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

[jaffe]

My own opinion is that 16 bit floats don't add much usefulness over 16 
bit ints.  They may provide more dynamic range for signals that are much 
smaller than typical in the dataset, but once you give the 
characteristic enough bits to be useful, you haven't got many bits left 
for the mantissa.

However, if there is a large user (e.g. the Rubin Telescope) that is 
already committed to storing or exporting data in 16-bit floats, then 
the FITS standard should probably accommodate them.

Walter

On 2025-08-07 13:48, Thomas Boch via fitsbits wrote:
> My understanding is that with 16 bits integers with BSCALE/BZERO, you
> have a linear uniform quantization whereas 16-bit floating points
> provides with a non-uniform quantization, with higher precision near
> 0.
> 
> --
> Thomas
> 
> Le 07/08/2025 à 15:39, Arnold Rots via fitsbits a écrit :
> 
>> But why not use an 8 or 16 bit integer with a scale factor and zero
>> offset?
>> 
>> Arnold H Rots
>> 
>> Research Associate
>> 
>> SAO/HEAD
>> 
>> Center for Astrophysics | Harvard & Smithsonian
>> Email: arots at cfa.harvard.edu
>> 
>> Office: +1 617 496 7701 | Cell: +1 617 721 6756
>> 
>> 60 Garden Street | MS 69 | Cambridge, MA 02138 | USA
>> 
>> cfa.harvard.edu [1] | Facebook [2] | Twitter [3] | YouTube [4] |
>> Newsletter [5]
>> 
>> On Sat, Jul 26, 2025 at 8:55 PM Barrett, Paul via fitsbits
>> <fitsbits at listmgr.nrao.edu> wrote:
>> 
>> The quick answer is that most telescope backends have 8-bit A2D
>> converters, so 16-bit floats provide sufficient range and precision
>> to store the calibrated data. If you need extended range, then a
>> scaling factor can be used.
>> 
>> -- Paul
>> 
>> On Sat, Jul 26, 2025 at 7:49 PM Eric Greisen via fitsbits
>> <fitsbits at listmgr.nrao.edu> wrote:
>> 
>> 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
>> 
>> _______________________________________________
>> fitsbits mailing list
>> fitsbits at listmgr.nrao.edu
>> https://listmgr.nrao.edu/mailman/listinfo/fitsbits
>> _______________________________________________
>> fitsbits mailing list
>> fitsbits at listmgr.nrao.edu
>> https://listmgr.nrao.edu/mailman/listinfo/fitsbits
>> _______________________________________________
>> fitsbits mailing list
>> fitsbits at listmgr.nrao.edu
>> https://listmgr.nrao.edu/mailman/listinfo/fitsbits
> 
> _______________________________________________
> fitsbits mailing list
> fitsbits at listmgr.nrao.edu
> https://listmgr.nrao.edu/mailman/listinfo/fitsbits
> 
> 
> 
> Links:
> ------
> [1] http://cfa.harvard.edu/
> [2] http://cfa.harvard.edu/facebook
> [3] http://cfa.harvard.edu/twitter
> [4] http://cfa.harvard.edu/youtube
> [5] http://cfa.harvard.edu/newsletter
> _______________________________________________
> fitsbits mailing list
> fitsbits at listmgr.nrao.edu
> https://listmgr.nrao.edu/mailman/listinfo/fitsbits