Re: [Gimp-user] Gimp 2.8 pixelation on resize

["Liam R. E. Quin" <liam holoweb net>]

On Sun, 2015-04-19 at 01:26 +0200, renat wrote:
> > scanned images are going pixelated
> Faced the very same (or similar?) problem while trying to resize 
> photos made by
> digital camera. Very similar "grids" appear on nearly-flat surfaces 
> with a bit
> of noise (like on sky). Surprisingly, faced the very same grids not 
> only in
> GIMP, but in some other programs as well (in Image Viewer in Ubuntu 
> 14.04, for
> example), so there may be a problem with underlying library (GTK?), 
> not with
> GIMP itself.
> Here is an full-size example image:
> https://drive.google.com/file/d/0B2nZFc31UFnoNUVTcGpoUHFSbm8/view?usp=sharing
> And it's resize (width 1920 px) - grid is easily visible:
> https://drive.google.com/file/d/0B2nZFc31UFnoT1ZvM0xxQW8xSU0/view?usp=sharing

Yes, there;s a Moiré pattern in the resized image.

How was the image created exactly? It looks like you photographed a 
printed image and then used rawtherapee to convert to a jpeg for gimp 
to open?? If so, the low frequency grid is from the four-colour print 
process.

I see this pattern in gimp scaling with linear but not with cubic -- 
see Tool Options.

Liam

> Tests were performend with gimp 2.8.10-0ubuntu1 on Ubuntu 14.04, and 
> with gimp
> 2.8.14 on Windows 7 Home.
>
> Attachments:
> * 
> http://www.gimpusers.com/system/attachments/195/original/gimp-ubuntu-scaled.png