Welcome to the second installment of Security Sales & Integration’s four-part series — “Networked Video for D.U.M.I.E.S.”

Brought to you by Pelco, this series has been designed to help educate readers on the fast and ever-changing world of video surveillance — specifically networked video systems — as found in the electronic security industry. “D.U.M.I.E.S.” stands for dealers, users, managers, installers, engineers and salespeople.

In Part 1 (see “Essentials of Networked Cameras and Lenses” in the April issue), we discussed how camera sensitivity and specifications could affect the outcome of a well-designed video networked system. The concepts covered included camera low-light sensitivity, automatic gain circuitry and signal- to-noise ratios.

In this installment, we will cover the hot subject of video over IP. Specifically, we will investigate the new and improved features manufacturers have incorporated into their cameras in order to help facilitate the integration of cameras and lenses into the world of video networking.

Bit-Rate Is Key to Controlling Traffic

Before we can consider the function of different options or camera features, let’s try to explain the reasoning for all the changes. It is simple really; it is all about system bandwidth and storage.

Bit-rate is defined as how much physical space an image occupies in one second on a network. The higher the bit-rate, the more space is required.

The bit-rate plays a very important role when dealing with networks that can have a limited amount of space available for the transmission of video. Things like adding more cameras, increasing movement in the video scenes and additional remote view locations are among the factors that can affect the bit-rate and choke a network.

The bit-rate number is also governed by the compression method incorporated by the system, a topic that will be discussed later in this article. As a comparison, the photo on the next page shows the bit-rate of a video scene under a low-light situation in which the AGC of the camera is enabled.

Let’s investigate some of the newer features — such as blanking, activity detection, flicker-less and compression — presented by the camera manufacturers to help lower the bandwidth introduced into a network.

Blanking Reduces Image Flow

This first feature is known as preset blanking. For those who don’t knowor understand the function of a preset,a little explanation is in order.

Many pan/tilt/zoom (p/t/z) camera assemblies have a feature in which an operator can place into memory individual p/t/z locations. So instead of having to manually adjust the camera to a desired position, the operator can have the camera and lens automatically go to that location.

This preset function is very helpful during remote alarm conditions or as a preprogrammed sequence of events. However, during the transition from one preset location to another, a great deal of unimportant video information is being digitized, compressed, transmitted and/or stored. This will result in excessive bandwidth as well as increased storage space.

To eliminate this problem, many manufacturers are now blanking out the video image until the new preset location has been obtained and then display the result.

The result, as shown in the photos above, is that the compression engine disregards all unnecessary video information. Therefore, any unnecessary increase in bits per second is eliminated before being introduced into the network.

Zone blanking is a feature that is almost the same as preset blanking except for one condition. Zone blanking will blank out an entire area or zone (which is set by a system operator) to eliminate any unnecessary video information from being processed. The blanking area is usually defined as one that is not required for video surveillance and, therefore, can be set to prevent an increase in video traffic over a network.

Record Only When Activity Occurs

Another feature that has been in place for many years but has taken on a new role is internal camera activity detection. This is where the compression process is activated only when motion occurs in a fixed on stationary scene.

Many digital surveillance cameras now have menus that allow an operator to set areas for motion. This detection is based on changes in video pixel signal strength levels as well as the number of pixels selected in the setup menus of chosen cameras.

(Author’s note: This form of activity detection is most useful for indoors applications, where the light levels are sufficient to provide high quality images. The use of this function in outdoor applications may result in many false alarms, which result in excessive bandwidth problems in a video network.)

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