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Resolution | Megapixels | Width for Face (Feet) |
|---|---|---|
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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The second step is to measure the “subject distance” (from lens to subject), and mounting height for the camera. In order to maintain a vertical slope of 20%, the camera can be mounted approximately .2 feet above face height for every foot of subject distance as shown below.
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Simple Formula: (D x .2 ) + E = H
Multiply the subject distance (D) value by .2 (for 20% slope). Add the result to the eye height (E). This equals the maximum mounting height (H).
Example: assuming a 5’ eye height and 15 foot subject distance:
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15’ (subject distance) x .2 (slope) = 3’
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Maximum Camera Mounting Height (based on average face height of 5' and a max vertical slop of 20%) | |||||
|---|---|---|---|---|---|
D- Distance to Subject | 10' | 15' | 20’ | 25' | 30' |
.2*D (20% of Distance to Subject) | 2' | 3' | 4' | 5' | 6' |
E- Eye Height | 5' | 5' | 5' | 5' | 5'' |
H: Max Mounting Height: | 7' | 8' | 9' | 10' | 11' |
Simple Formula: (D x .2 ) + E = H
Multiply the subject distance (D) value by .2 (for 20% slope). Add the result to the eye height (E). This equals the maximum mounting height (H).
Example: assuming a 5’ eye height and 15 foot subject distance:
15’ (subject distance) x .2 (slope) = 3’
3’ + 5’ (eye height) = 8’ mounting height
Remember, a 20% slope is a maximum number – a decreased slope will provide better results, (and mounting the camera with no slope, exactly at the average face height will provide the best results).
Example: A potential entry point offers 2 appropriate mounting positions, one at 12 feet away, the other at 24 feet away. In this case, the furthest mounting location is most appropriate.
Camera/Lens Specifications
Cameras designated for face-based recording must comply with a wide range of specifications, primary among them is the use of high-resolution cameras, (480 TVL or greater). The camera and lens must be appropriate to the scene lighting conditions. For example, black & white low-lux or day/night camera for poorly lit areas, and super-dynamic cameras where severe back-lighting can occur.
An appropriate 4’ wide field of view, (FoV), is the result of the focal length of the lens in relation to the object distance from the camera. While an appropriate “fixed focal length” lens can be utilized, a VariFocal Lens is strongly recommended because the selectable focal length range enables a flexible field-adjustment (fine-tuning) capability.
VariFocal Lenses are available with manual or automatic iris features. The automatic iris format is used in applications where lighting conditions may vary, for example, areas exposed to daytime sunlight.
Lens Selection
Typical VariFocal Lenses fall within the following approximate ranges; 3 to 8 millimeters (mm), 3 to 12mm, 5 to 50mm, and 20 to 100mm. The most common and least expensive are the 3 to 8mm versions, although most Face Capture applications will require the larger size VariFocal Lenses.
Guidelines for Determining Lens Focal Length
A 4’ wide FoV requires 1.2mm per foot of distance from subject; a 4½’ wide FoV requires 1.1mm per foot.
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The estimates on the previous page assume the use of 1/3” CCD (the most common size) camera format. Results will vary in applications using different size formats such as ½” or ¼”. Lens calculation tools are available from most camera manufacturers, (online and pocket ‘slide-rule’ versions).
With megapixel cameras, deployment no longer requires such a large telephoto range when comparing to analog and non-megapixel IP cameras. Evidently, this will depend on the particular application. Please refer to the table in the Field of View section for determining the maximum width for each application.
Camera Face Requirement Chart in 3VR
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In this case, the furthest mounting location is most appropriate.
Camera/Lens Specifications
Cameras designated for face-based recording must comply with a wide range of specifications, primary among them is the use of high-resolution cameras, (480 TVL or greater). The camera and lens must be appropriate to the scene lighting conditions. For example, black & white low-lux or day/night camera for poorly lit areas, and super-dynamic cameras where severe back-lighting can occur.
An appropriate 4’ wide field of view, (FoV), is the result of the focal length of the lens in relation to the object distance from the camera. While an appropriate “fixed focal length” lens can be utilized, a VariFocal Lens is strongly recommended because the selectable focal length range enables a flexible field-adjustment (fine-tuning) capability.
VariFocal Lenses are available with manual or automatic iris features. The automatic iris format is used in applications where lighting conditions may vary, for example, areas exposed to daytime sunlight.
Lens Selection
Typical VariFocal Lenses fall within the following approximate ranges; 3 to 8 millimeters (mm), 3 to 12mm, 5 to 50mm, and 20 to 100mm. The most common and least expensive are the 3 to 8mm versions, although most Face Capture applications will require the larger size VariFocal Lenses.
Guidelines for Determining Lens Focal Length
A 4’ wide FoV requires 1.2mm per foot of distance from subject; a 4½’ wide FoV requires 1.1mm per foot.
FoV | Distance from Object/Focal Length Needed for a Camera with 1/3” CCD | |||||
|---|---|---|---|---|---|---|
10' | 20' | 30' | 40' | 50' | 60' | |
4.0 ft.wide | 12mm | 24mm | 36mm | 48mm | 60mm | 72mm |
4.5 ft. wide | 11mm | 22mm | 33mm | 44mm | 55mm | 66mm |
The estimates on the previous page assume the use of 1/3” CCD (the most common size) camera format. Results will vary in applications using different size formats such as ½” or ¼”. Lens calculation tools are available from most camera manufacturers, (online and pocket ‘slide-rule’ versions).
With megapixel cameras, deployment no longer requires such a large telephoto range when comparing to analog and non-megapixel IP cameras. Evidently, this will depend on the particular application. Please refer to the table in the Field of View section for determining the maximum width for each application.
Camera Face Requirement Chart in 3VR
Face Size | 35 pixels between the eyes required. Rules of Thumb: The field of view when subject is in focus must be less than 4.5 feet ot the face, or the face width must be at least 1/7 of the field of view. |
Zoom | Zoom lens recommended: 5-50 mm (5%-15%) angle of view. |
Vertical Slope | Recommended 20% slope from eye level. (see example), rule of thumb: The middle of the nose should be higher or at least the same level as the bottom of the earlobes. |
Horizontal Angle: | Thumb Rule: The image must simultaneously show both ears of the subject. |
Lighting | High quality required with wide dynamic range. Well lit, no harsh shadows or glare |
Event Length | There must be a period of time during which the subject is in focus, large enough (face 1/7 of the field of view), well lit, facing the camera so that both ears are visible, and the middle of the nose is above the bottom of the earlobes. Recommended: 3 seconds, (minimum 2 seconds) |
Camera Features | B/W or Color (appropriate to lighting conditions). Back light control sometime helpful. Manual or Auto-iris lens(as appropriate to the application) |
Examples | Doorways, Hallways, Entrances, Exits Queue lines Teller lines |
Result
Quality Image
With better understanding on optimization of image quality you can now determine:
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