<div dir="ltr"><div>True, but if your data comes from an 8 bit A2D converter (Paul's example), nothing is lost - unless there is a nonlinear LUT.<br clear="all"></div><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><br><div dir="ltr" style="margin-left:0pt"><table style="border:medium none;border-collapse:collapse"><colgroup><col width="445"><col width="275"></colgroup><tbody><tr style="height:90pt"><td style="border-color:rgb(255,255,255);border-style:solid;border-width:1pt;vertical-align:top;padding:5pt"><p dir="ltr" style="line-height:1.2;margin-top:0pt;margin-bottom:0pt"><span style="font-size:9.5pt;font-family:Arial;color:rgb(34,34,34);background-color:transparent;font-weight:700;font-style:normal;font-variant:normal;text-decoration:none;vertical-align:baseline;white-space:pre-wrap">Arnold H Rots</span></p><p dir="ltr" style="line-height:1.2;margin-top:0pt;margin-bottom:0pt"><span 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<div>
<p>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.</p>
<p><br>
</p>
<p>--<br>
Thomas</p>
<div>Le 07/08/2025 à 15:39, Arnold Rots via
fitsbits a écrit :<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div>But why not use an 8 or 16 bit integer with a scale factor
and zero offset?<br clear="all">
</div>
<div>
<div dir="ltr" class="gmail_signature">
<div dir="ltr">
<div>
<div dir="ltr">
<div>
<div dir="ltr"><br>
<div dir="ltr" style="margin-left:0pt">
<table style="border:medium;border-collapse:collapse">
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<p dir="ltr" style="line-height:1.2;margin-top:0pt;margin-bottom:0pt"><span style="font-size:9.5pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-weight:700;font-style:normal;font-variant:normal;text-decoration:none;vertical-align:baseline;white-space:pre-wrap">Research Associate</span></p>
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<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">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:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="ltr">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.
<div><br>
</div>
<div> -- Paul</div>
<div><br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">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:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div>
<div dir="ltr">
<div style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
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.</div>
<div style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
<br>
</div>
<div style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
Eric Greisen</div>
<hr style="display:inline-block;width:98%">
<div id="m_-155294875179316924m_-8332966783569991369m_7732203089533686962divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> 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}</font>
<div> </div>
</div>
<div><font size="2"><span style="font-size:11pt">
<div>[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>
<br>
<br>
<br>
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