[fitsbits] [EXT] Re: 16-bit floats {External} {External}

[Eric Greisen]

I am perhaps the person with the longest exposure to FITS.  I expect that adding 16-bit floats would do little  harm.  But I have not seen a proper exposition of why it is needed.  And I have 50+ years of writing radio astronomy software.  At this stage I would vote against it until a proper set of examples are described.

Eric Greisen
________________________________
From: fitsbits <fitsbits-bounces at listmgr.nrao.edu> on behalf of William Pence via fitsbits <fitsbits at listmgr.nrao.edu>
Sent: Saturday, July 26, 2025 1:11 PM
To: Fitsbits <fitsbits at listmgr.nrao.edu>
Subject: Re: [fitsbits] [EXT] Re: 16-bit floats {External} {External}

[Have had technical difficulties posting here; here’s another attempt.]

Based on the discussion so far I am inclined to support adding the 16-bit floating point format to FITS, but not the 128-bit format, as a fundamental datatype in images and binary table columns. As a reminder, the numerical range of the float16 datatype is limited to +65504 to -65504 and the precision is limited to about 4 decimal digits.  That means the largest values (in the range of about 32000 to 65500) are only precise to +/- 32, i.e. the largest possible value is 65504 and the next smaller allowed values are 65472, 65440 and so on.   Based on my own experience in optical and Xray astronomy I can’t think of many applications (or any in fact) where this float16 datatype would be appropriate to use. Apparently it could be useful for some radio astronomy data however.

Bill



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