If you can use APP2 without memory issue, you don't have to use Ultratracer, which is to boost base tracers including APP2 for large-scale image tracing.

There are three parameters you can try to adjust:
1. auto-downsample: uncheck to use full resolution image for tracing.
2. background_threshold: lower the threshold if the signal is too week.
3. length_thresh: i mentioned it before.

Zhi