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Re: 256x256 px icons


On Aug 15 11:44, Charles Wilson wrote:
> On 8/15/2011 10:33 AM, Warren Young wrote:
> > The hard edges in the original art are causing stair-stepping when doing
> > a direct downsample, though.  (Look at the pointy bits.)  By blurring
> > the high-res version and then downsampling by a non-integral amount, you
> > can get a much smoother result.
> 
> This is only the case if the "downsample" operation used by GIMP, when
> d/s by an integral amount, is to simply pick every Nth pixel.  That's
> very fast -- but is not the correct operation (I'd posit a GIMP bug, in
> fact).
> 
> Sampling theory says a downsample SHOULD be preceded, automatically, by
> a low-pass filter (blurring) operation of a specific type and, er,
> "radius" for lack of a better word.  (IOW, GIMP /should/ be doing this
> blur FOR you, automatically).  There's lots of theory behind this, to
> select the proper kind of filter (gaussian is not correct -- but is
> probably a good enough approximation) and its 'radius' (which should
> scale with the downsampling factor).
> 
> Since GIMP is apparently not doing that, then yes -- you need to apply a
> blurring filter yourself, before using GIMP's braindead 'pick every Nth
> pixel' version of "downsampling".

Are you talking about recent gimp versions?  In my gimp I have the
choice of four different interpolation algorithms, "None", "Linear",
"Cubic", and "Sinc (Lanczos3)", whatever each of them means.  I guess I
just don't want to know in such great detail...


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat


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