ISO stands for International Standards Organization. It denotes the rating of a film's sensitivity to light (based on an arithmetical progression). Though digital cameras don't use film, they have adopted the same rating system for describing the sensitivity of the camera's imaging sensor. Digital cameras often include a control for adjusting the ISO speed; some will adjust it automatically depending on the lighting conditions, adjusting it upwards as the available light dims. For exampe, ISO 200 film is twice as fast as ISO 100 film but only half as fast as ISO 400. The scale is identical to ASA (American Standards Association). Generally, with higher ISO speeds there is more noise.