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Re: filmscanners: Beginner's question on which scanner to chose

When you see these claims of x in one direction and X times 2 in the 
other, typically the higher resolution is in the direction the head (in 
the scanner case) or the paper (in the printer case) moves in.

The easiest way to increase resolution, is to have the stepper motor 
that moves the scanner "head" or the platen on a printer, by smaller 
steps.  This requires a better quality motor, but no major improvement 
in anything else.  So, indeed, there can be more samples (scanner) or 
dots (printer) in one direction.  The way this usually works with a 
scanner is as follows:

Scanner is rated at 1600 x 3200 dpi.  If you select 1600, the scanner 
CCD elements across the scan bed are 1600 dpi (in some cases with Epson, 
it is actually two 800 dpi CCD chips in tandem).  When this is selected, 
the scanner also moves the stepper motor at 1600 dpi making a 1600 x 
1600 dpi image.  If you select the 3200 dpi setting, then the CCD is 
still only 1600 dpi (or 800 dpi x 2 chips, as the case may be), but the 
stepper motor moves at half the increment, and takes twice as many 
"samples in that direction.  The software then up-samples the 1600 dpi 
to 3200 dpi in the other direction.

In the case of the printers, you will notice that as Epson raises one 
resolution value (was 720, then went to 1440, then went to 2880) the 
other never has gone above 720 dpi.  It is because Epson hasn't risen 
the resolution in the direction the head moves in since the beginning 
(although they have continued to improve the dot size, making it smaller 
and smaller), but they have made the paper advance move at smaller and 
smaller steps.  So the current situation is you can choose 180 x 180 
dpi, 360 x 360 dpi, 720 x 720 dpi, 1440 x 720 dpi and 2880 x 720 dpi.


patton paul wrote:

> On Mon, 12 Feb 2001, Armando A. Cottim wrote:
>> Hi guys.
>> Sorry for this question.
>> I notice that your posts are all so high leveled that I almost feel ashamed 
>> for such a beginner's question but ... here it goes.
>> I 'm considering the acquisition of a scanner to scan slides for my magazine.
>> I've been given several options.
>> (Please consider that Portugal is not the best place to get the ultimate 
>> machine just by going to the shop) :-(
>> First of all I was shown the Epson 1640 Photo (which is a flatbed and is 
>> said to scan 1600x3200dpi)
> What does 1600x3200dpi mean?  Does it scan at 1600 dpi along one dimension
> and 3200 dpi along the perpendicular dimension?  I've also been puzzled by
> a similar claim on Epson's website.  It gives a maximum print resolution
> for the Epson 1270 photo quality printer of 1440x720 dpi
> -Paul Patton


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