[sane-devel] Artec E+pro almost working

[kilgota at banach.math.auburn.edu]

On Wed, 9 Jan 2008, Philip Aston wrote:

> Listed as minimal support.
> With the artec firmware 1200.usb installed, this scanner works with 2
> bugs:
> 1 crashes @ 1200dpi, ok other resolutions-
> 2 probably more important, there are slight discolorations, the colour
> is reproduced but slightly darker, running vertically every 5mm, giving
> an impression of vertical lines. This is OK for text but not for photos.
> I am a new-ish Linux user & would like to work on this although have no
> knowledge as yet... would anyone be able to suggest something/ offer
> assistance? I note that a previous user had the same problem with this
> scanner so I assume the fault is not with my computer or scanner.-Phil

Try interchanging the even and odd columns of the output? I don't know 
much about the format in which the scanner is reporting the data, but if 
it were a digital camera that would be the most likely thing to have to 
do.

The camera typically uses what is called a Bayer array on the sensor chip 
which is, in fact, a bunch of microsensors arranged in a grid or matrix 
pattern on the sensor chip, and each microsensor has on top of it a color 
filter. They are arranged in a pattern like this (or an equivalent 
variation of this)

RGRGRGRG until pixel width is reached
GBGBGBGB until pixel width is reached

above pattern of two rows is repeated vertically, until pixel height is 
reached.

Now, observe what happens if you start to interchange for example every 
odd-numbered column with the next even column. You get this:

RRGGRRGG
GGBBGGBB

which is a nonstandard color mapping (tiling, as it is called) and nothing 
much can be done unless it is put back. However, sometimes one encounters 
such a thing. It seems that either the circuits have been hooked up wrong 
or someone is trying to play Jedi mind tricks with anyone trying to figure 
out what is going on.

So, assuming that the output of the scanner is RGB bitmapped data, 
something like this may have been done and then the obvious thing to do is 
to try to rearrange the data just a little bit. If you know how to write 
the piece of code to do that and put it in the right place in the driver, 
then you might get the problem solved. No guarantees, of course. Your 
mileage may vary.

Theodore Kilgore
(not a regular here, but I do have a bit of experience with cameras and I 
have dealt with one which did exactly this)