Basic Knowledge of Vision Sensors

Image Sensor

What Is an Image Sensor

A semi-conductor device, Image sensor, is built in the vision sensor. The image sensor consists of many small photo sensors spread over the chip that receive light through lens and convert the light into electrical signal.
Generally, "CCD" and "C-MOS" image sensor are used for cameras.
Basic structure of those devices are shown as follows.

Image sensor

C-MOS Image Sensor

  • C-MOS image sensor Diagram

CCD Image Sensor

  • CCD image sensor Diagram

Color Camera

The image sensor without color filters is monochrome image sensor and it provides gray-scale monochrome image data. To get color image data, color filters are needed for each pixel. Most of color image sensors employ "Bayer filter" invented by Mr. Bryce Bayer of Eastman Kodak.
The filter has RGB (Red, Green, Blue) area and its ratio is 50% Green, 25% Red and 25% Blue. Human eyes are sensitive to green so this ratio provides efficient output for human eyes.

  • Four pixels are needed to reproduce colors for a pixel for color image sensor means that resolution of color image sensor is worse than monochrome image sensor.
Example of Bayer filter array Diagram
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