Image sensor

How they work

Photons striking a sensitive semiconductor area generate charge in light-sensitive elements called pixels. Each pixel accumulates electrons proportional to local light intensity; that charge is read out, amplified and converted to digital values by on-chip electronics. Important parameters include quantum efficiency, full-well capacity, read noise and the use of color filter arrays (for example a Bayer pattern) to record color information. See spectral sensitivity and noise characteristics.

Main technologies

Two solid-state approaches dominate modern imaging: charge-coupled devices (CCD) and complementary metal-oxide-semiconductor (CMOS) sensors. CCDs traditionally moved charge across the chip to a common amplifier, while CMOS devices place amplifiers or processing near each pixel, allowing lower power and higher integration. Recent design innovations include back-illuminated sensors to improve light collection and stacked architectures that separate sensing and processing layers.

• CCD: historically offered uniform readout and low fixed-pattern artifacts in many implementations.
• CMOS: offers faster readout, lower power use, integrated timing and per-pixel circuitry.
• Shutter types: global shutters expose all pixels simultaneously; rolling shutters read rows sequentially, which can distort fast motion.

Key characteristics

Sensor performance is usually described by resolution (pixel count), pixel pitch (physical pixel size), dynamic range (ability to capture bright and dark details) and color fidelity. Larger pixels typically gather more light and perform better in low light, while smaller pixels enable higher nominal resolution or smaller sensor packages. Designers must balance sensitivity, noise, resolution and power for each application.

Applications and specialized detectors

Image sensors are ubiquitous: consumer photography, smartphones, surveillance, industrial inspection, medical imaging and astronomy. Specialized detectors extend the same principles to other wavelengths—infrared cameras for thermal imaging, X-ray detectors in radiography and particle-sensitive arrays in research. Manufacturers optimize sensors for high frame rates, radiation tolerance or spectral selectivity; see technical guides at technical resources and application notes.

History and trends

From early phototubes and vacuum devices to solid-state CCDs and CMOS chips, sensor technology has advanced rapidly. Trends include shrinking pixel sizes, improved low-light sensitivity, stacked and back-illuminated designs, and increasing on-chip computational capabilities that enable features like in-sensor noise reduction and high dynamic-range imaging. These developments continue to broaden how and where images can be captured and analyzed.