I thought it was about time I reprocessed my data with a view to taking up Greg's (cybermystic's) challenge to show the IFN (read all about it here
) which he rightly believed I should be able to see. Here's the result:
M81, M82 and the IFN (Integrated Flux Nebula)
Quite a processing challenge starting from 8 x 1000 second subs of each of Red, Blue and H-alpha taken with an ML16803 camera through a TEC 140 'scope. The red and blue data was used to create a luminance channel which also subbed for Green to produce an RGB image which was subsequently used to colour the final luminance image. The luminance image destined, as all were, for processing in Photoshop was produced by combining, using an HDR technique, a normal stretch of the luminance data and an extreme stretch designed to really bring out the IFN. I also took the opportunity to apply some "multiscale" processing to the image to enhance the detail near the core of M81, all courtesy of PixInsight. With the IFN boosted in this way the challenge, as I see it, is to manage the transition between what is part of the galaxies, which are a very long way away, and the IFN which is local to our own galaxy.
I took a copy of the luminance image and manually removed all the stars, a process which is extremely tedious but necessary IMHO as my usual "Dust & Scratches" star removal routine really churns up the low level noise in the image and, unfortunately, it is exactly that low level noise which is host to the IFN signal. That allowed me to process the IFN quite separately in order to try and enhance the detail while controlling the noise. The galaxies were still there, of course, but I found it was possible to apply a Photoshop curve which effectively took them out in a loving and gentle way when the IFN was added back to the other components. The shape of the curve had to be tweaked so that adding in the "IFN" image (using a Photoshop Screen layer) was possible without having to airbrush out the galaxies themselves. There is still a slight artefact evident as a bluish extension to the disc of M81 but short of manually desaturating it my only other course of action would be not to colour the IFN at all.
The original luminance was also used to produce a "No Stars" and "Just Stars" image. The "Just Stars" image was fed back into PixInsight for a spot of deconvolution while the "No Stars" image, basically just the galaxies, was given a final spot of contrast enhancement. The two were combined to produce the final luminance image for the stars and galaxies. That was coloured by the RGB image produced earlier as the next Photoshop layer. The processed IFN image was added to the layer stack and coloured via a clipping adjustment layer. The choice of colour was arbitrary, although informed by some other images out there on the Net, and maybe for some colour shouldn't be applied at all. Finally some H-alpha extracted for just the galaxies was added. 1 used several clipping adjustment layers to tweak the various components and try and achieve a reasonable balance.
I imagine there must be a simpler way of doing all this. Combining H-alpha and RGB can be tricky enough, my being a bit of a newbie, but the IFN is fainter still compared to much of what is visible and if there are any recipe books for exactly how all the ingredients should be combined I haven't found it yet. The image is the result of a couple of days of processing so I hope it was worth while.
P.S. The light background of the forum doesn't do the IFN any favours. I've also posted over at the Stargazer's Lounge
where there is a darker background.