3091 backend: Brightness, Contrast etc.

From: Frederik Ramm (frederik@remote.org)
Date: Wed Mar 07 2001 - 13:18:05 PST

  • Next message: Gabriele Conrad: "Acer 300F"

    Hi,

       the scanner I'm writing a backend for does not support the setting
    of the usual image-altering values like contrast, brightness, gamme
    correction etc.

    Instead, you can load a so-called "LUT" translation table into the
    scanner. It's basically a mapping that assigns an output value to
    every possible input value. I.e. if I wanted a much brighter image, I
    would just download a table that maps

    0 -> 50
    1 -> 51
    ...
    204 -> 255
    205 -> 255
    206 -> 255
    ...
    255 -> 255

    or something similar. Since I don't have more than 8 bits on the input
    side, I cannot have the scanner do any translations that could not
    also be done afterwards (in fact, I could do in within the backend if
    I wanted to).

    So, should I bother to "emulate" a brightness/contrast/gamma setting
    using these LUT tables? And if I should, can anyone point me to useful
    formulas that generate such translation tables for certain values of
    contrast, brightness etc.?

    What's more, my scanner supports a few settings with funny names I
    cannot make sense of. Maybe somebody knows what they are, or what they
    might be. It would be interesting for me if it is worthwile to make
    them available through the backend.

    * Initial Slice: Specifies the initial binary threshold value when in
      floating slice mode.
    * Up value: Specifies the +UP count value used in floating slice mode.
      (Valid settings: 0-3, default: 1)
    * Down value: ... as above
    * Lower Limit Slice: Specifies the lower limit slice used in floating
      slice mode (0-15, default: 6)
    * Compensation line Interval: Specifies the compensation line interval
      slice when in floating slice mode (0-15, default 0)
    * Error dispersion upper limit slice (0-255, default 230)
    * Error dispersion lower limit slice (0-255, default 20)
    * Laplacian coefficient for enhancement mode: 0 (weak), 1, 2 or 3
      (strong)
    * Gradient coefficient for enhancement mode: as above
    * Laplacian slice: Specifies which Laplacian slice is to be used for the
      enhancement mode (0-15)
    * Gradient slice: as above for Gradient slice
    * Primary Scan Ratio Compensation: on or off.

    If anyone has the slightest idea...

    Thanks
    Frederik 

    -- 
Frederik Ramm  ##  eMail frederik@remote.org  ##  N57°48.10' W005°40.32'

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