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Calibration issue: Binning - Pixel Size - SGP vs. NINA  

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(@ventania)
Molecular Cloud Customer
Joined: 2 years ago
Posts: 3
April 13, 2021 17:48  

Calibration is fine for my Luminance subs with 1x1 binning. Unfortunately APP seems to be unable to calibrate my RGB subs with 2x2 binning. Sensor size is 2275x2200. Lights are captured with SGP, calibration frames have been captured with NINA. There is a difference though in the pixel size reported for the 2x2 frames. SGP informs these as 1375x1100 in the FITS header for the lights, while NINA lists the calibration frames as 1374x1100. I suspect this is just a rounding difference when dividing 2275 by two for the 2x2 binning.

APP is happy to process the 2x2 lights and report these as calibrated, it just does not apply any of the loaded 2x2 calibration frames. Would this indeed be due to the difference in pixel size (1374x1100 instead of 1375x1100)? If yes: could this be resolved by correcting the FITS headers or would that only confuse APP?

Using APP version 1.082

This topic was modified 5 months ago by Ventania

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(@wvreeven)
Quasar Admin
Joined: 3 years ago
Posts: 1112
April 13, 2021 22:09  

@ventania What happens if you shoot the lights and the calibration files with the same software? So all SGP or all NINA? That would certainly avoid the rounding off issue that you see now. And in general it is advisable to shoot all data with the same software to avoid issues like this and potential other issues as well.

Correcting the FITS headers would certainly not solve this since the sensor data itself would still be one pixel row higher or lower. Cropping the larger files such that it contains one row less could work but since you have a color camera you may delete essential data.


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(@ventania)
Molecular Cloud Customer
Joined: 2 years ago
Posts: 3
April 13, 2021 23:12  

Thanks for the quick reply! I understand that it is advisable to use the same capture software for both lights and calibration frames., I just like the flats wizard in NINA much better than the equivalent in SGP, while SGP is (still) better suited for my capture sessions. I can redo bias and darks with SGP, but it would be too late for flats then as the optical train has changed since capturing those lights. It would really be too bad if that now implies the RGB data has become useless.

May try cropping though, although I am not sure how I could strip a single pixel column. Can APP batch crop handle that? I am using a mono camera, hence the separate LRGB frames. It is really only one pixel difference in the width of the frame. Would be a shame to have to throw it all away or leave uncalibrated. At least the Luminance data is OK to calibrate and process.

Update: just used APP batch modify with a right offset of one to strip a single pixel column on the right hand side of a small sample of 2x2 light frames from SGP. APP is now perfectly happy to apply the 2x2 calibration frames from NINA. Seems all is not lost then for this set of data. Thanks for the tip on cropping. Going forward I will also make sure to take calibration frames with the same software as for the lights, but at least this seems to be a useful workaround for now.

This post was modified 5 months ago by Ventania

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(@wvreeven)
Quasar Admin
Joined: 3 years ago
Posts: 1112
April 14, 2021 00:40  

@ventania It is possible to do that in APP but since you need to draw the crop region by hand you need to be very precise. 


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