JPIV is a software package for Particle Image Velocimetry (PIV). The program is open source, platform independent, and available under the terms of the GNU General Public Licence.
JPIV is useful for:

A screenshot of the JPIV user interface. You can click it, to launch JPIV directly via Java Web Start.
The crutial advantage of JPIV over most commercial PIV packages is, that you have full access to a well documented source code. You can easily insert a few lines of code to extract some intermediate data for your studies, alter a few lines to test a new correlation or filtering approach, add a new class for a unique visualization, and so forth.
I used JPIV in the scope of my thesis about micro-scale blood flow measurements.
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