How to Create a Mosaic

[Gina]

I had a problem remembering how I did this before but I think I've sussed it out.  I have the odd question or two though for those that have worked all this out

I'm currently creating a mosaic of the Cygnus Loop and so far have just 2 (of 6) overlapping panes.  This is in narrowband with Ha, OIII and SII.  Here is what I've done so far.

1. Each colour set of each pane stacked in DSS
2. Ran the various stacked subs through RegiStar in Union mode to produce a canvas that contained the whole of all the stacks
3. Opened the stack images in Photoshop
4. Duplicated one Ha stack (pane 1) and created a New Layer
5. Copied the second Ha stack (pane 2) and pasted it into the new layer
6. Adjusted the curves for each layer to match them up roughly
7. Set Layer 1 to Lighten mode
8. Readjusted curves to match up and make the join invisible.
9. Flattened image
10. Resized and saved

Here is the result in a quick JPEG format.

Now a question .  Is it best to combine the panes of one colour first then combine the colours and process or the other way round ie. combine the colours of each pane and match them up before combining panes?

[ChrisLX200]

If I were doing it then I think at first I would try combining all three colours per pane, then stitch the panes together. I doubt the process of stitching panes together is 100% accurate and reproducible so colours could end up displaced at one point or other. Mind - I have never done it! Might be more problematic balancing colours and background across all panes done that way though.

ChrisH

[Gina]

Thank you Chris

[ollypenrice]

You don't mention Registar's Calibrate function, Gina. It makes life easier if you calibrate panels and doing it to the linear images might seem logical but it doesn't always work. One or more of the panes being calibrated can end up black clipped from the outset. I take partly stretched images into Registar, each with plenty of room to the left of the histogram pedestal to allow for clipping to match its neighbour. When they are all registered I apply calibration and ask Registar to make a full mosaic (knowing that it will have the odd visible join, but read on.) I also save all the registered-calibrated files individually.

I then go into Ps and open the Registar full mosaic, looking for edges. Now these edges are bound to be 'underneath' one of the panels so I open that panel, paste it on as a top layer and adjust it in levels and curves till it's a better match and then erase all but the bit over the line, which now gets covered. It's very quick.

I always work with RGB rather than single colours. I may use the method above or just open the registered calibrated panels on a big canvas and start making them match. Using channels you can see which channels need attention. Levels, Curves and the Dodge and Burn tools are good ways of getting a match.

Where one panel overlays another it is best to use a feathered eraser  and a wiggley movement to blend the panels, since the eye is a beggar for seeing straight lines!

When making very large mosaics (nine panels of full frame for instance) I have always find it necessary to use a template  of some kind. After beng pleased to find Registar could read a map from SkyMap I have since found that it doesn't always do so. Curses!!! You can use a camera lens image as an alignment template in Registar but you must upsize it to the size of the final image or you'll end up the size of the original lens image. We've just been doing a big one around 1396 and the Bat. Our panes all overlap each other so we have to have all the data, right? Wrong! When we put them all together some of the sides curved in towards the middle meaning that we didn't fill the full rectangle of the image. Some quick filler panels were called for!

Olly

[Gina]

Thank you Olly

First thing is that I need to RTFM of RegiStar   I've been missing a lot of it's capabilities

All you say makes perfect sense to me including the curved edges.  I've noticed some curvature even in the images I have combined from the Esprit 80ED and 460EX as shown above.  If you look carefully there is some curvature of the edges of the second (lower) pane.  It was registered against the top pane as reference.

So far I have used the linear images direct from DSS to feed into RegiStar without calibrating and this has worked.