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Restructuring Vector Quantization with the Rotation Trick (arxiv.org)
1 point by fzliu 326 days ago | hide | past | pdf | discuss on HN

In plain words: Compression systems snap encoder output to the nearest codebook vector, and gradients skip that step. Here the output is rotated and stretched into the chosen vector so the gradient keeps its angle and size, improving reconstruction, codebook use, and quantization error across 11 setups.

Abstract

Vector Quantized Variational AutoEncoders (VQ-VAEs) are designed to compress a continuous input to a discrete latent space and reconstruct it with minimal distortion. They operate by maintaining a set of vectors -- often referred to as the codebook -- and quantizing each encoder output to the nearest vector in the codebook. However, as vector quantization is non-differentiable, the gradient to the encoder flows around the vector quantization layer rather than through it in a straight-through approximation. This approximation may be undesirable as all information from the vector quantization operation is lost. In this work, we propose a way to propagate gradients through the vector quantization layer of VQ-VAEs. We smoothly transform each encoder output into its corresponding codebook vector via a rotation and rescaling linear transformation that is treated as a constant during backpropagation. As a result, the relative magnitude and angle between encoder output and codebook vector becomes encoded into the gradient as it propagates through the vector quantization layer and back to the encoder. Across 11 different VQ-VAE training paradigms, we find this restructuring improves reconstruction metrics, codebook utilization, and quantization error. Our code is available at https://github.com/cfifty/rotation_trick.

Christopher Fifty, Ronald G. Junkins, Dennis Duan, Aniketh Iyengar, Jerry W. Liu, Ehsan Amid, Sebastian Thrun, Christopher Ré
arXiv:2410.06424 · cs.LG, cs.CV · submitted Oct 8, 2024 · updated Mar 16, 2025
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