Title: A New Tracking Algorithm for Multiple Colloidal Particles Close to Contact,
Abstract: In this paper, we propose a new algorithm based on radial symmetry center
method to track colloidal particles close to contact, where the optical images
of the particles start to overlap in digital video microscopy. This overlapping
effect is important to observe the pair interaction potential in colloidal
studies and it appears as additional interaction in the measurement of the
interaction with conventional tracking analysis. The proposed algorithm in this
work is simple, fast and applicable for not only two particles but also three
and more particles without any modification. The algorithm uses gradient
vectors of the particle intensity distribution, which allows us to use a part
of the symmetric intensity distribution in the calculation of the actual
particle position. In this study, simulations are performed to see the
performance of the proposed algorithm for two and three particles, where the
simulation images are generated by using fitted curve to experimental particle
image for different sized particles. As a result, the algorithm yields the
maximum error smaller than 2 nm for 5.53 {\mu}m silica particles in contact
condition.