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Old 12-07-2016, 02:20 PM
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graham.hobart (Graham stevens)
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The weight of subs

HI
I have been playing with LRGB subs recently and I find it quite hard to get the balance right for a final colour balance that is pleasing to the eye. I have seen weighting subs mentioned and I think I understand it but I would like someone to confirm what I think it is.
So any one willing to give me a simple explanation?
I also think my lack of G2V colour calibration ( in Maxim)is not helping?
Cheers
Graham
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  #2  
Old 12-07-2016, 06:24 PM
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Camelopardalis (Dunk)
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The response/QE for a sensor isn't linear across the whole visual spectrum, so you need to calibrate and weight accordingly. For example, with my little Sony sensor, it's more sensitive in blue (1st) then Green (2nd, but close to blue) then Red.

I've been experimenting with calibration strategies...the first was to capture short images of a G2V star....I racked it out of focus a bit so it was easier to grab, and then calculated the average value over a 100x100 square of pixels from the middle. For better or worse

Knowing the ratios of response means you could also expose for different lengths to get you the 1:1:1 ratio. With my sensor, if I expose blue and green for 10 minutes each, then red looks about right when exposed for 12 minutes.
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Old 12-07-2016, 09:06 PM
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Atmos (Colin)
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There is a bit of free software called eXcalibrator, you put in the raw FITS files with WCS information and it checks your subs against astrometric data. I've only played with it once or twice but it seems to work quite well.
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Old 13-07-2016, 03:01 PM
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graham.hobart (Graham stevens)
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weights

cheers folks

I must try the excalibrator

I have noticed the KAF8300 seems to be more sensitive in red and green than blue - so a lot of my balancing is trying to get the blue back in images. Maybe I should take more blue subs!
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Old 13-07-2016, 03:58 PM
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Camelopardalis (Dunk)
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Not so much more blue subs, as that gets averaged out in stacking.

You need higher intensity blue subs...take a shot of a G2V star and vary your sub lengths until you get the same pixel values for each channel
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Old 14-07-2016, 09:58 AM
mountainjoo (Jerome)
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If you're using PixInsight, try using LinearFit on each of your channels before combining them. This will match their intensities.
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