BPP and misaligned masters

[Droogie2001]

Hi,

Being a new user I am using BPP to help get me started.

After using BPP I noticed that my master images for each channel are not exactly matched with each other.

If I simply place the Red, Green & Blue masters on top of each other and hold down the mouse I can see a misalignment.
When carrying out a Channel Combination the issue stands out even more.
I am using a Mono CCD so have LRGB stacks to carry out. In this example I have two nights worth of data for LRGB, one night on one filter had a meridian flip.

For simplicity I used this workflow (this maybe where my issue is)
I processed each of the filters separately with their 2 nights worth of Lights, select a reference frame for each job. I also used Flats, Darks, BIAS and a cosmetically corrected process on each of the job (used the same CC process for each LRGB stack, is that okay?) I am not binning so the images sizes are the same.

The resulting master images look fine, including the one with the meridian flip it is only when you place them on top as mention previously that the error becomes apparent.

Am I missing a step? Do I need to simply drop all of the 2 nights images into BPP and not process each Filter separately?

Thanks

[Droogie2001]

Okay I think I have found my own solution.
Well with the help of this thread anyway:

https://pixinsight.com/forum/index.php?topic=9965.msg63300#msg63300

Star Alignment. I believed that this was something that the BPP script automatically did.
From the linked thread it appears that you should use Star Alignment on all lights before stacking be it using BPP or manually stacking.

If anyone can add anything like whether I can use the same Cosmetically Corrected process for all BPP stacks then that would be useful. I guess it makes sense to do one for each Filter though as it is random noise it may not be necessary?

[aworonow]

I just add, that cosmetic corrections is a method to repair bad pixels in the RAW light images. It should be applied to every image individually. Of course you need to develop the template that identifies the bad pixels (also can use the master dark in the CC routine). Remember, the purpose of CosmeticCorrection is to repair individual pixel defects that lie in the camera sensor. You identify those pixels by the (X,Y) coordinates. So apply the CC before shifting pixels around by something like image registration.

Maybe this is not how most imagers do it it, but after CosmeticCorrection I select one crisp image then use the StarAlignment procedure to register all images (R,B,G,Ha,...) to it. Then I use the procedure ImageIntegration to make the individual R,G,B,Ha,...stacks. I prefer this to using BPP, but the same idea, I guess.

Alex

[eganz]

Droogie,

You should usually identify one image as your reference, and then stack all your separate colors to that same reference.
Then, BPP will automatically align all images to the same reference.
Otherwise, you are forced to align the images twice which can degrade them slightly.

And yes, you can typically use the same cosmetic correction on all of your RGB images, although you would often want a separate cosmetic correction icon for narrowband images that have higher noise levels.

Eric

[aworonow]

Very commonly, folks do not do a cosmetic correction for scattered pixel defects. Dithering and enough exposures takes care of those.

[Droogie2001]

Thanks for all of the replies. I have a lot to learn but I am enjoying the journey!