Notes

• Artec AT3
• BlackWidow BW4800SP (rebadged Artec AT3)
• Artec A6000C
• Artec A6000C PLUS
• Artec AT6
• Artec AT12
• Artec AM12S

	The Artec backend now supports the A6000C scanner.

	The following modes are supported:

		Colour
		Greyscale
		Halftone
		Lineart

	Remaining problems: (A6000C)
	-------------------

		- Halftone data varies from scan to scan (?).
		  Not sure if this is a noise problem or just the way the scanner works.

	General notes: (apply to A6000C, and others??)
	--------------
        - Robustness issues:
           - Cancelling scans: it should now be quite safe to cancel a
               scan in progress.
           - Starting scans: there are still outstanding issues relating
               to starting a new scan while the scanner carriage is returning
               to the start position.
               It seems to be safe to do this ONLY if the previous scan was
               cancelled.
               It is not safe to do this if the previous scan completed
               successfully.
                 - Doing so may require restarting the scanner program and/or
                   powering the scanner off and on.
   
            "Patient scanning" is recommended to avoid problems.
   
        - Speed issues:
            The Artec backend is not particularly fast.
            The scanner is capable of producing data faster than the
            backend can process it.  In particular, high resolution scans
            are quite slow.

	** NOTE by Chris Pinkham: The older model Artec/Ultima scanners seem to
	   have a max read size of 8K at a time, so I'm not sure how fast they
	   will ever be.  Newer models (some AT3 and all other newer models) do
	   not have this limit.

	A6000C support notes:
	---------------------

	These notes are based on personnal observations while implementing
	A6000C support based on the A6000C+ code.

	The A6000C uses the same command set as the A6000C+ with the following
	differences.
		Colour:
			- Colour is scanned in three passes
			- A single command is used to initiate all three passes,
			  no additional commands are involved between passes (the
			  data from the three passes is returned in a continuous
			  stream)
			- no line offset correction is required.

		Grey:
			- works identically to the A6000C+

		Halftone/Lineart (1bpp modes):
			- the A6000C sends back a continuous stream of pixels_per_line
			  lines (as opposed to a null filled (?) stream of bytes_per_line
			  lines).
			- the rows_available refers to pixels_per_line lines (as opposed
			  to bytes_per_line lines)
			- the data stream has to be manually converted to bytes_per_line
			  lines before being sent back to SANE
			- reading data in multiples of whole bytes means the first
			  row_available may not be an entire row of pixels_per_line
			  (some portion having been read with the previous line)
			  -> measures must be taken to ensure data is not read before it
				 is available.

             At present the backend waits until sufficient data is available
             for the whole buffer to be read (approx 8Kb of data).

	DAL