[filmscanners] Re: Dynamic range

["Todd Flashner" <tflash@earthlink.net>]

on 8/29/02 5:26 AM, David J. Littleboy wrote:

> but do you realize that the range that Austin is using as
> his Dmin for the ISO formula is the ENTIRE density range of the scanner?
> <<<<<<<<<<
>
> Austin's explained this: in any dynamic range calculation, the maximum
> signal level can be seen as corresponding to the range of levels handled,
> assuming the minimum level is defined. The noise (or minimum recognizable
> signal level) (and the maximum signal level) defines how many meaningful
> steps the maximum signal level is from the minimum signal level. That's all
> dynamic range is: the number of meaningful steps from min to max. That's
> normally expressed as a ratio...

Yes, I suppose if one is convinced that DYR is a resolution that is the way
they'd have to approach it as such, but David, tell me, have you seen a
cited reference that supports that approach?

I've wanted to believe Austin is right for a long time, but there is just
massive evidence against it. Do you really see the ISO's: (Dmax - Dmin)
supporting that, or Analog Devices: (Peak Level) - (Noise Floor) supporting
that?

Isn't it more "obvious" to presume that "Dmin" is a single value, as is
"Peak Level", and if they WERE a range extra attention would be paid to that
issue by the definitions? Would they really leave it vague for most EEs to
be mistaken? What Julian said about the term Dynamic Range makes sense: if
it's not really a range, wouldn't the definitions go out of their way to
have it be known it is a resolution, a resolution which is called a range,
and as such all max signal levels need to be understood as being relative to
min signal levels before they can be applied in the equation? Shouldn't they
hint somehow that while the equation they lay out may look like x/z, or x-z,
what it will look like in use will be (x-y)/z or (x-y)-z? In time wouldn't
the confusion of students of the subject demand they pay attention to this
possible source of massive confusion (and upset ;-)) ???

> My point is that a value reported by a scanner corresponds to a range of
> possible values in the film, and that the size of that range is given by the
> worse of the noise in the electronics or the bit resolution of the scanner.

I think we all share that point.

Todd

PS, I like the way your mail program quotes me, what do you use?

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