classic | mobile
Follow us on:
Follow us on Facebook  Share via Twitter  Share via LinkedIn
 

Search...
Hi-Tech Security Solutions Business Directory


Image generation: sensors and scanning - A guide to IP video, Part 3
December 2005, CCTV, Surveillance & Remote Monitoring

Image quality is clearly one of the most important features of any camera, especially for security surveillance and remote monitoring applications where lives and property may be at stake. Unlike traditional analog cameras, network cameras have processing power not only to capture and present images, but also to manage and compress them digitally for network transport. Image quality varies considerably and is dependent on several factors such as the choice of optics and image sensor, available processing power and level of sophistication of the algorithms in the processing chip. This article starts to cover some of the key areas that need to be considered when specifying network cameras for particular surveillance applications.

CCD and CMOS sensors

The camera's image sensor is responsible for turning light into electrical signals. There are two possible technologies for the camera's image sensor:

* CCD (charged coupled device).

* CMOS (complementary metal oxide semiconductor).

CCD sensors are produced using a technology developed specifically for the camera industry, while CMOS sensors are based on standard technology widely used in memory chips, inside PCs for example. Today's high quality cameras mostly use CCD sensors. Although recent advances in CMOS sensors are closing the gap, they are still not suitable where the highest possible image quality is required, though they may serve well for entry-level network cameras where size and price are key.

CCD technology

CCD sensors have been used in cameras for more than 20 years and present many quality advantages, including a better light sensitivity than CMOS sensors for better images in low light conditions. CCD sensors are however more expensive and more complex to incorporate into a camera. Besides, when there is a very bright object in the scene (such as a lamp or direct sunlight), the CCD may bleed, causing vertical stripes below and above the object, a phenomenon called smear.

CMOS technology

Recent advances in CMOS sensors bring them closer to their CCD counterparts in terms of image quality, but they still cannot deliver the highest image quality. CMOS sensors provide a lower total cost for the cameras since they contain all the circuitry needed to build cameras around them. They make it possible to produce smaller-sized cameras. Large size sensors are available, providing megapixel resolution to a variety of network cameras. A current limitation with CMOS sensors is their lower light sensitivity. In normal bright environments this is not an issue, but in low light conditions this becomes apparent. The result is either a very dark or a very noisy image.

Progressive scan versus interlaced video

Today, two different techniques are available to render the video: interlaced scanning and progressive scanning. The choice of technique depends on the application, and particularly whether the system is required to capture moving objects and to allow viewing of detail within a moving image.

Interlaced scanning

Interlaced scan-based images use techniques developed for TV monitor displays, with 576 visible horizontal lines across a standard TV screen. Interlacing divides these into odd and even lines and then alternately refreshes them at 30 frames per second. The slight delay between odd and even line refreshes creates some distortion or 'jaggedness' because only half the lines keep up with the moving image while the other half waits to be refreshed. Interlaced scanning has served the analog camera, television and VHS video world very well for many years, and is still the most suitable for certain applications. However, now that display technology is changing with the advent of LCD- and TFT-based displays, DVDs and digital cameras, an alternative known as progressive scanning, has been created.

Progressive scanning

Progressive scanning scans the entire picture line by line every sixteenth of a second. In other words, captured images are not split into separate fields as in interlaced scanning. Computer monitors do not use interlacing so there is virtually no flicker, which can be critical for viewing detail in a moving image such as a person running away. However, a high quality monitor is required to get the best out of this type of scan.

Capturing moving objects

When a camera captures a moving object, the sharpness of the frozen image will depend on the technology used. Compare these JPEG images, captured by three different cameras using progressive scan, 4CIF interlaced scan and 2CIF respectively and note the following:

* All image systems produce a clear image of the background.

* Jagged edges arise from motion with interlaced scan.

* Motion blur caused by the lack of resolution in the 2CIF sample.

* Only progressive scan makes it possible to identify the driver.

Note: In these examples, the cameras were using the same lens. The car was driving at 20 km/h.

In the next article in the series we will look at image compression methods.

For more information contact Roy Alves, Axis Africa, 011 548 6780, roy@axisafrica.com


  Share via Twitter   Share via LinkedIn      

Further reading:

  • Surveillance – The past, the present and the future
    September 2016, Sunell Security, CCTV, Surveillance & Remote Monitoring, Integrated Solutions
    Brains, beauty, seamless integration, excellent warranty and after-sales service, plus competitive pricing makes Sunell the brand of choice.
  • The mind, eye and hand speed and implications for slow motion viewing
    September 2016, Leaderware, This Week's Editor's Pick, CCTV, Surveillance & Remote Monitoring
    A recent publication on CCTV and reviewing video in slow motion came to the finding that where people viewed CCTV footage in slow motion, viewers would be more prone to convicting offenders.
  • Eliminating the fear factor of IP-based megapixel video systems
    September 2016, Arecont Vision, CCTV, Surveillance & Remote Monitoring, Integrated Solutions
    The market’s long-established dependence on analogue systems has contributed to a view that transitioning is just too difficult an obstacle to overcome.
  • Reliable surveillance at Mall of Africa
    September 2016, WD South Africa, CCTV, Surveillance & Remote Monitoring, Products
    More than 20 retailers record and store video footage on WD Purple Surveillance hard drives.
  • AHD outdoor speed dome
    September 2016, TeleEye (South Africa), CCTV, Surveillance & Remote Monitoring, Products
    TeleEye has released an AHD speed dome camera with a 20x optical zoom, full HD 1080p resolution, long IR range of 100 m and IP66 weatherproof design.
  • Eurobyte showcases Sunell
    September 2016, Eurobyte Technology, News, CCTV, Surveillance & Remote Monitoring, Training, Conferences & Events
    Eurobyte took its Sunell product range on the road last month and hosted events in Cape Town and Johannesburg.
  • ONVIF Releases Profile Q
    September 2016, News, CCTV, Surveillance & Remote Monitoring
    ONVIF Releases Profile Q for Quick Install, Advanced Security.
  • Arteco integration with Contact-ID
    September 2016, News, CCTV, Surveillance & Remote Monitoring, Cyber Security
    Arteco has announced the integration of Arteco’s suite of video event management software (VEMS) with Contact-ID, an alarm protocol for intrusion, fire and building automation alarm systems.
  • Cathexis Africa increases local staffing
    September 2016, Cathexis Technologies, News, CCTV, Surveillance & Remote Monitoring
    In line with its exceptional growth over the past couple of years, Cathexis Africa is increasing its staff complement to enable it to continue supplying excellent support to its growing market.
  • Complex wireless surveillance requirements
    September 2016, Dahua Technology, CCTV, Surveillance & Remote Monitoring, IT infrastructure in security
    Dahua Technology provided wireless solutions to provide extensive surveillance coverage for the Durrat Al Bahrain luxury artificial island chain.
  • Safety at the pool
    September 2016, CCTV, Surveillance & Remote Monitoring
    Geutebrück renews the security technology at the Aachbad in Singen, Germany, with a modern IP system.
  • The future of technology, a smarter, safer world
    September 2016, Axis Communications SA, This Week's Editor's Pick, CCTV, Surveillance & Remote Monitoring, Integrated Solutions
    Expect more change in the next decade or two than we saw in the last century with analytics key, and cameras fast becoming just another device on the network supplying valuable data.

 
 
         
Contact:
Technews Publishing (Pty) Ltd
1st Floor, Stabilitas House
265 Kent Ave, Randburg, 2194
South Africa
Publications by Technews
Dataweek Electronics & Communications Technology
Electronic Buyers Guide (EBG)

Hi-Tech Security Solutions
Hi-Tech Security Business Directory (HSBD)

Motion Control in Southern Africa
Motion Control Buyers’ Guide (MCBG)

South African Instrumentation & Control
South African Instrumentation & Control Buyers’ Guide (IBG)
Other
Terms & conditions of use, including privacy policy
PAIA Manual
         
    Mobile | Classic

Copyright © Technews Publishing (Pty) Ltd. All rights reserved.