420 TV Lines Security Cameras – What Are TV Lines ? 420 lines refers to the amount of vertical lines a camera can capture on video. This is also known lines of resolution. The higher the number, the clearer the picture will be. NTSC video, also known as standard definition has 525 lines of standard definition.
Since security cameras use an analog line source, often a coaxial cable, the range can be variable rather than fixed. 420 lines can still hold a considerable amount of visual information, though nowhere near 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.
In the analog world, the resolution is measured in TV Lines, which is where we get the 420 line measurement from. In the digital world, television is mostly progressive scan. In the world of video, progressive means one frame at a time. For example, if a TV show is filmed at 30 frames-per-second this means that every second 30 still images are displayed on the screen.
With analog video, which most CCTV security cameras use, a different scanning technology is used.
This technology is called 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 the alternation between the half field. At any given time, two different frames are displayed on the screen. If you’ve ever seen a flickering effect on your SD TV when a DVD was paused, this is because of interlacing. To return to the term “TV lines”, interlacing is possible because there are alternating lines with one frame and another going across the screen.