Harman Patil (Editor)

Motion History Images

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The motion history image (MHI) is a static image template helps in understanding the motion location and path as it progresses. In MHI, the temporal motion information is collapsed into a single image template where intensity is a function of recency of motion. Thus, the MHI pixel intensity is a function of the motion history at that location, where brighter values correspond to a more recent motion. Using MHI, moving parts of a video sequence can be engraved with a single image, from where one can predict the motion flow as well as the moving parts of the video action.

Some important features of the MHI representation are:

  • It represents motion sequence in a compact manner. In this case, the silhouette sequence is condensed into a grayscale image, where dominant motion information is preserved.
  • MHI can be created and implemented in low illumination conditions where the structure cannot be easily detected otherwise.
  • The MHI representation is not so sensitive to silhouette noises, holes, shadows, and missing parts.
  • The gray-scale MHI is sensitive to the direction of motion because it can demonstrate the flow direction of the motion.
  • It keeps a history of temporal changes at each pixel location, which then decays over time.
  • The MHI expresses the motion flow or sequence by using the intensity of every pixel in a temporal manner.

    • General Algorithm

    for each time t Bt := absolute_difference(It, It-1) > threshold end for for each time t for each pixel (x,y) if Bt(x,y) = 1 MHIt(x,y) := τ else if MHIt-1 ≠ 0 MHIt(x,y) := MHIt-1(x,y) - 1 else MHIt(x,y) := 0 end if end for

    References

    Motion History Images Wikipedia
    (Text) CC BY-SA