A digital camera's sensitivity to light is noted as an ISO value. ISO stands for 'International Organization for Standardization' and the film speed ratings they developed are used to indicate the amount of light needed to provide a proper exposure. Film speed is a term referring to the measure of a photographic film's sensitivity to light. A film with lower light sensitivity (lower ISO/ASA speed) requires a longer exposure time (slow film), while film with higher light sensitivity (higher ISO/ASA speed) can capture the same shot with a shorter exposure time (fast film). Similarly, the sensor in a digital camera can adjust its sensitivity in the form of electrical output, where the higher the output the less light is needed to properly expose an image.

However, with this amplification comes visible noise in the form of a grainy image. Lower ISO levels (50-100) require significantly more light than the upper range of ISO values (800-3,200) but, in turn, they produce a finer digital "grain," or a less noisy image. Many higher-end cameras have high ISO levels with little noise, but with many point-and-shoot cameras, taking a photo in a low-light condition (such as indoors) without a flash will result in grainy digital images.