Milkyway Panorama blending.

So, are you first creating the panels of the mosaic before trying to actually make a mosaic? It's best to do that first, giving you about 10 or so panels if I'm seeing that right? That should combine pretty fast and in a better way. You can then also first create the panels with the different camera data.

@vincent-mod I tried to do that but got some errors while attempting to put together a few frames at a time. When you say creating panels, you mean just putting together something like 3-4 frames at a time instead of stitching them all at once? You think that'll solve my blending issues? I'd definitely be willing to try that again. 

Yes sort of like that. Usually a mosaic consists of panels (the area's you used to divide the object into), these panels you create first. I can have a look at your data as well if you want, though my connection here is spotty at the moment. I can ask Wouter or Mabula to have a try if that's needed.

@vincent-mod I will give that a try again... was having issues stitching small panels but now that I'm in this forum I can at least troubleshoot when it goes wrong again. This will actually be helpful in integrating the extra data too as I just shot several more minutes in key areas last night.

Here's a folder with all the lights and calibration masters if you would like to give it a try! 

@vincent-mod Okay so I attempted to create a smaller panel rather than stitching everything at once - I am not sure how small to make panels (this panel ends up being about 1/3 of the size of the total mosaic) and it's very good in terms of blending but unfortunately, I still have two major issues. 

First, you can see in this example that the stars are not fully aligned between panels and get doubled up in certain areas. I'm not sure which setting to use to rectify this. 

From a distance, you can see the blending between panels in terms of LNC is really great.

Up close, though, you can see the issue of misalignment. It is only in certain areas though, and when I change the reference frame the misalignment happens in different areas.

The second concern I have is the projection method - what's the best way to choose a reference frame here? Centered to the panel, or as close to center to the final mosaic as I can? I would love for the Milkyway to come out straight and not have any stretching on Rho Ophiuchi as well, just like my ICE projection from my OP shows. 

I have additional data that is now calibrated if you'd like to give any of this a try yourself, I can upload it. 

Thanks!

@Mabula-Admin maybe you know what's going wrong here? I have spent many hours trying to stitch this mosaic and it's a commissioned project that will be printed in a very large format. I have tried 10,000 stars and it still does not align properly.

Sorry for the delay Michael, bit busy down here. I've asked Mabula to give it a look as well.

Hi Michael @mikeabr,

The first thing you need to do is create the mosaic panels itself using regular registration. Don't try to mosaic from mosaics.

Look at this tutorial first:

https://www.astropixelprocessor.com/mosaic-tutorial-milky-way-to-rho-ophiuchi-by-mabula/

The 11 mosaic panels are first created using normal integration with normal registration (not mosaic mode).

Then the mosaic is simply created from the mosaic panels with mosaic registration.

Do not set the star count higher than 3000-4000 stars, that will only make things unstable I think.

If it does not register then, you need to either increase scale stop, use triangles or increase the distortion margin I think.

Mabula

@mabula-admin Thanks for taking the time to respond! I followed the tutorial closely but maybe I'm just getting confused on what really defines a panel. 

I have data from four separate nights and don't have distinct "panels" per say, just many light frames. One night I opted to do shorter exposures and stack, so I did stack those using regular registration. I now have something like 60ish light frames (fits files) which have been calibrated in APP. I'll try again to integrate them all at once, but I had some issues with that in the past (described in first post) so I was trying to do smaller amounts at a time to see if I could dial in the settings.

I'll give it a shot again with your suggestions and keep you posted. 

@Mabula-admin I attempted to stitch again just 16 of the 60ish frames using those settings and here's what I got:

Here are all of the settings I used: 

Again, the colors/brightness seem to blend quite well, but not the actual star alignment.

Could you try disabling distortion correction?

@vincent-mod I just ran an instance with the exact settings of my last post but with DDC off (and that switched to projective instead of calibrated projective) and here's what I got:

Much better than before but still not quite aligned in ALL places. 

Rho looks great now

but other parts are worse now

Which settings can I tinker with to get this right? Just want to remind that this is only 16 of the panels out of the 60ish that I will need to use for the final integration, which shows much more of the milkyway above this region. 

This whole project is a commissioned print which will be printed in a very large format, so I need all the resolution I can get here.

Mm, tricky, I'll ask Mabula again to have a look, we might need the data ourselves to find out (which you shared, so that's not too hard 😉 ).

Hi @mikeabr,

The workflow is still not as advised in the mosaic video tutorial.

To make the mosaic work you need:

1) create mosaic panels using normal registration (no distortion correction) of the subs per mosaic panel. A panel is defined by a single field of view. So in your lights, the first 3 lights would be one panel, they show the same field of view.

2) Once all mosaic panels are created. Then you can load those panels as lights and register them as a mosaic using dynamic distortion correction enabled.

By not following this workflow, the current APP implementation will be unstable as you are experiencing.

I will try to process the mosaic myself in the coming days and will let you know if I can create it correctly or not.

Mabula

@mabula-admin Hey Mabula,

Thanks for your reply. I think I may have been unclear - My first attempts at stitching the mosaic were exactly as you described. Of course, it was so long ago at this point (and so many attempts ago) that I am not 100% sure where I may have gone wrong, but I distinctly recall following your tutorial closely before I ever posted here. 

I am very much looking forward to hearing how it goes for you, thanks for taking the time. If you feel the need to make another tutorial you are welcome to use my data. 

Just to clarify, the folder I provided here previously isn't all the data I would like to integrate in the final project since I got more integration time on certain areas of the mosaic on different nights. The folder includes just one session where I managed to cover most of the mosaic, though. And in my workflow, I did as you suggested: integrated each stack into a panel of its own (3x60, some panels got a few extra exposures for whatever reason). In my workflow, I also cropped out the bad edges of certain frames in order to avoid having coma in key areas that happened to fall on the edges of certain frames... but in the set that I provided that is not nearly as prevalent an issue. 

Thanks,

Mike

Hi Michael @mikeabr,

I have run a first test on your data.

First I would like to point out that your MasterFlat does not work very well, the calibrated data shows overcorrection of the vignetting profile unfortunately, creating dark circles in the middle of the calibrated images. I know that shooting good flats is difficult with short focal lengths though. If the masterflat would be good then the blending of all panels would be easier of course.

But let us focus know first on getting the data properly registered.

As a first test I looked at your 101 uploaded frames and was able to divide it into 33 panels where each panel has the same field of view.

I did not create the 33 panels for this test. I only loaded 1 single frame for each panel to see if I can make that register correctly.

Without a lot of effort I was able to get it to align nicely I think. I was using APP 2.0.0-beta4.

3) Analyse stars set to 2500 (so not too high, this is not needed since your panels have plenty of overlap 😉 )

4) Register, quadrilaterals, scale start 1, scale stop 10 (defaults for mosaic) dynamic distortion correction on, same camera and optics off (but on should work as well and more stable so will test that as well). Mosaic mode. Calibrated Projective model since we need to be able to project differently than rectilinear. Rectilinear only works for Field Of Views up to 120 degrees but then will already stretch the data strongly... We want to project this with Equirectangular or Mercator. So at the bottom of 4 set the projection to equirectangular or mercator.

5) for first test, just defaults

6) also defaults, except I set scale to 0,5x to run it a bit quicker for a first test.

This is what i get, already looks very good to me. You can see why I mention that your MasterFlat is not optimal ;-). Dark circles in all the panels are visible.

The reference was chosen to be the bottom right panel. I will keep it as reference and will try to adjust the projection center to get a vertical milkyway. as you mentioned next.

I checked for misalignment but I only see it very little in the extreme corners of the panels where the optical distortion is biggest. I would think that a high % of Multi-Bend Blending will solve that easily.

Mabula

@mikeabr, okay I have found near optimal projection adjustments 😊 

Keep in mind the reference is still the frame on the bottom right. This results in the mosaic looking like this (scale 0,2x for quick testing):

Side by side the 3 possible projections: rectilinear, equirectangular & mercator:

Mercator projection looks almost the same as equirectangular. Rectilinear is only for FOVs less than 120x120 degrees. The other 2 can project the whole circle of 360x180 degrees.

Mercator looks nicer than equirectangular, but that is personal of course. I will continue with mercator projection and will try to remove the seams/illumination differences now.

firs step, 5) advanced normalization with Multi-Band Blending at 50%:

2nd step: 2nd degree LNC 3x (still scale 0,2x):

Will now run it at scale 1.0x..

Hi Mabula,

Thank you for spending so much time on this, I truly appreciate it. 

So I just tried to completely replicate your settings but use (nearly) all the data I have from the other 2 nights and was greeted with this error: 

Just for reference, the data was all shot at 85mm, but the first session was single 3 minute subs for each panel and similar coverage to the data you processed (I'm just trying to boost the SNR and not let that first night go to waste) and I loaded the data from that first night as individual mosaic panels just like you did in the data I provided. The only difference was I shot it on a lower MP camera, a7iii instead of A7IV. 

The second set of data I also tried to incorporate was shot on my a7iv also at 85mm just longer exposure time on the core. Again, loaded as 3 stacked and calibrated mosaic panels with a single fov. 

I used the beta version you mentioned in your comment, so aside from simply using more data than you had to work with, I changed absolutely nothing, even the reference frame is the bottom right corner like you used. 

Do I need to upload the additional data in order for you to troubleshoot this bug? Or am I doing something wrong? Same camera/optics is not checked.

EDIT: I restarted APP and it is working now, we shall see what happens!

@mikeabr 

If you get that error, I think one of your mosaic panels has an issue and will not register to any of the other frames with those settings. Is there a panel with low star count  after star analysis?

This is the full scale result, no misalignment anywhere I think:

Gonna attempt to reshoot some flats to get better correction then will try stitching all of the data I have! Thank you so much for finding the optimal settings for this project, I can't wait to share the final result. 

Update: I was able to correct the frames from my a7iv today decently well. Here's the result:

Before

After

Now I really need to be able to fix my a7iii lights. The flats I shot for that camera seem to overcorrect really badly and I get dark in the middle with bright edges. Since I no longer have that camera, I can't really reshoot them. I attempted to follow the sticky on creating an artificial flat but I can't get the tool to give me a good vignette removal... Any suggestions? I tried scaling down the a7iv master flat but APP will not allow it to be assigned to the a7iii files even with matching resolution. I can upload just a few flat frames and a light frame if that would be helpful.

Did you follow the advice given below?

@vincent-mod That's exactly what I tried to do. When I try to use the tool for correcting the vignette, I do not get favorable results. I have watched tutorials on where to place the boxes (even mabula's) and just can't get a good correction. 

That aside, I am noticing that my masterflat is not being applied to my images often times. I recently shot 2 hours on cygnus with my 85mm lens, same exposure time and iso as the masterflat that I made for the mosaic project and it does not assign when I hit "re-assign masters to lights". 

Mm, that must mean there is some mismatch between the masterflat and the lights. Could you share a few frames and the masterflat that shows this issue?

Alright so something weird was happening, APP was not showing the proper resolution in the program for the lights. It should be 6000x4000, but Pixinsight showed 6024x4024, and APP was showing 6048x4024. Anyways, once I figured that out I resized my artificial flat (borrowed from my a7iv) and it worked quite well on some of my light frames.

I tried to correct frames from a previous session with the exact same setup and got the following errors: 

Does this mean my flat frame is mono for some reason? Not sure how that would have happened. I turned on debayering as suggested and it seemed to do the trick, but then...

I just have no clue what that means... my lights were fine, definitely not underexposed.

Appears to have corrected the data decently well, but when you zoom in:

Strange grid-like pattern. 

Any ideas? Seems like every time I solve a problem a new one pops up... the joys of our hobby!

@mikeabr The different sizes of the frames is because of the software you shot them with. DSLR cameras have dark strips next to the sensor which the camera software uses to determine the black spot. A sort of dark frame if you like. Some imaging software include those black strips and some don't. Let me therefore repeat an advice that we give a lot on this forum: ALWAYS take all frames (lights and calibration) with the same software!

The popup about the black and white flat possibly either originates from the image acquisition software not storing the bayer pattern in the exif data of the images or (more likely) is a result from resizing them. Forcing APP to debayer them indeed is the only solution.

The "serious data issue" popup happens because APP detects that some pixels clip after dark subtraction. This means that the signal value in those pixels in the lights have a (slightly) lower value than the corresponding pixels in the master dark. To the eye the lights may look exposed well enough but apparently there is a negative difference there between the lights and the master dark. This doesn't necessarily originate in the lights but may be caused by wrong darks/bias or a light leak (as explained in the popup). Once more, make sure to take ALL frames with the same software.

HTH, Wouter