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RE: filmscanners: Scanner resolution (was: BWP seeks scanner)



Here's a related resolution question.

McNamara quotes 60 lp/mm.  I arrived at my initial 75 lp/mm by doing a 
braindead calculation: 4000/25.4/2.  My calculation is obviously optimistic - 
I'm assuming that adjacent rows (or columns) of pixels each resolve "1 line".  
I would have expected (bit being bits and all that) that any degredation from 
that theoretical maximum would have involved a division by 2.  That's obvously 
not the case with McNamara's number.

So the question is:  what factors would conspire to lower the resolution 
fractionally like that?  The suspects I come up with are:

- CCD bloom
- An interaction between the analog detail on the neg and the discrete CCD 
pixels (leading to something like dither if I'm not mistaken)
- System noise

Anyone have any ideas?

Paul

-----Original Message-----
From: BHannaford@aol.com [mailto:BHannaford@aol.com]
Sent: Friday, June 15, 2001 1:28 PM
To: filmscanners@halftone.co.uk
Subject: Re: filmscanners: Scanner resolution (was: BWP seeks scanner)

In a message dated 6/15/01 11:53:29 AM Eastern Daylight Time, 
Paul_Chefurka@pmc-sierra.com writes:

<< After all, 4000 ppi gives a resolution of 75 lp/mm or so, and it takes 
pretty remarkable technique to actually get that kind of resolution onto 
film.  Or is my crude first-approximation assessment incorrect, and we 
actually can't resolve detail in the scan at more than half that - say 40 
lp/mm with reasonable contrast?  Even that level is still sufficient for 
prints that appear "sharp" at normal viewing distances.
 
 Paul Chefurka >>

Here is an interesting observation from Michael J. McNamara (PopPhotgraphy 
July, p58)at the conclusion of the article on their scanner tests: "...Even 
the best 4000 dpi scanners we've tested aren't capable of capturing all the 
detail found in a 35mm color original under optimum conditions (tripod, 
mirror lockup,etc). In our tests the highest res we've found in a 35mm color 
slide or negative is 77 lp/mm.  The best 4000 ppi scanner can capture about 
60 lp/mm, about 25% lower.  But that's perfect, because under normal shooting 
conditions (i.e., handheld instead of tripod mounted), 60 lp/mm is about all 
you'll ever get from an SLR."




 




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