DM-53465: Fix PSF normalization #171
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| warping_kernel_name, | ||
| ) | ||
| else: | ||
| psf_padding = 10 |
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The only other non-lanczos option is bilinear; why 10 for that and only 5 for lanczos3?
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5 for Lanczos3 is well-motivated because that is the support of the kernel and verified that making it 6 or 7 made no difference to the output. I didn't want to make any strong assumptions about the support of non-Lanczos kernels and took a more conservative approach of 10. I also didn't want to introduce it as a config option.
| psf_stacker.add_masked_image(warped_psf_maskedImage, weight=weight) | ||
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| if warped_psf_maskedImage.image.array.sum() < 0.995: | ||
| if not (0.995 < (psf_normalization := warped_psf_maskedImage.image.array.sum()) < 1.005): |
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I think at some point this needs to actually do something rather than warn, like try to increase the padding and then fall back to renormalizing by the sum (which should only happen if the PSF cut off, i.e. >0 at the edge).
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Maybe, but for now, I just want to monitor this to make sure this never happens. Piff guarantees that the model it returns is normalized and lanczos resampling shouldn't introduce deviations that are larger than 0.005. If the PSF normalization is off by more than 0.5%, it means something with the assumptions made is incorrect and I'd like to know that before padding is auto-adjusted.
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This PR addresses a bug with PSF not being normalized to unity in cell-based coadds.