Mick Barry, Don, 01 Mär 2001 :
> 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
> GetParameters (format=RGB, LastFrame=false)
> // Implies a new image cause we've read rgb image which only has simple
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
...as I said before, please correct me, if I'm wrong.
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