[sane-devel] Umax 2200 smearing/dangerous options

Henning Meier-Geinitz henning@meier-geinitz.de
Mon, 5 Jan 2004 22:58:37 +0100


On Wed, Dec 31, 2003 at 02:16:40PM -0500, Charles Sprickman wrote:
> This will hopefully be the last time I bother the list.  My Umax 2200 is
> now basically working, but the scans look pretty bad.  They have what I
> could best describe as "banding" or "smearing".  An example from a 300dpi
> scan is here (white areas on the left are the scanner lid and show the
> pattern rather well - looks like the output of a really bad inkjet
> printer):
> http://home.manymonkeys.com/out.png  (approx. 1MB png)

On first sight I would have said: the image is ok. When I looked with
gimp and it's magnifying option I found two effects:

a) There is a small line distance correction error. That means that
   the colors are not exactly centered vertically. You can see that
   effect best at the top edge of the photo. There is a blue/brown
   stripe. Possible causes: Bug in the backend or scanner firmware. Or low
   quality scanner.

b) High noise. The colors of two adjacent pixels should be (mostly)
   the same in the white area. Possible causes: Low quality sensor.
   Defective or old lamp. Bug in the backend or firmware (calibration).

I guess the horizontal lines that look like an old inkjet print are
cause by problem a). As I don't own such a scanner I have no clue how
to solve it (if possible), however.