Today, one of the must powerful tools to the study of a object movement behavior is the “Video Tracking”. In general, video tracking is the process of locating a moving object or multiple objects in a specific boundary over time using a camera. In other words, it associate target object in consecutive videos frames. Exist two way to do a video tracking, in two dimension or in three dimension. The 2-D tracking is a planar tracking that determine a trajectory (x,y) for a time sequences. The 3-D tracking is for rigid objects and determine the trajectory (x,y,z) for a sequences of time. To realize this type of analyse is necessary a algorithm.In summary, exist different type of algorithm that depend of the complexity of the application. One of these algorithms is the “Blop Tracking”, is a complex algorithms based in segmentations of objects and traduce it to a correlation and a optical flows. One of the must important application of this algorithms is in the security of Airports and Traffics. Other important algorithms is the “Kernel-Based” tracking. KB is a algorithms of interactive localization procedure based on the maximization of a similarity measure. Usually is used to track object that have similarity with the boundaries like night mode cameras, Military Projectile tracking “Thermal sensor modes”, and others. Finally, filtering algorithms based in tracking and object filtering or subtracting its boundaries. This is the must simple algorithm but involve high mathematic knowledge to develop behaviors in mathematic correlations. One of the filter algorithms is the particle filter. Particle filter called as “Video Particle Tracking”, is the must used tools in the studies of particle, microorganisms and cells behavior in Nanotechnology, Biotechnology, medicine and materials sciences. The VPT is the observation of a motion for multiple or singles particle within a medium. The motion is translate to a trajectory (x,y) for 2-D and (x,y,z) for 3-D over a series of time. The particle trajectory can be analysed to identify mode of motion or heterogeneous in the motion such as obstacle or region confront in a environment. This trajectory can provide a diffusion coefficient, velocity of the particle, rotational diffusivity, and others characterization of particles. To calculate some of this characterization is require some mathematic correlations and modifications. For example to calculate particle diffusivity is require the mathematic model called “Mean-Square Displacement”.
The MSD equations is writing of the following mode:
MSD = (Xi – Xf)2 + (yi – yf)2 + (zi- zf)2 ,
Where, xi , yi and zi are the initial position of the particle at time tiand xf, yf, zf are the final position of the particle at time tf. Next MSDis plotted in function of time to obtain from slope the diffusivity (Fig.1)
The essential tools to lead an VPT analysis are a high resolution camera (> 14.0 Mpixel), an microscope with a good light intensity, an Objective 40x (This is for particle Large than 500nm) and any VPT software linked in the following list:
- MatLab: http://www.physics.emory.edu/~weeks/idl/
- CISMM: http://cismm.cs.unc.edu/resources/software-manuals/video-spot-tracker-manual/-Excelent
- Able:http://apt.mulabs.com/ – Not Free but cheap
Recommendations to obtain excellent results from VPT:
- The microscope is needed to be in level. This is because any angle in the microscope can produce convective for to the particle.
- The sample to study must be in a capillary cuvette and sealed to avoid convective force caused by air motion, and hydrostatic forces.
- Keep a constant temperature in the suspension because diffusivity is directly proportional to the temperature.
- Keep clean the objectives and camera lenses because can produce fake particle in the video and the software take it like particle.
- Try to avoid noise because vibration produce convective force to the particles.
- Be sure to measure video dimension to later translate pixels to micrometers or nm
- When video are processing try to filter the background from the particle in gray scale imaging. ImageJ have plugging to do this.
Elvin A. Acevedo Gerena