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I have some data of the Flaming Skull nebula that was shot though my l-enhance filter. I’ll process this in the HOO colour palette but would like to shoot the stars through just a UV/IR cut filter to get better star colour. Is the process as follows: Stack dual narrowband data, DBE, BlurX, etc, remove stars Stack RGB data, BlurX, remove stars Then when adding the stars back in, just use the stars image from the RGB data. Also, how much integration time should I aim for with the stars? I’ve got about 20 hours of dual narrowband data so was thinking about 30-60 mins of data for the stars (maybe 20-30 second subs)? Am I on the right track here? |
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I only did this once as I'm new to this but I was quite satisfied with the result. I took 2 hours of RGB subs with 180s each (depending on your sky). For the RGB stack, I did the following: Gradients removed (GraXpert), Background neutral., SPCC, BlurXT + NoiseXT (but just a little bit), GHS stretch, Saturation increased + minor adjustments (e.g. CA around stars removed). Then it's important to StarAlign the RGB image with the DNB image before extracting the stars. And then just combine the starless DNB with the RGB stars using PixelMath or any kind of script like ScreenStars. |
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| Sounds perfect. Thanks for the advice. |
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30 min. to 1 hour should be fine. I do 30 sec. subs X 30 each RGB. However I shoot at F3.6. Higher F ratios may require longer. At F3.6 the stars were blown out at 1 min subs. Remember, stars will be high S/N and the noisy background will be removed/eliminated. Lynn K. |
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Interesting thread, I am about to do the same. I was planning to do the alignment of the UV-IR-cut stars with the DNB image by using a common reference frame in WBPP. That was based on a similar discussion I saw on Cloudynightshttps://www.cloudynights.com/topic/890846-getting-proper-star-alignment-when-adding-rgb-stars-to-narrowband-images/ Mike |
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Just a hint: You will get much better results by adding the stars by to the DNB image by "Screen blending" ... and not just adding (+) them. Best of course in that case would be to generate the stars from the RGB by using an "unscreen" method, which is e.g. provided by StarXTerminator ... do not know if Starnet++ provides this feature as well ... Alexander implicitly suggested this above by using the ScreenStars script ... Chris |
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Here's my first attempt at combining RGB stars with Dual Narrowband data: https://www.astrobin.com/v3qv5e/ |
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That's pretty much what I do too. But make sure you align the dnb stack with the uv-ir cut stack. I use Deep Sky Stacker for this. This is my recent attempt of combining dnb data with rgb: https://astrob.in/sqfmsi/B/ |
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If you just want to use the narrowband data,j Alberto Ibanez has a nice explanation and tutorial here....RGB Stars from Narroband Data – AIASTRO (wordpress.com) It just used the H and O channel in a combination he describes as very close to RGB. I've used my spin on this for a long time and I really appreciate him sharing this, I think it works quite well. If your narrowband subs are really long and the stars are blown out, then this may not work for you, but just something to think about. |
1.81
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| If you don't want to shoot the target with a uv-ir filter, you can just use the HOO stars from the dual-band data processed through SPCC choosing the appropriate filters. The colours come out pretty close; not perfect but if you blend them back in, you're probably going to bring them in with much less stretch than for the main event, so you get star reduction at the same time that makes them much less noticeable anyway. You might try this and see if you find it acceptable. Of course, if you do want to get RGB stars, then the advice above is fine. Shorter exposures in rgb should be better than longer to avoid clipping... |
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| For a lazy and fool-proof method of extracting faux-RGB stars from HOO data, Foraxx works pretty well. You can just discard the nebula result it produces and use only the stars. Here's an example: https://www.astrobin.com/fih1b5/B/ |
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Jeff Horn: Thanks for that article. I have actually been looking for a detailed explanation like this. I have been lately generating stars using the Foraxx script in PI and they look decent, but never actually did a apples to apples comparison with an RGB aquisition to see how they stack up. |
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| I had a go at just taking the stars from a colour calibrated image (SPCC) and I can confirm that this works really well. The colours are pretty good and when I applied a bit of SCNR, the green cast was easily removed too. It does bring into question whether it's worth devoting time to imaging just for the stars. The shorter exposure time does help a lot though. |
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For my image, I made the stacking, the alignment and the pollution removal with APP After with Pixinsight, I make a RGB layer, I treat it in classical way: BXT + NXT + HT In non-linear mode, I add the luminance mask after adjusting the color level I finish by adding the LRGB mask to the SHO mask without stars. At the beginning, I made 60x60s by level Now, I made 30x60s for RGB and 60x60s for L the time has been fixed with the 3 sigma rule. |
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HI, I am pretty lazy and I think it comes out pretty well using SPCC on the HOO. I then destar and GHS stretch that as my NB image (HaHb below) in the following script... note the credits.... I get the RGB stars from the same set of images stretched and saturated in GHS to get the stars then remove the stars with StarX to use in the script (RGB_stars and RGB_starless). Drag script over RGB_stars and voila. This is brainless... he did all the work. All he asks for is credit... a PixelMath magician. /* RGB Stars-to-Narrowband Transfer using PixelMath - V11by Bill Blanshan */ //Drag the bottom left arrow over to your RGB image with stars Img1= RGB_starless ; // <-- RGB Starless Image nameImg2= HaHb ; // <-- Narrowband Starless Image nameM= 5 ; //<-- <Method (1-4) & 5 is a blend Example:  Minkowski 2-55 |
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Just coming back to this with a couple more questions if I may. I've been collecting data where I can and now have the following data sets: 300 second subs with L-enhance filter 300 second subs with UV/IR (Astronomik L3) filter 20 second subs with UV/IR (Astronomik L3) filter for the stars. I've created two separate stacks so far using WBPP in Pixinsight: Stack 1: 300 sec L-enhance data Stack 2: 20 sec subs to be used just for the stars. (I'll extract the stars from this data and delete the starless so I can re-screen these stars with the main data set at the end - My hope is by using short exposures for the stars, I will maintain the star colour) For the main stack (I'll call it stack 3), should I just use the 300 second subs of broadband data or should I also include the 20 seconds subs that I used to create the stars and the 300 second subs with the L-enhance filer? my understanding is that when combining Ha data with an RGB image, I separate the colour channels, delete the green and blue and just use the red. As I'm using a OSC camera, is this just a waste of data and should I therefore include this data in the main stack? Does that all make sense? |
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| I do this all the time, using my dual band filter to get the image and a separate broadband rgb image for stars. I always use 1 hour of exposure for it. Works every time. I remove the stars from the dual band image and work it. Then I’ll create a stars only image from the rgb and process the stars. I’ll usually use GHS to stretch the stars. Then it’s just a screen operation to put them onto the dual band image. |
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Stack dual narrowband data, DBE, BlurX, etc, remove stars I always add RGB stars to my narrowband images and using StarXTerminator too late in the process can leave some marks. Especially if by "etc" you mean that'll you'll perform some color calibration. The author states that StarXTerminator should be ran right after stacking for the cleanest removal. Try this:
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Craig Dixon: As you use PixInsight, my question is why do not use a DynamicAlignment? I also capture the nebulosity and stars separately: usually 300s exposures with L-eXtreme (as many as possible) and the stars as 30 x 30s with an IDAS LPS-P2. You can take more subs of the stars if you want, but the 30 x 30s gives me nice small stars which are not the most important in the final image. Before removing the stars from the processed image of nebulosity I align the image of stars with the DynamicAlignment and then remove the stars from the first and everything excluding stars from the second. It works unbelievably well. CS Martha |
