# Re: Writing Fujitsu M3091 backend

From: Mick Barry (mick@objects.com.au)
Date: Thu Mar 01 2001 - 02:26:36 PST

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  Pls don't make it your last comment, at least until we all understand
  how it is MEANT to work :-)

  mh wrote:
  >
  > Mick Barry, Don, 01 Mär 2001 :
  > > Tom,
  > >
  > > Thanks muchly for this.
  > >
  > > I'm still unclear on how a f/e knows that there is new image, and not
  > > just a new frame for the current image. Is it implied by what frames
  > > have been recieved.
  > > So if we looked at just the getparameter replies is the following how it
  > > is intended to work:
  > >
  > > GetParameters (format=Red, LastFrame=false)
  > > GetParameters (format=Green, LastFrame=false)
  > > GetParameters (format=Blue, LastFrame=false)
  > > // Implies a new image cause we've already read r, g & b
  > > GetParameters (format=Grey, LastFrame=false)
  > > // Implies a new image cause we've read grey image which only has simple
  > > frame
  > > GetParameters (format=RGB, LastFrame=false)
  > > // Implies a new image cause we've read rgb image which only has simple
  > > frame
  >
  > Hi,
  > ok, I hope, one last comment is allowed (and please correct me, if I'm wrong):
  >
  > According to the current SANE Standard, there's absolutely no way for a frontend
  > to determine, whether there's another image available, especially not by
  > a call to sane_get_parameters().
  > The member last_frame is *always* false, if your scanning a single frame image
  > (like RGB or grayscale). This member is only used if you are scanning a
  > multi frame image.
  > See SANE Standard 1.02, page 28:
  >
  > "Member last_frame is set to SANE_TRUE if and only if the frame that is
  > currently being acquired (or the frame that will be acquired next if there is
  > no current frame) is the last frame of a multi frame image (e.g., the current
  > frame is the blue component of a red, green, blue image)."
  >
  > There is no "well known option" or a flag in SANE_Parameters which tells the
  > frontend that it should continue with image acquisition. Therefore you
  > have the following possibilities:
  > -let the user hit the scan button for each single scan operation
  > -let the user set the number of scans, and then try to acquire this number of
  > scans.
  >
  > ...as I said before, please correct me, if I'm wrong.
  >
  > Michael
  >
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