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Field of View
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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.
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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 difference 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:
A subject in the foreground is in significantly clearer focus than the background.
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 dimensional 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 requirements 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.
Camera Placement for Facial Analysis - 4 Factors
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Resolution | Megapixels | Width for Face (Feet) |
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1024 X 768 | 0.7 | 6.5 |
1280 X 1024 | 1.3 | 8.0 |
1600 X 1200 | 2 | 10.5 |
2048 X 1536 | 3 | 13.5 |
The appearance of the field of view is obviously different with a width of 8.5’.
Pixels Between the Eyes
The same principles that apply to lower resolution cameras apply to megapixel cameras; 3VR still requires 35 pixels between the eyes. However, analysis is conducted on the full megapixel frame of the camera’s output. For example, with a resolution of 1280 x 1024, 3VR conducts facial analysis at 1280 x 1024 versus an analog camera at 4CIF (704 x 576).
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Digital images such as photographs and mugshots can be imported
CCTV cameras can be connected to a 3VR and video can be continuously analyzed
Best practices for each source differ significantly. Both sources are described and in Imported Images section below.
Imported Images
Any image that is in a supported digital format may be imported into the 3VR system. Supported formats include: BMP, JPEG and GIF. Only faces in images that meet the requirements enumerated in the previous two sections (pixels between the eyes, angles, lighting) may be successfully analyzed by the 3VR system.
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