# Re: [BUG] Epson 1640SU, xsane preview problem

From: Oliver Rauch (oliver.rauch@rauch-domain.de)
Date: Thu May 24 2001 - 05:08:36 PDT

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  mh wrote:
  > Errm, it displays the wanted subpart, but uses the *wrong* preview for this.
  > (I think that's what the original poster was talking about).
  >
  > BTW, this should happen independently of the backend(?):
  > -insert a document and scan a fullsize preview
  > -insert a new document, change the previewsize to A5 e.g.
  > -If you now start a preview scan, the new document is shown for a short moment,
  > but gets immediately replaced with the subpart of the *previous* document
  > (p->filename[0], which is a preview of the first document, and not of the
  > current document in this case)
  > Or is this intended; does one have to scan a fullsize preview first ?

  Hi Michael,

  may be I know what happens.

  The strategy of xsane is:
  - 3 different preview levels available:
  level 0 is full scanner surface
  level 1 is reduced surface, reduced area seleced in preview window
  level 2 is zoomed area (zoom function in preview window)

  - when everthing works like expected then:
  level 0 is done with a low resolution
  level 1+2 are done with a higer resolution
  this means that the qualtiy of level 1 and level 2
  are normaly higher than the quality of level 0

  - xsane does calculate the quality by the resolution
  of the part of the image that shall be displayed

  - when the preview has to be redrawn xsane does load
  the preview image with the higest qualtiy.

  I think what happens is that the level 0 preview
  has a higher quality than the level 1 preview.
  Normally this can not happen because xsane does
  set a higher resolution for the level 1 preview than
  for level 0.
  The epson backend uses a resolution list with
  a strange correction routine that does not
  allow to set exact resolutions (that are
  part of the list).
  The plustek backend defines a range and internally
  selects a suitable value from a list.

  I think in these cases it can happen that the quality of
  level 0 image is the same or higher that the quality of
  level 1 and so the level 0 image is used.

  Please could you test the following:

  edit xsane-preview.c line 2066

  if (quality < min_quality)
  {
  return min_quality;
  }
  change
  if (quality < min_quality)
  to
  if (quality <= min_quality)

  bye
  Oliver

      --
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