[filmscanners] Re: scanning at less than optical res

["Arthur Entlich" <artistic@telus.net>]

Maybe it should have been called "larger file scanning" or Larger format
  output scanning?

It would be nice to know which scanners did what when lower resolution
modes are selected.

My UMAX Astra 1200S (Flatbed) definitely, at least in the direction of
the scan "head", doesn't scan full optical if you choose a lower than
optic resolution.  I can both see and hear the stepper motor change
number or size of the discreet steps it uses.  I don't know what it does
in the other direction, but based upon the speed difference, I'm
guessing it is not interpolation from a full optical scan, but instead
just ignoring the intermediate ones.

Art

Laurie Solomon wrote:

> Yes, I did understand that; but I did not think that too many scanners out
> there used this approach except to produce low resolution preview scans. But
> I could be wrong.  What I did not get and may have been a terminological
> confusion was his reference to "large format scanning" with respect to the
> discussion.  I suppose he really meant to say - now that I re-examine it -
> "high resolution scanning" as contrasted to "large format scanning."
>
>
> ----- Original Message -----
> From: "Arthur Entlich" <artistic@telus.net>
> To: <laurie@advancenet.net>
> Sent: Friday, December 10, 2004 5:58 AM
> Subject: [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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