3D-SLARM: Practical Lossless Volumetric Image Compression via a 3D-Scanning Lightweight Autoregressive Model

Volumetric images often encapsulate critical information, making it essential to employ lossless compression to preserve data integrity. Although various learned methods have demonstrated effective lossless compression for volumetric images, balancing high compression ratios with rapid coding speeds and lightweight architectures remains challenging. In this paper, we propose a 3D-scanning lightweight autoregressive model (3D-SLARM) for practical lossless volumetric image compression. 3D-SLARM integrates a novel 3D plane scanning module, a lightweight feature extraction (FE) module, and a lightweight distribution parameter and adaptive range predictor (DPARP) module. Initially, 3D-SLARM leverages a 3D plane scanning module to determine the scanning order of each voxel, allowing parallel coding of voxels within the same plane. Next, the lightweight FE module captures both intra-slice and inter-slice dependencies in the receptive field defined by the 3D plane scanning module. By incorporating our proposed serial re-parameterization (SerRep) technology alongside non-centric masked convolution (NCMC), the FE module attains a lightweight design while effectively capturing complex dependencies. Finally, 3D-SLARM employs a lightweight DPARP module to compute distribution parameters for both 8-bit and high bit-depth volumetric images. For high bit-depth images, the module further generates an adaptive probability range for each voxel, resulting in compact, voxel-specific PMF tables that facilitate efficient compression. Extensive experiments demonstrate that our 3D-SLARM achieves state-of-the-art lossless compression performance on majority volumetric image datasets and maintains fast coding speed with a lightweight design, underscoring its practical applicability.