grainy scanned images

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grainy scanned images

Olivier-24
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!

Olivier Lecarme
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Re: grainy scanned images

Ofnuts-2
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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Re: grainy scanned images

Pat David
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 <[hidden email]> 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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> gimp-user-list mailing list
> List address:    [hidden email]
> List membership: https://mail.gnome.org/mailman/listinfo/gimp-user-list
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>
--
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Re: grainy scanned images

Alexandre Prokoudine
On Wed, Aug 9, 2017 at 1:33 AM, Pat David wrote:
> Just echoing everything Ofnuts already said.  Not sure what the "eye of
> MATE" viewer interpolation might be. :(

https://bugzilla.gnome.org/show_bug.cgi?id=665897#c35

Since MATE is based on older GNOME, they might not have the patch.

Alex
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Re: grainy scanned images

Olivier-24
2017-08-09 1:23 GMT+02:00 Alexandre Prokoudine <
[hidden email]>:

> On Wed, Aug 9, 2017 at 1:33 AM, Pat David wrote:
> > Just echoing everything Ofnuts already said.  Not sure what the "eye of
> > MATE" viewer interpolation might be. :(
>
> https://bugzilla.gnome.org/show_bug.cgi?id=665897#c35
>
> Since MATE is based on older GNOME, they might not have the patch.
>
> ​Thanks to those who answered me. I see that my problem is not due to
GIMP, and that GIMP uses a better interpolation algorithm than MATE​. I use
MATE because I dislike Unity and GNOME 3, and XFCE crashes too often for
me. Maybe I should try still another window manager.

The GNOME image viewer (3.24.0) has a better, although surprising,
behavior. The granularity of the image changes when the mouse pointer
enters or leaves the window, then returns to something I like.

Anyway, since these photos are intended to be displayed on a web site, it's
more important to check whether the appearance in Firefox or Chrome is
acceptable. Fortunately, it is.

However, how could GIMP be used for correcting the strong defects of the
initial image?

Olivier Lecarme
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Re: grainy scanned images

Alexandre Prokoudine
On Wed, Aug 9, 2017 at 10:48 AM, Olivier wrote:

>> https://bugzilla.gnome.org/show_bug.cgi?id=665897#c35
>>
>> Since MATE is based on older GNOME, they might not have the patch.
>>
> Thanks to those who answered me. I see that my problem is not due to GIMP,
> and that GIMP uses a better interpolation algorithm than MATE. I use MATE
> because I dislike Unity and GNOME 3, and XFCE crashes too often for me.
> Maybe I should try still another window manager.

Maybe you could install a different image viewer before switching to a
whole new desktop environment?

Alex
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Re: grainy scanned images

Olivier-24
Since I already have the GNOME Image Viewer, with a good interpolation
algorithm, I'm satisfied without switching to a new desktop environment. I
choose this viewer as the default tool for displaying an image, and that's
all.

Thanks to all for having made me aware about the behavior discrepancies
between viewers.

Olivier Lecarme

2017-08-09 11:43 GMT+02:00 Alexandre Prokoudine <
[hidden email]>:

> On Wed, Aug 9, 2017 at 10:48 AM, Olivier wrote:
>
> >> https://bugzilla.gnome.org/show_bug.cgi?id=665897#c35
> >>
> >> Since MATE is based on older GNOME, they might not have the patch.
> >>
> > Thanks to those who answered me. I see that my problem is not due to
> GIMP,
> > and that GIMP uses a better interpolation algorithm than MATE. I use MATE
> > because I dislike Unity and GNOME 3, and XFCE crashes too often for me.
> > Maybe I should try still another window manager.
>
> Maybe you could install a different image viewer before switching to a
> whole new desktop environment?
>
> Alex
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>



--
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