Digital BW, The Print

Hi Martin,

> Of the CCD scanners generally in use here, flatbed and film, does the user
> have any actual control over the physical operation of the
> scanner or is it
> all just software manipulation of the data after the analog to digital
> converter?

There are only two things that you have control over.  The exposure time and
the tonal curve (the LUT in the scanner that gets loaded with values from
the scanner driver).  There is no control over any of the A/D process.

> I know some scanners allow you do things like adjust focus, run multiple
> passes to reduce noise or control the speed of the scanning head to adjust
> resolution but this would not seem to have little or no effect on the
> dynamic range of what you ultimately get in your scan file.

Correct.  Except, you can run multiple passes with different exposures...and
can get higher dynamic range from this technique under certain
circumstances.

> It seems to me that the scanning software presents "controls" in a manner
> that gives the impression the user is actually effecting the
> function of the
> scanning operation itself when in reality they are not. Hence a great deal
> of confusion among the users as to what they are actually
> accomplishing when
> the tweak the scanner controls.

That seems to be true.  Setpoints are one example.  The setpoints are PURELY
software (firmware actually, but same thing really).  The scanner scans the
film into it's range of values, 0-4095 let's say.  No matter what your tonal
curve is, or what your setpoints are, the data will be exactly the
same...and the setpoints/tonal curves get applied to that same data, giving
different results.

When you change the exposure time, you merely shift the data up or down in
the values it converts.  Now, I have to actually see if you do in fact get
more/less number of values when doing this.  As I mentioned, I went through
this exercise not too long ago, but don't remember what I concluded.  I'll
let you know.

Regards,

Austin