[sane-devel] Avision AV220 Questions (LED digit, Buttons, Backends, Paper size)

[Crypto]

Hi,

I bought a used Avision AV220 document scanner recently and I am mostly happy 
with it. Fast duplex colour scanning of sheets, and it is so silent compared 
to the scanner I used before.

Now I have got a few questions:

1.) The scanner has got a single digit LED, an arrowed button, two more 
buttons labelled "Cancel" and "Scan". Though I can imagine what the latter 
two might do, I cannot guess the meaning of the digit and the arrow button. I 
can switch the number displayed from 1 to 9 and then to 1 again, but cannot 
see a meaning of that. I downloaded a manual for this scanner, in which the 
LED and the buttons are displayed but not explained. So what do these do?

2.) In scanning software such as gscan2pdf etc. there is an option to set 
contrast and brightness. Brightness goes from -100 (I suppose to make scans 
darker) to +100 (makes scans brighter). I can set this option to positive 
values and get brighter scans, but when I attempt to get darker scans I get 
an error message "Unknown message: Argument "" isn't numeric in subtraction 
(-) at /usr/bin/scanimage.pl line 357". This also happens if I use different 
backends for scanning such as scanadf.pl. In scanadf.pl it's line 380 but 
same error otherwise.

3.) After I enter sheets into the sheetfeeder, I select the page size and scan 
them. BUT: regardless which page size I have entered there always is a slight 
cut-off of the very top part of the sheet. The scanner always draws in the 
first page of a pile of sheets so there is no way for me to see if it did 
that correctly. Is this a problem of the back end that I use?

4.) Is the scanning area of a sheet influenced by the two red paper guides in 
any way? Or is only the paper size setting in the backend influencing the 
page size and the area that is scanned?

Thanks for any hint here and kind regards,
Crypto.