Re: Backtracking in color scanning
Wolfgang Jung (woju@keep.in-berlin.de)
Mon, 1 Sep 1997 10:47:50 +0200
On Fri, Aug 29, 1997 at 02:13:36PM -0400, shendrix@gypsy.atlantic.infi.net wrote:
>
> In message <199708291754.KAA02430@hopper.mosberger>
> David.Mosberger@acm.org (> ) writes:
>
> > >>>>> On Fri, 29 Aug 1997 17:04:01 +0200, Rainer krienke <krienke@mailhost.un
> >i-koblenz.de> said:
>
> > Rainer> What suprises me a lot, is that under windows doing the same
> > Rainer> scanprocess at the same resolution (via the mustec-twain
> > Rainer> driver) does not cause backtracking to occur and is
> > Rainer> completed much much faster (not even half the time).
> >
> > What size scan-buffer are you using? If you're using the default size
> > of 32KB, could you try increasing it to 127.5KB? See sane-scsi(5) for
> > info on how to do that.
> >
> > If increasing the scan buffer size to 127.5KB doesn't help, the
> > backtracking could be due to timing problems. If the scanner software
> > is too slow to issue the next "read data" command then backtracking
> > would occur. What kind of computer are you using and how much memory
> > does it have?
>
> Since I'm having the same problem, I'll reply here.
>
> I have a Pentium 200 with 96mb RAM and the scanner is on its own Adaptec
> 1540 controller. The buffer is 128K and my scanning is very slow and does
> the backtracking. Turning backtrack has no substantial speedup and the
> colors are completely screwed up.
>
> Grayscale is great, and fast. Color under Windows is fast too. Of
> course, now I cannot use it under Windows because the TWAIN driver
> won't support my Adaptec.
Just calcualte the Data the scanner needs to transfer.
As Far as I could find the Mustek Scanner justs uses async transfer
to the HOST which could be as slow as 1.5MB/S (even if you Adapter
could get up to 7MB/s )
An tiny Area of 1" times 1" brings you with 24 Bit and 1200 dpi Color
into 4320000 Bytes of Imagedata. if the scanner is able to scan that within
1 Second the scanner needs to stop to get rid of the
Data.
I Observed this with the TWAIN Stuff.
iScanning with Win95 (*shiver*) everythings scans as it should even if there
are small stops (No Distortion or something.
While tring to get the SANE running, I had to manually stop
the make from using the WORKAROUND an MUSTEK Bug (since the 1.04 of MFS 12000SP)is running OK without this bugfix.
This made the image better. (I need to recheck this)
BUT triing to scan in GRAY I get Lost Chunks of lines
I tried to estimate those, and it seems the scanner or the sane
or at least one piece from:
Scanner -> SCSI-Driver->SANE is losing those lines, but in a way
that SANE thinks it scanned all the lines.
Using a Buffer which scans 1 line with each command makes the scanner
move (for a 10mm/10mm Area) thrue about 16 times as far.
I could imagine the scanner sends MORE Lines then ordered, but Sane
does not read them...
Gruss
Wolfgang.
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