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Re: filmscanners: Grain aliasing



>I've read (but haven't had a need to try it so far) that grain in sky areas
>can be corrected/retouched using the blue chanel as a mask. I'd be
>interested in hearing from those who've used that technique.

I have read about performing some filter operations just on the blue channel 
but have not tried any of those techniques. 

One technique that I do use I first read in a 1996 Adobe (Photoshop) article 
titled Repairing Digital Photographs by Russell Brown.  (It used to be 
available in a pdf on Adobe's site but I don't think it is there now.)

Duplicate the image on a second layer.  Apply Guassian blur to this duplicate 
layer.  Brown writes "Choose values based on the resolution of the image. You 
want to soften the imagenot lose the image completely, but soften it  
especially in the troubled area of the blue channel."  Then change the blending 
mode of this layer to Color and flatten image.

You can test the effect of this procedure by looking at the blue channel before 
and after.  I'll see a lot of noise there "before."  With a good selection for 
blur amount that noise will be substantially reduced after the above procedure.

--
Bob Shomler
http://www.shomler.com/gallery.htm




 




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