White balance correction

Discussion in 'Digital Photography' started by ahs, Jan 30, 2007.

  1. ahs

    ahs Guest

    Hi all,

    I have hundreds of photos of fairly similar scenes (ice and
    snowcovered ice), which I'm going to classify into different regions
    automatically. The photoes were taken with a canon eos300D with auto
    white balance. Using the camera with auto white balance was a big
    mistake, and now
    my photos varies from bluish to very bright.

    Does anyone know how the auto white balance works on the eos300D?

    The images were taken under fairly the same ligth conditions (cloudy).
    Can you suggest a "smart" methode I can employ, to revert the auto
    white balance setting, i.e. to make all my images look as they would
    if I had used some custom white balance setting instead.

    ahs, Jan 30, 2007
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  2. ahs

    Harris Guest

    Usually, digital cameras employ simple and fast histogram-based methods for normalization or
    equalization (CDF), in order to avoid unbalanced over- and under-exposed areas of the image.
    Unfortunately, normalized/equalized images do not contain any inherent information about the real
    exposure conditions (so that they be "reverted" afterwards). However, you can process the complete
    set of images, calculate some limits and mean values (RBG) of the histogram of all the images and
    then "normalize" them in the same way, so that all of them look roughly the same. That is, if the
    objects, background and exposure conditions are similar (i.e. not mix daylight photos with night shots).
    In any case, I would not depend much on this approach if you plan to do some analytical (algorithmic)
    image analysis on them.
    Harris, Jan 30, 2007
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