[filmscanners] RE: Suggestions for scanning 4x5 transparencies

["Laurie Solomon" <laurie@advancenet.net>]

>The 720dpi figure (360 for large format printers) is the exact resolution
>that the Epson driver converts to _before_ dithering.

That was not my understanding; but I am willing to stand corrected.  My
understanding was that the input resolution should be between 200 and 300
dpi for the desk top photo inkjets where the printer would convert it to 720
or some higher multiple of that as a result of the dithering process and
that the 720 dpi or higher figures should not be used to determine input
resolutions since one does not have a means of factoring in the dithering
factor unless one had Epson's proprietary algorithms.

>And since the conversion to 720dpi is an unfiltered
>conversion, there are situations where it causes visible aliasing, and you
>get better results by manually resampling.

Here again, that is not my understanding; but I am willing to be corrected.
Alas, in such situations, I am not sure how one determines if the artifacts
and alaising are a product of what you suggest or some other factor in the
process.  I do know that many suggest using an input resolution that is a
even multiple of 360 dpi and that an uneven multiple of that resolution will
cause some of the same problems as you suggest.

Thus, in light of your post, I would suggest that the user would have to
test for themselves to see if they needed to resample or not.  I,however,
would suggest ( and I do not know if you would agree or not) that the least
amount of resampling one does the better in most cases; so use interpolation
and downsampling sparingly and only when absolutely needed.

-----Original Message-----
From: filmscanners_owner@halftone.co.uk
[mailto:filmscanners_owner@halftone.co.uk]On Behalf Of Paul D. DeRocco
Sent: Sunday, October 27, 2002 5:10 AM
To: laurie@advancenet.net
Subject: [filmscanners] RE: Suggestions for scanning 4x5 transparencies


> Laurie Solomon wrote:
>
> You should not need to upsample at all to resize a 4x5 at 2400 ppi to
> 13x16.25 at 600ppi which is more than enough.  The 720 dpi figure
> that Epson uses is really not to be taken literally since it is an
> extrapolation of the what the approximate resolution is after
> dithering and is accomplished not in terms of actual imputs but in
> terms of what goes on within the printing process by the printer
> regardless of the input resolution.  In terms of actual input
> resolution, the 720 is equivalent of from 200 dpi to 300 dpi before
> dithering.

The 720dpi figure (360 for large format printers) is the exact resolution
that the Epson driver converts to _before_ dithering. After dithering, it is
some multiple of that. And since the conversion to 720dpi is an unfiltered
conversion, there are situations where it causes visible aliasing, and you
get better results by manually resampling.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@ix.netcom.com

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