Identification and Recognition Tutorial
Camera positioning, motion and compression
Camera placement
In this example, light is favorable both in intensity and direction. The camera is placed in level with passing people and the lens offers both focus and depth of field.
Camera placement is critical for successful identification. This is not only for the purpose of avoiding difficult lighting situations, but also to ensure that persons or objects are captured at a favorable angle. If, for example, cameras are placed high above the ground, images will have a birds-eye perspective, making persons or objects distorted and difficult to identify.
The camera should be firmly fixed in order to minimize blur caused by camera movement. This is of particular importance for PTZ cameras, where maneuvering the camera may induce vibrations that affect image quality.
Stability can be challenging if the camera is mounted on a tall pole and you are using a zoom lens with a long focal length. Then, even small vibrations will translate to large movements in the resulting image.
Motion
Your system design needs to consider motion. For identification purposes, a minimum frame rate of 5 to 8 frames per second is often recommended. Your surveillance objectives may require higher frame rates, for example if you want to get a clearer picture of a series of events. If the captured scene includes persons or objects that cross the field of view at high speed or close to the camera, you will probably want to increase the frame rate to ensure that the camera will not miss any of the action.
Also, in order to capture sharp footage of fast-moving persons or objects, you will need to use short shutter speeds. Using cameras that support progressive scan eliminates the blur that affects moving objects when using interlaced video.
Compression
Compression can greatly affect the usability of recorded materials for identification and recognition. High compression ratios will introduce blur or pixelation that makes identification difficult. If the compression algorithm uses a bit rate limit, the compression could increase when motion occurs, making otherwise clear footage unusable. When using variable bit rates, on the other hand, the compression remains unchanged, but bandwidth usage will increase when there is motion.
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