What determines the shades of gray that are assigned to incoming signal amplitudes?

• A. Gray-scale map assignment
• B. Dynamic range
• C. Apodization
• D. Persistence

Answer: (A)

The shades of gray on the display are determined by the gray-scale map assignment—the display’s transfer function that maps incoming signal amplitudes to brightness levels. When echoes return, their amplitudes are converted into digital values, and the gray-scale map decides which gray level each amplitude corresponds to. This mapping can be linear or nonlinear (often logarithmic) to fit the wide range of echo strengths into the limited number of display shades, so that both weak and strong echoes are perceptible.

Dynamic range, apodization, and persistence influence image quality in other ways—dynamic range sets the overall contrast span the system can display, apodization shapes the beam and reduces artifacts, and persistence smooths frames over time—but they do not determine the specific shade assigned to each amplitude.