# Re: [snapscan] High resolution scanning

From: Sebastien Sable (Sebastien.Sable@snv.jussieu.fr)
Date: Wed Apr 11 2001 - 02:44:59 PDT

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  Oliver Schwartz <Oliver.Schwartz@gmx.de> writes:

  > 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?

  I had the same thing with my Acer 300F when switching to 600dpi (that
  is half of the picture is junk) and the optical resolution is 300dpi.

  > 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.

  I am not sure but I think this one has been corrected for some
  models. My scanner used to hang with higher resolutions and this code
  corrected this:

  in snapscan-sources:

  if(ps->pss->pdev->model == ACER300F
  ||
  ps->pss->pdev->model == SNAPSCAN310
  ||
  ps->pss->pdev->model == SNAPSCAN1212U
  ||
  ps->pss->pdev->model == SNAPSCAN1236S
  ||
  ps->pss->pdev->model == SNAPSCANE50
  ||
  ps->pss->pdev->model == VUEGO310S
  ||
  ps->pss->pdev->model == VUEGO610S)
  {
  ps->pss->expected_read_bytes = (size_t) ps->absolute_max;
  }
  if (ps->pss->expected_read_bytes == 0)
  {
  if (!warned_expected_bytes)
  {
  warned_expected_bytes++;

  DBG (DL_MAJOR_ERROR,
  "%s: Hung up because expected bytes is 0. Please report!",
  __FUNCTION__);
  }

  }

  Maybe adding your model there would correct it. In this case, it seems
  that we should just remove the if test and put that as default
  behavior.

  I will release an new version of snapscan today (if sourceforge works
  that is, it was broken for upload yesterday) with support for e20, e40
  and e50 and your patch for xsane crash.

      --
      Sébastien Sablé <Sebastien.Sable@snv.jussieu.fr>
      http://inova.snv.jussieu.fr/~sable/
      --
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