The Function and Introduction of Machine Vision Light Source Filter

Ⅰ. What is the function of the filter of the machine vision light source?

The function of the filter is to attenuate the light intensity of the machine vision light source, change the spectral composition or limit the vibration plane, mainly to select the required radiation band.

A commonality of filters is that no filter will make the image of the target brighter, because all filters absorb certain wavelengths, making the object darker.

Flat glass or gelatin sheets of various colors have a transmission bandwidth of hundreds of meters, and are mostly used in broadband photometry or installed in stellar spectrographs to isolate overlapping spectral orders. Its main feature is that the size can be made quite large.

Ⅱ. Thin film filter for machine vision system

It is divided into two types: thin-film absorption filter and thin-film interference filter. The former is on a specific material substrate, using chemical etching to make the absorption line just at the required wavelength. Generally, the transmitted wavelength is longer, and it is mostly used as an infrared filter.

Optical filter products are mainly classified according to spectral band, spectral characteristics, film material, application characteristics, etc.

1. Spectral band: UV filter, visible filter, infrared filter;

2. Spectral characteristics: band-pass filter, cut-off filter, spectroscopic filter, neutral density filter, reflective filter;

3. Film material: soft film filter, hard film filter;

The hard film filter not only refers to the hardness of the film, but more importantly its laser damage threshold, so it is widely used in laser systems, while the soft film filter is mainly used in biochemical analyzers.

Band-pass type: the light of the selected wavelength band passes, and the light outside the pass band is cut off. Its optical indicators are mainly center wavelength (CWL) and half bandwidth (FWHM). Divided into narrowband and broadband.

Short pass type (also known as low pass): Light shorter than the selected wavelength passes through, and light longer than the wavelength is cut off.

Long pass type (also known as high pass): Light longer than the selected wavelength passes through, and light shorter than the wavelength is cut off.

Ⅲ. The filter principle of machine vision:

The filter is made of plastic or glass with special dyes added, the red filter can only let red light pass through, and so on.

The transmittance of the glass sheet is almost the same as that of air, and all shades of light can pass through, so it is transparent, but after being dyed with dyes, the molecular structure changes, the refractive index also changes, and the passage of some shades of light changes.

For example, a beam of white light passes through a blue filter, and a beam of blue light is emitted, while green light and red light are very few, and most of them are absorbed by the filter.

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