A CCTV system is like having an extra eye because it allows you to monitor your property when you’re not there. However, not all security cameras are the same and each one will have a different quality and a different purpose. When deciding on a security camera to use, it’s important that you think carefully about what you are needing it to capture. One easy way to determine what a CCTV camera can capture is by using the DORI standard.
In CCTV, DORI is an acronym that stands for detection, observation, recognition, and identification. The DORI standard was made by the IEC and this defines what level of detail that a CCTV camera is able to capture. DORI is helpful in order to determine if a certain camera would be able to capture what you need.
- Detection (25ppm/10ppf): At the detection distance, you will be able to determine whether or not the object in the frame is a person, but you will not be able to make out specific details.
- Observation (62ppm/20ppf): At the observation distance, you will be able to make out distinctive characteristics about the person, such as what kind of clothing they are wearing.
- Recognition (125ppm/40ppf): At the recognition distance, the face of the person will be more clear so you can verify if you have seen this person before. License plate numbers will also appear more legible.
- Identification (250ppm/80ppf): At this level, you’ll be able to verify the identity of the person beyond reasonable doubt. License plate numbers will also be able to be clearly read.
If you’re curious about the numbers next to each DORI standard, the figures refer to how many pixels are in each meter or foot. If you can recall from our image resolution guide, each image is made up of pixels. More pixels will produce images that appear clear and crisp. Less pixels will make images look blurry and fuzzy. The same concept applies here; the more ppm or ppf, the more details you’ll be able to capture. The DORI standard requires each level to have a specific number of ppm/ppf which correlates to what a CCTV camera can capture.
Calculating Pixel Density
When you are choosing a security camera, you should first determine what you are wanting to use the camera for (which DORI level). After you decide on the purpose, then you’ll know how many ppm/ppf you will require. After that, it’s time to calculate. To calculate, you would take the number of horizontal pixels of the image and divide it by the width (in m or ft) of the scene you are looking at. The formula will look like this:
ppm/ppf = image width (pixels) / field of view (m or ft)
So for example, let’s say that you are wanting to use a 4MP camera at a FOV of 100ft. 4MP cameras will have a width of 2,688 pixels so 2,688/100ft=approximately 27ppf. Therefore, using this camera at this distance would be good for observation. If you wanted a camera to use for recognition or identification, then you’d have to use a higher-resolution camera or shorten the FOV distance.
Keep in mind that there are other CCTV factors that will affect DORI, but using DORI is a good way to determine if a specific camera will be able to carry out the desired purpose. Now, you can be sure that you’re investing in the right products that will give you the results you want.