What is another name for the H&D curve, the input-output curve used in film sensitometry?

• A. Exposure Curve
• B. Characteristic Curve
• C. Sensitometric Curve
• D. Dose–Response Curve

Answer: (B)

The input-output relationship of a photographic film to light exposure is summarized by how density changes as exposure increases. This is captured by the characteristic curve, which records the film’s specific response to exposure—hence the name. The curve is traditionally plotted with optical density on the vertical axis and log exposure on the horizontal, showing the toe (low exposure), the straight-line portion (where density rises proportionally with log exposure), and the shoulder (approaching saturation). From this curve you derive film speed (how quickly the film responds to light), contrast (the steepness of the straight-line portion, or gamma), and overall latitude. The term “characteristic curve” emphasizes that it is the film’s inherent response profile being described, not just a general exposure plot. Other terms are less standard for this exact input-output behavior: Exposure Curve isn’t the typical name, Sensitometric Curve is a broader phrasing, and Dose–Response Curve belongs to radiobiology, not film sensitometry.