Digital BW, The Print

Anthony,

> > Why would a B&W scanner be faster?
>
> One pass instead of three, less processing of the data, and so on.

1) you are assuming that a color scanner is three passes.  Not many, if any
made today, are.  Most all current scanners use a tri-linear sensor that
provides all three channels at once, so only one pass is needed.  Some
Nikons are an exception, as they have a tri-linear sensor, but with no color
filters.  The color filtration is done by the light source.  Their premise
failed, in that they expected to end up with the same scan time as a
tri-linear with filters, but because of banding issues due to calibration
errors in their firmware/hardware, these scanners are relegated to using
only one of the CCD rows.  That does not make it a three pass scanner, it
does do all three colors in the same pass, it's just that it will take three
exposures for each line.

2) processing of the data does not add any time to the scanning time (I've
designed scanners, and know what processing is done, and how it's done), as
the scanning time is far longer, and is the limiting factor.  Also, there
really is no "processing" that goes on in the scanner to the data that takes
any time.  The only thing that happens is the data goes from the A/D through
a LUT (Look Up Table), which is done in real time.  The only time any actual
processing is done is when you don't want the scanner to provide full
optical resolution data, and therefore it has to interpolate, but, this is
done "on the fly", and therefore adds insignificant time to the overall scan
time anyway.

3) and so on?  Would you be more specific?

Austin