Data compression on the sphere

Abstract

Large data-sets defined on the sphere arise in many fields. In particular, recent and forthcoming observations of the anisotropies of the cosmic microwave background (CMB) made on the celestial sphere contain approximately three and fifty mega-pixels respectively. The compression of such data is therefore becoming increasingly important. We develop algorithms to compress data defined on the sphere. A Haar wavelet transform on the sphere is used as an energy compression stage to reduce the entropy of the data, followed by Huffman and run-length encoding stages. Lossless and lossy compression algorithms are developed. We evaluate compression performance on simulated CMB data, Earth topography data and environmental illumination maps used in computer graphics. The CMB data can be compressed to approximately 40% of its original size for essentially no loss to the cosmological information content of the data, and to approximately 20% if a small cosmological information loss is tolerated. For the topographic and illumination data compression ratios of approximately 40:1 can be achieved when a small degradation in quality is allowed. We make our SZIP program that implements these compression algorithms available publicly.

13 pages, 8 figures, accepted for publication by A&A; We make our SZIP program that implements these compression algorithms available publicly from http://www.szip.org.uk

References in corpus (7)

• Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
• HEALPix -- a Framework for High Resolution Discretization, and Fast Analysis of Data Distributed on the Sphere
• Three-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Temperature Analysis
• Spatiospectral concentration on a sphere
• Wavelets, ridgelets and curvelets on the sphere
• Exact reconstruction with directional wavelets on the sphere
• Correspondence principle between spherical and Euclidean wavelets

Cited by in corpus (7)

• Hierarchical progressive surveys. Multi-resolution HEALPix data structures for astronomical images, catalogues, and 3-dimensional data cubes
• Localisation of directional scale-discretised wavelets on the sphere
• Second-Generation Curvelets on the Sphere
• Spherical Bayesian mass-mapping with uncertainties: full sky observations on the celestial sphere
• Wavelet-Bayesian inference of cosmic strings embedded in the cosmic microwave background
• SILC: a new Planck Internal Linear Combination CMB temperature map using directional wavelets
• Sparse image reconstruction on the sphere: analysis and synthesis