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

[Barrett, Paul]

We can then use the same argument for 32 and 64-bit floats. Why do we need
them, if we can use 32 and 64 bit integers with a scale and offset?

 -- Paul

On Thu, Aug 7, 2025 at 9:39 AM Arnold Rots <arots at cfa.harvard.edu> wrote:

> But why not use an 8 or 16 bit integer with a scale factor and zero offset?
>
> Arnold H Rots
>
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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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