Mosaic panels - Question of colour balance

[PKay]

Hope it's OK to post a question here :)

I am working on a 6 panel mosaic of the Rho Ophiuchi cloud.

Each panel is taken on a seperate night in RGB made up of 30x5m subs each.

Channels processed seperatly, background extraction, deconvolution, denoise, histogram stretch then combined to make one panel.

I have 'stitched' two panels together as a test and there is a difference in hue (see attached preview).

Playing with the curves (before stitching) helps, but it is tedious and 'hit an miss'.

Any ideas?

[multiweb]

The trick is to match the background ADU in the corresponding colour channels. So you pick a small square devoid of nebulosity in both panels blue channel for instance and match them to the red and green via pixel math. Add the difference. When in PS the auto blend layers is what you want to use. It does a great job provided you have a decent overlap.

[PKay]

Thanks Marc.

You twigged something in my memory (sometimes I am so brain dead).

Completely forgot about Gradient Merge Mosaic.

A lot of baarking around but it works.

[multiweb]

Looks great. :thumbsup: Hard yakka at that FL. It's quite faint. I guess you have good dark skies.

[gregbradley]

Firstly acquisition. Try to take each panel at the same time of night and under the same moon conditions.

Take each panel up to an early processing step and do each the same way.

Use Photoshop panorama tool (its ok sometimes and other times not) and stitch them together. Perhaps PT Gui, Microsoft ICE or some other stitching program.

Then process it further as a whole. You may still need to balance the subs with each other with regards to colour, lightness. Burn and dodge tools come into play at obvious border differences as does levels..

Greg.

[PKay]

Hi Marc, yes I live in a remote coastal village, no street lights.

The Emu is well and truly alive in the sky...


Thanks for commenting Greg.

One thing mosaics are is a lot of effort, that's for sure.
And a lot of planning and good house keeping.

All part of a wonderful journey :)

[ChrisV]

Glad you asked the question as I'm just starting on a 4 panel around that area and am starting to wonder about processing it ...

[PKay]

Hi Chris

Here is a youtube video that explains one way of doing the processing in PI:

https://www.youtube.com/watch?v=H2r3ZYqCaP8

This is after you have separately processed each tile.
Also he says use linear images.
I have done it with non linear and it works just fine.

I remember you use SGP?
In the framing & mosaic wizard, the default overlap is 10% don't go lower.