M51 - how to acquire or process the red nebulosity ? Are HA pictures useful for galaxies ? - Forums

Topic starter

Jun 12, 2021

Hi All,
So thanks to learning in this forum, I improved my image processing game (PixInsight) a lot and finally got an image I’m partially satisfied with
https://www.astrobin.com/full/bwmj3z/0/?real=&mod=
I see is most really good M51 pictures that the galaxy has a lot of red nebulosity. How to capture that do I need to take it with an HA filter and integrate on the RGB? Or this is an image processing trick and I don’t need to actually take HA pictures ?

thanks / looking forward for any constructive critique on the image too to make it better

Björn Arnold

Jun 12, 2021

Hi,

It depends on what your actual goal is. You're using dedicated OSC camera which records the Ha data that is there. If you use an Ha filter, you get a much higher contrast and could distinguish Ha data from "other red data". Hence, if your goal is to highlight Ha regions, it's helpful to collect Ha data and add this.
Otherwise, if you want to have a "balanced" color representation, I wouldn't add Ha data.

As a general point to your image. There's a strong background gradient which I would remove. In addition, I would apply a high pass filter or other technique to emphasize some finer detail to the galaxy.

Björn

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David Moore

Jun 12, 2021

I don't know if this helps but I have been having the same questions. I have an OSC camera and have wanted to enhance the Ha regions so I bought an L-Enhance narrowband filter for Ha and O3 and enhanced an image I had already taken of M51. I then overlaid the data from a mono camera I used to use for guiding for luminance to improve detail. I am no expert and have little experience having only started a year ago with astrophotography, so I am just trying to help. If you go to the big wall, type in Moorefam for search terms and M51 for subject you can see the before and after images. A Ha filter would have produced a similar results I suspect. I am just starting with anything other than an OSC camera so a novice in this area of filters and B & W.

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mousta

Topic starter

Jun 12, 2021

I don't know if this helps but I have been having the same questions. I have an OSC camera and have wanted to enhance the Ha regions so I bought an L-Enhance narrowband filter for Ha and O3 and enhanced an image I had already taken of M51. I then overlaid the data from a mono camera I used to use for guiding for luminance to improve detail. I am no expert and have little experience having only started a year ago with astrophotography, so I am just trying to help. If you go to the big wall, type in Moorefam for search terms and M51 for subject you can see the before and after images. A Ha filter would have produced a similar results I suspect. I am just starting with anything other than an OSC camera so a novice in this area of filters and B & W.

wow!! What a difference it made. Your image looks amazing!! I have a mono guide camera, so I should try with it too to get more luminance data!
I will try the HA filter with OSC and see if I can integrate it nicely. Never done it before so will be interesting. Any tutorials you have on how to do it will be super helpful!!
Thanks

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mousta

Topic starter

Jun 12, 2021

Björn Arnold:
Hi,

It depends on what your actual goal is. You're using dedicated OSC camera which records the Ha data that is there. If you use an Ha filter, you get a much higher contrast and could distinguish Ha data from "other red data". Hence, if your goal is to highlight Ha regions, it's helpful to collect Ha data and add this.
Otherwise, if you want to have a "balanced" color representation, I wouldn't add Ha data.

As a general point to your image. There's a strong background gradient which I would remove. In addition, I would apply a high pass filter or other technique to emphasize some finer detail to the galaxy.

Björn

Thank you so much for the feedback.
what is a high pass filter ? Is that a masking technique?

Björn Arnold

Jun 12, 2021

what is a high pass filter ? Is that a masking technique?

"Kind of" (non-technical answer): A high pass filter determines the areas of strong gradients and will increase contrast in these areas. These filters are typically adjustable (i.e., what is a strong gradient? and how strong should the contrast increase be?). Through a mask you can select on which pixels and to what extend this operation should be applied.

There are several techniques to sharpen an image. Using a high pass filter isn't the only one. There are others like unsharp masking, deconvolution etc. etc. And each program may use different sets of sharpening techniques.

BJörn

PS: Don't know about your image processing background, so sorry in advance if my answer's either too basic or too technical.

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Björn Arnold

Jun 12, 2021

wow!! What a difference it made. Your image looks amazing!! I have a mono guide camera, so I should try with it too to get more luminance data!
I will try the HA filter with OSC and see if I can integrate it nicely. Never done it before so will be interesting. Any tutorials you have on how to do it will be super helpful!!
Thanks

In the data sheet to your M51 image, you're using a color camera for guiding. With a colour camera, there is no point in trying further. If you have a mono camera, you should use the mono for guiding and not the color camera (given that the resolution isn't off and compromising your guiding).

One idea: If you shoot Ha data, you could add it as a mask to a saturation adjustment to saturate the red tones. In the end: experiment with different approaches.
IMHO, the goal isn't to replicate an image that you've seen somewhere else but to create an image that gives you satisfaction.

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GalacticRAVE

Jun 12, 2021

You need the narrow band to get the Halpha pop. On an OSC you also can use a dual-band filter and extract the R for Halpha. When you go for nebula, a combination of G and B gives you Oiii. Together with RGB for the stars this can give you quite nice shots, as you find a considerable number here on astrobin.

Regarding M51 and postprocessing: in PI you can combine it with the NBRGB script. Getting a good color balance is non-trivial and the different noise levels between NB and RGB can be challenging. What works nicely for galaxies is to create a composite with NBRGB, than use the Halpha as a mask to blend the HaRGB image with the RGB. Certainly still lots to learn and play with …

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Tom Marsala

Jun 13, 2021

I use the high pass filter in Photoshop. Just be careful and use it sparingly as it will bring out
noise in your photo as well (I speak from experience!)

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noodle

Jun 13, 2021

you have to use the Ha filter to get the small "red patch" in the spiral arm
here is my M51's Ha data:

https://www.astrobin.com/full/lsyk8h/B/?nc=user

Niels V. Christensen

Jun 13, 2021

FYI, an example on Ha narrowband info. applied to the red channel of galaxy M51,
https://astrob.in/368165/B/

Björn Arnold

Jun 13, 2021

Tom Marsala:
I use the high pass filter in Photoshop. Just be careful and use it sparingly as it will bring out
noise in your photo as well (I speak from experience!)

Where exactly did you have problems with the noise?
I strongly recommend using a layer mask to apply the high pass only on the areas/details that should be enhanced and especially background should be excluded.

Björn

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Tom Marsala

Jun 13, 2021

Thank you! I've done it both ways. I've applied it to the whole framee to sharpen for large fields and I've done the layer mask, which is much more controllable, I agree.