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The following video camera requirements should be met in order to ensure the recognition of license plate numbers using the Auto-Intellect system.

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№

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Property

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Range

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Comment

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1

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Camera type

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CCTV

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Analog and IP-cameras can be in use.

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2

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Camera resolution

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Not less than 520 TVL horizontally.

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Only high resolution CCTV camera usage guarantees the recognition rate declared in the technical characteristics of the system.

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3

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Illuminance of the monitored area

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Not less than 50 lux for cameras with 0.05 lux CCD sensitivity;
Not less than 20 lux for cameras with 0.0002 lux CCD sensitivity;
0 lux for cameras with IR illumination.

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At night time, standard auto road illumination devices are sufficient to provide 50 lux illuminance in full compliance with the building regulations.

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4

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Automatic amplification adjustment

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LOW or MIDDLE depending on the camera

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This function must be enabled. Unfortunately, the scene is usually not sufficiently illuminated, thus the image looks too dark in case this function is disabled. Enabling this function amplifies the whole video signal including the CCD noise. The amplification value is chosen for each camera separately.

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5

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Auto aperture and auto electronic shutter

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• not more than 1/500 sec for vehicle speed below 40 km/h;
• not more than 1/1000 sec for fast motions (vehicle speed above 40 km/h).

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The image should be sharp. Sharpness can be achieved by locking the shutter speed (exposure). Locking the speed of the electronic shutter is a very important function.
When the exposure is long, i.e. the shutter speed is low (1/100, 1/50 sec), the moving objects are blurred in the image. This most affects the small details, eg. the symbols in license plate numbers. The video sequence as a whole may look good enough, but the static frames that comprise it may be blurred, making LP number recognition partially or completely impossible. If the video camera is not forced to operate at high shutter speed, it will automatically switch to long exposure in case of poor lighting conditions, preventing plates recognition. With the same settings, the video camera can recognize the numbers in bright light only, automatically switching to short exposure.
If the video camera is installed at an angle more than 10 degrees to perpendicular to the license plate, we recommend to halve the shutter speed.

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6

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Color

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Black and white image

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It is recommended to use black and white cameras unless it is necessary to store color pictures of the vehicle. This is because clolr cameras while having same characteristics have less sensitivity and pictures appear less sharp.

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7

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Video stream speed (fps)

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Slow mode – 3 fps.
Fast mode – 25 fps.

For

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recognition

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For recognition it is necessary to make sure that frames with number plates fulfill the following characteristics:

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• height of the symbols is not less than 15 px, width is not less than 2px;symbols should be sharp, not smeared, undistorted, not overexposed, evenly lighted;
• symbols should be visually differentiated;
• technical requirements for the number plates should follow according government standards;
• minimum allowed contrast with evenly dirty number plate should not be less than 10% ) contrast differentiation of symbols to the background is 25 on 256 point scale);
• maximum allowed uneven dirtiness is not more than 12% (ratio of the dirty area of the number plate to its whole area);
• geometrical proportions of the number plate picture should not differ from such proportions of the number plate itself with more than 10%;without the effect of interlacing (on speed) for analog cameras.

Basic characteristics of used video cameras are presented in the General requirements for mounting and configuring of cameras section.