Scanner selection


Nick Makris (nick@mcn.org)
Fri, 22 Jan 1999 13:57:46 -0800


As I receive all the messages and surf the net for info regarding the scanner selection, I have made some progress. What has been missing here is the very info that I have required from time to time over the years - I might refer to it as a primer on scanning.
 
I found one on the web at ib.berkeley.edu/posters/scanning/scan.basics.html which gave some insight into what is needed. I was able to deduce (or assume) the following - please feel free to critique/comment/correct.
 
1) DPI and PPI are essentially the same and also referred to as SPI (samples per inch).
2) The final output device (in this case a printer of some sort with a 600 dpi capability) is the determining/limiting factor for the case of original scan resolution requirement. To quote/paraphrase the piece: If the original film/art to be scanned is 4X5 and the resulting image that is to be printed is 8X10 (this equates to a factor of 2 on either the X or Y axis) then the optical scan should be performed at 1200SPI (2X600) or greater. What this then provides is an image that may be printed on the predetermined printer at the desired size without any intermediate manipulation of the pixels/dots.
 
This association has escaped me when scanning reflective art in the past and is part of the reason for this thread. I have always been concerned with file size for purposes of download speed and not the association between scan res and printer output.
 
There are still some unanswered questions:

1) What is the association between lines on a screen (like in printing screen) and DPI on a scanned image.
2) What are the considerations/benefits/pitfalls (if any) of the higher interpolated resolutions.
 
I also downloaded the users manual on the Nikon LS4500 and found that the optical resolution is the same between it and the Agfa Duoscan - 1000H X 2000V. What is the advantage of the LS4500 for an additional $4000US? I have posed that question in a number of places and hope to have an answer soon. There is one other spec that falls in favor (I think) of the Agfa product - the number of CCD elements in the optics is 8000 vs 5000 for the Nikon. Any thoughts?

So, I still need to determine what will happen, or, how my soon to be decision on the selection of a film scanner should be affected, if I find I need to use a printer with say 1200DPI at some future time. It probably means that I should purchase the the film scanner with the highest optical resolution that I am willing/able to procure.
 
I hope that I haven't bored anyone with this exercise.
 



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