[filmscanners] RE: Digital Darkroom Computer Builders?

["Paul D. DeRocco" <pderocco@ix.netcom.com>]

The video card includes a 256-entry lookup table (for each color) which gets
loaded with a gamma correction curve (e.g., by Adobe Gamma Loader). Assuming
that table doesn't just have a straight line in it, some values will be
squeezed together, creating duplicates, and other values will be spread
apart, doubling their distance. For instance, at one end the table might
contain values like 5, 6, 7, 7, 8, 9, 10, 10, 11, 12, 13, 13, while at the
other end it might produce values like 240, 242, 243, 245, 247, 248, 250,
252. If the lookup table and DAC had two more bits of fractional resolution,
those low values wouldn't be duplicated, and the high values wouldn't have
such large steps.

How often this difference is visible, I don't know.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@ix.netcom.com

> From: Austin Franklin
>
> If it's 8 bit data, you are feeding the DAC only 8 bits, if you
> are using a
> 10 bit DAC, then the lower two bits are merely set to 0.  The rounding
> "error" occurs in the conversion from N bits to 8 bits, which, I
> believe, is
> unavoidable, no matter how many bits your DAC has.

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