blending mosaic sections together

[alcol620]

Managed to complete a 6 part mosaic of the N America and pelican Nebulae. A problem that I couldn't resolve and would welcome feedback on is how to bring all the parts into line. The mosaic attached has a section (top left) that using Pixinsight I couldn't get to blend in with the rest. It stood out from the start. Probably should have thrown the subs for this section away and took some more, but they didn't look too bad individually. I did use David Ault's DNA Linear Fit.

Each section of the mosaic were done at different sessions which probably resulted in the differences. I have read since that it is better to take images of each mosaic section in the same session and then repeat this at subsequent sessions rather 1 section in at a time?

Unfortunately the uploaded png image does not represent the xisf image of Pixinsight but it shows how the sections do not quite blend in with each other 

Views welcome

 

 

 

[gnomus]

There is a relatively new piece of software called Astropixel Processor.  Folks say it works well for putting together mosaics.  It normalises all the panels before stitching.  I haven't used it for a mosaic but I was quite happy with the job it did stacking.  You could try it out - there's a 45 day free period.  Documentation is spartan, however, so you might need to watch a few of the video tutorials to get the hang of how to use it.

[alan4908]

After performing a bit of research on the various options for mosaic construction, I decided to use Registar (which works out where each section goes) and PS which allows the various parts to be blended together. A tutorial on how to do this is here http://geoastro.co.uk/mosaic/mosaic.htm.  If you want to see how effective this is, have a look in my gallery post album "Deep Sky II" for the M31 mosaic. I haven't yet tried out the Astropixel Processor for mosaic construction, however, the initial feedback seems promising.

Alan

[gnomus]

I have used the Registar plus Photoshop method for the couple of mosaics I have done.

[AKB]

The good news: I have had good success with Microsoft ICE (free: https://www.microsoft.com/en-us/research/product/computational-photography-applications/image-composite-editor/#)

The bad news: I only tried once it on a 2-panel mosaic:

 

[toxic]

Microsoft ice works well if you don't try and add the images all together as Uranium235 (Rob) would agree you need to add them in strips or in blocks.

if your mosaic was 9 panels eg.

1 - 2 - 3

4 - 5 - 6

7 - 8 - 9

then i would add them 369 then 258 or 2356 - 1245 then add all the block back into ICE it should work fine.

but you will need to make sure your images a flat or you will see the joins.

i haven't tried astro pixel processor for mosaics yet but i will.

hope this helps

 

[alcol620]

Thanks for feedback folks, plenty of things to think about, may give them a try. Hadn't thought about ICE.

[ollypenrice]

The problem is partly one of geometry. We are trying to render a spherically curved surface (the notional 'celestial sphere') onto a flat surface (our screen.) This involves the kind of geometric solutions seen in making maps of the Earth. In the end it can't really be done and you have to choose between Mercator and Peter's projection, etc., each with its own distortions. The larger the area of sky covered in your image, the harder the problem becomes. It isn't connected with the number of panels. It's the amount of sky which matters.

Registar is a very capable programme but it lacks a key feature, a geometrically coherent template to which each panel might be registered. (You can get round this by taking a widefield lens shot centred on your mosaic target, resizing it upwards till it is the size of your prospective mosaic, and registering your panels to that. Our guest Paul Kummer suggests a refinement: you take the widefield template image in normal size, register your mosaic panels to it to enhance the quality, then resize that up to act as a full size template to which you then align you panels. Crafty!)

Without a template the shape of your final image in Registar will depend on which image you used as the reference image. Get this wrong and you'll get a bent image which, when cropped into a rectilinear one, will be missing important bits! We had this a couple of days ago.

Pixinsight, I believe, can make mosaics which are registered to a star chart to give a coherent geometry. The problem for me with PI is that it might as well be written in runes.

Which brings us back to APP. Today Sara posted a superb video on mosaic making and it seems that the programme calculates a cohenent geometry for the global image. Brilliant.

Olly

[alcol620]

Thanks Olly. Watched Sara's video amazing and it looks so simple. Unbelievable.