Archived posting to the Leica Users Group, 2001/07/25

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Subject: RE: [Leica] Nyquist again (was scanning)
From: "Austin Franklin" <darkroom@ix.netcom.com>
Date: Wed, 25 Jul 2001 21:46:32 -0400

> > 53 lp/mm is achievable with a 2700 SPI
> > scanner, ONLY if the lines were perfectly
> > lined up.  That's useless.
>
> 53 lp/mm is achievable with virtually any alignment of image
> elements, at 2700
> dpi.

The problem is "virtually any alignment".  You can not spec a system as
"almost" or "typical".  You obviously don't have any experience designing
electronics professionally.

> If you disagree, then please indicate the exact number of lp/mm that _is_
> achievable at 2700 dpi.

Of course I disagree, because your claim is wrong.  It would be a range,
equal to 53 lp/mm down to 1/2 that.  That is standard for any digital
acquisition system.  Typically, acquisition systems are spec'd at only the
minimum...which I said, is 1/2 that, since that is the only number the
system can guarantee under all circumstances.  At anything above that the
detection is "unreliable".  This is really really simple to understand.

> > Any company who would put in their spec that their
> > 2700 SPI scanner could reliably scan 53 lp/mm would
> > be laughed at, and would be lying.
>
> Fine.  What would the correct figure be, and why?

1/2 that and I've explained why.  You haven't explained why, nor have you
explained why my correction to your mistaken assertion is not correct.

> > I guess there is some other reason CDs have a
> > sample rate of 44.1kHz...in order to reliably
> > capture 20kHz.
>
> My understanding was that the intent was to capture up to 22 kHz,
> but it has
> been a long time since I looked into CD design.

Yeah...and isn't 44.1kHz slightly more than 22kHz?  Duh.  Nyquist...  It
applies to data acquisition of a film scanner too.

> > Modest?  That's quite an amorphous term.
>
> So is "reliable."

Reliable is hardly amorphous.  You're playing games here.  I have given you
a very clear definition of it.  As I stated, it is a standard term in signal
processing, and if you have any experience in signal processing, as you
claim you do, you would understand what "reliable" means, and that it is a
VERY specific term.

You made the original claim, and you still fail to substantiate it.

More wasted time...I am such a fool to engage with you in any discussion.  I
believe this is a game to you.

Replies: Reply from "Mxsmanic" <mxsmanic@hotmail.com> (Re: [Leica] Nyquist again (was scanning))