What does ISO control in photography?

ISO in photography relates to the sensitivity of the camera's sensor to light. It plays a crucial role in determining how much light is needed for an image to be properly exposed. When you increase the ISO setting, the sensor becomes more sensitive to light, allowing for better performance in low-light situations without requiring a longer exposure time or a wider aperture. Conversely, a lower ISO setting is used in bright environments to prevent overexposure.

The other options refer to different aspects of exposure and image quality. Saturation of colors is influenced by other factors such as post-processing rather than ISO. Aperture size controls the amount of light entering the lens and affects depth of field, while shutter speed determines how long the sensor is exposed to light. Each of these elements interacts with ISO, but it specifically governs sensitivity to light in the photographic process.