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:
Do you agree that Gimp 2.6 version looks still out much better?
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
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