[fitsbits] 16-bit floats {External}

Wed Jul 23 10:30:10 EDT 2025

Hi all,

Any such changes should be coordinated with the recent suggestion of adding JPEGXL support to tile compression.

If the IAU FITS WG is going through a period of rebuilding, the responsibility for maintaining FITS falls to Commission B2.

We looked into support for 16-bit floats when working on FPACK and tile compression. As I recall, it may not be as standardized as 32-bit and 64-bit IEEE floats. There were also some video (?) standards that used real-number representations that were fixed-point, not floating-point.

128-bit formats may need to coexist with complex number representations. The motivations for both shorter than usual or longer than usual floating-point representations in FITS should flow from explicit science and engineering use cases.

Tiled 32-bit integer compression is actually quite elegant, and the noise-sensitive floating-point tile compression quite powerful, see Paper I and Paper II linked at https://heasarc.gsfc.nasa.gov/fitsio/fpack/. There are also a number of interesting issues associated with efficient table compression, such as the benefit of transposing tables and shuffling the bytes. Simply adding another data type won’t address all the issues.

I am unaware of any coherent benchmarks comparing the speed of using 16-bit floats versus FPACK-style floating point compression. This should also be a prerequisite. Are 16-bit floats widely used in other scientific disciplines?

Rob Seaman
Lunar and Planetary Laboratory

On 7/23/25, 6:55 AM, "fitsbits" wrote:

External Email

On Wed 2025-07-23T13:34:54+0100 Thomas Robitaille via fitsbits hath writ:
> I am aware of some modern projects that would benefit from having 16-bit
> floats, since they consider it to be sufficient in precision to store very
> large datasets, and using 16-bit floats would perform a lot better than
> using compression on 32-bit floats for example, and 16-bit floats would
> allow a larger dynamic range than using 16-bit ints with BSCALE/BZERO.

This is not a breaking change, and with little more discussion than we
already see today an informal agreement cold quickly go into use and
then be adopted.
I think the harder part about making this change is establishing
the auspices under which the IAU FITS working group currently acts.

--
Steve Allen <sla at ucolick.org> WGS-84 (GPS)
UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855
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