gamma correction on hp 4200c

From: Boris Krivulin (boris@coalescent.net)
Date: Mon Jan 22 2001 - 23:45:05 PST

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    Hello,

    I have an HP-4200C usb scanner, connected to a PC running linux; a
    no-name video card, and a no-name monitor. The images that I scan are
    too dark. Users of hp4200c driver -- how do you scan your photos ?

    The options for this scanner do not include the brightness
    option, though there are --gamma-table options (separate for red, green,
    and blue).

    I could not figure out what table should I specify to fix my
    pictures. So I used ImageMagick's "mogrify -gamma 2.2" to lighten up the
    images. Nevertheless, the images turn out slightly different from the
    originals.

    Well, I knew how to use mogrify because it only wants a single value, namely
    the gamma correction ^ratio^. How would I do the same with a gamma ^table^,
    and would I get better results anyway ?

    Thank you,
    Boris

    P.S. Scanning often hangs my machine, particularly if I press Ctrl-C
    during a scan, and then try to scan again. I guess that the lamp is not
    returned into a proper place. Has anyone had this ?

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