Digital BW, The Print

"I'm impressed [with bicubic smoother]."  Me too.

Walt



--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "john dean" 
<deanwork2003@y...> wrote:
> I just did one comparison test by upsampling an rgb image of a
> landscape composite from 45 megs to 178 megs from a clients 8 bit
> file. The first was done with the new Stairstep Interpolation 2
> software, the second was done Bicubic Smooth in Photoshop CS2, both
> set to 300 dpi. No matter how I finessed the final sharpening of the
> final file, the Photoshop interpolation was always superior, both in
> regard to sharpness as well as smoothness of the irregular artifacts
> present from such a serious upscaling. 
> 
> Now I am going to do three or four more tests this week to 
investigate
> this furthur. Whatever they did to improve the Bicubic mechanism in
> Photoshop, it is a major improvement. I'm impressed.
> 
> John
> 
> 
> 
> --- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Bob Frost"
> <bob@f...> wrote:
> > Paul,
> > 
> > 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!!
> > 
> > Bob Frost.
> > 
> > ----- Original Message ----- 
> > From: "Paul D. DeRocco" <pderocco@i...>
> > >
> > > Stair interpolation refers to iteratively computing a spline 
over and
> > > over again, usually in fixed proportions, until you get the 
output
> size
> > > you want. For example, if you used bicubic interpolation and 
increased
> > > the file size by 10% each time, until you got where you wanted 
to be,
> > > that would be stair interpolation. If you used S spline the 
same way,
> > > that would also be stair interpolation.
> > 
> > It seems to me that any linear filter applied multiple times is 
just
> another
> > different linear filter, and can be precomputed as such in 
advance, and
> > applied in the same amount of time it takes to do any other single
> filter.
> > Doing it iteratively seems like the dumb way to do it (if you're
> writing the
> > software, that is), and might also build up noise due to 
accumulated
> > roundoff errors, especially if computation is done in 8-bit mode.