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.

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 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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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

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