As an optical component, filter is used to select the required radiation band. It is made of plastic or glass and then added with special dye. Its main feature is that the size can be quite large. Thin film filter, usually through a long wave of light, is often used as infrared filter. The latter is a kind of low-order, multi-stage series solid-state interferometer, which is formed by metal film with high or low refractive index or all dielectric film with a certain thickness on a certain substrate through vacuum coating.
The main functions of image filter are as follows:
1. Infrared filtering
Color CCD can also sense infrared, because it can sense infrared, which will lead to the inability to calculate the correct color, so you have to add a filter to separate the infrared part of the light, so only the color CCD needs to install the filter, not black and white.
2. Trim in the light
Because CCD consists of many photoreceptors (cells), light enters directly, but in order to avoid interfering with the adjacent photoreceptors, it is necessary to trim the light. Therefore, the filter is not glass, but quartz. It uses the physical polarization characteristics of quartz to keep the direct part of the incident light and reflect the oblique part to avoid affecting the sensitive points nearby.
Function of filter for security monitoring:
Today's cameras have night vision function. What this night vision depends on is what can see the object in the completely dark state. It depends on the infrared light led to emit infrared light, which is reflected into CCD imaging, so there is a contradiction. In order to filter out the infrared light generated by the sun in the daytime, we paste the blue glass in front of the CCD, cut off the infrared light, and the infrared light emitted by the LED at night is filtered out by the blue glass, so it can't be imaged. How to solve this contradiction? Cutting off infrared light in the daytime makes the image clear and real. At night, it can make the infrared light from LED completely enter the CCD to complete the night vision function, which is the function of double filter. It relies on a mechanical device to finish the filter cutting off infrared light in front of the CCD in the daytime, and automatically switches to the full transparent filter at night, so as to meet the requirements of infrared night vision camera. This mechanism is called a double filter switcher.