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RE: filmscanners: Nikon Scan & VS Negative dynamic range
> > Mapping the input data into 8 bit values has nothing to do with the
> > dynamic
> > range of the A/D data
>
> Arrgh... not this again! :-)
And that's because it's a misunderstanding of how the system works!
> Actually it does, because analogue voltages are mapped linearly
> by the ADC,
> so with 8bits the maximum ratio between min voltage (noise) and
> max voltage
> is 1:256
No, that's absolutely wrong. It's all representation. You can take two
bits, and say that 00 is a DMin of 0.125 or less, and 11 is a DMax of 4.2 or
greater...and anything in-between is 01 or 10.
The way the "typical" scanner works is the data from the A/D is, say, 12
bits. Setpoints are applied to some range of values within those 12
bits...and the remaining data between those 12 bits then has the tonal
curves applied, and is then either decimated or interpolated into the 8 bit
data. The 8 bit data represents only "a" dynamic range for THAT scan, not a
"specific" dynamic range. That is why a slide scan that has a dynamic range
of say 3.6 can map into 8 bit data, as well as a B&W negative that has a
dynamic range of 2.2 can map into 8 bit data.
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