Any way to specify reference image file for registration and stacking?

[cytan]

Hi Han,
I am taking 2 data sets: One stack of RGB, and one stack with L-extreme. These two stacks will be processed in StarTools. However, in order to do this properly in StarTools (which will open the L-extreme stack as L and RGB stack as normal RGB) I want the L-extreme stack to have its stars registered to the stars of the RGB stack and kept as a separate file, i.e. in the end I want one L.fit and RGB.fit file. I've read the ASTAP documentation but it's not clear to me how this can be done in ASTAP. Is there a way?

cytan

[han.k]

Hello Cytan,

ASTAP takes always the best quality image as reference. There is not manual override. In the latest version this reference image is indicated with a crown.

If you stack colour images in ASTAP, it will create first a red, green, blue and luminescence (if available) stack. They are visible in the tab results. You could take these four interim results to process in Startools.

Han

[cytan]

Hi Han,
Here's the link about what I plan to do with my OSC images, which requires 2 separate stacks: 1 stack with the L-extreme filter and 1 with the RGB stack:

https://forum.startools.org/viewtopic.php?t=1674

See Ivo's reply on Mon Jan 20, 2020 4:47 am where he says that by processing both the L-extreme dataset and the RGB dataset separately and then together in Startools, I get the "best of both worlds; the correct coloring of a non-filtered set AND the depth of a light pollution-filtered dataset."

Do you think this can be a feature in a later ASTAP release? Right now, I think what I plan to do is to stack my RGB (OSC) image in ASTAP, and then use the marked reference file in Nebulosity and then use Nebulosity to stack the L-extreme data registered to this reference file. Then I will have 2 separate datasets for StarTools.

Well, unless you have some trick in ASTAP to do what I suggest above :)

cytan

[han.k]

Hello Cytan,
I understand you want a seperate R, G, B set from your OSC images. You could use the astro simple algorithm to convert and stack the OSC to colour (and switch off options "auto colour" and "colour smooth") and split the result in a seperate R, G and B images or process it futher as RGB.

http://www.hnsky.org/astap.htm#osc_menu

You could align the RGB with your luminance using the stack option "Calibrate & alignmnet only"

Is that something you could use?

Han

[cytan]

Hi Han,
Thanks for the recommendation about using "Calibrate and alignment only". I will try it out.
What does "Calibrate and alignment only" do? And how do I use it? I can't seem to find it described in your documentation.

Right now my settings in this tab are those recommended for StarTools.

cytan

[han.k]

Calibrate is that it applies darks, flats, flat-darks if available.
Alignment, it shift the image such they all fit together. So each star is at the same X, Y place. The dimension don't change.

So it produces new images which can be stacked in Photoshop without alignment.

Yes may a little hidden. It is here:

[cytan]

Hi Hans,
Thanks for the explanation. I'll try it out, probably this weekend. I'll keep you posted if I can't make it work.

cytan

[cytan]

Hi Han,
I've done what you suggested: I separated the OSC image into P11, P12, P21, and P22 files. Since I demosaic with BGGR, so I'd assume that P11=B, P12=G, P21=G and P22=R, right?

Now after running the Calibration and alignment option in stack like you suggested, I get the aligned. fit files (the L_extreme aligned file and the P* aligned files) that you can see in the screen capture. And I checked that they are aligned. And they are! Woohoo!

But the problem is how do I stack back the P files to make an RGB file? I tried editing the files to change the filter names in the fits header to R, G and B according to math the P filter name above but that crashed ASTAP :(

Thanks for any help!

cytan

[han.k]

Changing/adding the keyword FILTER should work. you should get something in the header like

FILTER = 'G '

But if you split the OSC image and later combine back to RGB images, you better keep the image RGB. That will make the processing simpler. That could be done with astro simple.

I could also add a new option to combine the RGGB pixels of the OSC images to a RGB image by R + (G+G)/2+ R and reducing the resolution like 2x2. I think i have tried in the past, but result was not impressive but we can try again. Most camera have too small pixels for astronomy so binning is not bad.

Han

[cytan]

Hi Han,
I found Nebulosity was able to do what I proposed in my original question: Make aligned files from the L-extreme and the OSC files. Under Nebulosity->Align/Stacking, when the "Save each file" option is selected, aligned L-extreme and OSC files are created. So my problem is solved :)

Thanks for all your suggestions!

cytan