Current Status and Breakthroughs of Low-Illumination Camera Technology

At present, the low-light cameras on the market, whether manufacturers or customers, have different definitions of low illumination. This is also because there is no unified standard for low illumination in the domestic market. However, customers are currently demanding higher and higher low illumination, requiring 24-hour all-weather monitoring, and the application environment is becoming more and more complex, which has also brought a certain degree of blind obedience to customers. At present, the main imaging applications in low-light environments are thermal imaging, ICCD cameras, EMCCD cameras, CCD cameras, and CMOS cameras that are becoming more and more widely used, and active infrared cameras, starlight-level network cameras.

1. Infrared imaging: The night effect of infrared imaging is relatively good, but it can only be limited to nighttime, and it cannot show the normal imaging effect of the human eye. Not many people can accept the anti-white effect of the display. In addition, at this stage, due to the relatively expensive price of thermal imaging cameras, they are still in the promotion stage in China and should only be used in some special fields, such as the military, banks, armed police and public security systems, and forest fire prevention.

2. ICCD camera: an image intensifier is added to the front of the CCD sensor, which can also be called pre-amplification. It is excellent in processing weak light and weak signals, but the price is relatively high. Moreover, ICCD cameras are very easy to age or even damage when exposed to strong light. They are mainly used in military and some special industries, such as night vision navigation, astronomical observation, medical equipment, spectral analysis, bioengineering and other special industries.

3. EMCCD camera: a gain register is added to the back of the CCD sensor, which can also be called post-amplification. Compared with ICCD, the resolution and price are slightly better than ICCD, but the image noise is larger than ICCD. It is mainly used in some scientific applications.

The low-light effects of the above three low-light imaging cameras are all excellent, but their unique specific environment restrictions and high prices make them unacceptable for civilian use.

4. CCD and CMOS cameras CMOS cameras: currently the most widely used low-light cameras in the security market. The following will explain in detail the differences between CCD and CMOS in low-light environments and the main methods to improve low-light effects in the market.

Since all pixels of CCD use a single sampling and amplifier, while each column of CMOS has its own independent sampling and amplifier, and since multiple amplifiers cannot achieve consistency, the noise generated by the signal is much larger than that of CCD. It is not obvious when the signal-to-noise ratio is high in the bright state, but in low illumination, the effective information is weak, and even if the noise information does not change, the signal-to-noise ratio is naturally better for CCD than CMOS. From the overall image, the low-light effect of CCD will be better than that of CMOS (the above does not calculate the pixel photosensitive area of ​​CCD and CMOS, because most CMOS use microlens to make up for the duty cycle and indirectly increase the photosensitive area of ​​a single pixel).

Most cameras on the market use the following methods to improve low-light imaging effects:

color-to-black technology, which is currently used by many people and can be used in conjunction with infrared lights. There are two conversion technologies. One is to use infrared filters and switching circuits to perform color/black and white conversion. In the daytime, invisible infrared light is filtered out to avoid interference with color. At night, invisible infrared light is allowed to irradiate the sensor surface, which can improve the low-light effect of the camera to a certain extent. The other method uses electronic circuits to filter out color signals without the need for infrared filters. This method only improves the color noise problem under low light conditions, and does not improve the low-light effect much.

Digital noise reduction technology, in order to further improve the image height under low conditions, often requires increasing the gain (AGC). However, when increasing the gain, the brightness and noise of the image are increased together. Therefore, from the perspective of the digital noise reduction effect of some high-end low-light cameras, it can better improve the cleanliness and clarity of the image when there are too many noise points in low light, thereby improving the low-light imaging effect. However, the current digital noise reduction technology uses 3D or 2D technology, so the camera will still have problems with tailing and animation after the noise reduction function is activated.

Frame accumulation method: The mainstream CCD on the market. The real low illumination of the best 2/3-inch CCD camera on the market is only 0.01lux in black and white mode, but there are some cameras on the market with a nominal 0.0001lux or even lower. These all use the frame accumulation method, which uses computer memory technology to continuously accumulate several underexposed images to obtain a brighter and clearer image. However, this method cannot capture high-speed moving objects, resulting in smearing and inability to see objects clearly. Therefore,

the current CCD and CMOS can only meet the low-light monitoring requirements in specific environments that are not particularly dark.