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Old 02-09-2009, 09:30 PM
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dugnsuz (Doug)
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Synthetic RGB Question.

Hello all...
Recently got an Astronomik OIII filter to combine with my Ha filter in order to try my hand at Synthetic RGB work.

When I've taken Ha subs to combine with RGB files for "HaRGB", I've split the Ha into its component red, green, blue channels...discarded G and B and used the Red channel as my Ha file - seems to work better than just converting the entire image to greyscale.

Question: Do I do something similar with the OIII sub? i.e use the green or blue channel?? Then use that single channel to work with to produce the synthetic RGB image?

Cheers in advance
Doug

Last edited by dugnsuz; 03-09-2009 at 07:23 PM.
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Old 02-09-2009, 10:53 PM
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bump - desperate for answer!
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Old 02-09-2009, 11:04 PM
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Octane (Humayun)
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Doug,

I think you answered your own question.

You'll find that when imaging with a hydrogen alpha filter, that the red channel will be busiest, as you've mentioned. Similarly, the oxygen III filter will show more detail in one of the other two channels.

Pick and choose and hack as appropriate.

Regards,
Humayun
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Old 02-09-2009, 11:07 PM
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Quote:
Originally Posted by Octane View Post
Doug,

I think you answered your own question.

You'll find that when imaging with a hydrogen alpha filter, that the red channel will be busiest, as you've mentioned. Similarly, the oxygen III filter will show more detail in one of the other two channels.

Pick and choose and hack as appropriate.

Regards,
Humayun
Yeah right H - I'm ahead of myself!!
Thanks for the reply, and you're probably correct...experiment!
Cheers
Doug
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Old 03-09-2009, 05:26 AM
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Interesting. I had assumed you'd use the whole Ha data and put it all in one channel, all OIII in another channel etc.

Using the above method, what do you do if you want to add SII? It's primarily red also. If you were to only use the blue or green from it, be very faint? Or do you take from it's red channel only, and put that in the synthetic green channel or whatever? As I said, I had assumed you'd put it all in one channel.
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Old 03-09-2009, 08:49 AM
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Originally Posted by troypiggo View Post
Interesting. I had assumed you'd use the whole Ha data and put it all in one channel, all OIII in another channel etc.

Using the above method, what do you do if you want to add SII? It's primarily red also. If you were to only use the blue or green from it, be very faint? Or do you take from it's red channel only, and put that in the synthetic green channel or whatever? As I said, I had assumed you'd put it all in one channel.
Hi Troy,
This is the method I hope to try...
http://www.starrywonders.com/bicolortechniquenew.html

Re Ha - all the useable data is on the red channel, so I split the Ha into RGB components and use the red as my Ha for subsequent work. I've found a straight change of the original RGB file into grayscale loses all the contrast.

With this in mind, I wondered if most of the data in an OIII image resides in either the green or blue channels - which one to use!!??
Inspection of the images suggests there's an equal distribution of data over the G and B.
May try and develop my own method

Cheers
Doug
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Old 03-09-2009, 10:28 AM
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It's all very interesting.
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Old 03-09-2009, 11:15 AM
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It's all very interesting.
Certainly is Troy.
Check out Eddie's (ejcruz) synthetic RGB work...
http://ejcruz.smugmug.com/photos/621685798_svFeR-L.jpg
http://ejcruz.smugmug.com/photos/602052368_xrzVT-L.jpg

They're my inspiration for this project
Doug
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Old 03-09-2009, 11:42 AM
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Eddie takes stunning NarrowBand images with, I think, a Mono camera. From the sound of it, you guys might be using a colour camera which may add unwanted complexity??. A Mono camera gives all the images in grayscale and you assign whatever colour you like: HOS = Ha-Red, OIII-Green, SII-Blue. SHO ("Hubble Colours") = SII-Red, Ha-Green, OIII-Blue. There are other combinations as well.
A good intro - http://starizona.com/acb/ccd/advimnarrow.aspx

Charles

Last edited by cfranks; 03-09-2009 at 11:56 AM.
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Old 03-09-2009, 11:59 AM
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Thanks Charles and Doug. I'll be using NB filters on my DSLR, that's why I'm interested in this technique.
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Old 03-09-2009, 12:12 PM
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Quote:
Originally Posted by cfranks View Post
Eddie takes stunning NarrowBand images with, I think, a Mono camera. From the sound of it, you guys might be using a colour camera which may add unwanted complexity??. A Mono camera gives all the images in grayscale and you assign whatever colour you like: HOS = Ha-Red, OIII-Green, SII-Blue. SHO ("Hubble Colours") = SII-Red, Ha-Green, OIII-Blue. There are other combinations as well.

Charles
Hi Charles - correct I'm using a modified Canon 40D DSLR. The narrowband filters are the Astronomik EOS clip in variety which sit over the sensor in the camera body. I've achieved passable results with the 12nm Ha filter so far...
http://s327.photobucket.com/albums/k...urrent=20b.jpg
...and inspired by Eddie's work, I purchased the equivalent OIII filter to try my hand at widefield synthetic RGB - so as you see I don't shy from unwanted complexity!!
Detail on the 10min images I took last night using the OIII filter really is very faint (as expected) and I will have to push exposure times way out of the HEQ5 comfort zone I reckon.
But as you've said, a mono camera is the tool of choice for this stuff and this I don't have. So my question still remains - in the "RGB" produced by using the OIII filter, where does the useable data reside...in the blue or green channels? Or, does one just convert the RGB to greyscale and use that?
I'm starting to confuse myself I fear!!
Doug
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Old 03-09-2009, 12:16 PM
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Will kick my kids of 'Habbo Hotel' on the iMac tonight and give these ideas a workout...Doug
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Old 03-09-2009, 12:22 PM
cfranks (Charles)
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Not that I've got experience, but I would suggest setting the camera to mono and see how that goes. The Starizona docs show the Ha in the red, the SIII in the deep red and the OIII as turqoise. They also mention you could try HOO - Ha=red, OIII-green and OIII-blue. I just got my camera and filters last month but haven't used them yet.

Charles
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Old 03-09-2009, 02:44 PM
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Originally Posted by cfranks View Post
...but I would suggest setting the camera to mono and see how that goes.

Charles
Hmmmm interesting Charles, hadn't considered this. I suspect though that this would result in a loss of data - electronic pixel wells not being filled or some such thing!! Hopefully someone else can flesh out the science of my uninformed statement!!!
Doug
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Old 03-09-2009, 02:57 PM
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All the HA is the red channel. So discard the G and B. For O3 you will find that the O3 is recorded in both the G and B channels almost equally. So in this case dicard the red channel. This is why O3 is a lovely cyan colour. Cyan is the absence of red in an additive colour system.

The Bayer filters in a colour DSLR stop any useful light getting to the other channels. If you do use them you are basically only adding noise.


For something like the Helix Neb which is nearly all HA and O3 you will get what looks like a 'natural' colour image if you assign colours thus.

HA red to RED Channel
O3 green to GREEN Channel
O3 blue to BLUE Channel

See here

http://www.iceinspace.com.au/forum/s...light=achromat

and here

http://www.iceinspace.com.au/forum/s...light=achromat

Bert
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Old 03-09-2009, 03:46 PM
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All the HA is the red channel. So discard the G and B. For O3 you will find that the O3 is recorded in both the G and B channels almost equally. So in this case dicard the red channel.

Bert
Thanks Bert - confirmed!!
I remember those threads too - interesting idea, well executed.
Cheers
Doug
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Old 03-09-2009, 07:32 PM
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Image now uploaded to Deep Sky section...

http://www.iceinspace.com.au/forum/s...376#post488376

Cheers
Doug
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