The Definitive Guide to PPFby John Honovich, IPVM posted on Nov 05, 2012 About John Contact John
The most advanced yet most dangerous way to specify surveillance is pixels per foot (PPF, aka pixels per meter, PPM or pixel density). As much as it can help, it can make matters far worse, leading to overconfidence and poor performance.
PPF Established Metric
Yet PPF has become a critical established metric in the surveillance industry:
- Broad camera manufacturer support: Most of the major vendors advocate the use of this metric.
- Common A&E specifications: Architects and engineers who plan large projects regularly use PPF as the basis for their designs and surveillance plans.
- Need for Something: With so many resolution options today, the old metrics for 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 50ppf. 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 are nearly never addressed:
- 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
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