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

[Ofnuts <ofnuts gmx com>]

On 23/04/15 15:19, wk_ wrote:
> > So, if you scale down to 51% (which is about 2x) you first do a 2px
> > Gaussian blur. Result here:
> >
> > http://imgur.com/iZB3lmw
> Do you agree that Gimp 2.6 version looks still out much better?
>
> http://pasteboard.co/27ib9Dvx.png
>
> Wbr,
>
> Gunnar

I do agree that this specific implementation/version of the algorithm on 
this specific part of this specific photo looks better. Period(*)

But the point is, the frequency response of a specific algorithm and  
its implementation is not linear (especially with potential round-off 
errors in 8-bit) so you cannot tell in advance if the combination 
algorithm+image+scaling factor is going to produce artifacts or not. 
Maybe 2.6 is much worse at another scaling factor... Only the pre-blur 
will work in all cases.

Most digital cameras have a low-pass filter in front of the sensor to 
avoid this very phenomenon (hardware blur, so to speak), only a handful 
of DSLRs work without this (a specific Canon model for astrophotography, 
and now a Nikon).


(*) An engineer, a physicist, and a mathematician are in car in 
Scotland, and come across a sheep.
The engineer: in Scotland, sheep have a black head
The physicist; more accurately, it seems that in Scotland, most sheep 
have a black head, but there can be exceptions
The mathematician; sorry chaps, but the only thing we can say is that in 
Scotland, there is at least one sheep that has at least one side of its 
head black.