plustek@linuxhacker.org

Hi,

I have experimented a bit with my Canon Lide 20 and sane 1.0.13.

A few months ago, I had a discussion on this mailinglist about bad color 
quality with this scanner (too much red in the picture).
After playing with the (manual) gain values, I got a all colors scanning, but 
still in bad quality.

I wanted to try sane 1.0.13 because of the "new calibration" code, to see if 
anything was different.
Unfortunately, I still have red color scans (the only color that get scanned 
is red).

Then, I changed a piece of code in sane 1.0.13:
line 648 in plustek-usbdevs.c
Original: {{ 0, 110}, 35, 10, {2550, 3508}, {75, 75}, COLOR_GRAY16 },
Changed To: {{ 0, 110}, 25, 10, {2550, 3508}, {75, 75}, COLOR_GRAY16 },
-> Third value from 35 to 25

After compiling, I got this scan:
http://users.skynet.be/bluedigit/xsane.jpg
reference scan (vuescan): http://users.skynet.be/bluedigit/vuescan.jpg

As you can see, every color is there in the right proportion, the only problem 
is a dark picture. The preview mode of "xsane" displays an identical picture 
as vuescan when setting the "brightness" higher by 60 points.
Here's a scan of the brightness set to +40 points:
http://users.skynet.be/bluedigit/xsanebrightness.jpg

The same problem occurs with gray/b&w scans too. Brightness is too dark by the 
same margin.

What I can understand from the code, the changed value is a reference where 
the calibration strip is located. The only thing that still goes wrong is the 
brightness/contrast calibration.
Why is this value 35 while my scanner only responds to 25? (I understand I may 
have some exotic version of the Lide 20... but it's still fun to find the 
reason why sane is affected, while vuescan is not).

Any ideas are welcome...


Grtz

Alain