[Hp5400backend-devel] Re: [sane-devel] New release of the alpha version of hp5400 SANE backend

[Martijn v. O. <kl...@sv...>]

On Tue, Mar 04, 2003 at 07:23:06PM +0100, Thomas Soumarmon wrote:
> > Problems with scrambled images could be caused by an overflow of the
> > internal data buffer (at least that's what I found with niash12/14/19
> > chips). In that case, you should be able to correlate this to backtrack=
ing
> > (quickly moving back and forth of the lamp).
> > Do the scrambled images also occur if you scan only a narrow vertical
> > strip?
>=20
> At first I thought you would be right but even with a narrow vertival str=
ip,=20
> most pixels are "absent". I'll send you on a separate mail a tiny part of=
 the=20
> vertical strip. It shows colored vertical lines (red and green).
> It might be related to the query sent to the scanner. We have to check if=
 all=20
> the flags are correct.

I need to do some scans in windows at higher resolutions to see if any other
flags get turned on. Unfortunatly I havn't found a way to trap *all* the
data going over the USB link.

My theory on the colour corruption is one of two things:

1. Some kind of internal buffer length. In other words, when the line length
exceeds a certain amount it breaks into multiple blocks per line.

2. Since the intrinsic resolution of the scanner is only 300dpi, for
everything higher it needs to move the head from side to side (I don't know
if this is true, but it makes an odd sound at higher res). So this means
that if it's sending data back in order that instead of the normal:

Red   (row x)
Green (row x+k)
Blue  (row x+2k)

that instead it's sending:

Red   (row x, pixels 0,8,16,24,...)
Green (row x+k, pixels 0,8,16,24,...)
Blue  (row x+2k, pixels 0,8,16,24,...)
Red   (row x, pixels 1,9,17,25,...)
Green (row x+k, pixels 1,9,17,25,...)
Blue  (row x+2k, pixels 1,9,17,25,...)

etc

If this is true then it's going to *very* interesting to sort that out.

Does this have any precedent or am I making this up?
--=20
Martijn van Oosterhout   <kl...@sv...>   http://svana.org/kleptog/
> Support bacteria! They're the only culture some people have.