Processing help

[Kenboy]

Hi all,

I took this last night with a DSLR and mount (lot of moonlight!)

I stacked 30 x 1 min exposures 

Can anyone show me how to get any more details from this pic? how do I bring out any nebulae etc? 

I'm using GIMP curves function, but nothing really shows up 😕 (except the obvious light pollution) 

thanks !  

 

Astropic 05-07 n.TIF

[Aramcheck]

I think you'll need to provide the stacked but unstretched image of the RAW files, as this one has already been stretched. You would normally try to removed the light pollution background whilst the data was still in it's linear (unstretched) form.

It's always better to have more exposures (and/or longer exposures if the mount tracking will allow).

Also how dark was the sky? At the moment here in the UK there is only a small window of Nautical Darkness & where I am it never reaches 'Astro darkness' at the moment.

If the DLSR is un-modified that will also affect how much nebulosity you can capture, but that will vary between targets.

Cheers
Ivor

[bobro]

For straightforward processing Doug German's videos are a great start. He doesn't use GIMP, though GIMP has the same sort of processing functions Doug uses.

For gradient removal see: https://www.youtube.com/watch?v=yTEVMH_WE80

Below is your image processed with the methods Doug proposes (gradient removal and star masking) using GIMP, plus saturation increase and stretching. I'm no expert at processing and others will do much better, but it gives an idea of what can be done with the image - some of the nebulosity around Sadr is becoming visible.

Of course a night with less moonlight will help as image noise will be less.

[Kenboy]

6 hours ago, bobro said:

For straightforward processing Doug German's videos are a great start. He doesn't use GIMP, though GIMP has the same sort of processing functions Doug uses.

For gradient removal see: https://www.youtube.com/watch?v=yTEVMH_WE80

Below is your image processed with the methods Doug proposes (gradient removal and star masking) using GIMP, plus saturation increase and stretching. I'm no expert at processing and others will do much better, but it gives an idea of what can be done with the image - some of the nebulosity around Sadr is becoming visible.

Of course a night with less moonlight will help as image noise will be less.

 Ah yes, thanks very much! really helpful

[Kenboy]

7 hours ago, Aramcheck said:

I think you'll need to provide the stacked but unstretched image of the RAW files, as this one has already been stretched. You would normally try to removed the light pollution background whilst the data was still in it's linear (unstretched) form.

It's always better to have more exposures (and/or longer exposures if the mount tracking will allow).

Also how dark was the sky? At the moment here in the UK there is only a small window of Nautical Darkness & where I am it never reaches 'Astro darkness' at the moment.

If the DLSR is un-modified that will also affect how much nebulosity you can capture, but that will vary between targets.

Cheers
Ivor

I've attached the unstretched image

How is light pollution removed on unstretched files? is that gradient removal? 

Astropic 05-07.TIF

[wimvb]

8 hours ago, Kenboy said:

How is light pollution removed on unstretched files? is that gradient removal?

Yes. LP, especially in wide field images, shows a gradient as well as a general increase in brightness.

[wimvb]

Here's my attempt with PixInsight. In a wide field such as this, with a lot of stars and weak nebulosity, it's difficult to remove gradients.

A few tips:

• use flats to remove dust bunnies
• take more (and longer?) exposures in order to reduce the noise. In this image, it's dificult to see what's noise and what's stars.
• if you want to concentrate on this type of imaging, you should look into astro-modding your camera, so that it will pick up more Ha signal.

[Aramcheck]

12 hours ago, Kenboy said:

How is light pollution removed on unstretched files? is that gradient removal?

You can think of the light pollution signal as being added to the light that you're trying to capture, so to remove it you need to subtract the light gradient from the image.

How you subtract the gradient will depend on the processing software you use. You can mimick the gradient using a gradient tool, or create a blurred copy of the layer in GIMP, & subtract that - or in Photoshop there's also a Gradient Xterminator plug in.

@alacant has posted some great images using the free Siril software to remove light gradients & APP/StarTools also have processes to remove light pollution.

I prefer Pixinsight, but am not as adept at using it as a lot of folk & I could only do limited processing on your pic, as it was difficult to find areas without stars & I wasn't sure where the nebulosity was supposed to be. In Pixinsight the process used is called Dynamic Background Extraction (DBE), where you pick points in the image to model the background & then either subtract or divide from the main image. (Division is used where there  are multiplicative effects from scope vignetting).

I also took liberty to plug the (partially processed) image into Astrometry.net. http://nova.astrometry.net/user_images/3798032#annotated

Cheers
Ivor