Threshold selection for after-processing filters

Threshold selection for after-processing filters

Hi,

I am working with Prophesee event camera and using the following SDK filters in a post-processing pipeline:
  1. ActivityNoiseFilterAlgorithm
  2. SpatioTemporalContrastAlgorithm (STC)
  3. TrailFilterAlgorithm

I used the configuration with trail cutting disabled (cut_trail = False).

I tested a range of thresholds for each filter and noticed that they behave very differently across scenes with different lighting conditions.

For reference, reduction (%) refers to the percentage decrease in the number of events after filtering.

For example (see picture attached):
  1. In a high-light scene (scene 1), thresholds in the range 2000–20000 µs were tested. The Activity filter reduces events by about 13% at 2000 µs, and higher thresholds give similar reductions. In contrast, in a normal-light scene (scene 2), the same threshold (2000 µs) results in more than 80% reduction, and about 64% reduction at 20000 µs.
  2. With STC, in scene 1, the reduction varies from 88% to 37% for thresholds between 2000–20000 µs, respectively. In scene 2, however, the reduction remains high regardless of the threshold; for example, it is around 70% even at 200000 µs.
The camera is using default settings, focus has been checked, and no sensor-level preprocessing filters were used. The main difference between scenes is lighting.

This makes it difficult to select consistent threshold values across different environments, since the same filter can either have little effect or remove a large portion of the data, depending on the environment.

I wanted to ask:
  1. Are there recommended threshold ranges for these filters when used in post-processing?
  2. Is there an existing adaptive way to set these thresholds based on event statistics or scene conditions?
  3. Are there other filtering approaches you would recommend for handling varying lighting conditions?

Thanks in advance.

Regards,
Dalia
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