Understanding IP Megapixel Resolution

Many end users will specify a mega pixel resolution camera but not consider what they will actually see with the cameras themselves. Many manufacturers have their own numbers for the ability to identify people and license plates. This number is called the pixel density (how many pixels are available in a given space) and is stated as pixels per foot. We will use one manufacturer’s number of 45 pixels per foot to be able to read a license plate.

Let’s say we have a three megapixel camera and we want to know if we will be able to have license plate recognition (LPR). The formula for determining this is as follows:
Pixel Density (PD) = Pixels (camera resolution)/ Field of View.
For our example, our field of view is 30 feet.
The horizontal pixel count for a 3 mega pixel camera is 2048 pixels.

PD = 2048 / 30
PD = 68.2 pixels per foot

The answer is yes, we will be able to read the license plate with a field of view of 30 feet, using a 3 megapixel camera.

We can look at this from another perspective. What would my field of view be if I have a 5 megapixel camera and I still want to have the ability to view license plates?
The horizontal pixel count for a 5 mega pixel camera is 2592 pixels.
Field of View (FOV) = Pixels / Pixel Density

FOV = 2592 / 45
FOV = 57.6 feet

Before the camera system is installed, examine what exactly you want to view and don't just blindly install cameras in all locations.