If the problem is not listed here, please file an issue at Github.
JPIV stops and throws an out of memory error.
Allow java to use more memory. State
java -jar -Xmx4G JPIV.jar to allow 4 Gigabytes, for example.
The vector plots show steps and patches where I expect as smooth vector field.
Check, whether the images show a strong background. This could be a light reflecting structure. Also images with natural seeding (for example using erythrocytes in blood flow) show this effect. Remove the background by a rolling ball algorithm or as described in the HOWTO section. ImageJ is an excellent tool for preprocessing.