Re: [Gimp-user] Scanned negatives, moire patterns and GIMP?

[Liam R E Quin <liam holoweb net>]

On Thu, 4 Dec 2014 15:55:15 -0700 "Keith Purtell" <keithpurtell keithpurtell com> wrote:

> I recently had some 20-year-old color negatives scanned. About half the 
> scans had moire patterns. My understanding is that moire (in this case) 
> would be caused by contact between the glossy back of the negative and 
> another flat object such as a glass plate.

Any good transparency scanner comes with a mount for holding the slides away from the glass.

>  If they can't resolve this, what are my chances of solving the problem 
> with GIMP? I tried a few of the existing filters without visible results. 
> My first Google searches haven't turned up a good detailed tutorial on 
> moire removal.

There's a G'MIC filter for it. But it depends on the exact nature of the pattern as to what's best. I get 
them when scanning colour books, because of the way the books are printed (it's actually unavoidable unless 
you use a "descreen filter" in the scanner driver, but better to do it in GIMP). For that, separating into 
layers and using gaussian blur is often best, but another possibility is to use wavelet decomposition and 
delete that high frequency layers. G'MIC has a filter to do that, too.

If you can share a sample I can have a better look. 


-- 
Liam Quin - XML Activity Lead, W3C, http://www.w3.org/People/Quin/
Pictures from old books: http://fromoldbooks.org/