Re: Digicam vs. Scanner resolutions

[Kennedy McEwen <rkm@xxxxxxxxxxxxxxxxxxxx>]

In article <022501c212e8$d6a8bb10$6b64640a@stelex.com>, Igor Klinchin 
<karmen38@softhome.net> writes
>
>----- Original Message -----
>From: "Kennedy McEwen" <rkm@kennedym.demon.co.uk>
>> That is why MTF is so useful - all the components just multiply together
>> to give the end result.  The one exception is when you scan the image
>> you also introduce a "brick wall" limit and any residual resolution
>> above that is "reflected" to appear as the MTF of the aliased component.
>> Thus, appropriately tuning the MTF of the scanner can eliminate grain
>> entirely from the scanned image without loss of performance.
>
>Does it mean reducing scanner optics MTF? Or how can scanner do it
>otherwise? In other words scanner reduces resolution of the image to match
>the resolution of its sensors. I hope that I am using concepts of MTF and
>resolution in the same sence.
>
Yes, essentially that is what is necessary, although typically some 
residual low amplitude MTF above the brick wall is acceptable as with a 
drum scanner and a gaussian spot intensity profile.

>The first question about this issue is whether a drum scanner uses the same
>technique or is it inherently the "problem" of CCDs?

Drums use exactly the same technique - although only having a single 
optical spot the output of the PM is simply sampled faster than the scan 
rate of the spot to achieve this.  In a CCD scanner, the only realistic 
method of achieving this is the "HyperCCD" approach originally 
introduced by Epson although now standard practice in many flatbeds.
>
>The other question is a question of how large should this antialiasing
>degradation of MTF be comparing to let's say traditional darkroom prints.

How long is a bit of string?  It depends on the film you have and the 
sampling density you are working with just how much MTF beyond the ideal 
is acceptable.  To be absolutely certain, the only rule is to have no 
MTF beyond the brick wall, but that is very difficult to achieve 
optically.
-- 
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers
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