narrowband image capture and processing help

[troypiggo]

Recently I've tried my hand at some narrowband imaging in Ha, OIII, and SII. During the processing of my images, I've come to realise that there is more to it than meets the eye.

Image capture - I used exactly the same sub lengths for each filter. I know that narrowband would typically require longer subs than LRGB imaging. For simplicity I was going 8min subs, but I know I should be going for longer, maybe 15 or 20 min subs. That aside, do you capture all sub lengths the same for each filter? Or should SII be longer, because Ha is more dominant? Or should sub lengths be same but capture more of them for the SII?

Image processing - I had always assumed that for Hubble palette it was as simple as SII goes straight into R, Ha into G, and OIII into B. Then tweak the channels to get the right colour mix. I'm finding that the G/Ha is so overpowering and dominant, it's hard to control. On top of that, I've been doing some reading and finding that some blend some Ha into the other channels etc. So it's not as simple as one filter per channel. Correct?

Or perhaps if I did the longer sub lengths for the weaker filters, eg SII, it should be one filter per channel? ie get it right more at image capture time to make the processing simpler?

I know it's all subjective, and we're not talking about true colour balancing here. What I'm talking about is the true Hubble palette for example, everyone talks about it being SHO.

Any tips, recommended reading, etc?

[Mighty_oz]

This one http://www.flemingastrophotography.com/tipstricks.html
http://tech.groups.yahoo.com/group/narrowbandimaging/ and
and of course this guy :) http://www.narrowbandimaging.com/home_page.htm
and Pixinsight if u have it of course

hope they help, yet to do much myself.

Marcus

[bmitchell82]

Ken Crawford does a really good write up on how to blend narrow band together. He stacks them all in the program, but doesn't combine them. Imports into Photoshop and can really do some magic. :) google it

[Tandum]

Troy, you'll have to stretch the s2 way more than the others so you'll need more subs or it will tear apart. With what you have, stretch to balance the hystograms, ie: you might have to wind the Ha back while stetching the S2 a lot, it depends on the target, but if you get the hystograms looking the same it will mix better.

To get the hubble palette happening with the yellows and golds etc start with this page (http://bf-astro.com/hubbleP.htm). Then check out tone mapping (http://astroanarchy.blogspot.co.nz/2009/11/power-of-tone-mapping.html) for another approach.

I'll be back in ozzie next week if you need more help. I've been more than a little Internet challenged while travelling around NZ :rolleyes:

[troypiggo]

Thanks Robin. So more subs of the same length as the other filters, or do you reckon longer subs as well?

[Tandum]

I normally do 15 min subs. You'll see the weak ones and know which ones you need more of. It's really trial and error and when you have 92hours of data total you'll know you've gone overboard :)

[RobF]

Nah! There'll always be someone that says just a bit more data required....:lol:
Good thread Troy. I don't think I'm as far along as you, but rapidly realising many of the hard won tricks of LRGB imaging don't cut it in the NB world :rolleyes:

[troypiggo]

Thanks guys. Have all those links bookmarked and read. I'm pushing my subs out to 16 mins at the moment. Capturing some SII to go with longer subs of Ha and OIII from Wednesday night. We'll get there eventually...