A tone curve is a graph used in digital photography to display the tonal range of an image, showing the relationship between input and output brightness values. A straight line at a 45-degree angle indicates no change in contrast, while adjusting points on the curve allows photographers to increase or decrease contrast in specific tonal regions.
Photographers can also modify individual colour channels using the tone curve, affecting colour balance and enhancing image aesthetics. Mastering the tone curve provides precise control over highlights, shadows, and midtones, enabling professional-quality adjustments and creative image enhancements.