The traditional unit of resolution measurement typically used in film/screen imaging is

• A. Line pairs per millimeter
• B. Pixels per inch
• C. Spatial frequency unit
• D. Dots per inch

Answer: (A)

In film/screen imaging, resolution is described by spatial frequency—the number of alternating dark and light line pairs that can be distinguished in a given length. The standard unit is line pairs per millimeter, which counts complete line-and-space pairs within each millimeter. More line pairs per millimeter means finer detail can be resolved, reflecting the true resolving power of the film–screen system.

Pixels per inch and dots per inch are digital-era metrics tied to sampling, display, or printing, not to the inherent resolving capability of the film-screen chain. A spatial frequency unit is a broad concept, but line pairs per millimeter is the traditional, specific unit used to quantify resolution in film/screen imaging.