss:

• Formula: CrossEntropy(y_true, y_pred) = -Σ[y_true_i * log(y_pred_i)]
• Explanation: Measures the difference between the predicted probability distribution (y_pred) and the true label distribution (y_true) for each class.

2. L1 Loss:

• Formula: L1Loss(y_true, y_pred) = 1/N * Σ|y_true_i - y_pred_i|
• Explanation: Measures the average absolute difference between predicted values (y_pred) and true values (y_true). Robust to outliers.

3. Mean Squared Error (MSE):

• Formula: MSELoss(y_true, y_pred) = 1/N * Σ(y_true_i - y_pred_i)^2
• Explanation: Measures the average squared difference between predicted values (y_pred) and true values (y_true). Sensitive to outliers.

4. BCEWithLogitsLoss:

• Formula: BCEWithLogitsLoss(y_true, y_pred) = -[y_true * log(σ(y_pred)) + (1 - y_true) * log(1 - σ(y_pred))]
• Explanation: Measures the binary cross-entropy between the model's logits (unscaled output) and the true labels (0 or 1).

5. Focal Loss:

• Formula: FocalLoss(y_true, y_pred) = -Σ[α * (1 - p_t)^γ * y_t * log(p_t)]
• Explanation: Similar to BCEWithLogitsLoss, but introduces hyperparameters α and γ to downweight the loss for easily classified samples, focusing training on harder ones.

6. Kullback-Leibler Divergence Loss:

• Formula: KLDiv(p||q) = Σ(p_i * log (p_i/q_i))
• Explanation: This measures the difference between two probability distributions and can be used as a loss function. However, it is less common than Cross-Entropy due to its computational complexity and sensitivity to outliers.

Code Details

Requirements:

• Python 3.x
• PyTorch
• torchvision
• PIL (Pillow)
• numpy

Usage:

1. Install dependencies: pip install -r requirements.txt
2. Download and extract the both datasets or email the authors for datasets 😉
3. Keep only three classes of data, Fishing, Tanker and Cargo. Whereas keep Fusar data in tiff format, while OpenSARShip in png format.
4. Run the code in Jypyter Notebook: sar_loss.ipynb

Output:

• Prints training progress and loss values for each epoch
• Prints final accuracy for each loss function

Customization:

• Adjust hyperparameters like learning rate, batch size, and epochs in the code
• Add more loss functions to the loss_functions dictionary
• Experiment with different dataset directories and model architectures

Contributing:

• Fork the repository
• Create a branch for your changes
• Make your changes and tests
• Submit a pull request

License:

• [N/A]