Reducing false positives
Tune your object filters to adjust false positives: min_area, max_area, min_ratio, max_ratio, min_score, threshold.
The min_area and max_area values are compared against the area (number of pixels) from a given detected object. If the area is outside this range, the object will be ignored as a false positive. This allows objects that must be too small or too large to be ignored.
Similarly, the min_ratio and max_ratio values are compared against a given detected object's width/height ratio (in pixels). If the ratio is outside this range, the object will be ignored as a false positive. This allows objects that are proportionally too short-and-wide (higher ratio) or too tall-and-narrow (smaller ratio) to be ignored.
For object filters in your configuration, any single detection below min_score will be ignored as a false positive. threshold is based on the median of the history of scores (padded to 3 values) for a tracked object. Consider the following frames when min_score is set to 0.6 and threshold is set to 0.85:
| Frame | Current Score | Score History | Computed Score | Detected Object |
|---|---|---|---|---|
| 1 | 0.7 | 0.0, 0, 0.7 | 0.0 | No |
| 2 | 0.55 | 0.0, 0.7, 0.0 | 0.0 | No |
| 3 | 0.85 | 0.7, 0.0, 0.85 | 0.7 | No |
| 4 | 0.90 | 0.7, 0.85, 0.95, 0.90 | 0.875 | Yes |
| 5 | 0.88 | 0.7, 0.85, 0.95, 0.90, 0.88 | 0.88 | Yes |
| 6 | 0.95 | 0.7, 0.85, 0.95, 0.90, 0.88, 0.95 | 0.89 | Yes |
In frame 2, the score is below the min_score value, so frigate ignores it and it becomes a 0.0. The computed score is the median of the score history (padding to at least 3 values), and only when that computed score crosses the threshold is the object marked as a true positive. That happens in frame 4 in the example.