# Re: [snapscan] High resolution scanning

From: Rainer Hantsch (rainer@hantsch.co.at)
Date: Wed Apr 11 2001 - 00:46:26 PDT

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  I get the same with my ACER Prisa 620S.

  The image is squeezed in horizontal direction (or of double height)...

  It seems that my scanner supports equal X/Y-resolutions only up to 600 dpi but
  does 600x1200 (or 1200x600 ?) in the next higher resolution. And this gives
  this squeezed image. (But you can use gimp, cut the usable part and scale it
  back...)
  But another thing is more nasty than this: If I switch my scanner to 1200 dpi,
  I get big color shadowes. The image is sharp, but above and below each color I
  see light shadows in orange and blue respectively. And this is a bigger
  problem but may depend on this "high quality scanner".

  Ing. Rainer Hantsch

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  On Tue, 10 Apr 2001, Oliver Schwartz wrote:

  > 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
  >
  > --
  > Source code, list archive, and docs: http://www.mostang.com/sane/
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  >

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