The best metric for defining and projecting video quality is pixel density (PPF / PPM). As a result, it is easy to communicate estimated quality across many resolutions from VGA to 20MP+, AoV and FoV widths.
Common Problems With Pixel Density
Pixel density has one major limitation: pixels determine potential only, not actual performance. Three common problems:
- Low light / dark: As light diminishes, image quality diminishes, so a 60ppf image during the day might provide clear facial details, but not at night.
- Wide dynamic range: Camera performance directly impacts the quality of images in WDR scenes, as both light backlights and dark areas can diminish detail.
- Wide Angle Lenses: When comparing the center of a scene to the edges of the FOV, a wide angle lens will often produce blurred details.
Effective PPF or ePPF
The pixel density is determined by how many pixels are per foot (PPF) or per meter (PPM). The actual PPF or PPM may differ from the effective PPF or PPM delivered due to issues with lighting or lensing. As a result, video captures effective pixels per foot differently than physical pixels per foot.
People can reasonably disagree about the definition of ‘effective’ image quality, so determining the effective PPF is clearly subjective. In practice, however, it is evident that image quality is degraded relative to physical count.
Common Problems
In many cases, scenes with low light have the largest impact on ePPF. Analyzing images taken with a common integrated IR bullet, it shows that the effective PPF drops to 20 in a 50 pPPF scene, with little detail distinguishable.
It is common for ePPF to be reduced even in high-performance integrated IR cameras. However, these models typically experience less ePPF loss than super low light models.
Effective PPF is also affected by illumination evenness, in addition to IR power. Dark edges caused by uneven IR coverage, such as those at the edge of the field of view, result in a substantial drop in illumination, from ~50 ePPF during the day to only 10 at night. The amount of detail is significantly reduced even in cameras that have “even” IR illumination.
Low light issues are certainly common, but other lighting variations may also have a significant impact. Using a camera with digital WDR only as an example, ePPF is reduced by 30% against strong backlight. However, the camera cannot compensate for dark areas where it cannot produce useful images. Additionally, ePPF may be affected by other factors even in well-lit scenes. The distortion at the edges of the field of view is more noticeable with wide angle lenses, which are now increasingly common.
If you are looking to update security features for your business, like Pixels Per Foot let RC Security help. Our continued research and partnerships with premium brands allow us to offer better quality every time.
About RC Security Consulting
RC Security Consulting protects the heart of Texas with design, installation, retrofit, repair, inspection, and monitoring of commercial security systems. We are centrally located in Collin County and provide service for almost 200 miles in all directions. Connect with us on LinkedIn to learn more.
