  Particle Image Velocimetry (PIV) is a method to visualize the flows and
quantitatively map the flows. It is used to obtain the instantaneous velocity,
vorticity, divergence, shear in fluids, etc. Laser Doppler velocimetry and hot
wire anemometry are other techniques that are used to measure the flow. The
main difference between PIV and those techniques is that PIV produces
two-dimensional or three-dimensional vector fields. PIV uses two sequences of
images (frames) and the frames are split into a large number of interrogation
windows. The displacement vector is calculated for each window with the help of
auto-correlation or cross-correlation techniques. Missing data during these
processes leads to inaccurate results. To overcome this, preprocessing
techniques such as histogram equalization and intensity clipping are used to
enhance the PIV images to obtain accurate results.
