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

[Arnold Rots]

True, but if your data comes from an 8 bit A2D converter (Paul's example),
nothing is lost - unless there is a nonlinear LUT.

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

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On Thu, Aug 7, 2025 at 9:48 AM Thomas Boch <thomas.boch at astro.unistra.fr>
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 | Facebook <http://cfa.harvard.edu/facebook> | Twitter
> <http://cfa.harvard.edu/twitter> | YouTube
> <http://cfa.harvard.edu/youtube> | Newsletter
> <http://cfa.harvard.edu/newsletter>
>
>
> 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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