Under-Counting or Over-Counting
Video Turnstile is a conservative system and tends to under-count rather than over-count. During validation, if you find the system is under-counting then...
- Consider increasing the sensitivity of the people detection by adjusting the camera height. Do this first before trying any other fixes as this controls the size of a typical person in the picture. Between 2 and 3 metres above the floor, the area of screen taken up by a 1.8 m tall person changes considerably. A person viewed in a camera 2 metres above the floor will appear around 3 times as large as when the camera is 3 metres above the floor.
- If two people walking side-by-side are being counted as one, adjust the minimum gap between people.
- If small people are not being counted, decrease the minimum width that is detected as a person.
- If large people are not being counted, increase the Typical Area or Typical Width.
- If crowds of people are not being counted correctly, adjust the TimeoutRestore, Double Probability, BlobMidSplit and Diagonal Splitting settings.
- If a person pushing a pram, for example, is being counted as two people, adjust the TimeoutRestore setting.
- If people are leaving the counting zone without being counted, adjust the turn left and right settings, or whether the person is going up or down screen.
- If a person stays inside the zone and is therefore not counted, lengthen the freeze time.
- If you find poor counting from dark to light areas or delayed count registration from light to dark, reduce Threshold_limit by 4 (do not decrease by more than 1 step because it will become more sensitive to artefacts). You may now need to compensate for wider perceived width of a person.
- If you have checked the counting accuracy and tried the preceding steps and the count remains inaccurate, you can scale the count up or down. Go to the Channels tab and enter an appropriate scale factor. If it consistently misses 5% of people for example, you can compensate for this by entering a scale factor of 1.05 (to the nearest 2 decimal places).
Manual ref: VT-2.04, June 2007 |