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Old 27-04-2013, 09:46 AM
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Narrowband recipes

I have been shooting some narrowband recently and am about to process it. The data is quite good.

In the past as I recall (I haven't done one for a while) I used Ha to green, O111 to blue and S11 to red. But I weighted O111 x 8 and S11 x 4 to overcome the overwhelming Ha signal. I also tend not to like greens.

I particularly like Martin Pugh's colour scheme with the pale yellow/browns. Also Davey's work.

What formulas have you found effective?

Greg.
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Old 27-04-2013, 02:55 PM
jase (Jason)
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I think it mostly depends on the target as some are better suited to different palettes. Experimenting is a must. I still enjoy the Hubble palette but regardless of the palette you choose there is an underlying strategy that applies to all narrowband images. The goal is to emphasise differences between the different parts of the nebula. As you point out this is a challenge as Hydrogen Alpha typically dominates the signal. So to counteract this, you need to adjust the weight of each channel to maximise the use of the colour spectrum.

Russell Croman came up with a method which I've used with great success in the past. This approach is different to using photoshop clipping masks which I find gives finer control but in any case both work well.

On the FITS master of each emission line measure the background (in same location across all masters). If the background is 420 for Ha, subtract 320 using pixel math so that all emission line masters have a normalised background of 100. Now that the masters have been normalised. Perform a colour combine with weightings of 4:1:2.5 for SII:HA:OIII respectively. Check the balance of the combined image to see if these weightings aren't biased. If they are, you'll need to scale weaker emission line masters. I use MaximDL for this but CCDStack can do the same (I just fine MaximDL easier for this operation). To scale, use pixel math by reducing the constant and increasing the scale factor percentage. For example SII would have a constant of -400 with a scale factor percentage of 500 which still keeps your 100 count background ADU. You may need to scale higher if the emission is too weak. Once the weaker emission masters have been scaled they should closely match in intensity across the three emission line masters. You can then perform another colour combine with weightings of 1:1:1 as the scaling has counteracted the weighting. Make sure you turn off background auto equalize as you don't want to equalize a background that has already been normalised! Once done, save as a TIF and use this as the background image to a ha luminance for detail. Results should reveal 'punchy' details.

When it comes to colour mapping such as in Photoshop using clipping masks, its relatively simple to get the colours that Martin and others use. A colour map of R:240,G:150,B:30 will get you the muddy burnt orange hue that work well for SII data. Equally, OIII can be tweaked between aqua through to teal. Comes down to a matter of preference. I've always found the Hubble palette as the most aesthetic providing the Ha data is managed correctly.
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Old 27-04-2013, 06:18 PM
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Greg, Have a go at tonemapping NB as well. The guys at Astro Anarchy came up with it. Have a look at this old post for a preview of what it did for one of my images and a link to the docs.

Also, have a look at this NB 3D version of the veil from Astro Anarchy. You'll never see it the same way again.

I'm having issues identifying and using forum links with chrome on this hackintosh, hope these work.

Last edited by Tandum; 27-04-2013 at 06:42 PM.
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Old 27-04-2013, 09:45 PM
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Great info there Jase, thanks - bookmarking this thread.

Greg, here some info from Starizona, you probably know most of it though. http://starizona.com/acb/ccd/advimnarrow.aspx

Josh
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Old 28-04-2013, 09:08 PM
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Greg,

I have made some RAW data available on CloudyNights in an attempt to see what others are doing. Several people have processed the data showing their results. It's been interesting to see all the different results from the same data.

The RAW data and results of different processing are available on:

http://www.cloudynights.com/ubbthrea.../o/o/fpart/all

Terry
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Old 29-04-2013, 04:53 PM
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There's some great responses here. Thanks for the detailed info Jase and that's a good link at Starizona Josh. That's a fantastic thread Terry and all those examples really give you a chance to see which one you like.

That Veil is unreal Robin. That's worth pursuing. 3D images may be a trend for the future.

Greg.
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Old 29-04-2013, 06:34 PM
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Seen this video by Don Goldman?

http://www.astrodonimaging.com/tutorials/#t9
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Old 29-04-2013, 08:07 PM
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Nice link Troy.
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Old 30-04-2013, 07:16 PM
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Quote:
Originally Posted by troypiggo View Post
Seen this video by Don Goldman?

http://www.astrodonimaging.com/tutorials/#t9

That's a great tutorial Troy. Exactly what I was after - thanks!

Greg.
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