The image sensor utilizes the photoelectric conversion function of the photoelectric device. The light image on the photosensitive surface is converted into an electrical signal in a proportional relationship with the light image. Compared with photosensitive elements such as photodiodes, phototransistors and other "point" light sources, an image sensor is a functional device that divides the light image on its light-receiving surface into many small units and converts it into usable electrical signals. The image sensor is divided into a light guide camera tube and a solid-state image sensor. Compared with the light guide camera tube, the solid-state image sensor has the characteristics of small size, light weight, high integration, high resolution, low power consumption, long life and low price. Therefore, it has been widely used in various industries.
The image sensor is an array of photoelectric detection units, and contains a series of processing circuits. 
There are two main structures of the image sensor, and the basic difference is that the charge reading method of the pixel unit is different.
CCD type: direct reading 
CMOS type: 
the characteristics of the two read after conversion are compared as follows. The biggest feature of CCD is high accuracy, so it is used in industrial vision more, but with the continuous progress of CMOS technology, more It is an inevitable trend that the CMOS type image sensor is widely used.