This is going to be a stretch. So tonight we have another clear sky, 3 in a row in the UK this is getting to be something of a freak event! Earlier in the day I was browsing around Astrobin (if you aren’t familiar then you really should have a search around this site) looking for inspiration. I was hankering after something a little different. I came across some excellent shots in Gemini of the “Jellyfish” Nebula (IC443). Bringing this up in Skychart (Cartes du Ciel) I noticed than very close to this was another emission nebula NGC 2175. A little playing in N.I.N.A.’s Sky Atlas and Framing I could JUST get both targets at a diagonal in one shot, however this was going to be tight and even with the field flattener in place those images being so close to the edge of the frame will show elongation of he stars. Therefore here I am for the first time attempting a mosaic of the two objects. The following N.I.N.A screen grab shows the theory of what I am trying to capture tonight.
N.I.N.A.’s Framing Feature, IC443 on the left, NGC 2175 on the right
I have targeted both of the Panels tonight, with some luck I should get a good 4 hours on each. Scheduling a 10pm cut off of Panel 1 to move on to Panel 2. Post processing will be new to me, I’m currently assuming based on very little research that I will perform the registration and stack for each set of images separately and then bring them together in Photoshop before Stretching etc… Some late night internet research I think.
The following morning, Lights at first glance look ok, 47 on Panel 1 and 58 on Panel 2, although I think a number of Lights on Panel 2 will be dropped due to local horizon issues, so we may get roughly the same integration time on each. I was up early before daylight so I took 12 5m Darks and 30 flats.
Processing
As promised good or bad my first trial at creating a mosaic. The process I ended up going through was as follows:-
Treating the two Panels as completely different images I Registered and stacked them separately in Deep Sky Stacker (DSS).
After some research, many thanks to (Sara Wager’s site)I found that Microsoft released a research project which produced a product called Image Composite Editor (Microsoft ICE). Initially I passed the two image files into MCE but it was unable to find any common points to link the two files. After reading a little further I took both images into Photoshop (PS) and performed a Levels stretch to bring out the stars and nebula. Taking these two images into ICE the stitching of the two images worked.
From there I have taken into PS once again and performed a coupe more stretches using Level and Curves adjustments
The output you see below is my first attempt.
First try at a mosaic of two images – Jellyfish (IC443) top left, NGC 2175 bottom right.
Results
As is obvious from the image (I did say good or bad) there is a definite line where the two images are joined the main issue is getting the background black of the sky similar across the two sessions. One option I thought was perhaps to use a tool such as Gradient X Terminator to better blend the two together. This is going to take more research, perhaps I am missing something in PS that would allow to get the same black point across both images?..
Another major challenge was related to the hardware on which I am trying to processing these images. The Raw TIFF images I was dealing with were 300-400MByte each, once I had created the composite the final image was around 800MB. Performing any operations on my old 2015 MacBook Pro with 8Gb Ram proved painful. I resorted to dropping back to PNG and shrinking back the canvas size to make it a more manageable 30MB. Still something that I will not underestimate in future.
Comentarios