Motion Detection in surveillance was design to optimize the recording and storage in surveillance system and security DVR. Video motion detection (VMD) is a way of defining and comparing activity in a scene by analyzing frames captured from the security cameras, and analyzing differences in a series of frame images. This functionality is usually built in to the DVR and not to the security camera, as most people think. Motion detection zones can help define area in the picture which will trigger the recordings, the zone selection or masking can let you to define areas of the screen where you want to detect or ignore visual changes.
Security DVR (digital video recorder) systems
Most security DVR and surveillance system, there are cameras connected to a DVR, which performs the capturing of images and recording them to a hard drive from each security camera video stream. Motion Recording allows the security DVR to decrease the amount of recorded video, and optimize the recordings by recording only when motion activates, this technology use motion in a specific area of the image as a search term when searching for events. When a change between the frames is detected the DVR will capture and record the frames to the hard drive and will stop recording after number of seconds after the motion stops. Motion recording optimize hard drive storage and is benefit the user when searching recorded event. You can easily detect and search a recorded event during night time when you don’t need to watch whole night recording to find if there was any activity at night, so it’s simplifies activity searches in recorded material.
Some time ago we issued guidelines for the identification of persons and vehicles. This is fine, but many system engineers were trying to find what camera and lens combination will satisfy these identification guidelines. And what about end users who know even less about camera and lens formats, how can they understand the competing specifications? This article all will be revealed for both groups.
In this Charts we will try to show the horizontal and vertical fields of view for many lenses and four formats are given in ‘The Principles of CCTV’ and were published in the first article CCTV. These charts also show the % of the screen height of a 5-6 feet person. The DVRMaster guidelines had not been published for general use.
The values for different degrees of identification are given as the percentage the 5 feet figure would occupy of the monitor screen. we call this the ‘screen height ratio’. The complete guidelines are provided in several DVRMaster articles and so only the basic ratios are given in this article.
These criteria are now becoming increasingly used as part of the specification for many CCTV and security camera systems. Usually the specification will state the distance from the camera for each criterion, sometimes the specification will ask the question, ‘at what distances from the camera will the criteria apply’? In either case it involves calculations that are not too difficult but can be tedious to keep repeating for each lens and camera location.
Another problem that many installer find difficulty in resolving are the different fields of view obtained from various camera and lenses sizes, i.e. what is the result of fitting a 1/3″ lens onto a 1/2″ camera, and how does this affect the screen height ratio at certain distances?
Here are some visual example for security camera field of view.