Detailed Explanation of IR-CUT in IP Camera

There are various wavelengths of light in nature, and the human eye can see different colors of light through refraction, which is caused by the different wavelengths of light. In fact, there are still many light rays that cannot be seen by the human eye. The wavelength range of the human eye to recognize light is between 320nm and 760nm, and the light that exceeds 760nm cannot be seen by the human eye, such as infrared light (wavelength is generally 850nm) and so on. However, the CMOS sensor chip can see most of the wavelengths of light, which causes the situation that the sensor "sees" differently from the image seen by the human eye. The image processing algorithm only processes the image "seen" by the sensor, because some light is invisible to the human eye, so the processed image will appear to be color cast, such as black is grayish, green is purple, etc. In order to correct this problem, it is necessary to wear "glasses" on the CMOS sensor to filter out the infrared light invisible to the human eye, so as to achieve the same purpose as the image seen by the human eye. At night, because infrared lights are commonly used for supplementary light, the "glasses" must be removed at night to allow infrared light to penetrate the CMOS surface to achieve the purpose of supplementary light. Let us briefly discuss this issue from several aspects.

1. What is IR-CUT
The so-called IR-CUT can be simply understood as CMOS "glasses", which include "lenses" and "glasses removal device", "lenses" are filters, and "glasses removal device" is the mechanical structure of IR-CUT. There are 2 lenses, one for filtering infrared light during the day and one for full light transmission at night. The 2 lenses are controlled by the IR-CUT motor, and they work in turn. During the day, the infrared filter is used to ensure that the image does not cast color, and at night, the fully transparent lens is used to increase the sensitivity. The material of the filter can be divided into glass and quartz, and the place of origin can be divided into domestic and imported. Generally, in order to achieve the best effect, the filter is customized according to the spectral diagram of the chip. The various differences in the optical filter lead to a relatively large price difference, and a good optical filter can significantly improve the clarity and fineness of the image.

IR=infrared=infrared
CUT=filter, subtract

2. Under what circumstances should IR-CUT be used?
IPC network cameras generally have high requirements for images, and require no color cast in the images during the day, and use infrared lights to supplement the night vision effect at night, and need to use IR-CUT.

At present, there are three main types of CMOS usage occasions:

1. It is used in occasions that do not need supplementary light, such as hotel lobby, 24-hour convenience store, etc., there are sufficient light sources for 24 hours;

2. In occasions where white light is used to supplement light, such as road monitoring, the image needs to be always in color;
3. In occasions where infrared lights are used to supplement light, such as school monitoring and community monitoring, etc., supplementary light is required and must have a certain degree of concealment, with little interference to the surrounding environment.
For the third scenario, the IPC network camera must use IR-CUT. For the first scenario, IR-CUT can be considered to enhance the color reproduction.

3. Matters needing attention when using IR-CUT
To sum up, there are two scenarios for using IR-CUT:
1. Not equipped with infrared fill light, such as ordinary gun;
2. Equipped with infrared fill light as standard, such as waterproof bolt;
Because the filter of IR-CUT during the day will completely filter out the infrared light, so the infrared light is completely filtered out for the CMOS during the day, which is equivalent to no infrared light, and it is equivalent to a very bright flashlight for the CMOS at night. fill light.
So for scene 1, the IPC network camera needs to ensure that there is no infrared light source in the environment, such as other infrared guns, otherwise the IR-CUT will switch back and forth repeatedly. For scenario 2, the infrared light needs to have a synchronous signal output to the CMOS board to "tell" the CMOS board whether the current infrared light is on or off, and the IR-CUT switch is synchronized with the infrared light to prevent back and forth switching. .

In our client/WEB software, there is an option of IR-CUT working mode in Device Configuration -> Camera Parameter Configuration. Is it switched synchronously according to the infrared light or automatically switched according to the brightness? The default is to switch synchronously according to the infrared light. For occasions where no infrared light is used, it needs to be configured to automatically switch according to the brightness.

4. Special requirements for using IR-CUT
When using IR-CUT with infrared light, there must be a synchronous signal output on the light board to the CMOS board to "tell" the CMOS board whether the current infrared light is on or off. All CMOSs are needed, and ours is no exception. The light board needs to output a synchronous signal to our CMOS board. When the infrared light is off, the output is 0V, and when the infrared light is on, the output is 3.3V. It cannot be higher than 3.3V, otherwise it will burn out our main control board.

5. Enhance night vision effect skills
Some customers have higher requirements for night vision effects, hoping to see farther and more clearly, here are a few tips for reference.
1. Increase the power of the infrared lamp. This will improve the night vision effect immediately, for example, you can choose multiple array lights, etc.;
2. Set the night time period in the image color, and increase the brightness and contrast at the same time, which can improve the night vision effect;

3. Open the electronic slow shutter level in the camera parameters, which can be set to "strong", or choose a suitable level according to the needs. Note: When the electronic slow shutter is turned on, the frame rate will be reduced, and when there are large objects moving quickly in the picture (such as cars), there will be smearing.

6. Working principle
The function of IR-CUT double filter switcher for the camera is to correct the color cast problem during the day and improve the brightness at night. The principle of the IR-CUT dual filter switcher, the IR-CUT dual filter switcher is composed of: filter (one infrared cut-off or absorption filter and one full spectral filter) + power part (can It is composed of electromagnetic, motor or other power source). There are various wavelengths of light in nature. The wavelength range of light recognized by the human eye is between 320nm-760nm, and light exceeding 320nm-760nm cannot be seen by the human eye, such as infrared light, ultraviolet light, etc.

The camera's imaging components CCD or CMOS can see most of the wavelengths of light. Due to the participation of various lights, the color restored by the camera and the color seen by the naked eye have deviations in color. To try to solve the problem of color shift: the current solution It is to paste a single-layer or multi-layer (while allowing visible light and infrared light to pass) double-peak filter in front of the CCD. In the daytime, due to infrared and other stray light entering the CCD, it will interfere with color reproduction, such as green plants becoming grayish white, red clothes fading, etc. (especially in sunny outdoor environments); at night due to the filtering effect of the bimodal filter, the The CCD doesn't make good use of all the light, and noise and its low-light performance are unsatisfactory.

The IR-CUT double filter switcher works when the light is sufficient during the day, and the IR cut filter works, and the CCD restores the true color. The light sheet starts to work, allowing the CCD to make full use of all the light, which greatly improves low-light performance.

IR-CUT double filter switcher is good or bad
The quality of IR-CUT comes from three aspects:
1. Optical filter
2. Power drive part
3. Control circuit

working principle
In front of the camera lens, a full-spectrum lens film is built in, driven by a microelectronic motor.
When the CMOS/CCD photosensitive chip absorbs various wavelengths in nature, the double filter blocks/releases the light passing through the lens according to the actual light detected, so that the CMOS/CCD can obtain the most appropriate imaging light, so that the later stage can be obtained The image can get an optimal value, and of course get an optimal picture. All this is done automatically, no human intervention required!