Lossy Compression of Quality Values via Rate Distortion Theory

TL;DR

This paper introduces a theoretical framework for lossy compression of genomic quality values, achieving significant data reduction with minimal impact on downstream analysis, including regimes below one bit per quality value.

Contribution

It presents a novel rate distortion theory-based approach for lossy compression of quality values in genomic data, enabling ultra-low bit rate compression regimes not previously possible.

Findings

Significant compression with minimal impact on downstream tasks

Theoretical analysis supports practical effectiveness

Achieves compression below one bit per quality value

Abstract

Motivation: Next Generation Sequencing technologies revolutionized many fields in biology by enabling the fast and cheap sequencing of large amounts of genomic data. The ever increasing sequencing capacities enabled by current sequencing machines hold a lot of promise as for the future applications of these technologies, but also create increasing computational challenges related to the analysis and storage of these data. A typical sequencing data file may occupy tens or even hundreds of gigabytes of disk space, prohibitively large for many users. Raw sequencing data consists of both the DNA sequences (reads) and per-base quality values that indicate the level of confidence in the readout of these sequences. Quality values account for about half of the required disk space in the commonly used FASTQ format and therefore their compression can significantly reduce storage requirements and speed up analysis and transmission of these data. Results: In this paper we present a framework for the lossy compression of the quality value sequences of genomic read files. Numerical experiments with reference based alignment using these quality values suggest that we can achieve significant compression with little compromise in performance for several downstream applications of interest, as is consistent with our theoretical analysis. Our framework also allows compression in a regime - below one bit per quality value - for which there are no existing compressors.