Photometry linearity issue?

I am trying to calibrate a photometric measurement using reference stars in the field.
If I select an area around a star and select “PSF” from the drop-down menu, and in turn perform this for several stars with known magnitudes from an AAVSO search chart, I get a nice, consistent magnitude offset to apply to the target.
Siril_PSF

However, if I in stead use the “Pick a star” in the drop-down, I get a non-linear response, useless for calibration:
Siril_pickastar
Image Information > Dynamic PSF also gives this non-linear result.

I checked the same image using the python SEP package and got a nice result, similar to the PSF method.
SEP_phot

Could I have configured something wrong, or does this point to an issue with photometry in Siril?
Using linux Siril-1-2-1-x86_64.AppImage

Hello, ‘pick a star’ and the dynamic PSF window are designed to select stars mostly for astrometry purposes, the aperture photometry code doesn’t run for them, only a simple magnitude evaluation. That’s why you don’t get the same results.

Calibration from a catalogue may be available in a later version, we have ongoing work on that.

2 Likes

Ok, thanks for the explanation.

Built-in calibration from a catalogue would indeed be a great feature.