Image Sensor: Types, Working, and Applications Explained Clearly

What is an Image Sensor? How Does It Work?

An image sensor is a key component of a camera that converts incoming light and color information into electrical signals.

These electrical signals are then processed into digital data (0s and 1s), allowing the camera to create images.
Image sensors mimic the biological transduction process in humans, where one form of energy is converted into another.

Types of Image Sensors

There are mainly two types of image sensors:

• CCD (Charge-Coupled Device)
• CMOS (Complementary Metal-Oxide Semiconductor)

CCD (Charge-Coupled Device) Image Sensor

A CCD image sensor consists of millions of pixels. These pixels convert incoming light into electrical charge,
which is temporarily stored within the pixel array.

Once the charge is collected, it is transferred horizontally and then vertically through shift registers. In each shift register, the stored charge is converted into voltage and amplified using a charge-to-voltage converter and amplifier.

After the vertical register is cleared, the next row of stored charge moves in, and the process repeats for each row. Finally, the amplified analog voltage is converted into digital form using an ADC (Analog-to-Digital Converter).

CMOS (Complementary Metal-Oxide Semiconductor) Image Sensor

CMOS image sensors use fabrication technology similar to that of integrated circuits, enabling multiple supporting circuits to be integrated onto a single chip. The basic function of storing charge is the same as in CCD sensors. However, due to advanced fabrication techniques, each pixel in a CMOS sensor contains its own charge-to-voltage converter and amplifier.

This architecture results in higher processing speeds than CCD sensors. The voltage generated by each pixel is measured line-by-line. A pixel-select switch activates the first line of pixels and connects them to the column line. The column-select switch then reads each pixel one by one. The same process is repeated for all remaining lines.

Applications of Image Sensors

Image sensors are widely used in both analog and digital imaging systems, including:

• Digital cameras and camera modules
• Smartphone cameras
• Optical mouse devices
• Medical imaging equipment
• Night-vision and thermal imaging systems
• Radar and sonar systems

Industrial automation has seen significant improvements due to modern high-frame-rate image sensors. They are now widely used for inspection, quality control, and other automated processes.

Image sensors also play a vital role in security applications. Due to rising global threats, surveillance systems extensively use advanced imaging technology. These sensors are found not only in military systems but also in commercial and civilian setups.

Biometric identification systems rely heavily on image sensors as well. Almost all biometric characteristics — such as fingerprints, facial recognition, and iris scans — require some form of sensing, usually using traditional image sensors combined with specialized hardware or software for processing.