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  1. #1
    Join Date
    Nov 2005
    Location
    San Francisco, CA
    Posts
    506

    Red face Unanswered: what's the way to compare two images?

    HI,
    Can anybody tell me how to compare images?
    I think there is an algorithm for it.Please tell me if anybody knows somethign about this subject?
    I want to know the mechanism to compare an image with the images kept in the database.Just like the criminal tracking system..
    Thanks!!
    Joydeep

  2. #2
    Join Date
    Jun 2004
    Location
    Arizona, USA
    Posts
    1,848
    The short, simple answer is to load two images into memory, then compare each pixel in the two images to each other. Keep a running total of the number of differences, and a sum total ff the deltas. (probably a square-root of the sum of squares delta for R, G, and B)

    After the images are compared, use the above to determine of you have a "match"

    However, there are some chalenges that you'll need to address.

    to name one,
    Scale of the images. How do you handle it of one image is of a different size than another? What if you take an image, crop it, then strech it so that it's again the same size? What if one image is rotated a bit?

    to name another, brightness/contrast of images. You'll need to adjust the images so as to get an approximate duplicate of a brightness histogram.
    Lou
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