Low-light camera technology status and breakthrough

At present, low-light cameras in the market, whether manufacturers or customers, have different opinions on the definition of low illumination. This is also because there is no standard for low illumination uniformity in the domestic market, but customers are currently demanding less and less illumination. High, requiring 24-hours-a-day monitoring, the application of the environment is becoming more and more complex, which also gives customers a certain degree of blind obedience, the current imaging applications in low light environments are mainly thermal imaging, ICCD camera, EMCCD camera, CCD camera , As well as the CMOS cameras that are becoming increasingly popular, and active infrared cameras, star-class network cameras.

1, infrared imaging: infrared imaging of the nighttime effect is better, but can only be limited to night, and can not display the normal human eye imaging results, for the display of anti-white effect is not acceptable to many people, in addition, at this stage, Because thermal imaging cameras are relatively expensive, they are still in the promotion stage in China. They should only go to special areas such as the military, banks, armed police and public security systems, and forest fire prevention.

2. ICCD camera: The image intensifier is added in front of the CCD sensor. It can also be said to be pre-amplification. The processing of weak and weak signals is very good, but the price is relatively high, and the ICCD camera is in a strong light environment. Exposure is extremely prone to aging and even damage. It is mainly used in military and some special industries such as night vision navigation, astronomical observations, medical devices, spectral analysis, biological engineering and other specialized industries.

3. EMCCD: Adding a gain register to the rear of the CCD sensor can also be regarded as a post-amplification. Compared with ICCD, the resolution and price have slight advantages, but the image noise is larger than that of the ICCD. The main applications are also some scientific applications. .

The low-light effects of the above three kinds of low-light imaging cameras are very good, but their unique specific environmental constraints and higher prices are currently not yet acceptable to civilians.

4, CCD, CMOS camera: At present is the application of the most low-light camera in the security market, the following will explain in detail the difference between CCD and CMOS in the low light environment and the market to enhance the low-light effect.

Since all the pixels of the CCD use a single sample and amplifier, CMOS has its own independent sampling and amplifier for each phase. Because multiple amplifiers cannot achieve consistency, the noise generated by the signal is greater than that of the CCD. Much bigger. When the signal-to-noise ratio is high in the bright state, the performance is not obvious, but in low illumination, the effective information is weak, even if the noise information is unchanged, the signal-to-noise ratio is naturally CCD is better than CMOS, in view of the overall image, the CCD low-light effect Will be better than CMOS (the above does not calculate the CCD, CMOS pixel sensing area, because CMOS mostly uses microlens way to make up the duty cycle, indirect increase the photosensitive area of ​​a single pixel).

The majority of cameras on the market improve the low-light imaging effect mainly in the following ways:

The color-to-black technology currently uses this technology to a large extent and can be used in conjunction with infrared lamps. There are two kinds of conversion technologies. First, infrared filters and switching circuits are used to perform color/black-white conversion. Invisible infrared light is filtered during the day to avoid interference with color. At night, invisible infrared light is applied to the surface of the sensor. Can improve the camera's low-light effect to a certain extent; another use of electronic circuits to filter out the color signal, no infrared filter, this method only improves the low-light color noise problems, improve the low-light effect is not Great.

Digital noise reduction technology, in order to further improve the image height in low environment, often need to increase the gain (AGC) but increase the gain at the same time, the brightness and noise of the image is improved together, so the digital noise reduction from some high-end low-light camera From the effect point of view, it is possible to improve the cleanliness and sharpness of the image better under low noise conditions, thus improving the low-light imaging effect. However, the current digital noise reduction technology adopts 3D or 2D technology. Therefore, the camera will still have tailing and animation issues after the noise reduction function is activated.

With the frame accumulation method, the true low illumination of the best 2/3-inch CCD camera on the market in the current market is only 0.01 lux in black and white mode, but there are still some cameras on the market that are rated 0.0001 lux or lower. All of these methods use frame accumulation, which is the use of computer memory technology to continuously accumulate several under-exposed images to obtain a brighter and clearer picture, but this can prevent the high-speed moving objects from catching up. Smear now looks like it cannot see objects.

So the current CCD and CMOS can only meet the specific environment, not particularly dark low-light monitoring.

5. Active Infrared Camera: In the current market, where low light requirements are very high, active infrared cameras are basically used. In night vision, infrared light emits infrared light that is invisible to the naked eye to illuminate the object being photographed. Infrared is reflected by an object and enters the lens for imaging. What we see is an image formed by infrared reflection instead of the image formed by the reflection of visible light. In this way, we can capture objects that are invisible to the naked eye in dark environments. , which is what people often say can reach 0lux, but this has the following problems:

1) If it is a relatively empty environment, infrared light does not have a reflective object, so the image is completely black, the display is not good 2) If the monitoring environment is more complex, such as: there is a tree in the monitoring environment, behind the tree Is the monitoring of the image, so that the front of the leaves to all the infrared lights sucked and reflected, the back of the tree really want to monitor the object but can not see, that is, can only see the front can not see behind.

3) The remote monitoring infrared lamp can not be achieved, the effect of the infrared lamp over 100-120 meters can not reach the 4) the problem of the life of the infrared lamp. At present, all manufacturers have written 50,000 hours for the life of the infrared lamp - 10 Tens of thousands of hours, but in fact there are very few infrared cameras that reach this life span. Infrared lamps are overheated and the power is too large. Now the problem is widespread. The farther the camera is, the greater the power, the greater the power, and the amount of heat. The larger the infrared sensor is, the closer the proximity of the infrared sensor to the camera is, the same will also affect the service life of the camera. This is also the main problem of the active infrared camera.

6. Star-class cameras: Star-level cameras can clearly see images under the 0.001lux required for normal work. That is, there are more stars in the sky at night and there are many manufacturers in the domestic market. Level cameras, but basically all use the frame accumulation method to achieve the 0.001lux imaging, which also lost the significance of the starlight. China Star Electronics' latest star-class network camera adopts an independently developed star-level sensor to achieve low Read noise, high charge capacity, combined with the unique ISP function of Zhongxing Electronics, the minimum illumination can reach 0.001Lux, and can maintain a small image noise, and realize the true meaning of the star-class camera, fill the industry The gaps can be clear under starlit illumination, without smearing, 1080p Full HD images, high-definition images can be obtained without the use of infrared lamps in relatively dark environments, night imaging is closer to the ICD for special industries and military The EMCCD's nighttime imaging results have made the security industry a step closer to low-light technology development.

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