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[filmscanners] Re: scanning at less than optical res



I believe what Bob is stating is that some scanners literally skip lines
or sensors and just record the spaced information, rather than taking
the full resolution and then averaging the pixels out via a series of
algorithms.  This, of course, would introduce a great many sampling
errors, since it is a much coarser sample of the actual data.

Some scanners do seem to do just this, as the resulting scan takes as
little as one third the time to be scanned and produced as a raster
image when the resolution is quartered.

Art

LAURIE SOLOMON wrote:

>>If you scan at 1200dpi, the scanner usually either samples all the 4800
>>possible data points per inch and throws three out of every four away, or
>>only samples every fourth possible point. So you are only getting one
>>quarter of the possible data from the film. So why scan at large format if
>>you are throwing three quarters of the film data away?
>
>
> Bob, I beliee you are correct; but I do not understand your question. What
> do you mean by "scan at large format" in this case?  I must have missed
> something in the discussion.  The first method,which you note, involves the
> actual sampling of original data using sampling algorithms and does result
> in a loss of ortiginal data; but the second method, which you speak of with
> respect to Vuescan and is available in almost all other scnning
> applications, involves resampling of the original sample data using formulas
> for combining and recombining data on the basis of all existing data and the
> formulas.  Both methods, however, would involve the scanner reading during
> the scan all 4800 points; so both would involve a "scan at large format" -
> using your terms - or whatever optical format is used by the scanner.  After
> the scan, everything else by way of sampling or resampling is either digital
> conversion via hardware or software generated.
>
> -----Original Message-----
> From: filmscanners_owner@halftone.co.uk
> [mailto:filmscanners_owner@halftone.co.uk]On Behalf Of Bob Frost
> Sent: Thursday, December 09, 2004 4:10 AM
> To: laurie@advancenet.net
> Subject: [filmscanners] scanning at less than optical res
>
>
> Is this correct?
>
>
> "As I understand things, a scanner with an
> optical resolution of 4800dpi can take a sample reading every 1/4800 of an
> inch. If you scan at the optical resolution, that is what is does and you
> get 4800 readings per inch along that axis (usually a different resolution
> on the other axis).
>
> If you scan at 1200dpi, the scanner usually either samples all the 4800
> possible data points per inch and throws three out of every four away, or
> only samples every fourth possible point. So you are only getting one
> quarter of the possible data from the film. So why scan at large format if
> you are throwing three quarters of the film data away?
>
> With Vuescan software, you can set it to scan all 4800 data points per inch,
> but then to take the average of every four data points and reduce them to
> one, so that the file you get out is the equivalent of a 1200dpi scan, but
> all the data points have contributed to the final result."
>
> Bob Frost.
>
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