Analog and digital resolution are similar, but there are some important differences in how each is defined. In analog video, the image consists of interlaced lines since, as described above. In a digital system, the picture is made up of picture elements, also called pixels. No matter which system is used, higher resolution provides more visible detail. This is a very important consideration in surveillance applications, where a high-resolution image can enable a license plate to be read or a person to be identified.
When analog video is digitized, the maximum amount of pixels created is dictated by the number of available TV lines. Based on NTSC standards, the maximum resolution of an analog system is 400,000 pixels, or 0.4 megapixel, once the video is digitized by a DVR or video server.
Network camera technology renders NTSC resolution irrelevant and makes higher resolution possible. Network cameras today produce images that are at least one megapixel in resolution, which is 2.5 times higher than the best analog image. Cameras with two and three megapixel resolutions are also available.
Even with megapixel resolution it is still possible to generate lower-resolution images in order to save bandwidth. In this case, low resolution images are sent over the network until a trigger prompts the camera to send images with more detail. That way, the most significant images are presented with the highest possible level of detail.
In addition to providing clearer images, megapixel network cameras also provide different aspect ratios. Standard TVs use a 4:3 aspect ratio, while movies and wide-screen TVs use a 16:9 ratio. The advantage of 16:9 is that the upper and lower parts of most images take up pixels, bandwidth and storage space, but do not contain critical information.
When an analog installation is spread out over a long distance, the length of the cable will influence image quality. The further a user is from the video source, the lower the image quality becomes. However, IP-Surveillance does not have these types of problems. Viewing video from a network camera is just like viewing images from a Web site. The network camera produces digital images, so there is no quality reduction due to physical distance.
Also, IP-surveillance images are digitized once, and then stay digital throughout the transportation and viewing processes. When converting analog video signals to digital through a digital video recorder or other device, the image must go through several conversions from analog to digital, or vice versa. With each conversion, quality can be lost (see Illustration 2).
Network video resolution has steadily increased over the past few years. Now that technology developments have allowed network cameras to feature the same or better image quality as that of analog technology, the security market has a strong incentive to push ahead into the digital future.
About the author: As the general manager for Axis Communications, Fredrik Nilsson oversees the company's operations in North America. In this role, he manages all aspects of the business, including sales, marketing, business expansion and finance.