RBA & AF Astrophotography

Widefield Rosette and Cone nebulas

Posted: December 1st, 2009

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This project started as a H-Alpha 2x2 mosaic of the Rosette and Cone nebulas in Monoceros. The top-left pane was taken during full Moon (23 degrees away from this field).

You can see the H-Alpha image only here.

After having the Ha, I was hoping to gather LRGB to make a color image, however I could only squeeze one night for RGB before bad weather arrived, and on that night, I only had about 3 hours before the Moon would show up that night, so the only way I thought I could gather some color that I could use was by using my Canon 40D and a camera lens, and that's how I've got the color (18x10'). Not enough time to get separate RGBs and luminance, much less for a 2x2 mosaic.

Since the color data was so bad compared to the Ha, rather than combining the Ha with the RGB and getting a luminance out of that, I used the Ha as luminance - something often not recommended - then did some needed heavy surgical work to the RGB image and added it over the Ha-based-luminance, which not only created the expected salmon salad effect but also generated undesirable color blotch and other artifacts.

A "cherry red" version of this image was selected as NASA's Astronomy Picture of the Day on February 14th, 2010.

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Matts Sporre (Contact, Page), December 14th, 2009, 14:01

How to use Ha as a luminance (and how to partly mitigate the salmon effect) I know about, but you speak about your normal way of creating a luminance from Ha and RGB. How do you do that?

Also there are some bluish areas in the image. How do they show up when you have used only the red channel (Ha) as luminance?

Finally - super nice image! :-)

If the answer is too long for this format, pl be free to email me offline.


RBA (Contact, Page), December 15th, 2009, 17:11
Hi Matts!

If you know how to mitigate the salmon effect, I want to be your friend :-)

Regarding combining Ha with RGB, it's not *my* normal way of doing it but rather what I consider *a* good way of doing it. I say it's not mine not only because it's not my "invention" but also because I've only processed Ha(L)RGB 4 images in my life and I haven't got to try the HaRGB-only combination.

Having said that, the Ha RGB would/could be done by adding some rather high percentage of the Ha (say 60) to the R channel, then about 20% to te B channel, then build the resulting [R Ha B Ha G] as a regular RGB image, and process it as usual from that point, likely extracting a L from the complete RGB combination.

Regarding blue color. It didn't come to a surprise to me to see blue despite the luminance comes from the Ha. First, as I mentioned, I had to do quite some "surgical" work to the RGB, one of such was a heavy saturation/blur/desaturation. (I'm about to run out of space, I'll continue...)

RBA (Contact, Page), December 15th, 2009, 17:17
(continued from previous comment)

With that resulting RGB (and probably even without such "surgical process" on the RGB), when you add it over the Ha-based luminance, all you need in order to get colors other than red to flourish is that there's significant Ha signal, whenever your RGB image has those other colors. I don't know if that makes sense.

The center of the Rosette - and other areas - had enough Ha signal in it to "absorb" the colors in that same area from the RGB image, which in this case showed more blue than other colors. I'd imagine that the same thing applies for any other non-red (or red!) colors in the image: as long as the Ha-based luminance has significant brightness, it will cast the colors that are being "sent" by the RGB image. BTW I'm mainly saying what I think it makes sense from my observations. Does it make sense to you?

Anonymous (Contact, Page), December 16th, 2009, 10:19

I'll answer via "normal" mail.


ZOILA MIRANDA (Contact, Page), December 18th, 2009, 10:21
Excelente foto esta nebulosa, ojalá sea una APOD.
Te felicito.

RBA (Contact, Page), December 18th, 2009, 10:52
¡Gracias Zoila! ;-)

Matts Sporre (Contact, Page), December 19th, 2009, 5:26

did you get my mail?


Salvador Fernandez (Contact, Page), February 14th, 2010, 10:12
Felicidades por este trabajo al igual que los anteriores una maravilla.

Guillermo Marcus (Contact, Page), February 15th, 2010, 1:51
You can add an APOD tag to this beautiful one too, it was the photo of the day yesterday:


.. and last but not least, congrats for the beautiful work!


zoila miranda (Contact, Page), February 15th, 2010, 15:13
Mis felicitaciones Rogelio, viste que hice un deseo el 18de diciembre?. Se me cumplió!!!
Mil felicitaciones con esta foto tu primera APOD del año!!!.

RBA (Contact, Page), February 16th, 2010, 10:47
Thanks Guillermo!!

Sí Zoila, tienes buena intuición! Gracias! ;-)

Jeremy Hunt (Contact, Page), March 26th, 2010, 13:59
Fantastic pictures. Love your processing. Can you give me any tips on how to bring the nebulae out so well but no overwhelm the image with stars in such rich areas of the sky?

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