Re: [Gimp-user] grainy scanned images

[Pat David <patdavid gmail com>]

Just echoing everything Ofnuts already said.  Not sure what the "eye of
MATE" viewer interpolation might be. :(

On Tue, Aug 8, 2017 at 4:43 PM Ofnuts <ofnuts gmx com> wrote:

> On 08/08/17 18:37, Olivier wrote:
> > I'm  using GIMP 2.9 on Ubuntu Studio with MATE window manager. I'm
> > scanning black-and-white photos taken slightly less than 50 years ago.
> > This is working generally well, although of course I have to rotate,
> > crop, and sharpen the images, and use the Levels tool a lot. However,
> > for two photos a weird thing happens: the photo looks rather good when
> > displayed in the GIMP window, but it looks terribly grainy when
> > displayed by "Eye of MATE Image Viewer".
> >
> > I placed the photo at the address
> http://olecarme.homelinux.net/page0022.jpg
> > Clearly it's grainy, but not so much as in the image viewer, and in
> > the GIMP window it looks acceptable at a scale of 33.33%, and even at
> > a scale of 50%.
> >
> > Two questions:
> > - May anybody provide an explanation of this phenomenon?
> > - Is there a way to display the image correctly outside of GIMP?
> >
> > Thanks for any idea!
>
> To zoom out the image the application has to interpolate pixels.
> Different applications can use different algorithms, that don't behave same
> with noise (a.k.a grain). Some algorithms can even make the image look
> grainier than it is, when the zoom factor is close to an integer
> multiple of the grain size.
>
> If you want the image to display well at a given size, then make a
> scaled copy of the image. Then the viewer will display it
> pixel-for-pixel and you won't have to worry about the interpolation
> algorithm.
>
>
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