One feature that is important when designing a Security/Surveillance Camera System is the “Frame Rate,” or “Frames Per Second (fps).”
What is meant by frames per second or frame rate? Let’s take a look at motion video and how it relates to still photography to understand the concept of frames per second. First, still photography is basically the ability to capture and store a brief moment in time. Whenever we take a picture, we are basically “recording” a moment of time, something that is really difficult, although not impossible to do, using other methods. One alternative to capturing time via a photograph is by creating a sketch or painting, however, it’s obvious that this would be impractical for security/surveillance purposes.
If still photography can be defined as capturing a moment in time, motion photography can be defined as capturing an extended moment of time. For example, with video, we can capture 5 seconds, 5 minutes, 5 hours, or 5 days of time. This is an important concept in security/surveillance camera technology; but what really comprises a video? A video is just a collection of still pictures, taken at a given rate. If the pictures are taken in rapid succession, they give us the impression of fluid motion.
In film based video, the standard number of pictures taken to cover 1 second of time is 24. Old black and white silent films and amateur 8mm film “home movies” usually took 16 or 18 pictures per second. Digital video, such as computer video, digital animation, or DVD movies take approximately 30 frames per second. At these rates, the human eye and brain are fooled into thinking that we are seeing continuous motion, and not individual pictures. The number of pictures that are taken per a given unit of time is called the frame rate. When we consider how many pictures are taken or displayed in exactly one-second of time, it is called frames per second (fps).
Frames per second are important for security/surveillance applications for two reasons. The lower the frame rate captured the less fluid, and therefore the less realistic, the motion. On the other hand, the greater the frame rate, the greater the performance of the camera, digital processor, storage medium, and other components must be to handle the “workload” to store the pictures. For example, if a still picture takes up 1 unit of storage, and we take one picture every 5 minutes, in essence the frame rate will be 12 frames per hour. If we took motion video for 1 hour, at 30 fps, we would actually be storing 108,000 pictures for 1 hour of video.
Therefore, there are “tradeoffs” that can be made. Reduce the frames per second and fewer pictures are taken, lower performance equipment and storage mediums can be used, but the motion becomes jerky and “odd” looking or there may be no motion at all. Increase the frames per second, and the motion looks very realistic and fluid, but more pictures are taken an higher performance equipment is needed to process it.
Further, the faster the motion, the higher the frame rate needs to be to capture the event with good quality; to a point. Although 30 fps is a good quality standard, frame rates as low as 15 fps can still make good quality video. If fluid motion is not necessary for your security/surveillance applications than even lower frame rates such as 1 fps or less may be used.
Depending on the security/surveillance system applications, a frame rate of only one picture every five minutes may be needed. Of course, if it is important to monitor motion, then this frame rate would be far too slow. So how many frames per second are necessary for your application? Consult with your professional security technician to determine what is right for you as every situation is different.
Always determine the frame rate needed to satisfy your security/surveillance situation. Then design and purchase a system that can produce the desired frame rate. Never base your purchase of a security camera system on an arbitrary frame rate. A system that cannot produce a frame rate applicable to your situation would only provide you with a useless investment.