Cygnus Loop revisited

[bobharmony]

After staring at my first mosaic (the Cygnus Loop) I realized that I wasn't happy with the seams of the 4 photos and that it needed some work. After further study, I noted that my flats did not completely correct the vignetting, so went for a second process to correct the issue. StarTools isn't all that friendly for mosaics as all of the linear processing needs to be completed before stitching, so I took "snapshots" along the way of each panel and put those snapshots together in MS ICE to ensure I wasn't getting too far off with my data.

I like this one better than the original, it still could do with some improvement as I learn more about putting mosaics together. In any case here is my 4 panel (50 minutes per panel) shot with 120 second subs using the Nikon D5300 at ISO 200, calibrated with darks (17) flats (51) and dark flats (51).

Comments and criticisms welcome! In a perfect world this would be a 6 panel mosaic, maybe next year if I get better summer weather!

Bob

[messier 111]

nice shot , thx .

[STEVE333]

Hi Bob - You're making nice progress on this mosaic. Mosaics are always a lot of work.

You asked for comments, so, I downloaded your image and looked at it in PixInisght (the only program I know). The first thing I did was to look at the relative signal levels of the RGB channels. The picture below shows the result.

The graph is a histogram of the brightness in the image. The Vertical axis represents the number of pixels. The Horizontal axis represents brightness in the image with black being on the left end and white on the right end. The left edges of the R, G and B "hills" should line up to ensure that the background will be black/gray. So, I lined up the left edges with the following result.

The background now looks gray/black but there is still a bit of a purplish gradient on the right side of the image. After removing that gradient the following image resulted.

Sorry I don't know how to do this with Star Tools but hope this helps. Best of success.

Steve

[bobharmony]

Hi Bob - You're making nice progress on this mosaic. Mosaics are always a lot of work.

You asked for comments, so, I downloaded your image and looked at it in PixInisght (the only program I know). The first thing I did was to look at the relative signal levels of the RGB channels. The picture below shows the result.



The graph is a histogram of the brightness in the image. The Vertical axis represents the number of pixels. The Horizontal axis represents brightness in the image with black being on the left end and white on the right end. The left edges of the R, G and B "hills" should line up to ensure that the background will be black/gray. So, I lined up the left edges with the following result.


The background now looks gray/black but there is still a bit of a purplish gradient on the right side of the image. After removing that gradient the following image resulted.



Sorry I don't know how to do this with Star Tools but hope this helps. Best of success.

Steve

Thanks for going through the effort, Steve, and for your constructive comments. That is a nice way to get the background under control. The Color module in StarTools shows the histogram and adjusts it as changes are made to the settings. The R,G and B channels can be boosted/reduced independently in the module as well and that could be used to do something similar. I opened up the three images (my original and your two adjusted images) in new tabs in Firefox so I can blink between them to get the full effect of the changes you made. You have done a great job of neutralizing the background!

To me the issue with doing a Mosaic using StarTools is that each panel needs to be processed to its final state before stitching the panels together in MS ICE, so any slight difference in processing is going to show up in the final image. Maybe if I used the FilmDev module to stretch the images instead of AutoDev with a region of interest selected, the result would be more uniform.

I have received a suggestion to download the trial of AstroPixelProcessor and try to stitch the panels together in a linear state, and then load the result into StarTools so the entire mosaic can receive an even process. I suspect the "gradient" you cleaned up wasn't present in the original data, but that I introduced it while processing the panels with the Witches Broom in them.

In any case you have given me a lot to think about and I appreciate your efforts!

Bob

[STEVE333]

Thanks for going through the effort, Steve, and for your constructive comments. That is a nice way to get the background under control. The Color module in StarTools shows the histogram and adjusts it as changes are made to the settings. The R,G and B channels can be boosted/reduced independently in the module as well and that could be used to do something similar. I opened up the three images (my original and your two adjusted images) in new tabs in Firefox so I can blink between them to get the full effect of the changes you made. You have done a great job of neutralizing the background!

To me the issue with doing a Mosaic using StarTools is that each panel needs to be processed to its final state before stitching the panels together in MS ICE, so any slight difference in processing is going to show up in the final image. Maybe if I used the FilmDev module to stretch the images instead of AutoDev with a region of interest selected, the result would be more uniform.

I have received a suggestion to download the trial of AstroPixelProcessor and try to stitch the panels together in a linear state, and then load the result into StarTools so the entire mosaic can receive an even process. I suspect the "gradient" you cleaned up wasn't present in the original data, but that I introduced it while processing the panels with the Witches Broom in them.

In any case you have given me a lot to think about and I appreciate your efforts!

Bob

Bob - Glad my suggestions made some sense. I still struggle at times with a single image much less a mosaic. I applaud your courage in tackling the mosaic project. Here's wishing you a successful conclusion!

Steve

[bobharmony]

I had another run at this using a method laid out by Stefan B. in the StarTools forum in his 3 panel mosaic of M31. My goal was to tame the background as we have discussed a bit. The processing flow for me looks like this:


Stack the individual panels using DSS with Ivo's recommended DSS settings.
Load each panel into StarTools selecting the "Linear" option, bin 50%, crop artifacts, and run the Wipe module to get the background under control.
Save the resulting file as a .tif.
Load the 4 panels into MS-ICE and stitch them together.
Load the stitched result into StarTools using the "OSC" option and process normally. In this case I ran Autodev, Wipe, AutoDev with ROI, HDR, Deconvolution, Color, Shrink, and final noise reduction.


This is a rough cut to validate the process. I will go back and do a fine tuned version to see just how good it might get.

I like the way this is turning out. I think some tweaking of phases of the process can get a cleaner finish, we shall see.


Bob

[Juno16]

I like it Bob!

The background is really improved!

I think that you are on the right path and are making big improvements in the data!

Looking good!

[bobharmony]

After thinking about the process I realized that I had applied the Wipe module to the image twice, once when preparing each panel for stitching and again to the completed mosaic. My recollection is that this is not a recommended flow.

With that in mind I took another stab at process the stitched result, this time starting at the "AutoDev with ROI" step and moved forward from there. I like this result the best of what I have done so far. There are a couple of odd background spots showing up, but I am going to take a break for a while and leave it alone.

Comments and questions welcome.

Bob

[Makuser]

Hi Bob. I really like your latest revision of the Cygnus Loop mosaic. Excellent contrast, vibrant nebulosity colors and no signs of stitching. Thanks for sharing this with us on here Bob and I hope to see more of your great work soon.