Introducing Effective PPF (ePPF) - Improving Video Surveillance Designs

Author: IPVM Team, Published on Jun 11, 2018

Pixel density (PPF / PPM) is the best metric the industry has to define and project video quality. It allows simple communication of estimated quality across various resolutions (from VGA to 20MP+), AoVs (telephoto to panoramic) and FoV widths (from narrow entries to large outdoor areas).

It is not perfect.

Problems With Pixel Density PPF / PPM

The key limitation for pixel density is that pixels only determine potential, actual performance can vary. The most common practical reasons why performance varies are:

  • Low light / dark: Image quality tends to decrease as light diminishes so a 60ppf image in the day may deliver clear facial details in the day but not in the dark.
  • Wide dynamic range: Image quality in WDR scenes is directly impacted by camera performance, as both strong backlight and dark areas of the scene can drastically reduce details.
  • Wide Angle Lenses: Details at the edge of a camera's FOV are often frequently reduced due to distortion or reduced lens clarity compared to the center of the scene.

Introducing ePPF - Effective PPF

What pixel density defines is the physical pixels per foot (PPF) or pixels per meter (PPM). Because of lighting and lensing issues, this is often more than the effective PPF or PPM delivered. A loss occurs between the physical pixels per foot and the effective pixels per foot captured on video.

We overview this in the animation below:

ePPF Subjective But Real

Determining the exact effective PPF is clearly subjective since people can reasonably disagree about 'effective' image quality. However, the fact that image quality is degraded, in effect, in practice, relative to the physical count is clear.

Get Video Surveillance News In Your Inbox
Get Video Surveillance News In Your Inbox

Demonstrations - Low Light

For many users, low light scenes have the most frequent impact on ePPF. For example, looking at images from a common low cost integrated IR bullet, effective PPF drops to ~20 in a 50 pPPF scene, shown below, with identifying subject details significantly reduced.

50 low cost integrated ir

Even in a high performing integrated IR camera, ePPF is frequently greatly reduced, shown below:

60 high end integrated ir

However, ePPF losses seen in integrated IR are generally better than those in super low light models. For example, the 1/3" super low light model shown below loses ~80% ePPF, effectively only ~15 PPF at night.

80 1-3 super low light

Larger imager models fare moderately better, but performance is still reduced by ~66% in this 1/2" model, a high performing example.

60 1-2 super low light

And, even in 35mm super large imager low light models, losses are great, with a drastic drop from ~150 ePPF to 20 in very low light (~0.08lx).

170 35mm super low light

IR Coverage Impact

In addition to IR power, the evenness of illumination impacts ePPF, as well. For example, while the center of the field of view is well illuminated, with a ~10 ePPF drop, dark edges caused by uneven IR coverage result in a huge drop, from ~50 ePPF during the day to only 10 at night.

Even in cameras with "even" IR illumination, details are reduced significantly, with the camera below dropping to ~20 ePPF at night, a 66% reduction compared to daytime images.

Demonstrations - WDR

While low light issues may be most common, other lighting variances may have as much ore more of an effect. For example, ePPF in a camera with digital WDR only is reduced by ~30% against strong backlight, but produces no usable image at all in dark areas where the camera cannot compensate.

90 wdr entrance scene

However, high end true WDR models maintain much better ePPF, shown below, with clear details of the subject in both bright and dark areas:

110 high end true wdr

Demonstrations - Lens Distortion

Finally, even in well lit scenes, other factors may impact ePPF. Most notably, with wide angle lenses now increasingly common, lens distortion at the edges of the field of view.

For example, in a high end model with a ~100° angle of view, ePPF is slightly reduced (~12%) at the edge of the field of view compared to the center.

80 high end wide angle 100

However, in a low cost model, ePPF drops drastically (~70%), from 50 to ~15 at the edge of the lens' view.

Questions / Comments / Feedback?

Let us know below what questions, comments and feedback you have for this as we will incorporate this further into our courses and training.

Comments (19) : PRO Members only. Login. or Join.

Related Reports

Backboxes for Video Surveillance Tutorial on Aug 15, 2018
Backboxes are a necessity in surveillance, whether for managing cable whips, recessing cameras, adding wireless radios. But it can be confusing to...
Uniview Intrusion Analytics and VMD Tested on Aug 13, 2018
IPVM's IP Camera Analytics Shootout featuring Avigilon, Axis, Bosch, Dahua, Hanwha, Hikvision created some ill will with a Uniview distributor who...
Camera Focusing Tutorial on Aug 09, 2018
A camera's focus is fundamental to quality imaging. Mistakes can cause important problems. In this guide, we explain focus issues and proper...
Hikvision PanoVu Mini Tested (Multi-imager + PTZ For ~$500) on Aug 07, 2018
Hikvision has released their first PanoVu Mini multi imager, the PanoVu DS-2PT3326IZ-DE3, with four 1080p imagers, including a PTZ and integrated...
Panasonic 9MP Panoramic Fisheye Tested (WV-X4571L) on Aug 02, 2018
Panasonic has released their latest fisheye camera, the WV-X4571L, with 12MP sensor and 9MP resolution, claiming "extreme image quality" under...
Installing Surveillance Cameras Into Synthetic Stucco (EIFS) Tutorial on Jul 30, 2018
Mounting cameras into synthetic stucco, commonly known as EIFS finishes, can be problematic If not properly planned, EIFS/stucco can be downright...
IP Camera Analytics Shootout - Avigilon, Axis, Bosch, Dahua, Hanwha, Hikvision, Uniview on Jul 30, 2018
Video analytics are hot again. But whose analytics really work? IPVM bought and tested Avigilon, Axis, Bosch, Dahua, Hanwha and Hikvision cameras,...
Uniview Super Low Cost 4MP Tested on Jul 25, 2018
Even lower cost than Dahua and Hikvision, China's self-proclaimed 3rd place company, Uniview / UNV, is offering aggressive pricing including for...
Door Swing Tutorial on Jul 24, 2018
The direction a door swings might seem minor, but it can greatly impact door hardware selection. There are four basic ways a door can swing, and...
Avigilon "Self-Learning" Analytics And VMD Tested on Jul 23, 2018
Avigilon is a popular choice for video analytics, offering "self-learning" analytics built into their cameras as well as appliances. We tested...

Most Recent Industry Reports

Backup Power For Maglocks Guide on Aug 20, 2018
When the main power fails, many believe maglocks must leave doors unlocked. However, battery backed up maglocks are allowed according to IBC /...
Axis Strong Q2 2018 Results on Aug 20, 2018
Axis reported strong Q2 2018 financial results and, for the first time in many years, Axis grew faster than Hikvision. However, the company's...
2Gig Gun Lock / Motion Detector Tested on Aug 17, 2018
Safer guns for families and an opportunity for security dealers to sell more services? That is the aim of Nortek's 2GIG 'Gun Motion Detector'...
Video Analytics Integration Guide on Aug 16, 2018
Video analytics is hot again (at least conceptually) but integrating video analytics with VMSes can be challenging. This is especially significant...
Hikvision IP Camera Critical Vulnerability 2018 Disclosed on Aug 16, 2018
The same day that the US government passed a prohibition on Hikvision cameras, Hikvision disclosed a critical vulnerability for its IP...
ISS VMS / Video Analytics Company Profile on Aug 16, 2018
Who is ISS? In the past few months, they had one of the craziest ISC West promo items in years. Then, they hired industry veteran and ex-Dahua...
Chinese OEM Avycon Gets ADI Push on Aug 15, 2018
Who is Avycon? An American company? A Korean company? A couple of guys relabelling Chinese products? The latter is the best explanation. While...
Backboxes for Video Surveillance Tutorial on Aug 15, 2018
Backboxes are a necessity in surveillance, whether for managing cable whips, recessing cameras, adding wireless radios. But it can be confusing to...
Genetec Stratocast / Comcast 'Motion Insights' Examined on Aug 15, 2018
Comcast recently announced "SmartOffice Motion Insights", an extension to their Genetec OEMed cloud video service (covered by IPVM here). This...

The world's leading video surveillance information source, IPVM provides the best reporting, testing and training for 10,000+ members globally. Dedicated to independent and objective information, we uniquely refuse any and all advertisements, sponsorship and consulting from manufacturers.

About | FAQ | Contact