technical

disk storage

JetBase will constantly process live video images, searching each frame for plates. When a plate is located the portion of the image containing the plate is extracted and displayed - this is called the "Plate Patch".

s437nnr.jpg - 1500 Bytes   
This small 'Plate Patch' image in raw form (bmp) is about 6k.
It is then compressed down to a sub-2k jpeg file.

The original video image of the vehicle from which the plate was extracted can also be saved for reference. When using infra red Jet-Cams this image can be very dark apart from the number plate.

(in bright sunlight a good greyscale image will be seen - but in low daylight the image all-but disappears apart from the retro-reflective plate)

So - the size of this ANPR image is 768 x 288 x 8 bits per pixel = 222k.
This compresses down to approximately a 25k jpeg file.
A very useful feature of Jet is the facility to connect additional colour cameras to the ANPR system so that an overview image may be saved of each vehicle. This gives the user useful information such as vehicle make, model, colour - and possibly an image of the driver. (several colour cameras may be allocated to each ANPR 'Lane').

s437nnr-at-barrier.jpg - 10367 Bytes   
The colour overview image is 768 x 288 x 24 bit = 666k

This is then compressed down to a sub-30k jpeg file.



When a plate is recognised by JetBase, the plate details in ASCII form are also saved alongside the images. This data consists of the plate characters, the lane number to identify which camera it comes from and the time and date - thus:

S437NNR 10:55 15/12/04 Lane 1

Each text entry takes up approximately 100 bytes of hard disk space - so if a vehicle was captured every second it would take over 30 years to fill a 100GB hard disk! Some ANPR systems are just required to report plate text in ASCII form - whilst others may have to store several thousand traffic movements per day including overview images. It is therefore important to be able to calculate disk space required.

The images are compressed using software in the pc and written to disk. This operation takes up to about 0.1 secs on a reasonably fast pc. (The faster the better!)

So, in a typical system, the text data, patch image and colour overview image are stored for every movement.

This totals say 32k per record.

Thus a 100 Gigabyte disk will store approximately 3,276,800 records ( 3 million)

If a busy car park had 2000 movements in and out - i.e. 4000 per day, then this standard disk would store the last 815 days worth of information - nearly 6 months. Daily volumes will determine how long the vehicle data and any associated images may be stored before the disk becomes full.
Note: that JetBase contains an automatic purge facility wherby images and text data may be auto-purged from the disk at a pre-determined time - freeing up disk space)