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Fixed Cutout2D support for section objects #18548

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Fixed Cutout2D support for section objects #18548

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Description

This PR attempts to fix an issue where Cutout2D would raise an IndexError when attempting to create a cutout using an ImageHDU.section object using compressed FITS file.

Fixes #18467

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@bhpcv252 bhpcv252 requested a review from saimn as a code owner August 24, 2025 10:33
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pllim
pllim reviewed Aug 25, 2025
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pllim
pllim reviewed Aug 25, 2025
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astropy/io/fits/tests/data/compressed_2d_float.fits Outdated
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Did you check to see if we don't already have a qualifying test data?

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Yes, I initially checked the existing test FITS files but couldn't find one that reproduced the issue. AFAIK, the bug appears specific to compressed FITS files where the data is stored as int16 (rescales to float32) and includes blank values. Here _scale_data() tries to set the blanks, but once BITPIX changes to -32 (after first header update), any section[:, :] results in an error.

@pllim pllim added this to the v7.2.0 milestone Aug 25, 2025
@pllim pllim requested a review from astrofrog August 26, 2025 20:53
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@saimn saimn Awaiting requested review from saimn saimn is a code owner

@astrofrog astrofrog Awaiting requested review from astrofrog

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Cutout2D cannot handle partial cutouts on section objects
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