I was not sure what to call this article. I first thought it should be titled, “Why The Johnson Criteria is Wrong.” We use this criterion to predict how far away we can see something using a specific camera and lens. The criteria define the threshold for detection, recognition, and identification (DRI). The industry has used this criterion since World War II. It has not been updated to reflect today’s technology and resolution requirements.
Resolution required for Recognition, Detection, Identification depends on the type of camera
By Bob Mesnik
There is some confusion in the industry about how much camera resolution is required to detect an object, recognize the type of object, or identify exactly what or who it is. The criteria are different between thermal and optical cameras. Resolution for thermal cameras and optical IP cameras are measured differently.
For example, when defining the performance of a thermal camera we use the Johnson Criteria of “detection”, “recognition” and “identification” (DRI).
On the other hand, IP camera resolution performance is usually defined by the number of pixels in the sensor, and we are usually interested in the ability to identify a person.
How much resolution do you need? This article compares how resolution is defined using thermal and optical technologies.
This article was updated on 4/12/2018 to reflect new IP cameras
IP Camera manufacturers provide product specification sheets that help you select the right camera for your IP security and surveillance system. But, which specifications are important? They include such things as resolution, minimum light sensitivity, lens, WDR, signal to noise, etc. This article reviews the important camera specs, and how to avoid being fooled by specsmanship (from the marketing department).
The importance of each of the camera specifications depends on your objective and application for your IP camera system. For example, if you want to use the camera outdoors where it can get dark, then the low light specification is important.
If you are only using the IP camera indoors, you may be more interested in the how wide a viewing angle you can achieve. Here is a review of the important specifications.
What is the right lens and resolution for your IP camera? When you put together your IP camera system, you want to make sure that the camera you select for each location meets your expectations. It is important to first know the objectives for each area you are viewing. Do you want to identify a person’s face, a license plate, or just detect a person walking far away? In general, the more detail you want, the higher the resolution you need. This article shows you how to determine the viewing area and distance you should expect.
Note: this article was updated on 8/15/2017 to correct an error in calculation.
Why should I use an IP camera when the analog cameras are so much cheaper?
That’s a question we get especially from those people who have been using analog CCTV (closed-circuit TV) systems for many years. Actually CCTV has been around for over 45 years. Olean, NY was the first municipality in the US to use cameras on its main street to help reduce crime (according to Wikipedia this was back in 1968).
Not only have the analog CCTV systems been around for a very long time, but they also haven’t really changed from their original capability. Well yes, they have gotten much cheaper, and there are efforts to use higher resolution cameras, but their capability hasn’t changed. The first systems were based on the TV standards established by the National Television System Committee (NTSC). The standard indicated that there should be 525 vertical TV lines, with a frame rate of 30 frames per second. Take a look at our video, How the Video Camera Works.