title: QVZ: lossy compression of quality values.
abstract: Recent advancements in sequencing technology have led to a drastic reduction in the cost of sequencing a genome. This has generated an unprecedented amount of genomic data that must be stored, processed and transmitted. To facilitate this effort, we propose a new lossy compressor for the quality values presented in genomic data files (e.g. FASTQ and SAM files), which comprise roughly half of the storage space (in the uncompressed domain). Lossy compression allows for compression of data beyond its lossless limit.
  
  
  
  The proposed algorithm QVZ exhibits better rate-distortion performance than the previously proposed algorithms, for several distortion metrics and for the lossless case. Moreover, it allows the user to define any quasi-convex distortion function to be minimized, a feature not supported by the previous algorithms. Finally, we show that QVZ-compressed data exhibit better performance in the genotyping than data compressed with previously proposed algorithms, in the sense that for a similar rate, a genotyping closer to that achieved with the original quality values is obtained.
  
  
  
  QVZ is written in C and can be downloaded from https://github.com/mikelhernaez/qvz.
  
  
  
  mhernaez@stanford.edu or gmalysa@stanford.edu or iochoa@stanford.edu
  
  
  
  Supplementary data are available at Bioinformatics online.
authors.affiliation: Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA.
authors.forename: Greg
authors.initials: G
authors.lastname: Malysa
authors.affiliation: Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA.
authors.forename: Mikel
authors.initials: M
authors.lastname: Hernaez
authors.affiliation: Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA.
authors.forename: Idoia
authors.initials: I
authors.lastname: Ochoa
authors.affiliation: Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA.
authors.forename: Milind
authors.initials: M
authors.lastname: Rao
authors.affiliation: Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA.
authors.forename: Karthik
authors.initials: K
authors.lastname: Ganesan
authors.affiliation: Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA.
authors.forename: Tsachy
authors.initials: T
authors.lastname: Weissman
mesh_terms: D000465:Algorithms; D000818:Animals; D044962:Data Compression / Q000592:standards*; D030541:Databases, Genetic; D005838:Genotype; D060005:Genotyping Techniques; D006801:Humans; D020641:Polymorphism, Single Nucleotide / Q000235:genetics