Re: Multi-sampling and "2400x4800 dpi" scanners

Kennedy McEwen ha scritto:

> [snip]

I forgot one more thing I wanted to ask.

Assume I settle on a solution I like for downsampling my vertical 4800
dpi to 2400.
As I wrote in the other post, I'm trying to path my scanner driver to
have it output 2400 dpi on the *horizontal* axis instead of
interpolated 4800, but I'm afraid I might not make it.

(SANE doesn't even natively support 4800x4800dpi with interpolated x
axis, I have to patch it for that; and then, doing 2400x4800dpi
*without* interpolated x axis looks very hard, because the driver isn't
really written with different x/y resolutions in mind.)

So, assuming I only get 4800x4800dpi with interpolated x axis, how do I
downsample that axis?
Bicubic resize in Photoshop gives blurrier data, *on the x axis* (also
on the y axis, but I've treated that in the other post), than a simple,
uninterpolated 2400x2400 scan does.

Must I know the exact interpolation algorithm used by my scanner, in
order to recover the original data? Or doesn't even that suffice, and
some data gets lost irremediably with the interpolation?

I suppose an interpolation that works as
pixel1 -- (pixel1 + pixel2)/2 -- pixel2 -- (pixel2 + pixel3)/2 --
pixel3 -- etc

should be easily "reversed". But I currently have no clue about the
interpolation used by my scanner, and don't know whether some
interpolation methods are "irreversible".

Is there even perhaps a safe bet about my scanner's algorithm, that is
do most or all scanners use a specific algorithm?


by LjL
ljlbox@xxxxxxxxxx

.

Relevant Pages

  • Re: Is 300dpi good enough for playfield artwork?
    ... I usually work at double my target DPI and then downsample the image ... don't stop there for a scan resolution, ... resolution on a Cruse digital table scanner. ... resolution, the less need for interpolation, and the easier a time you ...
    (rec.games.pinball)
  • Re: 2D sinc
    ... interpolate along the x axis to the correct x-coordinate, ... interpolate the new values down the y axis to the correct y-coordinate. ... D, you only need to do one sinc interpolation. ... 'Separability' has ...
    (comp.dsp)
  • Re: Bridgeport EZ Trak Mill ?
    ... Yes ...It has the latest 3rd axis conversion. ... Z can be a royal pain in the ass when going from 2 to 3 axis mode. ... That machine will do a 4" circle with XY interpolation with about .004" ... You are getting .00075" on a "1938" BPT with backlash using XY ...
    (alt.machines.cnc)
  • Re: 2D sinc
    ... interpolate along the x axis to the correct x-coordinate, ... interpolate the new values down the y axis to the correct y-coordinate. ... D, you only need to do one sinc interpolation. ...
    (comp.dsp)
  • Re: Carlton 6HC HBM Allen Bradley 7320
    ... Check circular interp at several locations in X & Y too. ... ID interpolation is about .040 out of round, ... axis at about the 10 o'clock to 4 o'clock position. ...
    (alt.machines.cnc)