Making a Lunar Mosaic

[jgs001]

There has been a few discussions where it's been requested someone write up a tutorial on how to complete a lunar mosaic. I'm not the best at it, but I do have a workflow that seems to work very well for me, and I'll describe it here.

Firstly, setup in whatever the normal manner is for you mount. For me, it's balance and polar align (although that's not 100% critical, I have aligned by pointing it in about the right place with a compass), and plug everything together. As long as the tracking is pretty good, you'll be ok. If the tracking isn't pretty good, I think you'll get too much movement on an avi which will mean the mosaic won't be as good as it can be. Get everything running and tracking.

I'm using eqmod and a gamepad to drive my mount, the joystick makes easy work of moving around the moon, and I have to have a laptop to drive the camera anyway.

Adjust the exposure so you can clearly see the surface details (it doesn't matter if you have hot spots, the exposure will be setup properly later), aim for the terminator, the high contrasty shadows make this much easier. Rotate the camera in the focuser to make your job easier during capture. If the camera orientation follows the line of the terminator, it's much easier to build up the captures than if the camera is at a strange relative angle, and the number of frames you need will be less. Then adjust focus. Take your time doing this, it's probably the most important aspect of setting up. I tend to move back and forward, through focus slowly until I think I have it right. Then, if you can, zoom in on the screen. The capture software I'm using has a facility to zoom up to 400%, but I'm sure there must be other methods available if the capture software doesn't have that facility, some form of software screen magnifier maybe, and repeat the process, making sure that at the zoomed level it looks sharp. Watch you don't over zoom though, as the image will start to pixelate making focusing properly next to impossible.

If your capture software doesn't have an option to zoom in, then take a look at http://sweiller.free.fr/Softwares/ScreenVision/ScreenVision.htm as this appears to have the option so zoom.

Now you're focused, it's time to set the exposure. This is actually a tricky proposition as there are such significant changes in the surface brightness. If you're capture software has a histogram, then make use of it as you move across the surface of the moon, you want to set the exposure so you're either, only just clipping the highlights, or preferably not at all, whilst at the same time, capturing details in the darker regions. Take a little time doing this, I normally run across 2 or 3 times to check. Once set, don't adjust it, or your mosaic will look a bit odd.

Get over to the terminator, start at the top or bottom, and start capturing, making sure you cover the terminator first as this is the section that changes the fastest as the lighting angles change. I normally use 1000 frame captures, and try to balance the gain and shutter speed to maximise the framerate, whilst keeping noise down, I don't think there is any one particular good setting for this, there are too many factors involve. I try to keep over 25fps.

There's a very handy little trick you can use to make sure that you don't miss any bits. I discovered this by accident, but hey, that's fine. I was trying to work out how to take just the first frame from my AVI and put it into iMerge. I ended up loading the entire AVI. What iMerge does is just show you the first frame. Obviously the image is not going to be looking it's best, seeing will have affected it, and it needs processing, but it gives you a way of seeing how much overlap you have, accuracy is not too important in the mosaicing, but it's easier to see and messes with your eyes less if it's pretty close.

Now, as you capture each frame, you should be able to make a decision about how far to move the mount to capture the next frame, leave between 20 and 30% overlap, and start capturing the next frame. Then drag and drop the first avi into iMerge. Repeat this process until you have the first strip built up. I normally then just move across and start the next strip next to where I was, repeat until you have captured the entire disk. As you are building up a mosaic of the AVI's in iMerge as you work, you should easily see if you've missed any bits and can go and cover them, capture these as you go, it's probably easier than going back later. As a precaution, if I find I've ended up with insufficient overlap (the panes are just overlapping) I'll grab an extra one to make sure there isn't a slight gap in there once processing is complete, cos by that point it's way too late.

Work quickly yet accurately. If you have any tracking inaccuracies, it can be harder to find your place again, when you have to refer to iMerge and study the image. And the change in the view of the moon will, if you take too long, leave you with some panes that are rotated, not impossible to deal with, but even more of a pain. This is using an EQ mount, if you are using an AltAz mount, the speed really is of the essence if you're to complete without having rotation problems (if it can creep into EQ imaging it'll be a really major problem with AltAz).

If very thin clouds pass through, I'd suggest waiting if you can, as they will affect your exposure settings, and you need to keep everything identical to make it the best you can.

Once you have captured the avi's, and making sure you have good coverage of the entire surface, close iMerge and discard the mosaic you built up. You can't use it anyway, but it makes a really excellent ready reckoner.

If you wish, you can take a dark and flat avis to create a reference frames for later, I'm not totally convinced this makes any real difference, and if I'm honest, my flats for this stink... and actually totally ruin the image so I've never used one to date. But given how little time it takes...

Now onto the processing. There's going to be a huge range of methods for doing this, but this one works for me.

Open Registax (I'm using 5.1), iMerge, and your output folder (where you will save the stacked images). Open the first avi, using the arrows buttons at the bottom, start looking through the frames until you find one that looks the best, click on multi alignment. In the new box that pops up, click on the estimate alignment tab, set the radio button to method 2, then click the estimate align points (I normally use the default box size of 64, it works for me). The image will probably become covered in a load of boxes, one for each point. If you're tracking is 100% spot on, I understand that it's better to set the matrix method and using the boxes at the bottom of the tab set to 10 and 10, then click estimate, although I have had odd effects show up from using this where empty space is visible or when I've got some drift through the avi. Once you have the alignment points, click the align button. Some time later, depending on how many points and how fast your computer is, the alignment will be complete, and registax will have calculated what it thinks is the best frames based on the percentage for the method used. This always seems to come out at 85% for me. I use the slider to limit to 200 or 250 frames from the avi, then click optimise and stack. I know this doesn't use a reference stack of the best frames, but having tried that and found that it doesn't help me, I've stopped doing it.

Once the optimisation and stacking is complete, Registax will take you to the wavelets screen, for those that are not familiar with it, this is the sharpening tools, they are very powerful and very easy to over use, so be gentle. What you need to do, is work out a set of wavelets that give you the best result, after clicking Do All, then save them. At the bottom of the wavelets tab, there's a button labelled save scheme. Click it and save the scheme, this way you don't need to remember the settings you used, as you need to use the same settings for every frame. Click the final tab, perform any cropping you might need, I normally have to crop a small amount around the edge to remove a small white border, and save. Save the file to a separate folder from the avi, I just find this easier.

Close Registax, reopen, and repeat with the next file. Whilst this is aligning, load the saved image into iMerge. Nothing much to do with the first one, then the work begins with each after that. When each avi is at the wavelet stage, having followed the same process with each to this stage, under the wavelets, there is a drop down box, the saved schema from the first pane should show in the drop down list, click it, select the scheme, click do all and proceed as before. If the schema does not show in the drop down, click load, select it, and it will be in the drop down from then on.

Load each image into iMerge whilst the next avi is aligning, you can just drag it in from explorer, and do a rough alignment, you should be able to get pretty close. Then making sure the zoom is at 1:1 (default mode is adjusted with the mouse scroll wheel), click onto a pane already in the image (don't move the mouse as it'll move the pane), then click back onto the new pane. You should get an idea of what direction and how far to move the new piece to line it up. Adjust and repeat. Do this until the image is lined up as near to perfectly as you can. Then check with any other panes that this new piece might be adjoining, you should find, if they've all been done carefully then they'll be spot on, if not adjust until they are. Continue working through until you have completed building the mosaic. Save the image from iMerge. You can save the mosaic project if you wish.

One gotcha I've found with iMerge... if you use the file save option, the project is not saved. Only use the save as option and select to overwrite the original. Although if you just work straight through all the avi's this shouldn't be too much of a problem.

Once the mosaic is saved, load it into your editing program and adjust to suit. I normally apply a small contrast boost with curves and one or two, very gentle, high pass filter sharpens.

I hope this helps someone, and as I said on the threads requesting the tutorial, there are many better imagers out there producing mosaics, and I'm sure there are holes in my workflow so I'm happy for corrections.

Edits:

1) Added screen zoom "If your capture software doesn't have an option to zoom in, then take a look at http://sweiller.free.fr/Softwares/ScreenVision/ScreenVision.htm as this appears to have the option so zoom."

Edited March 7, 2011 by jgs001

[Psychobilly]

Nice one John

Peter...

[brianb]

Excellent note! I won't confuse the issue by saying that I do things a little differently (and compute microrotations when working in altaz mode), just one thing to point out: cover the terminator first as this is the bit with the fastest changing illumination.

My latest "work in hand" I've also started by making a smaller scale image so that any small gaps can be filled in by upscaling the missing bits from that. Doesn't take long & looks a lot better than black holes in the finished product!

[Psychobilly]

Nice additional tip Brian

[jgs001]

Thanks for the added tip, Brian, I'll add it in.

[Steve 1962]

That's really helpful John - many thanks for taking the time to produce it.

[Catanonia]

nice. I use Microsoft ICE for the final image. See this section of the forum for some file scripts I shared to help will all the files and even batch processing in Registax to save you processing each avi. Believe me it does help especially if you have 120 of the blighters

Edited May 27, 2010 by Catanonia

[AndyUK]

Hi John - I really wish I'd read this before I attempted my last attempt! Weather permitting, I'll have another go later this month... and I'll have to see if I can get to grips with registax a bit more (especially wavelets) - I must admit, I've always imagined using elements for sharpening...

[Llamanaut]

this is exactly what ive been looking for, thanks!

[cardconvict]

thanks for this post being looking for somethink like this for age's thanks jgs001 will have to give this ago

[jgs001]

you're welcome guys... Good luck ..

Just for reference, I've been reading about AVIStack v2 on here... I tried it today with some old data. Gotta say, it's much quicker than Regi5, I'm impressed by the quality of the results... and... it's got a built in batch processor... you give it a list of avi's, process one by hand, then click batch and it does the rest for you, processed the same as the first. I really want to get a new and decent set of data to try it with...

[Digz]

A great read, now Ive finally got round to it!!!

Just a thought for the masses, but how about merging in photoshop to create the mosaic once all the images have been registax'd? I know CS2 and above the photomerge function works extremely well.

[TopHouse]

I've had a play around with this and it seems VERY good :-

AutoPano Pro - Panorama stitching software - Panoramic photo software - image stitching

[jgs001]

There are numerous ways of creating the final image, use whatever you find easiest. ICE can do a good job, as does iMerge.. they are free, there are many others that are pay to use.

[Digz]

There are numerous ways of creating the final image, use whatever you find easiest. ICE can do a good job, as does iMerge.. they are free, there are many others that are pay to use.

Indeed

[jgs001]

If you'd like to... feel free to add the details of your preferred method in here. The more that are defined, the more others can choose which to use, depending on if they have the software in question.

[jgs001]

I've added a link to some software I've just stumbled across that allows you to zoom sections of your screen.

If your capture software doesn't have an option to zoom in, then take a look at Screen Vision as this appears to have the option so zoom.

[Diripio]

Good post, very informative. Will give this work flow a try this weekend