http://imagej.273.s1.nabble.com/Image-interpolation-and-display-tp3699590p3699595.html
thanx for the clarification. Continuing along those lines and thinking
> Hi Joachim,
>
> you are right of course, I have used the word "interpolation"
> not in the strict sense, and it is a kind of low-pass filtering
> that should be done when downscaling.
>
> Even if downscaling is by an integer factor, it is not so simple,
> and there are different ways to do it:
>
> (1) Average over n pixels (uniform kernel).
> (2) Distribute the pixel value of the input according to the
> distance from the output pixel (triangular kernel).
> (3) more complicated kernels.
>
> So the algorithms are quite similar to interpolation in the
> strict sense.
>
> (1) Has the disadvantage that it can shift the center of mass.
> (2) Has the disadvantage of blurring the image more than
> necessary.
> (3) When avoiding the disadvantages of (1) and (2), kernels
> may overshoot at steps (e.g., Photoshop "bicubic" overshoots,
> both on upscaling and downscaling).
>
> Again, similar to "real" interpolation...
>
> Michael
> ________________________________________________________________
>
> On 4 May 2007, at 16:58, Joachim Wesner wrote:
>
> > ImageJ Interest Group <
[hidden email]> schrieb am 04.05.2007
> > 12:34:26:
> >
> >>
> >> I once wrote some code for downscaling to arbitrary sizes
> >> with bilinear interpolation and I found it quite difficult
> >> to do it correctly - it seems the guys at Sun have not gone
> >> into that business...
> >>
> >
> > Maybe it´s only a questions of terms but is´nt any "interpolation"
> > inappropriate for "downscaling" to anything below, say, 50%?
> >
> > IMHO what you would need to do is an appropriate lowpass-filtering
> > (smoothing) of the data? (Where you later might again use
> > "interpolation"
> > to find the value at the downsampled pixel coordinate if it is "off
> > grid")
> >
> > Using only interpolation to solve the "off-grid" problem alone must
> > lead
> > to aliasing just because of the "undersampling" of higher spatial
> > frequencies
> > in the original image.
> >
> > Joachim
> >
> >
> >
> > ______________________________________________________________________
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