Let me start by saying that I am by no means trying to imply that DVR, NVR or any other digital or IP based video system cannot produce good quality video evidence. There are even 2 or 3 high-end, mega-pixel quality digital surveillance cameras and systems on the market today whose capabilities far exceed those of a traditional analog based system. However, to my point, it seems more often than not digital based systems are producing very poor quality video evidence regardless of the system's actual capabilities.
So why do DVRs typically provide poor quality video evidence? Here are a few of the common reasons:
- Record Settings:In order to store as much video as possible on the system and to reduce the bandwidth required for transmitting the video, often the following quality settings are less than optimal.
- Image size/Resolution - Digital systems save storage space and reduce transmission bandwidth requirements by reducing the image resolution or size (e.g. 320x240, 352x288, etc...). Analog NTSC video converted to digital using the ITU-R 601 standard produces and image size of 720x486. While some digital systems are capable of recording 720x480, or in a few cases even better, most are not configured to do so, and typically record at less than half the resolution of analog NTSC video.
- Compression - Data compression further reduces the necessary storage space or bandwidth required to transmit digital video. To-date I have yet to encounter a digital video security system that uses lossless compression, which means lossy compression is being used and data (detail) is being discarded. Higher compression ratios lead to a higher percentage of data loss, regardless of the type of codec or compression scheme being utilized. It is also important to note that some systems provide various options for exporting the video evidence that may further compress the image.
- Frame Rate (FPS, IPS) - Frames Per Second or Images Per Second, another characteristic used to reduce storage space and bandwidth; fewer images require less storage space or bandwidth.
- Camera Placement: - Location and field of view become even more critical with digital systems, as poor resolution resulting from any of the above issues makes it even more difficult to identify the people or objects recorded.
- Poor Lighting: - The most common characteristic of poor quality video images. Digital recorders are more susceptable to issues resulting from improper lighting.
While most of these are characteristics of analog based video surveillance systems as well, the vast majority of digital based systems provide a multitude of additional capability largely relying on these settings (e.g. longer recording times, remote viewing, etc...). In other words, in some cases the additional capabilities offered by digital would not be feasible without siginficantly reducing the file size and required bandwidth; and subsequently, the image quality.
You may be thinking "Well, what I see on the system monitor is as good or even better than my previous analog system." This very well may be true, because most DVR recorders use a video "loop through" to display what the camera is actually sending to the system. Unfortunately, that is the quality before it is actually recorded. Pull up a few of your actual recordings, from every camera, under varying conditions. That's the only way to know what the quality of your recording will be when it really matters.
There are certainly a number of other characteristics, as well as system components, that play a role in the quality and quantity of the evidence obtained from a digital video security system.
Proper system design, configuration, and maintenance are imperative to the successful deployment of any video security system, especially digital.
While it is clear that digital video security systems are undoubtedly the future of this multi-billion dollar industry application, those making or considering the transition from analog-to-digital should understand that in-and-of-itself, digital does not equate to better quality.
- View the SWGIT Recommendations and Guidelines for Using Closed-Circuit Television Security Systems in Commercial Institutions (pdf) - click here.
- Watch "An Introduction to Digital Video Evidence" - a brief roll-call training video I produced in 2007 while with Broome County Government, sponsored by LEVA - click here.
In 2010, the FBI released "Caught On Camera", a video directed toward business owners and end users relating to effective CCTV system setup.