Pixels per foot / Pixels per meter is the most fundamental and valuable, though imperfect, metric for specifying video surveillance image quality.
In a single number, this metric (e.g., 10ppf, 40ppf, 100ppf) conveys important information about what the projected quality that a camera can provide.
The image below, taken from our Camera Calculator, demonstrates examples of common pixel per foot (ppf) levels:
PPF Established Metric
PPF has become a critical established metric for several reasons:
Broad camera manufacturer support: Most major manufacturers use this metric.
Common A&E specifications: Architects and engineers who plan large projects regularly use PPF / PPM as the basis for their designs and surveillance plans.
Need for Something: With so many resolution options today (from 1MP to 12MP and beyond), the old metrics which used percentage of screen covered make no sense. PPF has filled this void.
The Goal of PPF
PPF is a single metric (e.g., 10, 50, 90, etc.) that when specified should deliver a specific level of quality. For example, the parking lot camera must deliver 50 PPF. Instead of guessing or just specifying more resolution, using this metric should enable selection of the ‘right’ resolution for the scene. The final image, following the PPF metric, will then deliver a predictable level of quality.
Alas, PPF suffers from many problems that must be factored in:
- Assumes even lighting and ignores the impact of bright sunlight
- Assumes day time lighting and ignores the impact of night time / low light viewing
- Disregards differences in lenses and compression
- Disregards that image quality needs are subjective and debatable
- Fails to specify related and critical metrics to complement PPF
Despite this, PPF does have value for estimation and planning. It just cannot be used blindly or simplistically. Inside the PRO Member’s section, we explain:
- How to calculate PPF
- How to recognize PPF limitations and make adjustments
- How to best use PPF productively