Saturday, July 2, 2011

TVL Camera Resolution

Digital video security cameras come in all shapes and sizes and with different degrees of resolution, often using the phrase “TVL Camera” such as a 600 TVL Camera. What does TVL mean and how does it relate to digital video security cameras?  We’ll answer that question and more in the following article.

First, It will make things much easier to understand if you know a little security camera industry history. Full security camera systems have been around for several years now, however not until relatively recently have the systems been based on binary (digital) data instead of its older analog data.

In the old days, (a few years back), security cameras were in a closed loop with an analog recorder, such as the older VHS or Betamax video recorders. Recorded security footage was either recorded on a looping video tape, so that when the tape reached its end it would start at the beginning recording new material over the previously recorded older data. Another method was to monitor the Video Recorder closely (and constantly) and eject the current tape when full and insert another blank tape (probably the least favorable of any of the methods).

The point here being that video security systems have been around for a long time, doing most all of its work based on an analog system and not a digital system. When Personal Computers became poplar and started creating all sorts of devices that could be digital instead of analog, the security video industry certainly wasn’t the last to be affected. Today, nearly all video security systems that are sold are DIGITAL video systems.

As the “digital age” came upon us, the security camera industry started assimilating advanced technology and digital based devices with just one problem. Sometimes the industry adopted the new digital nomenclature yet other times they would maintain the old analog nomenclature. So, TVL camera is actually a carryover from the analog days.

A TVL camera is referring to the detail it can display in different formats. It represents the horizontal lines of resolution that the camera is capable of displaying. Older CRT (Cathode Ray Tube) monitors and televisions created a picture by flashing a moving beam across the screen, usually about 60 times per second. TVL represented how many times the CRT would draw a horizontal line. The greater the number the more detail on the picture.

TVL camera carried over from the analog days and is still used today. However, today’s cameras are digital and produce their images by creating tiny dots that are circular or square called pixels. This is how the Digital Video Recorder or DVR displays its images. However, there is still some confusion, because the specifications for the DVR refer to the size of the image being recorded, not the detail. To make matters more confusing, they use a mixture of different terms. For example:

- D1 is the same as 720 x 480 pixels
- CIF is the same as 360 x 240 pixels
- 4CIF is 704 x 480 pixels

And these are usually the terms referenced in regard to what size image the DVR will display from a given camera; once again this is not detail but how big of a display it can create. However, TVL can be applied to these because TVL is the resolution or detail in each of the above examples. This means that a D1 camera/DVR combination should be able to display up to a size of 720 x 480 pixels with a 520 TVL camera. However, if the TVL camera produces a resolution higher than what the DVR can support, the detail resolution information is lost or in other words just not used.

For example, if a DVR displays the image in CIF format, using a 540 TVL camera is basically overkill because CIF format can only support about 280 TVL, the rest is wasted. Be certain to consider these picture sizes and resolutions when designing your system because you’ll want everything to match up.

Source : http:// www. security cameraking .com/ securityinfo /

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