The ratio of image to object as a function of spatial frequency is known as which concept?

• A. spatial frequency
• B. modulation transfer function
• C. contrast resolution
• D. dynamic range

Answer: (B)

The idea being tested is how well an imaging system preserves contrast as details get finer. Spatial frequency describes how fine the pattern is—the higher the frequency, the more rapid the brightness changes and the finer the detail. The ratio of image modulation (contrast) to object modulation as a function of spatial frequency is called the modulation transfer function. It shows how faithfully the system transmits contrast across different levels of detail: good fidelity means higher modulation at a given frequency, while increasing frequency typically reduces modulation as blur and aberrations blur fine details. This concept differs from spatial frequency itself (which is just a measure of detail level), contrast resolution (which is about the smallest detectable brightness difference), and dynamic range (the span of brightness the system can capture).