Optical flow-based representation for video action detection - Emerging Trends in Image Processing, Computer Vision, and Pattern Recognition - page 276

(5)
(6)
(7)
(8)
Now, the problem converges to the solution of . The solution will be the estimation of
optical flow. As there are two unknowns in the equation, it cannot be solved; additional con-
straints and approaches are needed for solution. This problem is known as aperture problem .
4.2 Algorithms
Many algorithms according to different approaches have been proposed for optical flow es-
timation. According to Barron et al. [ 25 ] , optical flow estimation algorithms can be grouped
according to the theoretical approach while interpreting optical flow. These are differential tech-
niques, region-based matching, energy-based methods and phase-based techniques .
4.2.1 Differential Techniques
Differential techniques utilize a kind of velocity estimation from spatial and temporal deriv-
atives of image intensity [ 25 ] . They are based on the theoretical approach proposed by Horn
and Schunck [ 26 ] . The proposed approach results in Equation (3) . Differential techniques are
used for solving the problem generally represented by this equation. Horn-Shunck method
[ 26 ] is a fundamental method among the differential techniques. Global smoothness concept is
also used in the approach. Lucas-Kanade method [ 27 ] is also an essential method solving the