[sane-devel] Re: Re: Re: epson 3490 - transparency unit problem

Oliver Schwartz Oliver.Schwartz at gmx.de
Wed Nov 23 19:13:35 UTC 2005


> On Fri, 2005-11-18 at 00:11 +0100, Oliver Schwartz wrote:
> > ah, ok. That makes more sense. I guess I'll disable 2400 dpi to
> > make sure the error doesn't occur.
> 1600 dpi seems to work OK. 

Ok. I've replaced the 2400 DPI resolution with 1600 DPI in CVS.

> Oliver, did you receive my previous post 
> in which I've tested almost all possible combinations of
> resolution/scan mode/bit depth? 

Yes, but your mail got buried under some other mail ;-)

> The aspect ratio (=real resolution) 
> is wrong in all but a few lineart modes. And halftoning was (at the
> time I've tested it) completely broken. 

Lineart and grayscale should be fixable. The aspect ratio is correct 
as far as I can see - it's rounded up to be dividable by 8, as each 
pixel uses one bit and the smallest unit to request is one byte, i.e. 
8 pixels. My guess is that 1600 DPI works fine for both lineart and 
grayscale, so the only remaining problem is 3200 DPI in lineart and 
grayscale. Currently the deinterlacer is used for grayscale but not 
for lineart, it seems that both settings have to be adjusted. Can you 
send me example scans for 3200 DPI for a lineart and grayscale scan?

As for halftoning: I've no idea how to fix it. If the windows driver 
doesn't offer it there's a good chance that the scanner doesn't 
support it at all. I guess it should be disabled.

> PS: will be 2400 dpi enabled in the future? And why does the
> windows driver allow 2400 dpi but not 1600?

You'd have to ask the epson guys. My guess is that the scanner scans 
at 3200 DPI if 2400 DPI is requested and the decimating to 2400 DPI 
is done in software. It could be done in the snapscan backend as 
well, but I'm not sure if it's worth the effort. I guess the better 
choice (in terms of image quality) is to scan at 3200 DPI and rescale 
the image in gimp.


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