[sane-devel] Umax 2200 smearing/dangerous options
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
> 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
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.