What is Digital CCTV?

Digital CCTV, or Digital Closed Circuit Television, is the technology used in modern surveillance systems. Traditional ,VCR, CCTV pictures are sent via cctv cameras to a closed area, e.g. a CCTV Monitor, this type of CCTV is likely to produce lower resolution images and have to be displayed via cabling in the workplace. Modern Digital CCTV Systems can be operated remotely via a pc or mobile phone, can monitor various locations and can be monitored from wherever there is internet or GPRS Access.

A History of CCTV Systems
The saving of CCTV footage has changed in the last 5 years. The industry move has been away from analogue to Digital CCTV Systems:

Analogue CCTV
In the past, all CCTV Cameras were attached to a Multiplexor (A device that will split multiple camera pictures onto an individual CCTV Monitor). The Multiplexor then sends the analogue camera images to a Time Lapse Video Player. These are special CCTV recording devices that can record up to 960 hours of footage on a three hour Video Cassette. This method is still used today for simple CCTV installations but the quality of recording is usually very low (1 Frame Per 12.8 Seconds).

Digital CCTV
Currently the majority of CCTV systems use Digital technology. Digital CCTV Surveillance uses current PC technology to digitize the CCTV camera images and compress them into a PC friendly format. These digital images can then be stored on a PC's Hard Disk Drive. As the digital cctv images are stored on a computers Hard Drive it is possible save digital cctv footage and access it speedily and easily. Digital CCTV also has the advantage over Analogue CCTV systems that the image are of a far higher resolution.

There are two types of Digital Surveillance Systems:

Digital Video Recorders
A Digital CCTV Video Recorders, (DVR's), are Stand-Alone units that are capable of saving digital CCTV images to a PC. DVR's look similar to a standard Video Cassette Recorders (VCR's).

CCTV Cameras are connected to the back of the unit via standard CCTV Camera connection referred to as BNC. By connecting a CCTV Monitor or standard Television to the DVR you are able to view your CCTV Cameras in different screen divisions (single camera, 2x2,3x3 etc) and also playback footage at the touch of a button.

Some DVR's can have built in Motion Detection Technology. This means that digital footage is only recorded when someone or something walks in front of your CCTV Camera.

It is also possible with some DVR's to view your cameras remotely via an ADSL (Asymmetric Digital Subscriber Line).

PC Based Digital Video Surveillance (DVR)
PC Based Digital CCTV Surveillance systems are a reasonably new technology in the CCTV Industry. This type of Digital CCTV system works in two stages. You then install the digital cctv surveillance card and software on to your PC. This Software (or program) will allow you to view your Digital CCTV Cameras, search through previously recorded footage, backup footage to CD/DVD, control PTZ Cameras either on the PC system or remotely and much much more.

Cameras are attached to the back of the DVRUSA PCI Card using the standard BNC connection used in all CCTV Cameras.

 DVRUSA Surveillance cards come in a variety of formats depending on:

1) The amount of cameras required (1-16)
2) The Frame Rate per Second (FPS) (120 FPS - 480 FPS)

Frame Rate is important, as the higher the Frame Rate, the higher the quality of recording and the more Real Time your cctv recording will be.

Real Time Recording for 1 camera is 30 Frames Per Second (NTSC). In order to capture 16 cameras in Real Time, you would need:

30 FPS x 16 Cameras = 480 Frames Per Second PCI Surveillance Card

How to choose a CCTV Camera?
Choosing the correct CCTV Camera for your digital surveillance system is very important. The Digital CCTV Camera, together with a CCTV Lens, uses a CCD (Charge Coupled Device) sensor that captures the image and turns it into a signal that is sent to the monitor or surveillance system.

You will need to decide the following when choosing a cctv camera & lens for a digital cctv system:

1. The Digital Camera Location : Will the camera be situated Indoors / Outdoors
2. The amount or variance of light conditions for the digital cctv camera : Will the camera have to record in low-light conditions such as at night?
3. The Field of View required for the camera : How wide or narrow an angle of vision is required
4. The Focal Length
5. How far away objects you wish to record will be from the camera
6. Your budget

CCTV Lens Guide including example distances
You need to understand the following when choosing a CCTV lens:

Focal Length
The Focal Length is measured in mm. As a guide:
a short focal length (e.g. 2.5mm) = a wide angle of view
a long focal length (e.g. 16mm) = a narrow angle of view
the smaller the CCD Chip - the narrower the angle of view

Depth of Field
The Depth of View is the distance within which objects in a picture are in focus.
A large Depth of Field means almost all objects in the Field of View are in focus.
A small Depth of Field means only a small section of the Field of View are in Focus.
The following factors can lead to a greater Depth of Field: Using a Wide Angle Lens High F-Stop, Using an Auto Iris
Camera Format
The size of the camera's CCD image device will affect the angle of view. CCTV Cameras come in different chip sizes - 2/3", 1/2", 1/3" and 1/4".

F Stop
F Stop or Aperture has 2 measurements. When the lens is fully open (Maximum Aperture / Minimum F-Stop), just before the lens completely closes (Minimum Aperture / Maximum F-Stop).
F Stop - is the lenses ability to gather light depending on the aperture and focal length.
C or CS Mount
The 2 standard cctv camera lens mounts. The difference between the two is simply the distance between the lens and the ccd image sensor. C Mount - 17.5mm CS Mount - 12.5mm
Auto or Manual Iris
For changing light conditions (e.g. cameras positioned outdoors), Auto Iris lenses are needed.
For indoor use manual iris lenses are sufficient as light levels will not vary too much.
Video or Direct Drive
The majority of CCTV Cameras will be able to use both types. Video Drive Lenses contain circuitry which converts video signal from the camera into iris control. Direct Drive Lenses require the cctv camera to contain the circuitry

CCTV Glossary

In order to choose the best CCTV Security System and CCTV Cameras you need to understand some of the basic terminology. Below is a glossary of CCTV terms to help you choose your Surveillance system and CCTV Cameras and CCTV Lenses.

Aperture
Aperture is the area of the camera lens that gathers light. The Iris of the cctv lens controls the size of aperture.

Auto Iris
Auto Iris Lenses adjust for changing light conditions in a camera view. If the sun shines on a camera with an auto iris lens, the lens will adjust the amount of light so the picture remains clear.

CCD
Charge Coupled Device - a light sensitive imaging device for almost all cameras. Typical sizes for CCTV cameras - 1/2", 1/3", 1/4".

C Mount
Type of screw-on mounting for CCTV Camera Lenses. C Mount lenses need an adapter ring when used with CS Mount camera (see CS Mount).

Compression
Compression Techniques are used in Digital CCTV to reduce the file sizes of recorded video images. Typical compression formats used for video are: MJPEG, MPEG-4 & H.264.

CS Mount
More recent type of mounting for CCTV Camera Lenses. Designed for 1/2", 1/3" 1/4" CCD cameras, CS-Mount is the more common lens mount used today in CCTV cameras.

Day/Night Camera
A camera that is 'Day/Night' means it can capture video in both day and nighttime.
In low light conditions, the Sony Day/Night chipset switches from colour to black & white at night to enhance the picture quality

DSP
Digital Signal Processing - a technique by which video quality can be improved by adjusting parameters of the video signal.

DVR
Digital Video Recorder - CCTV Footage is converted to a digital signal and stored on a PC Hard Disk. This is now the standard CCTV recording practice.

ExView
Sony Chipset type that offers very good images in both day and night time. Typically, cameras with Ex-View chipset have good Low Light (LUX) levels.

FStop
The Ratio of Focal Length to the diameter of the lens. The smaller the F-Stop number, the more light is passed.

Field Of View
The view of the camera - in relation to the angle of view and distance of the object from the lens.

Frame
A frame consists of 2 interlaces fields. 30 Frames are created every second

Frame Rate
The quality of a Digital Surveillance Systems is often determined by the Total Frame Rate it can record at. The higher the Frame Rate, the higher the quality of recording and the more Real Time your CCTV recording will be - Real Time recording for 1 camera is 30 Frames Per Second (NTSC).

IP Rating
Ingress Protection Scale - 2 numbers indicating the protection level of an outside enclsure - e.g. IP68

IR Cut Filter
An IR Cut Filter is an extra filter inside the camera that moves behind the camera lens when it gets dark. A camera with an IR Cut Filter will produce very high quality images in low light conditions.

Iris
Device inside a lens which opens and closes as light conditions change which adjusts the amount of light passed

JPEG
Joint Photographic Experts Group - an image compression technique used for still images

Lens Mount
See CMount or CS Mount

Luminance
The brightness of a video signal

LUX
Used to specify how sensitive cameras are to light (measured in lumens/sq metre).
e.g a camera with a LUX Level of 0 can see in pitch black. The lower the LUX Level the better the camera will see in the dark.

Motion Detection
Recording method for digital surveillance systems. When someone walks in front of a camera, the pixels change and the DVR defines this as motion. The surveillance system will then record these images to the hard disk. This is a popular recording setup as every event recorded is actually motion driven as opposed to a static image if the system was set to record 'round-the-clock'.

MPEG
Motion Picture Experts Group - a video compression technique for video images
MPEG-4 has fast become the Digital CCTV standard recording compression format.
MPEG-2 is used for DVD Recording quality.

Multiplexer
A Multi Screen CCTV device that allows input of 4, 9, 16 etc cameras and provides a 'Mutli-Plexed' (or split screen) display of those cameras

Noise
Video Signal interference that usually appears as graininess or snow on the picture.

PAL
Phase Alternate Line - Video encoding standard for Europe.

PTZ
Pan Tilt Zoom - a camera which can be controlled via Joystick or DVR and moved up/down, left/right and zoomed in/out.

Peak to peak
Video Signal measurement from the base of the Sync pulse to the top of the white level. A full video signal should be one volt.

Quad Splitter
A CCTV device used to display 4 cameras on one monitor.

Resolution
The number of horizontal lines a system can display.
Digital Resolution (e.g. 720 x 640)
720 = number of points in each row that make up the picture
640 = number of rows

RG59
A type of CCTV Coaxial cable used to transmit cctv camera video signals to a CCTV System.

Sensitivity
The sensitivity of a camera is often configured on your digital surveillance system.
Motion Detection based recording uses relies on the sensitivity of the cameras to trigger recording

Telemetry
Control of PTZ cameras is provided using Telemetry Control. This signal is sent down 'twisted pair' cable or along the same coaxial cable the video signal is being sent down. Typical Telemetry signals are RS-485 or RS-422.

Varifocal Lens
A cctv camera lens whose focal length / viewing angle can be manually adjusted to suit the camera view required.
Typical Vari Focal lens lengths are: 2.5mm-10mm, 3.5mm-8mm, 5mm-50mm

Video Splitter
CCTV device that splits the video signal from a camera (or cameras) so it can be used more than once.

Zoom Lens
A lens which has variable focal lengths. The image can be 'zoomed' in or out whilst the view of the camera remains in focus.