Video surveillance cameras and night technical analysis and its applications (1)

With video monitoring in the field of civil and more widely used, the application environment has become increasingly complex, one of the most important application requirements are monitored 24 hour nonbreaking.

Because color imaging general need high brightness and the actual environment may not be able to meet this requirement, so the camera low illumination technology (also known as night vision technology) is appropriate. Because monitoring needs are different, and therefore there is a different application technologies.

Due to cost and special materials, and other reasons, are widely used in the army of night vision technology has not been a large number of transplanted to civilian monitoring fields, so the current civilian monitoring products are usually used in this way several technology: high sensitive materials, digital slow shutter technology, caizhuan black technology, passive infrared imaging technology, and so on, because the monitoring requirements and applications, so in practice appears different application market.

High sensitive materials

Use a high-sensitivity material, including the use of high-sensitivity optical sensing material, ultra high signal to noise ratio signal analysis processors, signal processing to add some special processing technology, etc., as improved low light circumstances the effect of restoring the image acquisition, but because the cost and take into account the volume and other reasons, it is the best programme remains very difficult in a short time was widely used.

At present for CCD sensor component, increasing speed by two methods.

Because physically increase the photosensitive area, the device volume restriction cannot be realized, so one is in the component on each photo diodes (a single pixel) device micro lenses increase the photosensitive area disguise to gain speed, becomes effective. This design is like hanging on glasses help CCD, but CCD after 35 years of development, this technique is also elevated space is rather limited. Second, it is through a particular signal enhancement circuit, according to data operations to obtain a reasonable exposure, but this is usually because the CCD pixels speed sensitive photographic caused by uneven and formation of noise, then shooting out of the picture will be more obvious sense of particles. You also have to take measures to balance the high speed and superior picture quality between, thus inevitably brings higher cost of inputs.

Digital slow shutter technology

Digital slow shutter technology (digital slow shuttle), in fact it is not a shutter, but its functionality in a way similar to shutter, shutter (shuttle) and Iris (IRIS) is light on the camera, through the lens to achieve the effect of a light catching parts.

You can think about it this way, the aperture is light through the lens into a hole, the hole size is the size of the aperture, the hole bigger, the same circumstances, the more light, while the shutter is part of mastering aperture switch, control the aperture is always opened or follow a certain interval timer switch.

We know that, according to the human eye Visual interning characteristics, in order to ensure that what you see is continuous, PAL TV signal standard is 25 fps interlaced, i.e. each seconds after our immediate image actual is from 25 screens consisting of continuous screen in target shooting, every 1/25 second, a point can be scanned to a time, because it is interlaced, each 2 field in order to form a frame, so every 1 second, PAL image is 50 yards, 1 field is shutter interval, every second, shutter must work 50 times, to ensure that the output image is 50 fields/sec for PAL PAL image, so the minimum shutter speed of 1/50 seconds (this time the aperture is always open), practical applications, because the environment rays may be very strong, and this time you may need to control the amount of light, you need to control the shutter speed, the faster the speed, light to enter the less time you, into the less amount of light, relatively speaking, the image will appear to be relatively dark, on the contrary, the slower the shutter speed, the image becomes brighter illumination when light is low, even with 1/50 second image is still not enough light, this requires use of other technologies.

According to optical theory, the light can be superimposed, although in very dark environment each point to 1/25 seconds before it can be scanned to 1st, scanned, and the time is very short, its brightness very weak, if the before and after a period of time the brightness of the points are saved and overlay output again after this point can be lightened. So digital slow shutter technology principle is in accordance with the requirements of the corresponding period of the multiple image overlay and then output to improve signal strength.

[1] [2] [3]