COLI: A Hierarchical Efficient Compressor for Large Images

TL;DR

COLI introduces a hierarchical compression framework for large images that combines accelerated neural representation training with a novel hyper-compression technique, achieving high-quality results with reduced storage and faster processing.

Contribution

The paper presents COLI, a new method that significantly improves the efficiency and compression ratios of INR-based large image compression through pretraining, parallel training, and hyper-compression.

Findings

Achieves superior PSNR and SSIM at lower bits per pixel.

Speeds up NeRV training by up to 4 times.

Maintains minimal distortion with high compression ratios.

Abstract

The escalating adoption of high-resolution, large-field-of-view imagery amplifies the need for efficient compression methodologies. Conventional techniques frequently fail to preserve critical image details, while data-driven approaches exhibit limited generalizability. Implicit Neural Representations (INRs) present a promising alternative by learning continuous mappings from spatial coordinates to pixel intensities for individual images, thereby storing network weights rather than raw pixels and avoiding the generalization problem. However, INR-based compression of large images faces challenges including slow compression speed and suboptimal compression ratios. To address these limitations, we introduce COLI (Compressor for Large Images), a novel framework leveraging Neural Representations for Videos (NeRV). First, recognizing that INR-based compression constitutes a training process, we accelerate its convergence through a pretraining-finetuning paradigm, mixed-precision training, and reformulation of the sequential loss into a parallelizable objective. Second, capitalizing on INRs' transformation of image storage constraints into weight storage, we implement Hyper-Compression, a novel post-training technique to substantially enhance compression ratios while maintaining minimal output distortion. Evaluations across two medical imaging datasets demonstrate that COLI consistently achieves competitive or superior PSNR and SSIM metrics at significantly reduced bits per pixel (bpp), while accelerating NeRV training by up to 4 times.