Epson Stylus SX525WD: scanner resolution can only be 75, 300, 1200 and 2400

[Tim]

Allegedly, on or about 16 December 2012, Frédéric Bron sent:
> 2. with xsane, I have access to the following resolutions only: 75,
> 150 300, 600, 1200, 2400, with scanimage: 75, 300, 1200, 2400.
> Why is it not the same list?
> How can I have access to more values as with the Windows tool where I
> could select whatever value I wanted?

Educated guess:  The list is what's actually supported by the software
and the scanner.  Putting in *any* value probably doesn't reflect what
the scanner actually does, and probably is the software converting the
scanned data into the resolution that you think you've picked.
Interpolation often introduces horrible errors, or is quite CPU and time
intensive if you want to do it better.

A scanner can only scan at particular resolutions, if it's a traditional
flat bed type of scanner (it has a scanning head with optical sensors in
a horizontal line, with the sensors fixed distances apart from each
other).  The highest selectable resolution start with a 1:1 pixel
relationship between scanned pixels and saved data, lower resolutions
either skip alternate pixels, or merge them together.  It's easy enough
to merge one, two, or three pixels together.  It's impossible to merge 1
and a bit pixels together, any attempt to do so is a fake.  

And trying to do the converse, of producing higher resolutions than the
scanner can actually do, is also a fake.  Yes, you can do optical
smoothing to take out jaggies, and make things look higher resolution,
but you're not actually increasing the resolution, recording more detail
from the scanned object.  It's faking it.

-- 
[tim at localhost ~]$ uname -rsvp
Linux 3.6.9-2.fc17.x86_64 #1 SMP Tue Dec 4 13:26:04 UTC 2012 x86_64

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