Optical flowOptical flow or Optic flow is thesequence of visible motion of object in a displayed scene which is theresultant of relative motion in between observer and scene. Optical flowreflects the changes occurred in an image when objects of the given imagemoves, obviously it is inconvenient to say the objects in an image are moving,it will be the video with a constant environmental background and we are goingto consider it as a picture. Optical flow is the building block for somerobotics where we need navigation as well as motion detection.
There arevariety of motion which can be study with the help of Optical Flow e.g. movingobserver and static objects, static observer and moving objects, both moving.Optical flow is therepresentation of motion of an image or specifically the objects of the imagein term of motion vector. To draw the motion vector, we will analyses our imageat different time suppose at t1 and t2 we can then draw the estimation for thenext sequence of motion in term of Motion vectors.
There are number of methods toestimate the optical flow based on partial derivatives of the images i.e. loweror/and higher-order partial derivatives, such as:a. Lucas–Kanade method – regarding imagepatches and an affine model for the flow field.b. Horn–Schunck method – optimizing afunctional based on residuals from the brightness constancy constraint, and a regularizationterm expressing the expected smoothness of the flow field.c.
Buxton–Buxton method –based on a model of the motion of edges in image sequences.d. Black–Jepson method – coarse optical flowvia correlation.e.
General variational methods – a range ofmodifications/extensions of Horn–Schunck, using other data terms and othersmoothness terms. There is another term related toOptical flow which is optical flow field, it is the velocity field that representsthe 3-D motion of object points across a 2-D image. There are some restrictions forthe optical flow as well which are:· It shouldn’t be sensitive to illumination changesand motion of unimportant objects like shadow.· non-zero optical flow is detected if a fixedsphere is illuminated by a moving source.
· smooth sphere rotating under constantillumination provides no optical flow.There are some assumptions tomade while estimating the optical flow1) Thebrightness of the object is constant over time.2) Weknow that every image has some coordinates so we assume that the nearby planeof the image moves the same way as the image does, this is called velocitysmoothness constraint.