[Tig] new on the TIG wiki

[Jim Houston]

On May 10, 2007, at 3:28 AM, peter swinson wrote:
>
> OK, I think I see my mistake.

and I see the thing I was missing is that it was a completely  
different argument :-)


>  other person was quoting no point in sampling beyond Nyquist. i.e.  
> 2K.
> In the RHS examples using that argument where Nyquist sampling  
> limit =  2 x
> a cycle or Black to White transition on film I was showing that ...

Nyquist (and Shannon) were talking only about two things, sampling
and signal.  But it is important to keep them straight.   The signal  
from
analog film is quite noisy and goes down to a microscopic level:  but  
that
is kind of meaningless because we always look at it through a set of
optics as well as our eye at a certain distance in the theater.  The
sampling rate is just a question of how accurate can the reconstruction
of any signal be.

With respect to a 2K scanner, we have an imposed sampling rate in the  
capture device
which means that the Nyquist frequency is going to be 1/2 of that or 1K.
That only means that the amount of signal we can have faith is not
going to alias are those cycles that are below this frequency, so 500  
cycles
across the frame.  But this is also meaningless in a real scanner  
because
the lens 'blurs' the frame, the film is optically soft, and CCDs  
themselves
often have optical low pass filters to make up for the spacing  
between the
sample sites.   All of this means your aliasing limit is different  
than if you make
assumptions about a band-limited Nyquist sample. A 2K scanner often has
less aliasing than would be predicted just by the Nyquist theorem.

You can see though why we all want higher rez (4K or more), it just  
makes
a better sampling possible and we can pull more real results from the  
film
even when the resulting image is only going to be used at a 2K  
resolution.

>
> All I know is that  only a few years ago everyman and his dog said  
> 4K would
> never be needed, but we now seem to be moving in thjat direction!

Only the HD people argued that 4K would never be needed. The film
people have known 'the secret' for quite some time ;-)

>
> Jim I'm glad to see I have got you up to a possible 11K !

My gut always yells at me than more is better, but then
my head kicks in and says, get real...


Jim H.