With the development of CCD and DSP technology, low-light infrared cameras have become mature and stable. Many manufacturers (businessmen) have lower the standard of the camera's illumination parameters, from 1.0lux to 0.1lux to 0.001lux, etc. Does the camera really have such a high sensitivity? In order to truly understand the low-light infrared camera, the following aspects are explained.
Lens
As an important part of the infrared camera part, its role is to focus the light of the subject for the CCD of the infrared camera, so that the scene is imaged on the CCD. The amount of light that can be captured directly determines the clarity of the CCD image. To measure how much light is taken by the lens, it is called the amount of light, and the amount of light entering the lens is expressed by the F value (aperture). F value = f (focal distance) / D (effective aperture of the lens), which is inversely proportional to the aperture, and is proportional to the distance from the focal point. With the same focal length, the larger the aperture of the lens, the smaller the F value and the greater the amount of light entering the lens. The F value of common lenses is mostly 1.2, 1.4, and there are currently F1.0 lenses. Therefore, in order to make the infrared camera obtain the ideal low illumination effect, it is necessary to configure a lens with a suitable or configured F value.
Filters
It is a very small device of a color camera and plays a significant role in the imaging effect of the infrared camera. The filter removes infrared light. The CCD of the color camera can also sense infrared light, but because the infrared light can easily cause the DSP to calculate the correct color, it is necessary to add a filter to filter out the mid-infrared light. Therefore, only the color CCD needs the filter, and the black and white CCD does not installation.
In order to obtain lower illumination, low-intensity infrared cameras need to take in some infrared light in addition to visible light, and infrared light of different wavelengths is ingested and will have a certain impact on the imaging of the camera. Therefore, it is necessary to filter out unwanted light. The infrared light retains the required infrared light filter. At present, high-end low-light infrared cameras use dual filters, that is, non-inductive infrared filters are used during the day to obtain clear images, and infrared-free filters are used at night to obtain lower illumination. This kind of infrared camera will have a photo-resistor. When the photo-resistor senses that the ambient light is insufficient, the trigger circuit in the infrared camera will be activated, and the filter that does not sense the infrared light will be switched to the filter that senses the infrared light. Higher-end infrared cameras convert black-and-white images while switching filters, resulting in better image quality. Of course, during the conversion process, you will encounter a critical value problem. If the light just switches back and forth when it is set to a critical value, it will not only affect the imaging effect, but also affect the life of the filter due to non-stop mechanical motion. Therefore, some manufacturers add a delay circuit in the infrared camera, that is, when a critical value is reached, the delay is switched for a period of time. If the illumination continues to decrease during this period, the switching is performed. If the delay remains unchanged or increases, the delay is not performed. Switch.
Low-speed electronic shutter technology
The low-speed electronic shutter utilizes the technology of computer memory to successively superimpose several pictures that are relatively blurred due to insufficient light, and become a relatively clear picture of the image. In the CCD camera, the shutter is operated by the charge accumulation time of the surface of the optically-controlled image, and the electronic shutter controls the accumulation time of the camera CCD. When the speed of the electronic shutter increases, the CCD is focused on within the permissible time of each video field. The reduction in light will reduce the camera's sensitivity. The ordinary infrared camera's electronic shutter is PAL:1/50-1/100000 seconds, NTSC is 1/60-1/100000 seconds, the low-speed electronic shutter can slow down the exposure speed of the shutter, making the CCD can accumulate charge for a longer time. Low-light environment to get a relatively clear picture. Now the frame-accumulating camera slows down its low-speed electronic shutter by up to 128 times that of ordinary infrared cameras. However, with the slowdown of the electronic shutter speed, the camera image tailing phenomenon will occur. Such infrared cameras are more suitable for the monitoring of still pictures, and it is not suitable to use active screen monitoring.
CCD photosensitive device
At present, there are three major suppliers of CCDs for infrared cameras, namely SONY, SHARP, and LG. In these three types of CCDs, SONY's CCD sensitivity is relatively good. The commonly used SONY CCD low-light technology is SuperHADCCD; later SONY has developed super- Sensitivity CCD, SONY called REVIEWCCD, the sensitivity of the CCD is 5 times SuperHADCCD.
In addition, the size of the CCD also has a great impact on the sensitivity, the larger the size, the better the sensitivity. In order to make infrared cameras have a lower illuminance index, 1/2-inch CCD cameras are often used. Data shows that the 1/3-inch CCD has only 56% of the 1/2-inch CCD, while the 1/4-inch CCD has only 44% of the 1/3-inch CCD.
Image DSP processing
Since the development of low-intensity infrared cameras, not only has the development of hardware technology, but also outstanding performance for DSP image processing, such as color to black technology and low-speed electronic shutter, that is, the emergence of frame accumulation technology.
Color to black technology
The sensitivity of a black-and-white camera is usually much higher than that of a color camera. Since the black-and-white camera, the DSP operation only processes two colors, namely black and white, so a considerable part of the low-intensity infrared camera now has a color to black and white. The function, that is, the daytime color image, is converted into a black and white image by software processing at night, and a lower illumination is obtained by sacrificing the color effect.
The process of converting color to black and white is controlled by the charge converted by the CCD to collect light. When the charge intensity reaches a certain critical value, it is automatically converted to a black and white image. Similarly, to ensure that the critical value does not cause repeated switching, it will do A delay in processing.
Through the above analysis, the user can not blindly look at the minimum illuminance parameters marked by each merchant when selecting a low-illuminance infrared camera, but should select the corresponding low-illuminance infrared camera according to the application environment, requirements, monitoring objects, and economic capabilities.
Lens
As an important part of the infrared camera part, its role is to focus the light of the subject for the CCD of the infrared camera, so that the scene is imaged on the CCD. The amount of light that can be captured directly determines the clarity of the CCD image. To measure how much light is taken by the lens, it is called the amount of light, and the amount of light entering the lens is expressed by the F value (aperture). F value = f (focal distance) / D (effective aperture of the lens), which is inversely proportional to the aperture, and is proportional to the distance from the focal point. With the same focal length, the larger the aperture of the lens, the smaller the F value and the greater the amount of light entering the lens. The F value of common lenses is mostly 1.2, 1.4, and there are currently F1.0 lenses. Therefore, in order to make the infrared camera obtain the ideal low illumination effect, it is necessary to configure a lens with a suitable or configured F value.
Filters
It is a very small device of a color camera and plays a significant role in the imaging effect of the infrared camera. The filter removes infrared light. The CCD of the color camera can also sense infrared light, but because the infrared light can easily cause the DSP to calculate the correct color, it is necessary to add a filter to filter out the mid-infrared light. Therefore, only the color CCD needs the filter, and the black and white CCD does not installation.
In order to obtain lower illumination, low-intensity infrared cameras need to take in some infrared light in addition to visible light, and infrared light of different wavelengths is ingested and will have a certain impact on the imaging of the camera. Therefore, it is necessary to filter out unwanted light. The infrared light retains the required infrared light filter. At present, high-end low-light infrared cameras use dual filters, that is, non-inductive infrared filters are used during the day to obtain clear images, and infrared-free filters are used at night to obtain lower illumination. This kind of infrared camera will have a photo-resistor. When the photo-resistor senses that the ambient light is insufficient, the trigger circuit in the infrared camera will be activated, and the filter that does not sense the infrared light will be switched to the filter that senses the infrared light. Higher-end infrared cameras convert black-and-white images while switching filters, resulting in better image quality. Of course, during the conversion process, you will encounter a critical value problem. If the light just switches back and forth when it is set to a critical value, it will not only affect the imaging effect, but also affect the life of the filter due to non-stop mechanical motion. Therefore, some manufacturers add a delay circuit in the infrared camera, that is, when a critical value is reached, the delay is switched for a period of time. If the illumination continues to decrease during this period, the switching is performed. If the delay remains unchanged or increases, the delay is not performed. Switch.
Low-speed electronic shutter technology
The low-speed electronic shutter utilizes the technology of computer memory to successively superimpose several pictures that are relatively blurred due to insufficient light, and become a relatively clear picture of the image. In the CCD camera, the shutter is operated by the charge accumulation time of the surface of the optically-controlled image, and the electronic shutter controls the accumulation time of the camera CCD. When the speed of the electronic shutter increases, the CCD is focused on within the permissible time of each video field. The reduction in light will reduce the camera's sensitivity. The ordinary infrared camera's electronic shutter is PAL:1/50-1/100000 seconds, NTSC is 1/60-1/100000 seconds, the low-speed electronic shutter can slow down the exposure speed of the shutter, making the CCD can accumulate charge for a longer time. Low-light environment to get a relatively clear picture. Now the frame-accumulating camera slows down its low-speed electronic shutter by up to 128 times that of ordinary infrared cameras. However, with the slowdown of the electronic shutter speed, the camera image tailing phenomenon will occur. Such infrared cameras are more suitable for the monitoring of still pictures, and it is not suitable to use active screen monitoring.
CCD photosensitive device
At present, there are three major suppliers of CCDs for infrared cameras, namely SONY, SHARP, and LG. In these three types of CCDs, SONY's CCD sensitivity is relatively good. The commonly used SONY CCD low-light technology is SuperHADCCD; later SONY has developed super- Sensitivity CCD, SONY called REVIEWCCD, the sensitivity of the CCD is 5 times SuperHADCCD.
In addition, the size of the CCD also has a great impact on the sensitivity, the larger the size, the better the sensitivity. In order to make infrared cameras have a lower illuminance index, 1/2-inch CCD cameras are often used. Data shows that the 1/3-inch CCD has only 56% of the 1/2-inch CCD, while the 1/4-inch CCD has only 44% of the 1/3-inch CCD.
Image DSP processing
Since the development of low-intensity infrared cameras, not only has the development of hardware technology, but also outstanding performance for DSP image processing, such as color to black technology and low-speed electronic shutter, that is, the emergence of frame accumulation technology.
Color to black technology
The sensitivity of a black-and-white camera is usually much higher than that of a color camera. Since the black-and-white camera, the DSP operation only processes two colors, namely black and white, so a considerable part of the low-intensity infrared camera now has a color to black and white. The function, that is, the daytime color image, is converted into a black and white image by software processing at night, and a lower illumination is obtained by sacrificing the color effect.
The process of converting color to black and white is controlled by the charge converted by the CCD to collect light. When the charge intensity reaches a certain critical value, it is automatically converted to a black and white image. Similarly, to ensure that the critical value does not cause repeated switching, it will do A delay in processing.
Through the above analysis, the user can not blindly look at the minimum illuminance parameters marked by each merchant when selecting a low-illuminance infrared camera, but should select the corresponding low-illuminance infrared camera according to the application environment, requirements, monitoring objects, and economic capabilities.
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