MixNeRF: Memory Efficient NeRF with Feature Mixed-up Hash Table

Neural radiance field (NeRF) has shown remarkable performance in generating photo-realistic novel views. Since the emergence of NeRF, many studies have been conducted, among which managing features with explicit structures such as grids has achieved exceptionally fast training by reducing the complexity of multilayer perceptron (MLP) networks. However, storing features in dense grids requires significantly large memory space, which leads to memory bottleneck in computer systems and thus large training time. To address this issue, in this work, we propose MixNeRF, a memory-efficient NeRF framework that employs a mixed-up hash table to improve memory efficiency and reduce training time while maintaining reconstruction quality. We first design a \textit{mixed-up hash table} to adaptively mix part of multi-level feature grids into one and map it to a single hash table. Following that, in order to obtain the correct index of a grid point, we further design an \textit{index transformation} method that transforms indices of an arbitrary level grid to those of a canonical grid. Extensive experiments benchmarking with state-of-the-art Instant-NGP, TensoRF, and DVGO, indicate our MixNeRF could achieve the fastest training time on the same GPU hardware with similar or even higher reconstruction quality. Source code is available at \url{https://github.com/nfyfamr/MixNeRF}.