[gnuastro-devel] [task #14191] Enable FITS input and output using Lzip

[Antonio Diaz Diaz]

Follow-up Comment #5, task #14191 (project gnuastro):

There are (among others) two very different kinds of data to be considered
here. Lets call them "text" and "continuous functions". The main feature of
"text" compression algorithms like gzip is not that the size of its
compressing element is fixed at 8 bits, but the fact that they search for
exact matches in the data. For gzip a miss is as good as a kilometer; 'foo' is
as different from 'for' as it is from 'fox'.

OTOH, algorithms designed to compress data of the "continuous function" type,
usually take advantage of the fact that differences between consecutive data
elements tend to be smaller than the values of the elements, and therefore
easier to compress efficiently. This is the case of the rice algorithm.

IMO, the two kinds of algorithms are so fundamentally different that it does
not make sense to mix them.

Regarding the use of gzip/lzip to compress binary tables in fits files, the
first attempt does not seem promising. The table seems to compress much better
if it is in text (ASCII) format than in fits format:


-rw-r--r-- 1   8603322 2017-01-30 10:45 uvudf_rafelski_2015.dat
-rw-r--r-- 1   1877246 2017-01-30 10:45 uvudf_rafelski_2015.dat.gz
-rw-r--r-- 1   1164719 2017-01-30 10:45 uvudf_rafelski_2015.dat.lz
-rw-r--r-- 1   7450560 2017-01-09 08:23 uvudf_rafelski_2015.fits
-rw-r--r-- 1   4625937 2017-01-30 10:43 uvudf_rafelski_2015.fits.gz
-rw-r--r-- 1   3603977 2017-01-09 08:23 uvudf_rafelski_2015.fits.lz



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