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

["Austin Franklin" <darkroom@ix.netcom.com>]

> RGB values mean diddly squat.
> They are just a measurement of the amount of current in a scanner
> ccd

Only if it is a raw scan.  A typical scan has the data setpointed and
tonally adjusted.  That means that 0 IS the darkest value in the resultant
file, and 255 IS the lightest value in the file, if we are talking about 8
bit files that is.

> or the
> output voltage of a video card.

Yes, bit as above, it's NOT raw data...

I really think you're missing some basic understanding here...

> (extreme example) You could have a scanner that mapped mid grey
> at 20,20,20

Huh?  What does that mean.  Scanners don't just "map" mid gray to some
value.  I really think you don't know how a scanner really works.  I suggest
you search the archives for some more info, or see Wayne Fulton's
www.scantips.com for more info on how scanners work.

> It all gets majorly complex when talking about scanning film, as the CCDs
> are only registering a value that they see between their black and white
> points.

That is not right.  The CCD does not have a "black and white point".  That
gets set in software, or in an analog front end (but not in any regular
scanner).

> The first problem with doing all of this is 'has the film been
> processed exactly the same way as the one the profile was generated from'
> and 'is the exposure totally spot on?
>
> The answer to both of them is generally no :-)

Well, you got that right.  That is why film profiling is really not very
useful.