Cygnus Constellation

[Jules]

Hi

I have currently been recording data in Ha and OIII in the above constellation. I would eventually like to use my two data sets to make a colour image, with blends of Ha and OIII to form a third colour (if thats appropriate).

I am not sure how I could do this in Pixinsight, I would be fairly happy with this in Photoshop, but I would like to concentrate on Pixinsight.

There seems to be a lot of information on the web about the 'true' colours of Ha and OIII.

I would be interesting to read other peoples opinions.

Julian

[Jack Harvey]

Steve Cannistra's bicolor technique should allow you to do what you want.  http://www.starrywonders.com/bicolortechnique.html  We have used it several times successfully (Since our setup at CTIO lacks a Sii filter and we can only use Ha and Oiii for NB).  Combine the Ha and Oiii data using Channel combine or Pixel math.  This then becomes a "green" channel and the Ha is red and the Oiii is blue for combining in LRGB combine tool.  You might have to play with the amounts of each channel to get the results that pleases you.

ie  http://www.starshadows.com/gallery/display.cfm?imgID=418

[Jules]

Jack

Thanks for the information and getting back to me.

Julian

[Jules]

Hi Jack

What are the true colours of Ha , OIII, SII. Making a synthetic channel from Ha and OIII would that be construed as compromising the image.I know what I am doing is not science but I would like to reproduce a true likeness of what is actually there. It would be interesting to hear your thoughts.

Julian

[GB_10D]

Hi Julian,

I made several times RGB-pictures out of Ha and OIII images. Asign Ha to red and asign OIII to both green and blue which gives you quite a realistic color rendition.
The only thing that won't match are star colors.

See an example of the Vela SNR: http://www.pbase.com/gbachmayer/image/115938912/original

I added RGB just for star colors, the nebula itself has been assembled with above described procedure.

Best regards,
Gerhard

[Jules]

Hi Gerhard

That is a lovely image. Did you assign the OIII directly to blue or did you blend with the Ha and would that be same with the green?

Interesting point on star colour, I did not think about that.

Thanks

Julian

[GB_10D]

Hi Julian,

I assigned OIII directly to green and blue. Its spectral line is halfway between green and blue, so this is a physically correct procedure. Ha is deep in the red, I wouldn't mix it with the green channel. What you could do is mixing something like 10-15% Ha to blue to emulate the contribution of Hb.

Best regards,
Gerhard

[Jules]

Gerhard

Interesting stuff, I will give it a try and see what happens. Thanks for your time.

Julian

[jmtanous]

I added RGB just for star colors, the nebula itself has been assembled with above described procedure.

Nice images Gerhard,

How do you replace the stars colors? I mean how do you do it to achieve the beautiful results you are getting?

I've tries similar things with star masks and the results are very mediocre...

Cheers,

Jose

[GB_10D]

Thank you, Jose.

Usually the stars are brighter in the RGB-image, but the nebulae are not.
In the narrowband images the nebulae are brighter, but stars are not.
The trick is to balance both images - the RGB and the Ha-OIII - and MAX them in pixel math in a way that stars are defined by the RGB image and the nebulae are defined by the narrowband image. It is a bit of try and error, but usually I find the proper weight factors to have a satisfying result.

Best regards,
Gerhard

[Alejandro Tombolini]

Very interesting Gerhald, and an excellent result! A very harmonious balance of colors.

Best Regards, Alejandro.