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

[Arnold Rots]

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

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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
>>
>>
>>
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