Fits file open/export size discrepancy

Software GIMP
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Curious if anyone can comment why exporting a .fit file is a few bytes smaller in size than the file imported. Like by about 3?

Relevancy: This causes a mismatch when moving files between Siril and Gimp processing, ex. if one has extracted RGB channels for separate processing, expecting to re-combine later in Siril using pixel math. Work around requires loading all related sub files into Gimp, even if files aren’t processed, inorder to export similar size files for later pixel math operations.

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FITS files contain metadata (and even free form comments it seems). So you can’t expect file sizes to be always identical after editing?

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@Gbert Hi! Would you be willing to try the latest development version, 2.99.16? GIMP - Development Downloads

We switched to using NASA’s cfitsio library for importing/exporting FITS files, so in theory it should sync up with Siril better. If there are still issues, I’d be interested in knowing so we can improve it for the next release.

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Thanks, I’ll try it!

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