High definition camera glasses

At present, the commonly used high-definition cameras for security monitoring products usually have such technologies: high sensitivity materials, digital slow shutter technology, color to black technology, passive infrared imaging technology and so on. Due to the use of different environments, so the requirements are different, the following is to analyze the technical characteristics.

High sensitivity materials

High sensitivity materials are used, including high sensitivity light sensing materials, ultra-high signal-to-noise ratio signal analysis and processing devices, and some special processing technologies are added to signal processing, so as to improve the restoration effect of image acquisition under low light conditions. However, due to the cost and consideration of volume, etc, Although this is the best solution, it is still difficult to be widely used in a short time.

At present, there are two ways to improve the sensitivity of CCD sensor. Due to the physical way to increase the photosensitive area, it can not be realized due to the limitation of the size of the device. Therefore, it is effective to increase the photosensitive area by installing a micro lens on each photosensitive diode (single pixel) of the element in a disguised way. This design is like putting glasses on the CCD, but after 35 years of development, the space to improve this technology has been quite limited. The second is to get a reasonable exposure according to the data operation through a specific signal enhancement circuit, but this usually causes the uneven sensitivity of the pixels due to the rapid sensitivity of the CCD, resulting in the formation of noise. At this time, we have to take measures to balance the contradiction between high sensitivity and high image quality, which is bound to bring higher cost.

Digital slow shutter Technology

In fact, digital slow shutter is not a kind of shutter, but its function is similar to that of shutter to some extent. Shutter and iris are parts of the camera that control light passing through the lens to achieve light capture effect. It can also be understood that the aperture is a hole that light can enter when passing through the lens, and the size of the hole is the size of the aperture. The larger the hole is, the more light will pass under the same situation. The shutter is the part that controls the aperture switch, which controls whether the aperture is always on or timed according to a certain time interval.

We know that, according to the visual persistence of human eyes, in order to ensure that the image seen is continuous, the standard of PAL TV signal is 25 frames per second interlaced scanning. That is to say, every second of the image passing in front of us is actually a continuous picture composed of 25 pictures. When shooting the target, every 1 / 25 second, a point can be scanned, because it is interlaced scanning, Every two fields can form a frame, so every one second, the PAL system image is 50 fields, and the time of one field is the shutter interval. Every second, the shutter must work 50 times to ensure that the output image is a PAL system image of 50 fields / second, so the minimum shutter speed of PAL system is 1 / 50 second (at this time, the aperture is actually always open), Because the light in the environment may be very strong, at this time, you may need to control the amount of light input, so you need to control the shutter speed. The faster the speed is, the less time the light can enter, and the less the amount of light input. Relatively speaking, the image will appear darker. On the contrary, the slower the shutter speed is, the brighter the image will be. When the light illumination is insufficient, Even if using 1 / 50 second, the image is still not bright enough, which requires the use of other technologies.

According to optical theory, light can be superimposed. Although in a very dark environment, each point can only be scanned once in 1 / 25 seconds, the scanning time is very short, and its brightness is very weak. If the brightness of the point is saved and superimposed for a period of time before and after output, the point can become bright. Therefore, the technical principle of digital slow shutter is to superimpose multiple images in a corresponding period of time and then output them according to the requirements, so as to improve the signal strength.

Because this technology does not need any changes to the external environment, it can be said to be the most ideal solution under the condition of meeting the monitoring requirements. But in fact, this technology can be applied in a very narrow range, because the premise of point by point accumulation is the accumulation of brightness at the same point at different times, and once the object changes or moves, The accumulated time of the former and the latter two may not be the same pixel, so moving objects on the whole image will appear "drag shadow" phenomenon. If the object moves too fast and the accumulated time of the frame is too long, the moving objects will even become virtual shadows. Therefore, frame accumulation technology is generally used to monitor the still scene in the weak light environment.

Color to black Technology

When the light is not enough, the image will be switched to black-and-white image, the interference of color carrier and color synchronization will be removed, and the AGC will be increased, which can improve the image quality in low visibility environment to a certain extent. However, this scheme can only solve some very special environment, which can not solve the weak light environment, and the image quality can be improved is also very limited, Generally, this technology should be used together with other technologies.

Under certain light source conditions, the image is changed from color to black and white by means of line switching. In the evolution of color / black-and-white line conversion technology, two sensors (one color sensor and one black-and-white sensor) were used to share a set of circuits before switching. At present, such cameras have adopted a single CCD (color) design, which is a color camera in the daytime or when the light source is sufficient, When the night comes or the light source is insufficient (generally in 1lux-3lux), the digital circuit is used to eliminate the color signal and turn it into a black-and-white image. Although this method can achieve the goal of "low illumination" at night, it has the disadvantages of blurred image and unnatural color during the day.