motion-detection biomedical-image-processing piecewise-polynomial spline-curves fluorescent-speckle-microscopy automated-kymograph time-lapse-image-sequence visualize-motion-of-fluoresecnt-speckles represent-dynamic-processes-on-one-image greyscale-image-gradient kymograph-slope-represents-speed visualize-biological-processes display-intensity-over-time 2d-representation-position-vs-time curve-trajectory-tracing molecular-cargo-motion-analysis low-signal-to-noise-ratio interpolating-curved-tracks spline-curve-mathematically-interpolated cubic-spline-data-interpolation