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Gamma Values for LCD modules

Discussion in 'Electronic Design' started by [email protected], Sep 8, 2006.

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  1. Guest

    Hi folks,

    How do I calculate the gamma values for LCD module? I am trying to
    design a LCD driver board.

    Cheers
    P
     
  2. Guest

    What LCD module? A started point is from the LCD spec. Look for
    things relate to the LCD illumination charactistic then figure out the
    equation... If it's linear then you don't need the gamma correction,
    unless your board is designed for optical clinic

    cheers,
     
  3. Guest

    Hi,

    I am currently looking at the AUO M190EG01V0. Would this be the
    luminance uniformity which is 75 to 80%? The board would also be
    designed for smaller modules.

    For a FPGA point of view, I guess the functional blocks are as follow;

    Analog RGB-> YUV->gamma correction->Hue, saturation, contrast->Digital
    RGB (8 bits per color for a 24 bit screen)->LVDS output

    For the smaller module would I have to scale it down to 6 bits per
    color by rounding the RGB values from 8 bits to 6 bits?? Would tha
    affect the gamma correction??

    Cheers
    P
     
  4. Guest

    I guess that would affect the gamma calculation as it will be dependent
    on the LCD characteristics.

    I guess the equation used will be

    value_new = pow (value, 1.0 / factor)

    where factor will be the gamma value. For the LUT, I will have to
    calculate for the 0-255 that is assumming the gamma value is applicable
    to red, green and blue instead of separate gamma values for each
    colour. The previous design flow would have been wrong as I can't apply
    the gamma to the YUV, I would need to convert the YUV to RGB and then
    apply the gamma correction using the LUT.

    Sorry, I am new to this subject.

    A question on the AUO LCD module, from the datasheet I don't seem to be
    able to find the gamma value for the monitor. What will be the name
    within the datasheet?

    The url for the datasheet is
    www.bluecubelcd.com/php/content/panels/pdf/19/M190EG01V0.pdf

    For the gm2221 chipset, the adaptive color and contrast seem to be
    applied to the YUV values. aitendo.sakura.ne.jp/download/gm2221.pdf

    I guess I can always use this chipset instead of the FPGA options but
    if I were to scale it down below 18 bit RGB, I will have to round it
    down to required RGB and change the bit order for the LVDS
    transmission.

    Cheers
    P
     
  5. Guest

    Assume your factor > 1 and your value is normalized to range [0, 1],
    then I would like to call the above equation "pre-gamma". This
    equation is used to compensate the non-linear illumination
    characteristic of CRT tubes, it has more the gain in dark area. If
    plot the equation, the curve's slope decreasing in x-> direction

    If your display device is linear AND the input video has "pre-gamma" in
    it then you need an invert function, let call it de-gamma:

    value_n =pow(value, factor), where value in range of [0,1]. This plot
    has the slope increasing in x-> direction

    IMO, if having room in desing then add a LUT for each color, they give
    you a whole flexibility.

    It doesn't matter when you round from 8 to 6 bit, keep in mind that
    the equations apply for normalized signal: value is in range of [0, 1]

    cheer,
     
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