What is the main function of fill flash in photography?

The main function of fill flash in photography is to illuminate subjects when they are silhouetted. When a subject is backlit by a strong light source, such as the sun, the background may be adequately exposed, but the subject can appear dark and underexposed. Fill flash provides a burst of light that helps to bring out detail in the foreground subject, ensuring it is properly exposed despite the brighter background. This technique helps to reduce harsh shadows on the subject's face and creates a more balanced image overall, making it especially useful in outdoor settings where lighting conditions can be challenging.

While other choices suggest effects related to light, they do not accurately describe the primary purpose of fill flash. For example, creating strong shadows is generally not a goal of fill flash, as it is intended to soften and balance lighting instead. Enhancing contrast in natural light or balancing exposure across the entire scene can be influenced by fill flash, but the specific and immediate function of fill flash addresses the issue of silhouetted subjects directly, making illumination of the subject in such scenarios the most appropriate and accurate description of its main purpose.