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

[Barrett, Paul]

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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