Processing a nightscape in Siril: a tutorial

[Jossie (Hermann-Josef)]

@ggbutcher
What I had written above applies to both detectors, CCD and CMOS. In professional astronomy only CCD-cameras are used due to the higher fraction of light sensitive area.

Hermann-Josef

[Biff (Alex)]

@sguyader

Edit: @Biff before trying my tutorial, did you by any chance select yourself “One star registration” in a previous attempt? I see that if you just select “One star registration” and close the program, on the next program launch it keeps the algorithm you have selected the last time.

As far as I can recollect, no. Your tutorial was my first attempt at running, and using, Siril. Whether I inadvertently selected the ‘One star registration’ is something else. I don’t think so.

Anyway, the correct selection is now documented: I couldn’t find anything on the Siril website either.

Thanks anyway.
Cheers,
Biff

[gee_kohler]

Hi Sabastein,
Thank you for the excellent tutorial on Siril stacking! I have been struggling for 6 months and keep getting one error or other and now able to use the program like a charm. Thanks again. I am new to GIMP (don’t have photoshop) and just started learning. Could you put up a brief tutorial on the masking and adding or stacking pictures please! K. Gee

[sguyader (Sébastien Guyader)]

Hi @gee_kohler,

A quick tutorial showing what I do (but there are several ways to do it):

1. In Gimp, click on File > Open as Layers... to load both the foreground and sky images. You end up with 2 layers
   

   

2. Here the foreground is the top layer. Right click on that layer and choose Add layer mask... and check White (full opacity), this adds a layer mask to the foreground layer. As the mask is white, the foreground will still mask out the bottom (background) layer:
   

   

3. Painting black over the sky area will reveal the background layer. if the sky occupies a large portion of the image, you can draw a large selection rectangle over the sky and use the Bucket Fill Tool to fill the selection with black color (make sure to click on the layer mask before applying the bucket fill tool, so it will apply the color only on the layer mask):
   

   

4. Remove the selection (Select > None), and refine/finish the layer mask with a brush. Check the mask itself with right click on the mask > Show Layer Mask:
   

   
   

5. When satisfied with mask, merge the layers with Image > Flatten Image, and do whatever you want in Gimp with colors/contrast/dodge/burn… or export the result if you’re satisfied.
   

   

Hope this helps!

[jrickards (Julian Rickards)]

I’ve heard that it is better to create a (proper) dark frame master (created from multiple dark frames, same iso/temp/duration) than use the single dark frame that is built in to cameras when the duration is longer than 1sec, whether the photo is astro or just dark (such as night scenes in town). Can Siril be used for this purpose, night photos around town?

[vinvin (Vincent Hourdin)]

I’m not sure about cameras that manage dark frames on their own, I guess cameras only use one frame, while in siril you can use a master build from several. Yes siril can be used for that. It does not preserve white balance and other camera settings though, so post-processing will be required.

For city pictures, I’m not sure you will see a lot of difference because you have some bright lights in the picture where signal is high, while in astronomy we are more interested in parts of the images where signal is very low and where the dark current is relatively important.

As you said, you need to have the same iso/temp/duration as the real frames, so it would require a lot of work if you have a long session with different expositions…

[jrickards (Julian Rickards)]

Yes, there are differences between the amount of light in a night cityscape and astrophotography but what I was/am concerned about is, in the dark regions of my city photos (night sky above the city), can I use a series of master dark frames taken that same night and put them in Siril, along with the (single) light frame and have Siril try to remove noise from the dark areas of the sky. It appears that Siril will do that, which is perfect. I was concerned that Siril might be trying to match the image with a constellation in the sky (which it wouldn’t be able to match it with). Thanks

[greyghoster]

The script fails using version 0.99.10.1 and 0.99.8.1running the rl 10 0.6 command “Error in line 62: ‘rl’”. When I comment the line out, the script completes however there output looks very sparse.

Had a good look and realised that the ‘rl’ command syntax has changed ‘rl 1 0.5 10’ excutes though what the values should be is a mystery. Still look very sparse.

[lock042]

I moved this topic into the Siril section.