Making an (L) RGB image from stacks

[Paulkirk]

Hello Han, I looked in the help file to find about LRGB synthesis. Now that I have stacks of L, R, G and B images, how can I register those stacks ready for processing in photoshop or Nebulosity? I tried to load up the three stacks (RGB) into ASTAP and 'analys and organise', then stack, but this did not work because the blue stack was left unchecked.
thanks for help
Paul

[han.k]

That should go automatically. It's normaly the second step after combining the individual L, R,G,B files. Or as you stack them seperately as you do.

I assume the blue file is a problem for ASTAP. You could try to use either star alignment instead of astrometric alignment on the LRGB files. Ot align them manually.

Share them anf I will have look what works best for your files. No problem.

Han

[Paulkirk]

Thanks Han, link to files below. Is it possible to register/ align the files so that I can open them individually into a program for LRGB synthesis such as photoshop/ Nebulosity etc?
Paul
https://drive.google.com/drive/folders/1QNB2ELuDT3DlEcP7Q2DjBB6-jtLTm7yr?usp=sharing

[Paulkirk]

Just to let you know Han, I have just tried stacking the images manually by double clicking a red line in the ASTAP image list. I then use the mouse wheel to zoom in / out and click a star, but no circle or square appears no matter how much I zoom in.
thanks,
Paul

[han.k]

Hello Paul,

Here I can stack the LRGB image with star or astrometric alignment. See attached. Maybe you have change the "tetrahedron tolerance" at tab alignment. You can set it on 0.007 or 0.005. The galaxy looks good but the stars are bad.

All four files are stacked from images with a different angles. Probalby the result wouldl be better if you stack images with the same orientation or from the same series.

The manual stacking seems broken for your colour images. When I test it on my images it works. A bug I have to fix. So this exercise helps in developing the program.

Han

[han.k]

The colur of the stars can be fixed in the viewer by holding the right mouse down and pulling a square around a star and select from the pop-up local remove colour or local colour smooth. But its better to do a preselection in the orginal files and see how that improves the result.

[Paulkirk]

Thanks Han , yes I have just noticed myself that the 300 sec exposures are at a different angle from the 600 sec ones, which makes the processing a mess. This was because those images were created on different nights and I dismounted the camera to insert a tilt adjuster in between the two sessions. I think that would be a real challenge for stacking as well, as the angles are significantly different. So I think my NGC 3628 data will have to wait until I can acquire some more subs matching one angle.

Just one query on the LRGB synthesis. Does ASTAP register the L, R,G, B stacks and create separate files for each registered stack so that they can be pasted on top of each other in Photoshop?

Paul

[han.k]

Rotation or flipped image is not a real problem forASTAP

Yes it will make seperate L. R, G, B files. If you add all files to the image tab it will first build a red, green, blue and luminance master with the name extended with _ stacked.fits. Then it will combine those four files. You could export these seperate L, R, G, B masters to 16 or 32 bit tiff and load them in different layers in Photoshop and combine them there. I assume you can not only shift but also rotate them in Photoshop. The files are not registrated in a way maybe DSS does. ASTAP aligns them but doesn't record any alignment info it in the files.

I have forgot to apply a smooth using LRGB stacking. See attached. As soon the RGB images are stacked, you should smooth the RGB colours before using it to colour the luminance channel image. Just tried it again but didn't work as expected. Something I will work on. LRGB stacking in ASTAP was ignored for a year or so. Too much other things ongoing in solving and stacking of mono and OSC images.

I assume you have stacked them also in an other program. With good results?

Han

[han.k]

Hello Paul,

I found why the star colour is so bad. There is no option for smoothing star of 45 pixels in diameter as in your image.. I have extended the option up to "Colour smooth(50)". Then the stars look better. This ASTAP version is not released yet:

[Paulkirk]

Hello Han, Yes I used Nebulosity 4 which allows manual stacking of RGB or LRGB whichever is chosen. I used RGB stack, then took that into photoshop for process with Noel Carboni's actions, they work well for nebulae/ galaxy images. Usually I then add in the luminance stack as another layer. However, with the different angles, the image backgrounds are a mess and my photoshop skills aren't good enough to normalise the bacgrounds, so I'll separate the original subs into their respective angles and restack and reprocess.
best wishes
Paul

[Paulkirk]

That's really nice Han. What s/w did you use to process the galaxy?
I'll keep a look out for the new release. I am about to start processing an Arp image - NGC 3718. I'll let you know how it goes.
best wishes
Paul