Analog Systems Fade Out, As IP Gathers Steam

March 31, 2007 SSI Staff

Capturing Fluid Motion Digitally Demands More Electronics Power

When video motion is considered, however, the choice is less obvious. Analog videotape systems generally record at the rate of 30 fps (frames per second). This rate is identical to that of a broadcast television image and represents a rate at which the human brain easily perceives the image stream as fluid motion. Take the rate much below 24 fps and one begins to see the gaps in the motion similar to an old silent film.

While the technology for transmitting 30 fps analog video has been with us for decades, the transmission of fluid motion digital images is much more recent — and much more demanding. Whereas analog images are sampled and transmitted, digital images are compressed and transmitted. The process of sampling is lossy, meaning a lot of video information is lost. The act of compressing the image retains a lot more information, but it also requires more complicated electronics, more time and produces a larger data stream.

The cost of the electronics involved has been coming down rapidly, mostly due to the demands of consumers and consumer broadcast equipment. The amount of data required to represent an image has also been reduced somewhat due to the introduction of better compression algorithms — the mathematics involved in fitting a large amount of information into a small space.

The pesky problem that remains, though, is digital image streams have to be moved from the camera to the display unit and stored on a digital medium, such as a hard disk. The larger the image, the more bandwidth is required to transmit and store it.

IP-Based Systems Tend to Eat Up a Lot of Network Bandwidth

Once the video image is sampled (analog) or compressed (digital), the task of getting it from the source to the destination begins. When working with analog video, that destination is usually not very far from the source because analog signals decay as transmission distance increases. To combat this, a number of methods exist to digitize the analog stream and transmit the video over digital connections. Fiber-optic digital connections that can carry large amounts of video work this way.

Digital cameras do the work of converting video to digital at the source, reducing the amount of equipment required. Digital cameras equipped with IP connectivity further take the digital data and put it into TCP/IP packets suitable for transmission over shared data networks along with other types of data. Because the data is digital and in a commonly recognized form, it can be easily transmitted, retransmitted and stored without loss of content.

The richness of the information contained in digital images, however, comes at the cost of bandwidth. In practical terms, when comparing analog and digital video for an application, image size (and, hence, bandwidth) is the major issue. Banerjee notes, “Bandwidth is the single most precious commodity.” This is true, he observes, not only because higher bandwidth connections cost more, but also because the resulting images require more storage space.

Whereas the video systems introduced to the security industry in the 1970s used a fixed amount of tape for a fixed amount of time, determining how much
storage is required by your digital video system is not so easy. “Tweaking color saturation, low-pass noise filters, avoiding AGC [automatic gain control] in low light and vibration all have a major impact on bandwidth, and hence the amount of storage required,” says Banerjee. As a result, digital video takes up a lot of space, typically gigabytes per day per camera, in order to get the same frame rates as analog.

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