Variational Autoencoder (VAE) on FashionMNIST

This project demonstrates a Variational Autoencoder (VAE) implemented from scratch using PyTorch to learn a compact, 2D latent representation of the FashionMNIST dataset. It highlights core deep learning principles including encoder-decoder architectures, the reparameterization trick, and latent space sampling — making it an ideal showcase of applied machine learning proficiency.

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Objective

• Develop and train a Variational Autoencoder (VAE) using PyTorch.
• Learn and visualize compressed latent representations of image data.
• Generate synthetic FashionMNIST images using decoder sampling.
• Gain insights into model interpretability through visual analysis of the latent space.

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Tools & Technologies

Purpose	Tool/Library
Deep Learning	PyTorch
Data Handling	torchvision.datasets
Visualization	Matplotlib, NumPy
Dataset	FashionMNIST
IDE	Google Colab / Jupyter

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Core Components

• Encoder: Maps flattened image (784D) to a 2D latent space (mean & log variance).
• Reparameterization Trick: Enables backpropagation through stochastic sampling.
• Decoder: Reconstructs original image from latent vector.
• Loss Function: Combines reconstruction loss (binary cross-entropy) and KL divergence to regularize latent space.

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Results

Training Loss Curve

The model demonstrates steady convergence over 10 epochs.

Loss Curve:

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Latent Space Visualization

• Unlabeled Latent Space

Shows 2D clustering of 5000 samples in latent space.

• Colored by Class

Each cluster corresponds to a different FashionMNIST category.

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Image Generation

• Grid Sampling from Latent Space

Samples from a 15x15 grid across 2D latent dimensions:

• Class-Averaged Latent Sampling

Each row shows slight variations around the latent mean vector for one category:

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Key Learnings

• Dimensionality Reduction: Compressing high-dimensional image space into 2D latent representations reveals structure in the data.
• Generative Modeling: Once trained, the decoder can generate new, realistic-looking images conditioned on sampled latent vectors.
• Model Interpretation: Latent space plots provide intuitive insights into how the model separates categories.

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Challenges Faced

• Balancing the trade-off between reconstruction loss and KL divergence.
• Maintaining meaningful variance in a low-dimensional latent space (2D).
• Avoiding mode collapse during training with small latent vectors.

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How to Run

1. Install Dependencies

pip install torch torchvision matplotlib numpy