Plate Solve fails: XPIXSZ and XBINNING double-multiplication

Software Siril
1

Hello team,

I am experiencing an issue with how Siril reads the pixel size from binned FITS headers, which causes the internal Plate Solver to fail.

When capturing in Bin2 with SharpCap, the software writes the already scaled pixel size inside XPIXSZ (7.52 um instead of the native 3.76 um), with the comment / microns, includes binning if any.

Since XBINNING = 2 is also present, Siril multiplies XPIXSZ * XBINNING, resulting in a double-binned pixel size of 15.04 um inside the Plate Solver panel. For comparison, PixInsight reads this exact same file and interprets the pixel size correctly as 7.52 um without double-scaling.

This means Plate Solve fails out of the box. Since Plate Solving is a mandatory step to run the Photometric Color Calibration (PCC), having to manually change this value every single time becomes very tedious in the daily workflow.

You can see the header breakdown and the Siril panel in this screenshot:

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Could an evaluation check be added to Siril’s FITS reader to avoid this double-multiplication?

Alternatively, as a workaround, would it be possible to slightly widen the acceptable scale error range in the Plate Solver? Right now it is strictly below a factor of 2; if the tolerance were just slightly above 2, the solving process wouldn’t fail.

Clear skies,
Lorenzo

2

Hello, this is a behavior you can change in the FITS option of the Siril preferences.

3

Hi Cécil,

Thank you so much, that solved it completely! I missed that option entirely. Siril is an amazing piece of software, and the native Python scripting integration is fantastic.

If I may drop a tiny suggestion regarding the UI: the option name “Update pixel size of binned image” is a bit ambiguous, as it can be interpreted in opposite ways.

While the hover tooltip explains it perfectly, changing the checkbox label to something like “Recompute pixel size from binning keywords” or “Apply binning factor to FITS pixel size” might make it more immediately intuitive for users coming from software like SharpCap.

Thanks again for your awesome work and support!

Clear skies, Lorenzo