A G curve is the average gradient of a photographic characteristic curve, similar in concept to gamma. It measures the slope from a line connecting the lower and upper limits of the curve that are actually used in practice, providing insight into the tonal response of film or paper.
Understanding the G curve is important for photographers and printmakers, as it helps predict how shadows, midtones, and highlights will reproduce in the final image. By analysing the G curve, professionals can better control contrast, exposure, and the overall tonal quality of photographs or prints.