Unit mismatch between v24 (instrumental flux) and v29 (nJy) science images in image subtraction?

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Hello,

We’re currently upgrading our AP pipeline from v24 to v29, and we’ve noticed a potential issue regarding flux units in image subtraction.

In v24, the science images (calexp) use instrumental flux units.
In v29, the calexp images are now stored in physical units (nJy).

However, for our current workflow, we plan to:

  • Use a template image built from v24 processing (instrumental units)
  • Subtract it from a new v29 science image (in nJy)

This means the image subtraction will be performed between two images with different flux units.

Our concern:
Will this unit mismatch cause incorrect pixel values in the difference image, leading to biased DIA Source flux measurements (e.g., psfFlux, apFlux)?

Thanks so much for your guidance!