[sane-standard] clarification on the standard, specifically frames

[Johannes Berg]

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Hello,

Assume the following situation:
I have a digital camera that I want to have a SANE backend for, and it
can give me -- for each image -- extra information like the shutter
speed, date&time, "Blende" [sorry, no English word for that in my
vocabulary] etc.
Let text/x-camera-info be the MIME type of a format capable of holding
such information (in textual form).
Let each image acquired contain 3 colour channels: red,green,blue.

Would my backend now first transmit a frame of type SANE_FRAME_MIME with
the information about the image, with SANE_PFLAG_LAST_FRAME set to 0,
and then a second SANE_FRAME_RAW with SANE_PFLAG_LAST_FRAME set to 1,
continuing with the next image in further sane_read calls? [or of
course, the other way around, first the raw data and then the mime
stuff]
However, the standard specifies that SANE_PFLAG_LAST_FRAME MUST be set
when transmitting a MIME frame, so does that mean I have to transmit the
RGB data first?

Also, would SANE_PFLAG_MORE_IMAGES be set during the transfer of both
frames, or would it be set only during the second frame?
[But as I understand the specification it can basically always be set,
unless it can be guaranteed that it is impossible to acquire more data
after the current frame]

johannes

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