3vr P-Series SmartRecorder, Руководство по установке

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3VR SmartRecorder Installation and Configuration Guide
Industry participants commonly cite different CIF levels. These CIF levels have a significant impact on whether
imported images or captured video can be used for facial analysis.
For example, an image of a person recorded with 4CIF resolution may be able to be used by the 3VR system for
facial analysis, however, the same image recorded at CIF resolution will probably not contain enough detail to be
used for facial analysis unless the face is extremely large (at least a quarter of the width of the field of view).
See
“Camera Placement” on the following page for more information and examples on field of view for facial analysis.
Field of View
Field of View is the size of an area that can be seen while looking through an imager such as a photographic or
CCTV camera. Below are two examples of images with different horizontal fields of view.
The difference in the field of view is not very significant – the one on the left is only 2 feet wider than the one on
the right. However, despite this seemingly minor difference, we shall show later how this makes a significant dif
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ference on the suitability of the images for facial analysis.
An image does not have a singular width for the field of view. The width of the field of view increases as the
subject moves from the foreground of the image to the background.
The two major visual differences are:
(1) A subject in the foreground is in significantly clearer focus than the background.
(2) The width of the field of view is significantly smaller in the foreground than in the background.
The variation in the width of the field of view is a product of projecting a 3 dimensional world onto a 2 dimen -
sional medium (the image). All images will always exhibit this property.
This is very important because good facial analysis requires a narrow field of view (less than 4.5 feet at the point
at which the subject is in best focus). So, a subject in the foreground of an image that meets the field of view re
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quirements for facial analysis will be too small if they are a step or two further away from the camera, where the
field of view for the same camera placement will be significantly wider.
See “Camera Placement” on the following
page for more information and examples on field of view for facial analysis.