Luminous Landscape Forum
Equipment & Techniques => Beginner's Questions => Topic started by: Christoph C. Feldhaim on August 14, 2010, 06:28:28 am
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I tried the following in CS4 with a scan from a b/w negative which had a grainy sky:
I first inverted the scan and applied the levels tool to have some sane grey values (Background layer).
Then I duplicated the background layer and applied some aggressive denoising (Denoised layer).
Then I duplicated the background again and applied various filters, like emboss, find edges, blur and such (Mask layer) to
get a layer where the originally detailed areas were black (=masked out later) and the big low-detail areas, like sky or house walls were white.
(depending on the filter it can be vice versa, but you can invert later ...).
I created a layer mask for this mask layer and selected the white tones to be applied as mask.
This mask I dragged over to the aggressively denoised layer and Voilá-there were my details back.
The intermediate mask layer I simply turned off.
Has anyone similar experience or better ideas on how to mask out detailed areas when denoising ?
Input welcome!
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For me, it really depends on the end use. I won't spend the same amount of time (and therefore use the same method) for a web gallery as I would for a magazine/newspaper print, or a larger print (20x30,etc) framed on a wall.
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Just found this article - it seems my idea wasn't new.
http://www.luminous-landscape.com/tutorials/smart_sharp.shtml
Most likely the inverse technique can be used to select areas to de-noise.
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When I need to remove noise from an image I select the area that needs it, usually the sky, and apply noise reduction to that area. Select the area any way you want. The magic wand usually works for flat areas like the sky.
Have Fun,
Jeff
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At the risk of derailing this thread...
What exactly is "denoising film grain"?
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At the risk of derailing this thread...
What exactly is "denoising film grain"?
Actually, you're not denoising film grain. You're removing the noise from a digital image. Film grain is found on... yep... film. Noise is to a digital image what grain is to a film image.
Have Fun,
Jeff
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Actually its not exact and due to my insufficient english.
The gritty stuff you see in skies e.g. when scanning film usually is not grain,
but the aliasing interaction between grain and the scanners CCD sensor.