Calibration algorithms

From: Glenn Ramsey (glenn@componic.com)
Date: Sun May 20 2001 - 17:13:04 PDT

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    Hi,

    When we make a scan on the Microtek Scanmaker 3600 the brightness
    of the resulting image is uneven, being darker at the left and
    right edges and lighter in the centre. Scans made using scanwizard
    under windows do not show this unevenness.

    I have tried to find evidence in the usb snoopy logs of parameters
    being set to compensate for this but there don't seem to be any.
    Also the backend currently makes scans by pretty much just
    reproducing the command stream that scanwizard makes so I strongly
    suspect that the compensation is done in software.

    The inside of the scanner cover has, in front of the scan area, 3
    black dots, spaced at 2in apart, and a white strip which is as
    wide as the scan area. Scanwizard appears to make scans of this
    area before it does the first scan after starting up and sometimes
    when parameters are changed. There is a photo of the strip and
    dots at http://sm3600.sourceforge.net/calstrip.jpeg .

    I guess the sm3600 backend also needs to use the dots and white
    strip to do some sort of compensation.

    Does anyone have any references that discuss how this is done or
    do any of the other backends have code that does this? Any help
    would be greatly appreciated.

    BTW if you want to try out the backend we have released a patch
    against sane 1.0.4 at our sourceforge project page:
    http://sourceforge.net/projects/sm3600 .

    Thanks
    g 

    -- 
Glenn Ramsey
glenn@componic.com

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