----- Original Message -----
From: "Rob Geraghty" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Monday, December 04, 2000 3:57 AM
Subject: Re: Re[3]: filmscanners: Film Scanners and what they see.
> bjs <[EMAIL PROTECTED]> wrote:
> > One can design a scanner that doesn't have aliasing and they will find it
still
> > has the softness.
> > The whole aliasing argument in this context is based on a fundamental
> > misunderstanding of aliasing AND basic filter theory as far as I can tell.
>
> Maybe now I'm seeing why this thread has persisted. Byron am I right in
> understanding that you're saying aliasing does *not* cause scanner image
> softness.
Yes.
> On the other hand you *aren't* saying that the enhancing of
> apparent grain caused by the interference between scanner resolution and
> film grain (dye cloud patterns) - is something other than aliasing?
Agree.
>
> Turning the last point around - do you agree that the enhancement of
> apparent grain caused by the interference between scanner resolution and
> film grain *is* aliasing?
Yes.
Basically, I'm trying to say that scanner softness has many causes but the
inherent reason is not related to aliasing at all It is the from low pass
filtering due to the individual CCD cell. In fact, I'm aware of empirical
studies showing that introducing aliasing into a non-aliased system actually
INCREASES apparent sharpness (to a point). Apparently the eye perceives the
increased "grain" as more sharp than the smoother non-aliased image.
Aliasing certainly occurs in a scanner when the ARRAY BANDWIDTH is insufficient
for the sampled signal. In this case, the effect Tony has quoted in his Kodak
reference applies. The visible effect of aliasing is increased "apparent
grain" in the image and not "softness".
Sigh,
Byron
