On Sun, 2015-04-19 at 22:20 +0200, wk_ wrote:
> Steve wrote:
> > I have never seen anything exactly like this, so I am confident
> > that it is not an artifact introduced by scaling an image in the
> > GIMP.
> I don't understand your way to this conclusion. In my original post I
> source scan,
If it is a scan of a printed document is is to be expected that there
may be moiré patterns, even if the scanner is set to apply a "descreen
If that's the case, the "grid" is liable to appear at any time on
scaling down the image, or possibly with other image editing
operations, both in gimp and in other programs, especially with 8-bit
per channel colour. It's a function of the image, not of the software.
I deal with these often in processing scans. You can use a frequency
decomposition to remove them, or you can do a guassian blur as I think
others have suggested, before scaling down.
> which I scaled down with 3 different tools (Gimp 2.8, Gimp 2.6 and
> ImageMаgick). With first one Moire pattern appears, but not with
> others. How it
> could be not realated to Gimp 2.8? The process is easily
It depends on the interpolation method that's used - in a recent gimp
2.9 snapshot I found the pattern appeard with one interpolation method
but not another. The default interpolation method I think changes from
time to time in different GIMP releases.
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