RBA & AF Astrophotography

Widefield Rosette and Cone nebulas: Comments

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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