What is WDR?

The Wide Dynamic Range (WDR) function of a camera is intended to provide clear images even under back light circumstances where intensity of illumination can vary excessively, namely when there are both very bright and very dark areas simultaneously in the field of view of the camera. WDR enables the capture and display of both bright areas and dark areas in the same frame, in a way that there are details in both areas.

Wide Dynamic Range is a technology utilized by security cameras in order to balance out images that have a large dynamic range. An example of this situation would be if an indoor security camera were pointing towards a window or building entrance. During daytime, the image produced by the camera would be extremely washed out due to the high brightness of the incoming light. This effect is commonly seen in restaurants, stores, offices, and other buildings that have large windows or entrances.

In order to solve this problem, CCTV camera manufacturers have been employing Back Light Compensation (BLC) to help compensate for high brightness situations. However, Wide Dynamic Range technology has recently become the most popular solution to washed out images. WDR cameras are fitted with two Charge-Coupled Devices (CCD), one high speed, and the other low speed which are designed to take multiple scans of the same image in order to provide a clear and balanced image. The two CCDs take 2 scans of the same image instead of only one scan like typical cameras. The first CCD scans the images in normal light conditions while the second CCD scans the image at high speed in order to get an image with a strong light in the background. The image processor in the CCDs will then process and combine the two images to provide one clear and balanced image which shows both the indoors and outdoors clearly.

Choosing a CCTV Camera in Low Light Levels

Selecting the correct camera to operate in the ambient light conditions can be the most important although most difficult specification to understand.

Light levels are usually measured in Lux. This is a measure of the light energy arriving on an area 1m squared of surface per second.

The average light levels are as follows;
• Full Summer Sunlight: 50,000 Lux
• Dull Daylight: 10,000 Lux
• Dawn/Dusk: 1 – 10 Lux
• Shop/Office environment: 500 Lux
• Main Street Lighting: 30 Lux
• Side Street Lighting: 0.5 – 3 Lux

The golden rule when deciding which camera to use for a given lighting condition is not to choose one that will only just give a picture. Try to give the camera approximately 10 times its quoted minimum scene illumination. Most cameras will be able to cope with excess light, due to Back Light Compensation (BLC). The major problem is when they do not have enough light to produce a picture.

The sensitivity of covert cameras with pin-hole lenses are often quoted as 0.1Lux @f1.4. This seems to indicate that the camera will work in ¼ moonlight. Actually the pin-hole lens will have an aperture ratio of something like f4 and so the camera will need approximately 1 Lux to produce a picture.
Unless your house is directly under main-street lighting the light level is probably less than 1 Lux at the front and even lower at the back. Bright security flood lights in theory help but often produce dark shadows a short distance from the house.

A monochrome camera rated at 0.05 Lux will produce reasonable results. Colour needs a little more. However, colour cameras achieve good night-time vision by switching to a monochrome mode. You will never get good night-time colour pictures without huge amounts of additional lighting. So think carefully about the added cost of colour over monochrome cameras. As most people are used to colour television it sets a standard so it is very common to still select a colour camera knowing it will switch to monochrome mode at night.

Monochrome cameras respond well to additional IR (infra red) lighting. With this in mind true night-vision cameras include a ring of IR LEDs. Colour cameras also offer IR illumination but as stated previously will switch to monochrome at night even with the IR LEDs turned on. These are true night-vision cameras and are rate at 0 Lux.

In order to choose the best CCTV Security System and CCTV Cameras you need to understand some of the basic terminology. Below is a glossaryof 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 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.

CCDCharge 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 night time. 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. 25 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 25 Frames Per Second (PAL).

IP Camera - A CCTV Camera that can transmit video and audio over TCP/IP network. An IP Camera can connect to a local network and streams it’s video over the network to a Network Video Recorder. IP Cameras can come with additional features including Power over Ethernet, wireless lan connection and Mega Pixel Resolution.

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.

Mega Pixel Resolution - Mega Pixel resolution refers to video resolutions now achievable using IP Cameras. Unlike Analogue cameras, whose resolution is usually limited to around 752 x 582 (0.4 Mega Pixels), a Mega Pixel IP Camera can achieve far greater resolutions such as 1280 x 1024 (1.3 Mega Pixels) or 1600 x 1280 (2 Mega Pixels). This increase in resolution produces far better image quality than a traditional analogue camera could ever achieve.

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.

Power Over Ethernet (PoE) - Power Over Ethernet is a method by which power is tramitted over a CAT-5/6 cable. This is often used with the installation of IP Cameras saving time/money by reducing cabling. An IP Device would need to be fitted with a PoE RJ45 port to use this functionality.

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.

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

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 576)720 = number of points in each row that make up the picture 576 = 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.