In digital cameras, the ISO sensitivity parameter indicates the amplification level of light entering through the lens inside the camera.

The amount of incoming light is determined by aperture and shutter speed. Based on the received light volume, the camera amplifies the signal to produce a properly exposed image. ISO sensitivity quantifies this amplification. For example, ISO 200 offers twice the sensitivity of ISO 100. This means shooting at ISO 200 requires only half the light to achieve the same brightness compared with ISO 100.

In most shooting modes, ISO sensitivity is automatically determined by the camera according to scene conditions. Nevertheless, manual adjustment is available in P/A/S/M modes to suit specific requirements.

A higher ISO setting enables faster shutter speeds even under low-light conditions. This helps reduce blur caused by camera shake in dim environments or moving subjects during motion capture. However, since light signals are amplified electronically, high ISO values tend to introduce noise (grain) and reduce image sharpness.

The nightscape photos above were captured handheld. Image [1] was shot at ISO 3200, while image [2] used ISO 800.

Increasing ISO prevents motion blur, yet the buildings in the left photo exhibit noticeable grain.