Pensacola Surveillance equipment including security cameras video formats

Surveillance System Camera formats, resolution, and pixels.

A basic familiarity with camera terminology is probably adequate for most school administrators who plan to go out on bid for a CCTV system. However, for the benefit of those who might be responsible for choosing or upgrading camera equipment, the following discussion presents these technical specifications in more depth.

Formats . Camera format relates to the size of the camera imaging device. Most solid-state cameras used in security applications today are 1/2-inch or 1/3-inch format. There are some 2/3-inch cameras still in use, and some 1/4-inch format cameras are beginning to appear on the market. The trend has been to make camera formats smaller as picture element densities have increased, giving the manufacturer more imaging devices per production run, reducing costs, and allowing for smaller cameras.

Resolution . Resolution is the ability to resolve or see small details in an image. Resolution for CCTV cameras (as well as for TV monitors and recorders) is usually specified in terms of horizontal lines of resolution. Horizontal lines of resolution relates to the number of independently resolvable elements (small details) in three-fourths of the picture width. CCTV cameras range from 200 to more than 1,000 lines of horizontal resolution. Higher resolution cameras generally cost more than lower resolution cameras. For a typical color security camera system (system includes camera, cabling, recorder, and TV monitor) that uses a standard National Television Systems Committee (NTSC) color video signal format, 300 to 400 lines of horizontal resolution are common. Black-and-white systems for tighter security applications typically range from 500 to 700 lines of resolution. Cameras with more than 800 lines of resolution are commonly used in broadcast TV, medical, or industrial applications.

Pixels . Active picture elements, sometimes referred to as pixels, is a term used specifically with cameras and is directly related to horizontal lines of resolution. Active picture elements are the actual number of light-sensitive elements that are within the camera imaging device. Active picture elements are expressed with a horizontal number (the number of elements horizontally across the imager device) and a vertical number (the number of elements vertically on the imager). A camera specified with 768H by 494V picture elements has 494 rows of picture elements vertically, with each row having 768 elements horizontally. For black-and-white cameras, horizontal lines of resolution relate to picture elements by a three-fourths factor (by definition of horizontal lines of resolution) so a black-and-white camera with 768 active picture elements will have 576 horizontal lines of resolution. This would hold true for color cameras as well, except that the NTSC format limits signal bandwidth which reduces resolution.

Lines of resolution, camera format, and lens focal length (discussed later) are the camera-specific part of what determines if a camera scene will be useful for a particular application. Other items to consider include lighting, shadowing, camera aiming, and camera sensitivity. Before selecting a camera and lens combination for an application, one must determine what is desired to be seen in the image. Just being able to see a person in a specific area, such as a parking lot, will require one set of minimum criteria for camera and lens selection. Being able to identify a person by facial features (if the person faces the camera) will require a different set of criteria. For identification purposes, a person must be much larger in a scene than for the purpose of just determining if a human is present.

Because a camera scene is observed on the TV monitor, the entire CCTV system resolution must be considered. This includes the camera and lens combination, the camera signal transmission equipment (such as coaxial cable and amplifiers), the TV monitor, and the recorder. All components of the system must have adequate resolution for the application desired.

For observation of a camera scene to determine only if a human is in the scene (or to be able to distinguish between a person and an animal), a minimum criteria of 6 horizontal TV lines across a 1-foot-wide object within the scene is used. (In terms of active picture elements, this means that a 1-foot-wide object would cover 8 horizontal active picture elements for each row of picture elements for the height of the object on the camera imager.) For identification of a person by facial features, 16 horizontal lines (21 pixels) of resolution subtending a 1-foot-wide object is needed.

The lens focal length (discussed in the next section), camera format, and how far an object is from the camera will determine how large an object is within the scene, as well as how many active picture elements the object covers on the camera imaging device. Higher resolution cameras (for example, 576 horizontal lines or higher) can be used to distinguish objects farther away (smaller in the scene) than a lower resolution camera (approximately 250 horizontal lines) allows. In other words, an object can be smaller in the scene for higher resolution cameras and still meet the minimum horizontal resolution criteria. The significance of this is that fewer higher resolution cameras will be needed than low-resolution cameras in some interior and many exterior applications.