M51 Image Processing Help

[chriscoles]

Hi, I have taken mono LRGB images of M51 with my new ASI1600mm-PRO.

I have a mix of 30s, 60s, 120s subs. 100 darks, and 100 flats for each filter. About 4 hours total.

I Used DSS for alignment and stacking, then Pixinsight for LRGB combination.

My issue is that i'm not happy with the colours, the stars all appear white and the background is strange.

I have attached the Aligned LRGB images.

Can anyone point me in the right direction? Thanks!

Green.TIF red.TIF Lum.TIF B.TIF

[wimvb]

I downloaded your data, and it seems that you have some calibration and stacking errors. For one, your luminance has an inverted vignetting pattern. Are your calibration files working ok? With cmos cameras, your darks MUST match your lights in temperature and exposure time. If you use 3 different exposure times, you need 3 different darks. Scaling darks doesn't work.

I'm processing your data, and will get back with the results.

[chriscoles]

14 minutes ago, wimvb said:

I downloaded your data, and it seems that you have some calibration and stacking errors. For one, your luminance has an inverted vignetting pattern. Are your calibration files working ok? With cmos cameras, your darks MUST match your lights in temperature and exposure time. If you use 3 different exposure times, you need 3 different darks. Scaling darks doesn't work.

I'm processing your data, and will get back with the results.

Hi, all images are taken at -20. I have dark's for all my light exposure times. 

I will investigate the inverted vignetting, and double check DSS to make sure its using the correct files.

Thanks for you help!

[wimvb]

I can't get colour calibration working. The histogram also shows that your R and B masters are identical. Can you check that the stacking process produced the correct output.

[chriscoles]

15 minutes ago, wimvb said:

I can't get colour calibration working. The histogram also shows that your R and B masters are identical. Can you check that the stacking process produced the correct output.

Okay, interesting... I will regenerate them more carefully and repost them. Thanks again!

[chriscoles]

31 minutes ago, wimvb said:

I can't get colour calibration working. The histogram also shows that your R and B masters are identical. Can you check that the stacking process produced the correct output.

Hi, I have generated new LRGB from DSS. As far as I can tell, they are using the correct files.

B.TIF G.TIF R.TIF L.TIF

[wimvb]

Ok, I'll try again. Anyway, here's the luminance so far.

 

[chriscoles]

Given your advice about B and G being the same, i have had more luck with the new DSS generated frames!

Still getting to grips with image processing, so happy to hear more suggestions.

[wimvb]

A bit noisy. Cmos works best with LOTS of subs. Try to collect at least 100 L subs. You can collect fewer rgb and blur the rgb image before lrgb combination.

My process in short:

• aligned the new r, g, and b masters with the first L master. The newest L has subs that were rotated too much, so I used the old L
• cropped L and R, G, B masters, then applied DBE to all.
• rgb combination

RGB:

• background neutralization
• photometric color calibration
• arcsinh stretch
• desaturated the background with a range mask to protect the galaxy and stars
• convolution 
• saturation enhancement

L:

• deconvolution
• histogram transformation
• hrd compression
• curves transformation

LRGB combination

[chriscoles]

9 minutes ago, wimvb said:

A bit noisy. Cmos works best with LOTS of subs. Try to collect at least 100 L subs. You can collect fewer rgb and blur the rgb image before lrgb combination.

My process in short:

• aligned the new r, g, and b masters with the first L master. The newest L has subs that were rotated too much, so I used the old L
• cropped L and R, G, B masters, then applied DBE to all.
• rgb combination

RGB:

• background neutralization
• photometric color calibration
• arcsinh stretch
• desaturated the background with a range mask to protect the galaxy and stars
• convolution 
• saturation enhancement

L:

• deconvolution
• histogram transformation
• hrd compression
• curves transformation

LRGB combination

Okay  Great result! Yes I agree, more subs.

I shall try your process. Still a lot more to learn but I'm getting there.

Thanks for the help, it means a lot!

[wimvb]

9 minutes ago, chriscoles said:

Yes I agree, more subs.

A rule of thumb that I use is that if the main target looks noisy when only stf applied, but otherwise still linear, then more or longer subs are needed.

[chriscoles]

 

On 12/04/2020 at 23:34, wimvb said:

A rule of thumb that I use is that if the main target looks noisy when only stf applied, but otherwise still linear, then more or longer subs are needed.

Okay, so last night was clear  And I have more subs. I have stacked them again. I also took more darks for good measure.

I combined the channels in Pixinsight, however don't yet know how to bring the colours out...?

Using the gimp I can, though would like to do it all in PI eventually.

I tried Photometry-Based Color Calibration but got errors, see below.?

Getting there... Thanks!

 

B_new.TIF G_new.TIF R_new.TIF L_new.TIF

 

 

 

 

 

Edited April 14, 2020 by chriscoles
repeated images

[chriscoles]

I kept trying with  Photometry-Based Color Calibration and got it working, I had incorrect pixel size.

[wimvb]

Yes, you need to enter your pixel size and fl for plate solving to work.

After colour calibration, stretch the rgb with arcsinh stretch. This preserves and boosts colour.

[wimvb]

Excellent data to work with. Here's my result.

[chriscoles]

Wim, that's fantastic! Thanks, it shows me what to work towards with my image processing. I only installed PI on the weekend, so looking forward to achieving results like that

[teoria_del_big_bang]

Wow, what a great image 🙂 

I think I too need to drastically improve my processing. I think with me it just takes so long at the moment, mostly because I always have to follow some instructions as I cannot remember what to do off my own back. I guess if you practice and you understand fully what you are doing instead of blindly following some instructions written by others then it will both be quicker to process and the results will improve.

I have just purchased this great guide for PI. Whilst it will not give me great images immediately I think it will greatly help me in the long run. I don't know whether it is something that may help you ?

 http://www.deepskycolors.com/mastering-pixinsight.html

Steve

[wimvb]

3 hours ago, teoria_del_big_bang said:

it just takes so long at the moment, mostly because I always have to follow some instructions as I cannot remember what to do off my own back

That's how I started too.

3 hours ago, teoria_del_big_bang said:

I guess if you practice and you understand fully what you are doing instead of blindly following some instructions written by others then it will both be quicker to process and the results will improve

Yes, it just takes time.

 

3 hours ago, teoria_del_big_bang said:

I don't know whether it is something that may help you ?

 http://www.deepskycolors.com/mastering-pixinsight.html

Steve

It definitely will. Study not just the processes, but also the PI methodology: an image consists of lightness zones, and also levels of detail, called wavelets or layers. The layer concept of PI has nothing to do with the layer concept of PS/GIMP.

[chriscoles]

Thanks for the book recommendation, for now i'm quite happy playing around with PI. May look at books when I get deeper into it.

Made improvements to my image, and because of all the clear nights I have started on the Cigar Galaxy too.