With analog technology a surveillance camera captures an image and renders it in the form of 420 to 600 alternating vertical lines on a monitor. This is also known as lines of resolution. The higher the number, the clearer the picture will be with the technology reaching its maximum potential at 600 lines. NTSC video, also known as standard definition has 525 lines of resolution.
Since most security cameras use an analog line source – often a coaxial cable – the range can be variable rather than fixed. Even 420 lines can hold a considerable amount of visual information, though nowhere near as much as HD. Most security cameras still use this analog format which means they are limited to the range of 420 to 600 lines. In the digital world, images are measured in pixels. For example, the highest HD format is 1080 x 720 pixels. It is important to note that despite the fact that most of the cameras currently in use, use the less advanced analog technology, the images that are transmitted are converted by the DVR to digital format and are viewed as such. This however does not mean that an HD image will be produced on the monitor. Instead it will be a digital image with the resolution quality of the analogy source. If however an analog monitor is being used, the image will be rendered using a process known as interlaced scanning. In this type of scanning, a 30 frame-per-second video is actually made up of 60 fields or half-frames. Video is created by alternating between the two fields. An individual field is composed of the aforementioned lines, where only half, either the odd or the even lines are present in a single instance. This means at any given time, only one of the two fields is displayed on screen but alternates so rapidly with its opposing field that the human brain perceives one complete image. This process of alternating between odd and even fields is where the term interlacing comes from. The reason the images are transferred in alternating half frames is to reduce the use of bandwidth. If you’ve ever seen a flickering effect on your SD TV when a DVD was paused, this is because of interlacing.
In the more advanced digital world, a process known as progressive scan is used. Although it similarly renders an image at 30 frames-per-second – which means that every second 30 images are sequential displayed on the screen – it differs from interlacing in that each frame is a complete image and is not rendered in lines but in pixels. Just as the greater the number of lines present in an analog image make for superior resolution, so do a greater number of pixels on a digital monitor produce a clearer, more detailed picture.
For all your surveillance needs and inquiries call Panopticon Solutions: 647-706-8650