The following term best matches the concept of a gradient that describes speed of density change on the H&D curve.

• A. Average gradient
• B. Subject contrast
• C. Long scale contrast
• D. Gradient

Answer: (D)

On an H&D curve, the gradient is the slope, the rate at which optical density changes as exposure changes. This steepness tells you how quickly the film’s density responds to increasing exposure, which directly relates to image contrast—a steeper slope means a larger change in density for small increases in exposure, giving higher contrast. The idea of an average gradient describes a mean rate over a range, which isn’t as precise for describing the instantaneous rate of change. Subject contrast refers to the differences in attenuation in the object being imaged, not the film’s density response. Long scale contrast describes the overall tonal range the system can produce, not the rate of density change. So the term that best matches the concept of the speed of density change on the H&D curve is gradient.