Thread: Imaging mosaics
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Old 10-06-2012, 06:42 AM
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gregbradley
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Hi Dave,

That's why I am thinking that a program like PTGui Pro may be the go as it does all that automatically.

I am about to process a 4 panel mosaic and use it to do the stitching so I can let you know.

As I say Photoshop CS4 and above does a reasonable job but I think its still not as good as purpose built software.

My workflow would be like this:

Plan out the mosaic and allow plenty of overlap (20% on all sides).
Take each panel at similar times over several nights (hard with weather moon) Or take 2 in one night (it will mean more gradients to handle).

Take same exposures, same binning etc etc.

Do a modest mosaic - 2 to 4 panels. 24 panels would be for an expert and doomed to fail. I would take a 10 minute luminance and save it for each panel. I would do a quick and dirty Photoshop CS4 stitching of the 4 luminance panels to make sure they fit before committing to an imaging run. I also open up the luminance file of the last panel and compare on the same screen to the focus image that I am about to take to make sure they are aligned and will work. Label them well so you know which one goes where - important! (not with 2 panels but do 12 and you can easily get lost).

Process each exactly the same way. Don't do different steps to each.

Don't worry about the final colour, noise control etc etc leave that until after it is stitched.

Stitch the panels using PTGui Pro or CS4.

See how it looks. It may need gradient handling on each panel, some curves to balance each one, perhaps try normalising the backgrounds of each.

Once successfully stitched then do your final colour tweaking, sharpening, noise control etc etc.

The hardest part of mosaics I have found is the imbalance in brightness levels between panels so when blended one will stand out. Also colour hues can shift significantly between panels so the Photoshop selective colour tool (especially tweaking "neutrals" s vital.


Greg.
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