Analog Cameras vs IP Cameras: The Evolution of Resolution

Today we take a look at how your choice of an IP-based system of digital cameras or a CCTV system of analog cameras will impact the resolution of your surveillance video. 

Historically resolution was understood to mean limiting resolution or “the point at which adjacent elements of an image cease to be distinguished.” But the introduction of digital thickened the plot. For  our purposes, when we refer to a camera as being analog or digital we will be referring to the type of transmission it uses to send video to a computer or storage device: 

§  Analog transmission takes the video signal and modulates it into a continuous signal, amplifying its strength or varying its frequency then transmits it through coaxial cables to a security station for viewing on a PC or recording.  Upon reaching its destination, the wave is converted back to the original video signal. The term analog stems from the fact that the variations in the carrier wave are similar or analogous to that of the video signal itself.

In analog the term horizontal lines of resolution is important in understanding the clarity of an image. Horizontal resolution cannot be looked at without considering vertical resolution.  Horizontal resolution defines the capability of the system to resolve vertical lines thus affecting the clarity of an image on the screen. The vertical resolution is fixed by the standards defined by NTSC (525) or PAL (625 lines).  The terms originated with television and the test pattern below harks back to the good old days of TV. 

Engineers add converging vertical lines until they reach the point where the lines can no longer be distinguished one from another. This is called the measured resolution point. At this point the maximum resolution of the TV has been reached. Because the lines are stacked from left to right, the number of discernible lines across on the screen is called the horizontal resolution. This is expressed in a ratio. A television system with a 4:3 aspect ratio expresses the number of distinct vertical lines, alternately black and white which can be satisfactorily resolved in three quarters the width of a television screen.

Like TV, analog cameras use horizontal resolution as a measure of clarity, and since today’s cameras adhere to  established standards, the same number of scanned vertical lines is always transmitted depending on NTSC or PAL standard used. However, several factors impede the ability to display them as transmitted:

• The camera electronics
• The transmission
• The reception and reproduction of the picture
• The storage and re-processing of the picture.

Any of these can result in distortion, “noise”, or loss of clarity. But in the world of analog that is just a matter of fact, similar to pre-cable days when TV viewers  had little choice but to live with  interference, ghost images, and other vagaries associated with rabbit ear or roof antennas.

 As cable did for television, digital transformed viewing capability in IP cameras.

§  In digital transmission the signal is converted to binary form. Each sequence of numbers represents the color or brightness of a frame. Throughout its transmission, the signal retains this information  and  when it arrives at its destination, the computer or server takes all those 1’s and 0’s and reassembles them  back to the original frame. Digital as a term refers to this use of numbers code

A digital signal knows what it should be when it reaches the end of transmission and can correct any transmission errors that may have occurred. This translates into clearer, distortion-free images. Another advantage is that digital technology takes up a lot less space than analog with the result that a lot more 1’s and 0’s can fit into the same file that analog would use.

Each frame equates to one digital picture file and the more 1’s and 0’s, in that frame, the more information contained. While analog cameras measure resolution in terms of lines, digital technology measures it in units called pixels. The more detail and clarity captured, the more pixels used. Cameras capable of capturing detailed images are called megapixel cameras.

As with analog, horizontal and vertical fields are captured and blended together to make a single frame. Here too, the resolution is expressed in a ratio. In ascending order of clarity, the standard resolutions are

·         VGA (640x480 pixels),

·         SVGA (800x600 pixels) and

·         XGA (1024 x 768 pixels).

Obviously, the more pixels it contains, the larger the file. And here we run into the need for compression, a nice tidy break point if ever there was one!

In a future post we will discuss pixels, megapixel cameras, what they are capable of capturing, how the information is stored, and how the necessary compression translates to frames per second.