Pixel Density in CCTV
Pixel density (PPM) determines image quality and whether you can identify faces, read plates, or just detect motion. Learn the critical metric.
What is Pixel Density?
Pixel density, measured in pixels per meter (PPM), describes how many pixels of video resolution you have for each meter of distance from the camera. Higher PPM equals more detail.
PPM is calculated as: PPM = Horizontal Pixels / FOV Width at distance (in meters)
Pixel density is more useful than raw resolution because it accounts for distance. A 4MP camera at 30 meters has lower effective PPM than a 2MP camera at 5 meters.
Pixel Density and DORI Levels
The DORI standard (Detection, Observation, Recognition, Identification) is based on pixel density. Each level requires specific PPM:
| DORI Level | Min PPM | Description |
|---|---|---|
| Detection | 25+ PPM | See that something is present |
| Observation | 62.5+ PPM | Determine type, color, direction |
| Recognition | 125+ PPM | Identify known individuals |
| Identification | 250+ PPM | Identify strangers, read plates |
How to Calculate Pixel Density
The formula accounts for both camera resolution and viewing distance:
PPM = Horizontal Pixels / FOV Width at distance
Example: 4MP camera (2560 × 1440) with 80° FOV at 10 meters
FOV width = 2 × 10 × tan(40°) = 16.8m
PPM = 2560 / 16.8 ≈ 152 PPM
This 4MP camera meets the Recognition standard (125+ PPM) at 10 meters distance with an 80° lens.
Practical Examples
Retail Entrance — 5m, 90° lens
Need Recognition level (125+ PPM). FOV width = 2 × 5 × tan(45°) = 10m. A 2MP camera (1920px): 1920 / 10 = 192 PPM (sufficient). A 4MP camera (2560px): 256 PPM (excellent).
Parking Lot — 30m, 80° lens
Need Identification level (250+ PPM) for license plates. FOV width = 2 × 30 × tan(40°) = 50.3m. A 2MP camera (1920px): 38 PPM. A 4MP (2560px): 51 PPM. An 8MP (3840px): 76 PPM. Solution: use a narrower lens (e.g., 30°) to reduce FOV width to 16.1m, giving 8MP: 238 PPM.
Warehouse Aisle — 15m, 80° lens
Need Observation level (62.5+ PPM). FOV width = 2 × 15 × tan(40°) = 25.2m. A 2MP camera (1920px): 1920 / 25.2 = 76 PPM (sufficient). A 4MP camera (2560px): 102 PPM (comfortable margin).