Hi,
is there anybody out there who's successfully using the snapscan backend with
resolutions of 1200 dpi and above? It doesn't work for me, and if I'm not
mistaken for no one else either.
I looked into this and found that
1) x-resolution can only be increased up to the optical resolution. It's
possible to request higher resolution from the scanner, but it will only
return the image data with maximum resolution padded with junk. On my
scanner, which has an optical resolution of 600dpi, this means that for a
scan in 1200 dpi I get the scanned data on the left half of the image and
junk in the right half of the image. However, it's possible that there are
some scanners out there that do an interpolation in their firmware - anybody
seen this?
2) Performing a scan on a wide scan area with high resolution will lead to a
hanging backend, because the size of one image line becomes larger than twice
the size of the SCSI buffer. Some computations inside the backend calculate
bufferSize/lineSize, which will evaluate to zero - the rest is left to your
imagination.
The best solution is probably to use different resolutions in x and y
dimension. The x resolution may than be increased up to the optical
resolution, which avoids problem (2). If a frontend requests a higher
resolution the backend can use some decent interpolation algorithm.
This will probably take some time to implement. Until then, I suggest to
disable the higher resolutions to avoid problems. If however there are
scanners with firmware interpolation those resolution settings can be left
untouched.
Oliver
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