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[fitsbits] BZIP2 FITS image compression feasibility study
The FITS tiled-image compression convention (see
http://fits.gsfc.nasa.gov/registry/tilecompression.html) currently supports 3 general-purpose image compression algorithms: Rice, Hcompress, and GZIP. Recently, I did some comparison tests using the BZIP2 compression algorithm to see if it offers any unique advantages that would justify adding it as one of the supported algorithms. A link to the complete feasibility report is available from the fpack web page at http://heasarc.gsfc.nasa.gov/fitsio/fpack/ and the main results are as follows: - The Rice algorithm generally provides better compression than BZIP2 when the image is compressed using the default row-by-row tiling pattern. BZIP2 only produces (slightly) better compression than Rice or Hcompress when using much larger sized tiles (e.g., compressing the whole image as a single tile), but this can seriously degrade the I/O performance for software applications that read the compressed image on a row by row basis. - Compressing an image using BZIP2 typically takes 15 to 30 times more CPU time than the Rice algorithm, depending on how much noise is in the image. - Similarly, BZIP2 takes 4 to 6 times more CPU time than Rice to uncompress the image. Thus, based on these tests, there appears to be little justification for adding support for BZIP2 within the FITS tiled-image compression convention. -Bill Pence -- __________________________________________________ __________________ Dr. William Pence NASA/GSFC Code 662 HEASARC +1-301-286-4599 (voice) Greenbelt MD 20771 +1-301-286-1684 (fax) |
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