(Closed Circuit TV) A self-contained surveillance system comprising cameras, recorders and displays for monitoring activities in a store or company. Earlier analog CCTV systems used a single VHS tape machine for each camera, specialized “quad” VCRs that recorded four low-resolution images or time-lapse recorders that handled multiple cameras. Although analog cameras are still used, VHS gave way to specialized digital video recorders (DVRs) with multiple composite video inputs.
As with any imaging device, the analog CCTV camera has a sensor which captures the video image. The resolution of the sensor varies but for reasons which will be described later, it is limited to 720×575. This is 720 pixels across the screen (horizontal resolution) and 575 up and down (vertical resolution).
The video is captured at 60 intervals called “fields” and transmitted to the receiver. Two fields together are called a “frame.” This is called interlaced transmission. More on this later.
To get the video out of the Analog CCTV Camera into a recording and display device, a single coax cable is used. To maintain compatibility with analog televisions (and hence make it easier to use off the shelf products for display and recording), the signal that comes out of the camera complies with broadcast television standards.2