Mosaics

Andys_Astropix
13 Feb, 2017 22:47
Hi Folks, I'm just starting out on my first mosaic, and looking for suggestions, tips & tricks on the process to make tricolour NB images of large objects. I tried Photomerge in PS 2017 but it aligned my 3 NB file sets out of register.
Then I found Sara Wager's and using MSICE very helpful and easy. But still not quite right.
I've also played with demo versions of PT Gui and Autopanogiga.
Being a mac user, I would prefer a mac based solution.
What's best, do you merge the files prior to stretching? If so in what format do you load them in the package?
All input welcome, thanks in advance.

Cheers
Andy
whwang
13 Feb, 2017 23:31
Mac user here too.  I user PixInsight for many processing.  It has Mac version.  Many people use it for mosaic and narrowband composition.  It's extremely powerful but also has an extremely steep learning curve.

On the other hand, as a mosaic maniac, I strongly recommend Registar.  It's specifically created for mosaicking, fast, easy to use, and robust.  Unfortunately it only runs on Windows. If you have Parallels Desktop or VMWare, you can give it a try.  I use Registar exclusively for mosaicking for more than 10 years, and I haven't found any other software does better than Registar, including PixInsight.

Regarding stretching before or after merging the mosaic panels, it doesn't really matter.  The point is to bring the panels to equal brightness/contrast/color. Both Registar and PixInsight can do this well, when there are no sky background gradients.  When there are gradients, things become trickier.  In order to achieve equal brightness/contrast/color on all the mosaic panels, you either do not stretch them before mosaicking, or apply identical stretch to all of them.  If you stretch them differently, then things may quickly grow out of control in the subsequent processing.

Cheers,
Wei-Hao
Andys_Astropix
13 Feb, 2017 23:35
Thanks Wei-Hao for your in depth reply - looks like I'll have to fire up bootcamp and give Registar a go.
The US$179 price factor is a bit of a hurdle but if it works well, then I guess it's worth it!

Cheers
Andy
whwang
14 Feb, 2017 00:29
Hi Andy,

You may use its trial version on the images you already have, and then decide whether it really fits your need.
AtmosFearIC
14 Feb, 2017 20:11
I personally use Autopano Giga on my Mac and I found it worked better than PTGUI. PixInsight is powerful BUT there is no way it'll do a large mosaic, not without many many many MANY hours.

Below is an 80 panel mosaic, pre-processing done in PI (only very basic stretching and colour), run through AutopanoGiga and then curves and colour touched up in PS.

http://www.astrobin.com/278004

For this one I found that I had to be gentle in the PI processing and AutopanoGiga "destroyed" the image but only took 5 minutes to correct in PS. The "destruction" was simply AutopanoGiga background and colour matching everything.
Edited 14 Feb, 2017 20:37
whwang
15 Feb, 2017 00:04
Thank you for the info.  How long does it take for Autopano Giga to stitch your 80 D700 images?  Is it fully automatic?
AtmosFearIC
15 Feb, 2017 09:37
Probably took 5-10 minutes but I set it to maximum frame points (200) and told it to be more precise than fast. I still usually had 1-3 frames that I had to manually put in (select panel 5-5 & 5-6 and tell it the region that they intersect) which took maybe another 5 minutes.

Actually outputting the image took about 20 minutes but that was a Photoshop Large Format file of 11GB.
whwang
15 Feb, 2017 15:37
Wow….  If it is really that efficient, I have to give it a try.  Thanks again!
rob77
16 Feb, 2017 08:01
I usually make very big mosaics using pro data, hundred of pieces. I use Registar and I give to each piece a low stretch before registering.

Cheers
astrofotoperu
11 Sep, 2018 20:13
Hello everyone, please I need some help on processing an image mosaic with Pixinsight. I have already stacked 3 panels of M31, but after doing so, the colors are slightly different between each panel. Noise levels are also different (maybe because the galaxy has fainter signal on the edges?)

My main steps were:

1. Stack the 3 panels and apply background neutralization individually.
2. Apply linear fit to level out intensities.
3. Apply gradient merge mosaic (previously using star alignment).

After all this, I see that the mosaic is done, but its not perfect. I still see that noise levels are different between panel 1 (center), and panels 2 (left) and 3 (right). The color is slightly different between them.

Any advice? Thanks! smile
RQKimball
12 Sep, 2018 17:33
I have made many mosaics with pixinsight with great success.  Are you useing a "synthetic starfield" for alignment.  It is great.  Are you using dnaLinearFit under scripts?  That helps match intensity levels.  Make sure you don't have any pinched stars.
gnomus
12 Sep, 2018 18:54
Hi Andy

I've tried 3 mosaic methods:

1) Registar followed by Photoshop
2) PixInsight
3) AstroPixel Processor

They each have their advantages and disadvantages.  Registar does a reliable job.  However there can then be quite a bit of messing around with masks.  PixInsight has (for reasons I don't know) started working much better for me recently.  When I started doing mosaics with it, I would often get odd artefacts (like little blowouts)  around stars and frame edges.  PI is great when it works, but when it doesn't it can be an awful job finding out why not.  And finally APP - this does a pretty good job most of the time, and is probabaly the simplest method of all - when it works.  Once again, there is an APP 'method', however, that takes a little getting used to.  There are 'how to' videos on Mabula's website that hekp considerably.

I did use ICE for a lunar mosaic some time ago, but I haven't tried it for any DSO work, so cannot comment on that one.

You can probably get trials of most of these options and play around with them to find what suits.

Steve
Edited 13 Sep, 2018 09:54
huerbsch
13 Sep, 2018 03:05
APP and PS CC have worked really well for me.  I also own Registar but never need to use it as APP or PS does it really well. You may want to consider the $$ on APP inatead of registar (which is a much older program).
dvj
13 Sep, 2018 22:27
I am currently using Micosoft ICE Image Composite Editor for my large hydrogen alpha mosaics.  It is required that you spend time equalizing all of the images as close a possible to create seamless tiles before loading into ICE.  It's free and worth experimenting.    I have tested APP for small mosaics (4x4 arrays), and it works great from raw .fits files without any adjustment, but it crashed my PC when going to 20+ tiles.  And my mosaics are over 200 16803 tiles sometimes.  ICE handles the high number, but my machine crunches for multiple hours with that many tiles.  PTGUI has a number of adjustments that take some experimentation.  And sometimes it will not assemble my tiles regardless what I do, but ICE will.   PTGui can and will do excellent work with smaller arrays.
AtmosFearIC
13 Sep, 2018 22:50
Just further on for John, APP doesn’t allow for image sizes larger than 46300x46300 for mono images or 26700x26700 for RGB images.

I’ve used Microsoft ICE for mosaics and found that it does a pretty good job as long as you can remove the gradients before hand.
I tried PTGUI a while back and wasn’t too impressed with its ability to do starry fields.
For the last few years I’ve been using AutoPano Giga and found this to be the best when not dealing with mono images (only accepts RGB images). Converting mono TIFF into RGB is easy but ICE accepts mono TIFF natively.

PixInsight has MosaicByCoordinates which works well as long as there isn’t any  distortions. I’m creating a 500 panel mosaic with a Nikon D810 and my spacing is off by 1.5mm which causes a little distortion far off-axis which gets a little messed up when using GradientMergeMosaic.

In short, they all have their pros and cons.
dvj
13 Sep, 2018 23:07
I am going to play around with AutoPano Giga a bit.  My grayscale will need to be converted to RGB.  I use an FSQ at native f/5 which has very little linear distortion from tile to tile.  Another factor  to consider is your tile overlap amount.  I am at least 40 arc minutes overlap at my image scale.  This significantly helps with blending.    Colin, that explains why APP crashed.  I did not know there was a size limit.  Bummer.
astrofotoperu
14 Sep, 2018 17:10
Thanks everyone for your coments. I finished my mosaic yesterday with linearfit, star alignment, and gradient merge moisaic. I had a little trouble with different noise presence on panel A VS panels B and C (maybe due to atmospheric conditions), but I corrected it with photoshop.

Thanks all!
RQKimball
14 Sep, 2018 18:02
If you haven't watched this YouTube video you should.  https://youtu.be/p6UaFbh5_SI
Link to YouTube video on mosaics

It help me tremendously.  He has an elaborate method for removing pinched stars, but I found I could use the "Clone Tool" easier.

When can we see your mosaic?
 
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