Digital BW, The Print

I thought the SHARPEN mode in PSCS2 Bicubic was designed for down
sizing, not upsampling? Right?

John



--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Paul D. DeRocco"
<pderocco@i...> wrote:
> > From: Bob Frost
> >
> > I've always thought 'stair interpolation' is a very peculiar way to
> > interpolate an image, and I don't understand how/why it is
> > supposed to work.
> > When you upsample an image by 10%, what happens is that the 10th,
20th,
> > 30th, etc., lines are 'interpolated' and a new line inserted in
front of
> > each of them, based on that line and the surrounding lines
> > (depending on the
> > method of interpolation). When you then do the second step of
> > another 10%,
> > the 10th, 20th, 30th, etc lines are again interpolated, the only
> > difference
> > being that the original 20th, 30th, etc lines have all got pushed
> > along by
> > the insertion of the previous new lines. And so on. Seems a
> > strange way to
> > upsample an image!!
> 
> That would be strange, but that's not what happens. All pixels are
> interpolated. Each pixel in the result maps to some possibly fractional
> pixel position in the original, and its value is computed by
filtering the
> original pixels in that region. Even if an output pixel lines up
perfectly
> with an input pixel, it is still computed by filtering that input
pixel with
> its neighbors, so that it won't look different from those pixels
that don't
> line up. Yes, this does soften the image, by discarding some high
spatial
> frequencies, but this is often masked by including a bit of high
frequency
> boost--I think that's what the new "sharpen" option in PS Bicubic is.
> 
> --
> 
> Ciao,               Paul D. DeRocco
> Paul                mailto:pderocco@i...