[fitsbits] Update to the FITS Tiled Image Compression Convention

[William Pence]

Yes, the latest version of CFITSIO (v3.35) supports the new features 
described in the tiled image compression document.

Bill

On 07/25/2013 10:58 AM, Erik Bray wrote:
> On 07/24/2013 05:33 PM, William Pence wrote:
>> This is to announce that a new version (v2.3) of the document
>> describing the FITS Tiled Image Compression Convention has been placed
>> on the FITS Support office web site at
>>
>>       http://fits.gsfc.nasa.gov/registry/tilecompression.html
>>
>> The main changes in this new version of the document are:
>>
>> * A new variant of the GZIP algorithm, called GZIP_2, is supported, in
>> which the bytes in the pixel array are shuffled into decreasing order of
>> significance before being compressed with gzip.  This is especially
>> effective with floating point arrays.
>>
>> * The algorithm for dithering floating point values before quantizing
>> them into scaled integers has been expanded and improved.  There is a
>> new variant in which the pixels that are equal to 0.0 are not dithered,
>> and instead the value is exactly preserved.
>>
>> * A new ZDITHER0 keyword is defined, to record the random seed value
>> that is used to generate the dithering pattern.
>>
>> * If the compressed file is larger than about 2.1 GB, then the '1Q'
>> variable length array FITS column format (with 64-bit pointers) must be
>> used
>> instead of the '1P' format.
>
> That's great news--I've had an issue open in PyFITS [1] for a while about the
> last issue.  It was impossible to compressed larger files without allowing the
> use of Q-type VLAs.
>
> Has CFITSIO been updated to support this too.  If not, is there any sense of
> when to look for that?
>
> Thanks,
>
> Erik
>
> [1] https://trac.assembla.com/pyfits/ticket/159
>
> _______________________________________________
> fitsbits mailing list
> fitsbits at listmgr.cv.nrao.edu
> http://listmgr.cv.nrao.edu/mailman/listinfo/fitsbits
>

-- 
____________________________________________________________________
Dr. William Pence                       William.Pence at nasa.gov
NASA/GSFC Code 662       HEASARC        +1-301-286-4599 (voice)
Greenbelt MD 20771                      +1-301-286-1684 (fax)