Welcome to Part III of the latest in Security Sales & Integration’s acclaimed “D.U.M.I.E.S.” series: “Understanding IP Video for D.U.M.I.E.S.” Brought to you by Pelco, this four-part series has been designed to educate readers about networked video — the next phase of surveillance technology following the quantum leap from analog to digital CCTV systems. “D.U.M.I.E.S.” stands for dealers, users, managers, installers, engineers and salespeople.

In Part 1 of this year’s series (see “Using Camera Specs to Solve IP Application Issues” in the March issue), we discussed the design of cameras, their specifications and how it relates to IP cameras as well as their networks.We also discussed how to determinethe quality of cameras and whetherthey are designed for indoor or outdoorapplications.

In Part II (see “Clear Eye for the IP Video Guy” in the May issue), we investigatedways to enhance IP cameraimage quality and basic system layouts.The material also addressed howimage file sizes as well as bit rates affectboth system bandwidth requirementsand the amount of storage requiredfor different applications.

This month’s lesson takes it all astep further by explaining the needfor video bandwidth compressionand the different methods used in reducingsystem bandwidth for use onany IP network.

CIF Is 1 of 3 Forms of Compression

There are three basic forms of bandwidth compression found in the industry: 1. Common Intermediate Formats (CIF) sizing; 2. Standard video compression methods (.jpeg, .mpeg); and 3. Images per second (ips) transmitted.

CIF was discussed in Part II of this series; however, as a refresher or for those who missed that installment, a quick review can help you better understand the complete process incorporated into IP camera setups.

The pixel size of an image is normally referred to as the CIF size. CIF is a standard video format used in videoconferencing. CIF formats are defined by their resolution and standards, both above (2CIF/4CIF) and below (QCIF/SQCIF), with CIF being the original established resolution reference. The original CIF is also known as Full CIF (FCIF). The bit rates shown above are for uncompressed color frames.

A Little Bit About Bit Rates

Bit rate is defined as how much physical space an image occupies in 1 second on a network. The higher the bit rate, the more space it requires. While often referred to as “speed,” bit rate does not measure distance/time but quantity/time, and thus should be distinguished from the “propagation speed” (which depends on the transmission medium and has the usual physical meaning).

For example, a single camera incorporating a 4CIF (high quality, uncompressed color image @ 30 ips) using a DSL (1.5Mbps) would take in excess of 20 minutes to transmit over the network.

And, as we all are aware of, adding more cameras and/or increasing the movement within video scenes demands greater bandwidth requirements of the network. This bit rate number can and is governed by the compression methods used by the IP camera.

Compression Means Concessions

In its basic form, compression is the art process of removing information that is deemed irrelevant to the viewer. In this case, the viewers are dealers, systems integrators or anyone else who relies on high quality recorded images. The amount and type of information that is removed varies from system to system and can be controlled by system setup parameters.

Why do we need compression? To help answer this question, let’s evaluate the requirements needed to transmit a single minute of uncompressed composite video to a remote location.

Without compression the ability to transmit video over a network would be next to impossible. Referring back to that 1 minute of uncompressed video, incorporating a DSL modem with a 1.5Mbps transmission speed, it would take more than 20 minutes to transmit from point A to point B.

In today’s surveillance community, which depends on the ability to see this information remotely, that is completely unacceptable.

There has always been a tradeoff between the quality of the video and file size. If you require a high quality image, then you must deal with a large file size. On the other hand, if you are willing to settle for a lesser-quality image, your file size will be reduced lower than the required bandwidth to transport the video packets.

With a few exceptions, the majority of IP cameras used in surveillance incorporate JPEG, MJPEG or MPEG-4 for their compression method. However, there has recently been an increase of multiple video stream cameras entering the marketplace.

A quick description of the basic components involved in compression will help set the stage for some of the theory and explanations discussed later in this article.

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