# Re: Writing Fujitsu M3091 backend

From: Oliver Rauch (oliver.rauch@rauch-domain.de)
Date: Thu Mar 01 2001 - 09:21:45 PST

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  Mick Barry wrote:
  >
  > 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 Mick,

  there is missing a way for the backend to tell the frontend that there are more images.

  Last_frame can not be used for this:
  SANE.TEX:
  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).

  XSane does it in the following way:
  The user can define a multiple image scanmode (ADF-Scanmode).
  E.g. the backend defines the following scanmodes (see saneopts.h)
  front side
  back side
  both sides

  "both sides" is defined as multiple image scanmode in xsane.
  If "both sides" is selected, xsane scans until sane_start
  answers with sane_status_no_docs.

  Bye
  Oliver

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