Blink and SubFrame Selector

[midnightlightning]

Hi,
I'm new to PI and have ben reading up about the above but have a few questions.

At least one tutorial suggests running calibration before using these tools. I use Astro Pixel Processor for pre-processing and have options to export subs after Calibration, the first step in the process, and also after Normalisation which is the last step before Registration.

Should I use the calibrated or normalised subs?

Second question, I dont know how calibration/normalisation works. If each sub is processed independently of the others I'm comfortable but I suspect each sub must be standardised (averaged) against the other subs at some point(s) in the process.

If this is the case then surely putting bad subs into pre-processing must adversely affect the good subs through this standardisation. In which case i'm thinking that Blinky and SS should be used prior to pre-processing?

I would be grateful for advice on when to use Blinky/SS and also what to look for.

I want to drop the worst frames, without being overwhelmed by science are there any simple rules/things to look for to acive this. FWHM and Noise seem to be key to me, can I just drop frames with outliers in these criteria?

Thanks
Jon 

[mcgillca]

Dear Jon,

Hi - I personally run both before I do any pre-processing at all. I think the majority of the things I test for (FWHM, eccentricity, median value) are largely independent of calibration (the exact value of too high a median value will change, but since this is mainly to take out frames to close to dawn or near the moon, this isn't a big deal).

I will then take a quick look using Blink at the remaining subs to make sure there are no real problems with the remaining subs (I often remove subs with satellite trails etc since I generally have sufficient data to be choosy, but this is less problematic with large scale removal).

Doing it this way typically removes something like 30% of my subs, giving less work to do in preprocessing (I image remotely and frequently have 30 plus hours of data on an object).

Hope this helps,

Colin

[midnightlightning]

Thanks Colin.

When I first open files in Blink I can see lots of my images have a milky appearance, probably haze, and I am tempted to remove them.

However if I apply the automatic SFT using the upper button of the two they all look pretty much the same - so I'm thinking perhaps they are ok as the processing will compensate for the haze.

Does anyone have any thoughts on this?

Thanks

Jon

[pfile]

that's normal - you're seeing the offset from light pollution. after stacking you can use DBE to remove the gradient/offsets, or if the LP is really well behaved, just a histogram transformation can compensate for it.

rob

[midnightlightning]

Thanks Rob, that fits with what I am seeing.
I have started a comparison test of running Blink on Raw vs Calibrated vs Normalised frames so will see how that turns out. Would have had results tonight but got dragged to the pub