[filmscanners] RE: Repeated "Tonal correction", is it god?

["Austin Franklin" <austin@darkroom.com>]

Hi Laurie,

> I would say first that I would be
> reluctant to do my
> tonal correction or adjustment at the pre-scanning stage and would tend to
> reserve it for the post scan stage.

That depends.  If you are getting high bit data out of the scanner, you are
fine doing it that way.  If you are getting 8 bit data out of the scanner,
then doing it pre-scan will do the tonal corrections to the high bit data in
the scanner BEFORE it converts it to 8 bit data...so you are better off
doing any major tonal correction pre-scan.  It also matters if it's B&W or
color.  8 bit color data, which is actually 24 bit color data BTW, can
tolerate "more" tonal correction than 8 bit B&W can.

As far as doing tonal corrections to high bit data, B&W or color, you are
fine doing it quite a few times, if not an infinite number of times,
depending on how drastic your corrections are.  The reason is you are only
going to be able to print a VERY small number of tones compared to the
number of tones in the file...so as long as you end up with a full histogram
of 8 bit data for B&W, and a mostly full histogram of 8 bit data for color,
you should be fine.

As far as doing tonal corrections to low bit data, you don't have much room
to do this with 8 bit B&W data, so I strongly suggest doing any B&W tonal
corrections to high bit data, or in the scanner driver which will always do
it to high bit data, even though it gives you 8 bit data out.

As far as doing tonal corrections to low bit color data, it's actually 24
bits of data, and it can withstand quite a bit of correction.

Regards,

Austin

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