The motion history image (MHI) is a static image template helps in understanding the motion location and path as it progresses.[1] 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:[2]
- 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
- ^ "Research: Motion History Images". Retrieved 13 November 2014.
- ^ Ahad, Md Atiqur Rahman. Motion history images for action recognition and understanding. Springer Science & Business Media, 2012.
