Optical density is a technical measurement of how much light is blocked by a material, such as photographic film, paper, or filters. In traditional photography, it reflects the amount of silver deposit formed during exposure and development, with higher optical density corresponding to darker areas that transmit less light.
This measurement is crucial in film processing, printing, and quality control, helping photographers and technicians achieve accurate exposure, contrast, and tonal reproduction. Understanding optical density allows for better control over image quality, ensuring consistent results across negatives, prints, and reproductions.