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[filmscanners] Re: Film resolution - was: Re: 3 year wait




"Anthony Atkielski" <anthony@atkielski.com> writes:
>>>>>>>>>>>

> Whether you believe 1000:1 is practical or
> not, isn't relevant, as film CAN record that.

Only if you have 1000:1 contrast ratios in the scene you are photographing,
which is extraordinarily unlikely.  If the contrast is lower, the fact that
film can record this at such high contrast is entirely irrelevant.
<<<<<<<<<<<

Yes. And even worse, the detail in a given area will never have local
contrast more than a few stops.

>>>>>>>>>>>>>
> Also, keep in mind that to scan RELIABLY you
> need to scan at around 2x the resolution you
> are trying to scan...so to reliably scan 4k
> per inch, you would need to scan at a resolution
> of 8k per inch.

Line _pairs_ per millimetre already account for this.  So to scan 120 lp/mm,
you need 120 pixels per millimetre.
<<<<<<<<<<<<<<<

But, unless I'm misunderstanding what you are trying to say, this is wrong
by at least a factor of three and in practice a factor of 6.

To represent a 120 lp/mm pattern reliably in digital, the zeroth level
requirement is that your sampling be at least at the Nyquist frequency.
Which requires two pixels per line pair. But in practice, you can't even
represent a 120 lp/mm pattern with 240 pixels/mm, since that only works at
the exact phase. It turns out that even 3 pixels/mm is pretty poor, but that
6 pixels/mm is adequate.

See: http://www.clarkvision.com/imagedetail/sampling1.html

David J. Littleboy
davidjl@gol.com
Tokyo, Japan



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