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filmscanners: Vuescan grain removal idea



I was going to send this message just to Ed Hamrick, but then I thought 
people on this list might have comments.

I was looking forward to Ed's implementation of grain removal in Vuescan, 
but unfortunately it softens the image too much so I rarely use it.  I use a 
Minolta Scan Elite that has an infrared channel so cleaning without grain 
removal (Clean set to Light) does not soften the image.

Here are two cropped sections of just the sky from a 2820 dpi scan of a Fuji 
ISO 100 color negative.  One has been sharpened with unsharp mask and one 
has not.  They both have minimal JPEG compression.  As you can see, it is 
not just the grainy appearance but the multi-colored character of the grain 
that makes it very ugly.

http://www.geocities.com/hr1066/sky-grain.htm

I have few grain problems with slide film, but color negative film is 
another story.  I often get grain aliasing in the sky but other areas of the 
image rarely have much of a grain aliasing problem.  I'm not sure why this 
is so, but it has been my pretty consistent experience.  Even stranger, even 
other highlight areas don't exhibit the problem.  It is mostly just the sky 
-- blue, cloudy, or overcast doesn't matter.  My guess is it takes a 
combination of a fairly light area plus some  amount of blue.  I have tried 
exposing the sky from -1 to +3 stops to see if that makes a difference in 
scanning.  It doesn't seem to help with the sky grain aliasing problem 
though.  I have also tried from 1 to 8 multi-scan passes in Vuescan, but 
that also does not improve the sky grain aliasing.

I wonder if Vuescan could have a grain removal option that would only work 
on the highlight areas of the image or something like that?  Reducing the 
ugly grain aliasing from the sky without softening the rest of the image 
might get a lot closer to solving the problem, as I see it.

By the way, before anyone suggests selecting the sky and doing a Gaussian 
blur, blurring only the blue channel, sharpening only the luminance channel, 
using PSP's Edge Preserving Smooth filter, or some other technique I want 
you to know that I know about them and have used them from time to time.  
Sometimes the result is satisfactory and sometimes it isn't.  Sometimes it 
is very difficult to get a good selection of the sky because of tree 
branches, leaves, and other numerous small details.  Since Ed has said that 
the grain removal algorithm in Vuescan examines the individual grains in 
some way to do it's work it probably can do a better job anyway.  If there 
was an option to restrict it's work to only the highlights or highlights 
with some blue or something else that might help with the sky and not soften 
the whole image then that would make it much more useful.

Maybe Ed or someone else has a better idea about how the Vuescan grain 
removal option could be expanded and in a practical sense work even better.  
If you do then please give us your input.

Henry Richardson
http://www.bigfoot.com/~hrich
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