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Author Topic: Image calibration in PI  (Read 4149 times)

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Offline chris.bailey

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Re: Image calibration in PI
« Reply #15 on: 10:30:44, 10 March, 2015 »
Good. Try re-doing star alignment with a lower clamping threshold. Your images are a bit undersampled so you tend to get overshoot on the interpolation. If 0.25 does not fix it drop it to 0.2. If they persist trying using BiCubic B-Spline as the interpolation mechanism.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
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Offline chris.bailey

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Re: Image calibration in PI
« Reply #16 on: 10:36:25, 10 March, 2015 »
Phil

Due to the varying gradients I did a DBE on the individual colour channels before colour combining. Then make a big preview and do background neutralisation with an upper limit of 0.03 and then add a preview round M81 and do colour calibration with structure detection off and limits (lower for white and upper for background at 0.03). Stretch. ACDNR. L Mask. Saturation Curve (twice). SCDNR (Green Neutral)

Rough and ready but ...

Chris
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Offline Phillyo

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Re: Image calibration in PI
« Reply #17 on: 10:40:14, 10 March, 2015 »
Awesome, thanks chris. 

That took me about three hours haha. I'm just about to walk the dogs but I'll take another look when I get back.

Phil
Astrotrac | Avalon Linear Fast Reverse with EQmod | WO Star 71 | Astrodon 3nm Ha, 5nm SII and 5nm OIII | Astro-modded Canon 450D | QSI 583wsg | Lodestar X2 Guidecam | Sequence Generator Pro | Pixinsight

Offline chris.bailey

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Re: Image calibration in PI
« Reply #18 on: 11:44:56, 10 March, 2015 »
Phil

Getting colour calibration right at the linear stage is the key to RGB image processing in PI and it is always a two step process. Background neutralisation lines up the peaks of the background and colour calibration adjusts the relative magnitudes of the colour components. The settings I used are as below. DBE often leads to a neutral background but if there are strong gradients and/or colour casts it can sometime not.

HTH

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
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Offline chris.bailey

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Re: Image calibration in PI
« Reply #19 on: 11:50:07, 10 March, 2015 »
And spending a little more time with it.

Those black specks around stars really throws out the histogram tool so it is worth trying to suppress them at the pre-processsing stage.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

Offline Phillyo

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Re: Image calibration in PI
« Reply #20 on: 15:36:41, 10 March, 2015 »
Thanks again Chris,

I'm just sitting down now to have another look at it. What is causing the stars to lose shape and look so bright? Is that just due to CCD and Scope combination?

Thanks,
Phil.
Astrotrac | Avalon Linear Fast Reverse with EQmod | WO Star 71 | Astrodon 3nm Ha, 5nm SII and 5nm OIII | Astro-modded Canon 450D | QSI 583wsg | Lodestar X2 Guidecam | Sequence Generator Pro | Pixinsight

Offline chris.bailey

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Re: Image calibration in PI
« Reply #21 on: 15:51:09, 10 March, 2015 »
Phil

A few thoughts

At 3.2 "/pxl you are a bit undersampled and that shows when you start cropping. Are you dithering, if so try drizzling. How are you focusing. Being slightly off focus wrecks the FWHM very quickly. The star registration issue wont help.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

Offline Phillyo

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Re: Image calibration in PI
« Reply #22 on: 16:34:14, 10 March, 2015 »
Chris,

I've just re-calibrated all the subs and I had to use the BiCubic B-spline interpolation but it has got rid of those black rings, so that's a start. Yes I use a high dither between each image. I've never heard of/tried drizzling before so I'll take a look at that too. I'm using auto focus so the focus should be pretty spot on each time. Focus changes per filter and per 2 degree change in temp.

Still looking at a longer FL telescope to try hitting these galaxies but money is an issue!

Phil
Astrotrac | Avalon Linear Fast Reverse with EQmod | WO Star 71 | Astrodon 3nm Ha, 5nm SII and 5nm OIII | Astro-modded Canon 450D | QSI 583wsg | Lodestar X2 Guidecam | Sequence Generator Pro | Pixinsight

Offline chris.bailey

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Re: Image calibration in PI
« Reply #23 on: 16:37:12, 10 March, 2015 »
Phil

If you use a decent dither then x2 drizzling will take you up to 1.6 "/pxl but the file sizes do make it a bit of a processing chugathon.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

Offline Phillyo

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Re: Image calibration in PI
« Reply #24 on: 19:26:46, 10 March, 2015 »
Ok so final try for now, getting more data tonight hopefully. Not that I think it'll help much but I've run out of targets with my little scope. Suggestions on a post card!!



This is a combination of HaLRGB. I've burnt the cores out on the stars and I've lost a bit of the IFN, but maybe more detail in M81? *shrug* I dunno. Learned a lot over the last few days so I'm happy :)

Thanks again Chris; I definitely owe you a few pints!!

Phil
Astrotrac | Avalon Linear Fast Reverse with EQmod | WO Star 71 | Astrodon 3nm Ha, 5nm SII and 5nm OIII | Astro-modded Canon 450D | QSI 583wsg | Lodestar X2 Guidecam | Sequence Generator Pro | Pixinsight

Offline chris.bailey

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Re: Image calibration in PI
« Reply #25 on: 19:29:28, 10 March, 2015 »
Loads of targets up there mate.... a lifetimes worth!

Have a look at the Sharpless catalogue, lots of them are BIG but a little faint.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

Offline Phillyo

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Re: Image calibration in PI
« Reply #26 on: 00:08:03, 14 March, 2015 »
Had another play with this. Core of M81 blown out, but I think I know where I went wrong there.

Phil
Astrotrac | Avalon Linear Fast Reverse with EQmod | WO Star 71 | Astrodon 3nm Ha, 5nm SII and 5nm OIII | Astro-modded Canon 450D | QSI 583wsg | Lodestar X2 Guidecam | Sequence Generator Pro | Pixinsight

 

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