Stacking and Dark substraction

[Nocturnal]

Hi,

I'm a new user of PixInsight Core. The lack of documentation is a bit of a problem for me as I'm also new to imaging in general so perhaps I'm not seeing features because they have names I don't recognize. I've used the HistogramTransform and a few other processes but I'd like to try stacking and dark substraction.

It's not clear to me how I build a list of images to stack. At first I thought there is no stacking functionality but then I saw DynamicAlignment so maybe it's there after all. Can I stack subs in PCL?

Let's say I can't stack, what if I have a single exposure and would like to substract my dark frame. How do I do that?

Thanks,

  Sander

[David Serrano]

but then I saw DynamicAlignment so maybe it's there after all. Can I stack subs in PCL?

AFAIK, with DynamicAlignment you can align just one image against another one. It may be that an ImageContainer could be used to improve this, but honestly I don't know. And for stacking, you can try this little script I've done. It needs previously aligned images.

Let's say I can't stack, what if I have a single exposure and would like to substract my dark frame. How do I do that?

Use a PixelMath instance. If the identifier of the main image is "Light" and that of the dark is "Dark", use the following expression:

Code: [Select]

Light - Dark

Straightforward, isn't it? I think you should uncheck the Rescale option but I'm not sure of that.

[Nocturnal]

Very cool, will try that. Thanks for the reply.

  Sander

[David Serrano]

You're very welcome. Don't hesitate to come back with any problem you may encounter .

[Nocturnal]

Alight, dark substraction works great. Well, I assume it does because my dark image is shooting holes in my light frame I assume my dark somehow is not quite representative even though I took it the same night and they're both 3 minutes.

I added the KSintegration script and it runs, great. It's currently integrating my subs but I'm not clear how to align them first. At least it seems that needs to happen first, right? Ah, it just finished and indeed my M31 has two cores now :-)

I searched the forum for 'aligning' but got no relevant hits. I'm sure it's described elsewhere so please feel free to post a link.

I have to say that pixinsight exudes 'power' so I'll be following it closely to see where it goes. Good luck on the project!

[David Serrano]

I assume it does because my dark image is shooting holes in my light frame I assume my dark somehow is not quite representative even though I took it the same night and they're both 3 minutes.

Dust in the sensor or any component may be causing that dark spots. You should also take a set of flat frames to avoid these.

I searched the forum for 'aligning' but got no relevant hits. I'm sure it's described elsewhere so please feel free to post a link.

I don't know of a method for aligning more than two images, so the process can get a little boring. Align the second image with the first, save, open the third, align with the first, save... until all are done. Then you'll end with N-1 frames aligned with the first one. At least, the same DynamicAlignment process can be reused every time.

Glad to know KSIntegration worked fine for you . When stacking, don't forget to include the first, unmodified one.

[Nocturnal]

Hi,

well, the script ran fine but the result wasn't so fine since the images weren't quite aligned :-) I'll have to examine other stacking techniques and use PCL for post processing for now. The images I have (M31) don't have many stars oddly enough so DeepSkyStacker can't handle it. I'm about to learn how Iris does this.

I took flat frames but I'm not sure they are any good. In any case, I can see the hot pixels on the dark frames are brighter than on my light frames so that's why they punch holes. Something must have gone wrong there.

Luckily is clear out again tonight so I can try again.

Thanks,

   Sander

[Juan Conejero]

Hi Sander,

Welcome to PixInsight Forum :wink:

It's strange DeepSkyStacker can't align your images. Have you asked in DSS's Yahoo group? I'm pretty sure Luc would find a solution; perhaps it's just a matter of adjusting some alignment parameters in DSS.

[Nocturnal]

Hi Juan

thanks for the welcome, it's nice to be here :-)

I do indeed belong to the DSS group. I haven't asked Luc for help yet as I'm pretty sure he'll tell me there aren't enough stars in the images. DSS needs at least 8 stars in each image before it will try to align them. No matter how aggressive I am with looking for these stars DSS won't find enough of them. In fact I have the same problem with some M57 subs I took last night. I have suggested some improvements to DSS to help the user debug why DSS can't stack but Luc isn't receptive of the ideas, unfortunately. For some reason he's concerned about CPU and storage usage. I dunno, that's why I have a computer, so it can do the heavy lifting and I don't :-)

Anyway, I'll be learning how to use Iris and Meade's IP to stack my subs. I think those can stack with fewer alignment stars. I'll then use PCL for post processing.

Regards,

   Sander