Resolution: Not Just for New Year's Anymore

Alright, even the name of this post is a misnomer, as it has nothing whatever to do with your resolve or decision making.  It's another discussion of the use and deployment of CCTV (Closed Circuit Video Surveillance) for additional peace of mind.

Recently, a client asked for an "above average" CCTV system; not just standard residential equipment.  I love these challenges, so I researched a number of offerings from various manufacturers and finally settled on and sold this solution to my client.  He was delighted by the installation, clarity of the video and outstanding remote viewing capability.  So satisfied in fact that he asked for a similar treatment at a second residence.  This time, however, he asked for even more "resolution."

Here is where we get into the meat of the discussion.  In the age of "HDTV" and digital imagery, and since everybody has seen crime shows like "CSI" and "NCIS," reality has been blurred into obscurity.  I guess the technology might exist that would allow the identification of a bug on a windshield based on footage from a traffic camera a hundred feet feet away in the dark on a vehicle moving 70Mph, with rain falling at two inches per hour...you get the idea, but it forces you to ask a couple of very obvious questions, the answers to which make it unlikely that this type of camera would be in very high demand.  First, at a price point around $25k or more per camera, who could afford it?  Second, how often will this kind of information really come in handy?

Here are some basics that should clarify (no pun intended) what is meant by the term "resolution" in reagard to video surveillance:

First, understand that cameras capture images in one of two ways; analog and digital.  We won't go into digital much, as they are not as prevalent in the majority of residential and small business applpications.  As for the more typical CCTV setups, there are basically two standards  or formats by which analog "resolution" is figured; they are international standards.  PAL and NTSC.  In places like the United States and Canada, NTSC is the governning standard.  In many other places around the world, PAL dictates how many lines of video appear on a monitoring device.  The reason for this is so that a recorded picture (video) is more universally available to various viewing devices.

NTSC format means that a video is limited to a frame consisting of 720 pixels width and 575 pixels high.  Technically, you will only see about 480 horizontal lines worth of information, and even this image is in reality two fields of interlaced video sent one after the other, very quickly (about 30 times each per second) so that your eye and your brain recognize one solid image.  Let's do math so we have a frame of reference to digital imagery, for which most people have a better feel.  Digital imagery is measured in "megapixels."  For example, your phone may have a 1 or 5 megapixel camera.  So how many Megapixels are in this analog image we are talking about?  Here's the math part...

720 pixels multiplied by 575 pixels, or 720 x 575 = 414,000 pixels.  Now recall that only half of these are really on the screen at one time. (Your brain is filling in the rest) So this is 207,000 pixels.  So at any given instant the maximum number of pixels on display might be 0.2 megapixels.  Now there are other factors that come into play that negatively affect this number as well, such as the speed of the transmission source, noise corruption of the signal as it passes through the wire to the monitor, etc...

You might say "but, the camera I bought says it captures 600TVL of resolution..." and I will tell you they are NOT lying!  NTSC doesn't limit the number of lines of signal that can be gathered, only the number that can be translated correctly by a recording or viewing device.  Capturing more TVL allows the camera to make up for some of the negative factors I mentioned in the last paragraph.  It is an indicater that the manufacturer is concerned with quality, that they used a better sensor to collect the information.

Of course a happy medium might be to select a camera that has a zoom feature.  It won't increase the number of TVL captured, but it can be more selective in regard to what those lines include.

Well, this is mind-numbing stuff, so we'll save the discussion of digital video for another time.