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

[Thomas Boch]

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
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> SAO/HEAD
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> 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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