Using DBE and CC on a dusty background?

[whitenerj]

I am going to my dark site tonight and will be imaging M45 with long exposures to capture all the grey dust around the nebula. This will be my first image to process in PI with any if hardly black background. How do I go about using tools like DBE, Background neutralization, and color calibration with a completely dusty background?

Jason

[jkmorse]

Jason,

Key is you need to find areas where there is no nebulosity.  See the M45 image I just posted in the Gallery.  There, I wanted to bring out even the very faint dust that you can see in the lower right, for example.  But the key for DBE is not to target any off the nebulosity or you will kill that faint stuff.  Best method I have seen is to make a copy of the image, the do a HistogramTransform stretch of the copy, but really blow it out so that you can see where all the nebulosity is in the image and those few places where it isn't.  Then hand place a limited number of points in those empty areas.  You only need a handful.  I probably had less than a dozen points set all told.

Another thing you may want to try to avoid blown out stars on you final stretched image is to use MaskedStretch.  As you can see from my posting, you can really reduce the amount of star blow out by using MS instead of HT.

Best of luck and please post the result.

Jim

[jkmorse]

Jason,

I should have mentioned that for an image like this, you may be best served by using LinearFit instead of ColorCalibration and BackgroundNeutralization, especially if your filters are close to 1:1:1.  That's what I did, particularly since there is so much blue it is hard for ColorCalibration to give you a good white point.  When using LF, go with the strongest image stack as your base, in this case likely the Blue stack.

Best,

Jim

[topboxman]

I have been fairly successful using Automatic Background Extraction (ABE) for images full of nebulosity. Start with default settings.

I typically use BN and CC but if the whole image is full of nebulosity, I only use CC and use the whole image for white and background references and check "Structure Detection". CC is very powerful.

Peter

[whitenerj]

Thanks guys. I ended up zooming into the photo close and placed my DBE samples carefully around. Worked great. I never have much luck with CC. I stack with DSS and get better color results from that.

Jason

[jerryyyyy]

Good discussion.  I have been working with Spider & Fly, which is 90% H-alpha nebulosity.  I am trying a bunch of these in variations.  I seem to be getting better results with ABE... than careful DBE...

I forget, but am familiar with the use of MS to dim the stars, but what steps do you use afterwards to stretch more the nebulosity?  HDRM the followed with masked LHE? 

So many different ways to process....

[msmythers]

Just to chime in on the discussion of bring out more faint nebulosity. I sometimes use ExponentialTransformation with a mask, very carefully. I also really like using the BackgroundEnhance script.



Mike

[jerryyyyy]

Just to chime in on the discussion of bring out more faint nebulosity. I sometimes use ExponentialTransformation with a mask, very carefully. I also really like using the BackgroundEnhance script.



Mike

I'll give these ideas a go and compare.  I like using a number of small previews to see what turns out best.  This is what i got with the abovfe processing:

[jerryyyyy]

This is what I got with the BackGroundEnhance script.  I can see why you like it. The Preview mode is very helpful.  These are the default settings.  I guess you can get equivalent results by many routes.