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<p class="MsoNormal">Hi all,<o:p></o:p></p>
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<p class="MsoNormal">I think we’re still waiting to see a few use cases for 16-bit floats. Either they will be persuasive to the group, or they won’t be. I have no philosophical antipathy to supporting new data types in FITS images or tables, but such support
does cost the community not-insignificant effort, including revised documentation. Is this particular change to the standard worth the expense?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Imagine the change were made tomorrow. Which projects would adopt the new data type(s) in the near future? What future technologies would be enabled? I am genuinely interested to know what new tricks FITS can be taught.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">There is nothing magic about IEEE floats (of whatever precision) or 2’s-complement integers. The FITS checksum is an ASCII-encoded 1’s-complement number, and Rice compression even uses unary numbers. Indeed, ASCII itself is now a flavor
of UTF-8, a way to express Unicode. Perhaps FITS should allow UTF-16? Back in the day, IRAF strings were two-byte representations for portability. (Still are, I guess.) Fixed point numbers are even still an option.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Give us a couple of good use cases for 16-bit floats. We’ve heard that IEEE is drafting a standard for Machine Learning which includes small floats (perhaps even smaller than 16-bits). How would users benefit from FITS interoperating with
this standard? Do we need IEEE to finish first?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">And it might be interesting to consider how 16-bit floats would interoperate with floating-point tile compression. FPACK might read in a 32-bit image array with some aggressive q-scaling (for instance), while FUNPACK could provide the option
to write out a 16-bit image. Note that both input and output images would be bigger than the intermediate tile-compressed bintable representation. (The default q of 4.0 corresponds to about 6-bits per pixel.) Or maybe FPACK would support converting 32-bit
images directly to 16-bits with a noise-sensitive threshold of some sort.<o:p></o:p></p>
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<p class="MsoNormal">Rob<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">On 8/7/25, 7:25 AM, "fitsbits" wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">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?<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"> -- Paul<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">On Thu, Aug 7, 2025 at 9:39 AM Arnold Rots <<a href="mailto:arots@cfa.harvard.edu">arots@cfa.harvard.edu</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">But why not use an 8 or 16 bit integer with a scale factor and zero offset?<br clear="all">
<o:p></o:p></p>
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<p style="margin:0in"><b><span style="font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222">Arnold H Rots</span></b><o:p></o:p></p>
<p style="margin:0in"><b><span style="font-size:9.5pt;font-family:"Arial",sans-serif;color:black">Research Associate</span></b><o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">On Sat, Jul 26, 2025 at 8:55 PM Barrett, Paul via fitsbits <<a href="mailto:fitsbits@listmgr.nrao.edu" target="_blank">fitsbits@listmgr.nrao.edu</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">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.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"> -- Paul<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">On Sat, Jul 26, 2025 at 7:49 PM Eric Greisen via fitsbits <<a href="mailto:fitsbits@listmgr.nrao.edu" target="_blank">fitsbits@listmgr.nrao.edu</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:12.0pt;font-family:"Aptos",sans-serif;color:black">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.<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:12.0pt;font-family:"Aptos",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:12.0pt;font-family:"Aptos",sans-serif;color:black">Eric Greisen<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><b><span style="color:black">From:</span></b><span style="color:black"> fitsbits <<a href="mailto:fitsbits-bounces@listmgr.nrao.edu" target="_blank">fitsbits-bounces@listmgr.nrao.edu</a>> on behalf of William Pence
via fitsbits <<a href="mailto:fitsbits@listmgr.nrao.edu" target="_blank">fitsbits@listmgr.nrao.edu</a>><br>
<b>Sent:</b> Saturday, July 26, 2025 1:11 PM<br>
<b>To:</b> Fitsbits <<a href="mailto:fitsbits@listmgr.nrao.edu" target="_blank">fitsbits@listmgr.nrao.edu</a>><br>
<b>Subject:</b> Re: [fitsbits] [EXT] Re: 16-bit floats {External} {External}</span>
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<p class="MsoNormal" style="margin-left:.5in">[Have had technical difficulties posting here; here’s another attempt.]<br>
<br>
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. <br>
<br>
Bill<br>
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