Thanks everyone for the encouragement and helpful suggestions. I’m gradually learning that when people suggest more data, they mean hours (rather than larger portions of an hour).
Regardless of seeing conditions, my images always seem a bit noisier in warmer weather – no doubt from sensor thermal noise, but possibly also due to some increased sky glow after long hot summer days.
Quote:
Originally Posted by spearo
Hi Jeff,
I had a quick play with your image hope you dont mind.
I couldnt just raise the black point in PS without losing too much of the faint neb so I used apply image. Basicaly this will create an imag of the background noise and remove it from the main image. There are sophisticated ways of doing this but here' a very basic process for it.
here's how: (crude instructions, adjust to taste...)
duplicate your image twice
first copy use gaussian blur pretty much max
second copy: selection tool , select highlights (stars mainly), modify by expand by 4 pixels, modify feather by 2 pixels, invert selection (so everything BUT the stars is selcted) adjust levels-black point- to make everything dissapear except the stars. deselectuse a very mild guaaussian blur to softer if you wish this is now your mask. may increase contrast a tad if you wish
(all these steps require a bit of experimenting and playing with settings)
then go back to main image, lick on it so it is the one that is active
go image and click on "apply image"
inthe new window in the drop down select the first copy
in the bottom of the window click on mask and select the copy 2
then in the setting boxes you'll probably want to use subtract , i changed the offset to 3 to get the attached pic.
hope this helps a bit
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That’s great Frank – I really appreciate the time you’ve taken to help me cut some more baby teeth in Photoshop. It’s impressive how the background noise from DSLR sensor heat and light pollution can be reduced or removed with the use of layers. I followed your steps this afternoon on another image, with reasonable success.
I’ve combined my Jan 9th data with some more captured on Jan 6th to give a total of 3 hours (DSS stack of best 60 from 77 3min frames).
Following the gist of Frank's suggestions, I blurred the background a little in another layer to reduce noise, and made the stars a little crisper. I'm much happier with the result, and no longer afraid of horses. Thanks Frank!
Fresh image attached ... which is better than I expected to get from the burbs with current equipment.
Jeff
Try using some narrow band filters if you think its light pollution. Looks more like camera noise or something?
