NGC6992 - HST palette

[GordonH]

Hi

I managed to get some SII data last night to go with the other two channels from a week or so ago, there was a large patch of cloud that interupted the session for half an hour or so but luckily no more for the rest of the evening. This was taken with a FSQ106ED at f5, ML8300 and 5nm Ha, OIII and SII filters on a Paramount ME, auto guiding was taken care of by a lodestar and OAG using dithering.

Exposures are 6x30 minutes Ha, 8x30 minutes OIII and 9x30 minutes SII. These were then mapped using the wavelength ordered palette of SII:Ha:OIII = R:G:B

The full size image can be seen at the following link

http://www.pbase.com/imaging_the_heavens/image/145300616/original

Thanks for looking

Best wishes

Gordon

[TC_Fenua]

That's a fantastic image ! I really like the processing and all the details, the sharpness ... Well done Gordon !

[squeaky]

Very nice

[squeaky]

Actually you've managed to collect a whole lot more data in your subs than shows here. I had a quick play and here's a comparison...

I'm sure it can be done better, though

Just so I can remember what I did... it was a few lifts in curves, with a bit of sharpening (high pass wide 60+px and a high pass small 3px) and a small (1.6px) unsharp mask. Then created a copy layer and equalised it to see what was there. This came out quite well (it doesn't always work) so I changed the mode to soft light, reduced the opacity a LOT, then eased it back up to bring it up behind the sharpened layer (about 14%).

[GordonH]

It is possible to extract more detail out of the data but at the expense of introducing noticeable artefacts from using sharpening and other filters,this results in an over processed image which i try to avoid, just as a guide to what i did to my data, levels on the individual channels to equalise the histograms, colour combine, combination of levels and curves and selective colour adjustments, thats it, no sharpening, noise reduction or software filters.

Best wishes

Gordon

[fwm891]

Super image Gordon - especially the full-size link

[squeaky]

You're right and, as I said I'm sure it can be done better. But honest boss, take a look at an equalised version of your image - while it blows out the brighter areas, and bloats the brighter stars; it does show up some of the finer structure that's there in your data. Then, of course, the trick is to grab it without doing the bloating - something I need a lot more practice at.

Anyway - curves only so there can't be any artefacts, and, given that I'm doing this with the JPG rather than a nice detailed TIFF it's not too bad...

[Gina]

Incredible - quite amazing

[GordonH]

Hi 'squeaky'

Your second crack using just curves definitely looks better than the first although the main nebula area is starting to look affected by the extra stretching. As you say I am sure there are better ways of getting the fainter detail to show, I will have another go at processing this when time allows

Best wishes

Gordon

[squeaky]

You've clearly got an excellent set of subs there. I mean really good!

As for the main nebula area... yeah, I think I missed out on putting "stoppers" on the upper part of the curve when tweaking the bottom end. Hang on and I'll grab a screen shot and annotate it to show what I mean.... (forgive me if I cover stuff you've been using for years, but there'll be readers who've never used this stuff)

I pick a dark point in the image somewhere close to the main target area. (Hold the CTRL key and click to set a point on the curve)

Then pick a "lift point". An area that is already quite faint.

If you were to lift NOW - you'd lift the entire curve above that point and pretty soon blow out your brighter bits. So pick a medium bright point in your image where you don't really want to increase the level any more. Remember at the moment we are aiming at only lifting faint stuff.

I've done a much larger lift here to show that while we've lifted the fainter stuff - we've also, because of the way curves work, made the bright stuff fainter - which is not what we want...

So if you add an extra point directly onto the curve rather than using an image - each outside your upper and lower picks...

Now you can lift your target area only (again exaggerated to show the curve)

I wouldn't normally lift by anything like as much as I have done in this example - normally I'd only lift the target point by 5 or 6 and apply. Then I'd do the whole thing again picking new points. Anywhere between three and five iterations. NOTE that I don't normally use levels to stretch or clip - that can also be done with curves.

Anyway, here's a before and after for that exaggerated lift...

Note that rather than using levels to darken the main background you can actually pick your lower dark stopper point and reduce that by 2 or three. So no levels stretching needed.

Best way to do this, btw is not to put the mouse on your point and lift it - but to highlight the number in the output box and then use either the up and down arrow keys or your scroll wheel to change them up and down.

So that's lifting the faint detail without affecting (much) of your main areas.

You can then, if needed, do this the opposite way round with the brighter main areas - but this time dropping the target point, as long as those areas aren't blown out originally.

No two images are the same, obviously, so it's a case of feeling for it. I normally do this to a copy of the previous layer so that if I think I've made things worse instead of better I just bin the layer and have another go.

EDIT: I still reckon it needs a sharpen - and I did an unsharp mask at 1.6px with a threshold of 2 which to my eye just helped with those fainter stars as well as the nebula areas. It'll be worth a try once you've finished with curves.

[Gina]

Thanks for that - very useful - I'm very much still learning PS

[squeaky]

Thanks for that - very useful - I'm very much still learning PS

ME TOO !!!!