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On the left you can see the "Video Spot Tracker" at work. The program is tracking a trajectory of Navicula sp. In this time-lapse, playback is performed at double speed.
(Navicula sp. was isolated by Mr. Oliver Skibbe and provided in form of a pure culture) |
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| I like to thank Computer Integrated Systems for Microscopy and Manipulation (CISMM) at UNC Chapel Hill, supported by the NIH NIBIB (NIH 5-P41-RR02170) for free of charge use of Video Spot Tracker. | |
Motion Tracking of Diatoms
The visual tracking of movements gives only a rough impression of the pathways of the diatoms, especially when they are moving slowly. Some movements can only be recognized in time lapse.
It is helpful to combine the frames of a video recording or a picture sequence into one picture. If the diatoms are darker than their surroundings, one can achieve this by calculating the minimum. If they are brighter than their surroundings (dark field) the maximum is calculated. This can be done very easily and fast using the CISMM Video Optimizer. Information about the dynamics of the movement is thereby lost.
The possibility to get an impression of the sequences by using the filter "motion blur" in VirtualDub has already been pointed out. This is visually appealing but has hardly practical benefits.
Motion tracking of Diatoms helps in tracking the movement on the basis of a video recording or a sequence of images. This is not primarily about the visualization of the trajectory but a quantitative determination of the position information, which allows numerical analysis.
For motion tracking the Video Spot Tracker was used. It provides circular and rectangular trackers (called rod).
If circular trackers do not adhere stably to the apices of the diatoms, even if the parameters are favorable, the change to a rectangular tracker often helps. For Navicula and others, it has proven useful to record videos in the phase contrast, because here the diatoms get a highlighted apex. The Video Spot Tracker displays the traces of the trackers in the video and saves the recorded coordinates to each frame in a csv file (comma-separated values). This can be imported and analyzed, for example, in MS Excel.
For a rectangular tracker, only the trace of its center is displayed (see picture on the left). However, because the orientation of the tracker is also outputed, the coordinates of the apices can also be determined by knowing the length of the diatom. The analysis can then be carried out in the same way.