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

[Oliver Schwartz]

Hi, 

> > Lineart and grayscale should be fixable.

I've commited a fix to CVS, please test.

> What does the snapscan backend for halftoning? Are there halftoning
> algorithms implemented in software or does it only pass a flag to
> the scanner? I'm asking this because there is a kind of halftoning,
> though broken. If it's done by the scanner, it could indicate then
> it is capable of some kind of halftoning.

The backend only calculates some matrices and downloads them to the 
scanner. The actual halftoning is done by the scanner itself.

> > > 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.
>
> Yes, it was also my guess. There is also decimation at 1600 dpi,
> isn't it (and at all resolutions below 3200)? The decimation
> patterns are evident for most if not all small resolution modes (I
> checked it last time), only this decimation is maybe done in
> hardware instead of software. But of course it is easier to throw
> away every other column/line instead of one of four.

Below 3200 DPI only one sensor line is used. 3200 DPI uses two sensor 
lines with a small offset (that's why the deinterlacer is needed for 
this resolution). For all other resolutions the decimation is done by 
the scanner itself.

> One further question: do you know what the real hardware resolution
> of the Perfection 3490 is? In the technical data sheet Epson states
> it is 3200x6400 dpi. These 6400 dpi are maybe attained with the
> stepper motor (as was the case with my former 600x1200 dpi
> scanner).

Yes, thats correct. However, the vertical resolution is fixed at 3200 
DPI. For a usable image the backend would have to do some kind of 
interpolation to deliver 6400x6400 DPI. 

/Oliver
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