RE: filmscanners: creating correction curves from scanned calibration chart?

["michael shaffer" <rarewolf@roadrunner.nf.net>]

Ned writes ...

> >From: "michael shaffer" <rarewolf@roadrunner.nf.net>
> >   Because my system is calibrated, I am not assuming.  If
> >my monitor is truely gamma calibrated, and I use a gamma=2.2
> >working color space, then a 18% gray card's RGB value should
> >be R=G=B=117aren't mine).  ...
>
> your assumption being that 0,0,0 is totally black and 255,255,255
> is totally white in that 2.2 gamma colour space.  Would be a pretty
> daft colour space as you can't get either on a monitor or printer
> ...
> generate an icm profile for you monitor (i.e. with a color sensor)
> and scanner and ignore the rgb values.

  Quite independent of whether my monitor or scanner have an accurate device
profile, is whether the scanner software accurately calculated the
whitepoint for a given film scan.  There are numerous examples for film
combinations and real life whereby the scanner software is not given enough
info, or assumes the wrong RGB information, and subsequently calculates a
wrong whitepoint (e.g., garden scenery or miscalculating the orange mask).
The result, of course, gamma space is miscalculated, as is well the
neutrality of what should be gray.
  It is this problem I'm trying to address by photographing a color chart
... I've already taken care of the rest of my hardware.

shAf  :o)