Sensitometry

Sensitometry is the scientific study of the response of photographic and imaging materials to exposure to light or other forms of radiant energy. It involves measuring the relationship between the amount of light an emulsion receives and the resulting density or signal produced by that emulsion. This relationship is often visualized and analyzed using a characteristic curve, also known as a H&D curve, named after its developers Ferdinand Hurter and V.C. Driffield.

The process typically involves exposing a strip of photographic material to a series of known, increasing levels of light. These exposures are created using a sensitometer, which is a device that can control the intensity and duration of the light. After processing the exposed material, the resulting density of each exposed area is measured using a densitometer. The data collected is then plotted on a graph with exposure on the x-axis and density on the y-axis.

The characteristic curve reveals important properties of the imaging material, such as its speed (sensitivity to light), contrast (how much the density changes with exposure), gamma (a measure of contrast at a specific point), and latitude (the range of exposures that produce usable detail). Sensitometry is crucial for understanding and controlling image quality in traditional photography, radiography, and other imaging fields. It allows for the calibration of light sources, processing chemicals, and imaging detectors to ensure consistent and predictable results.