Which term describes the processing operation that increases image contrast using a lookup table (LUT)?

• A. Edge enhancement
• B. Automatic brightness control (ABC)
• C. Lookup table (LUT)
• D. Histogram analysis

Answer: (C)

This item focuses on how image contrast can be increased by mapping gray values through a lookup table. A LUT is a table that defines, for every possible input gray level, what output gray level should replace it. When you apply the LUT, each pixel is rewritten to its mapped value, creating a new image with a designed contrast response. Because the mapping can be non-linear, you can boost contrast—for example by expanding the range of darks and lights while shaping midtones—to achieve the desired radiographic appearance.

Edge enhancement, by contrast, sharpens edges using filters to emphasize boundaries rather than changing pixel values through a predetermined gray-level mapping. Automatic brightness control adjusts overall brightness, not through a fixed gray-level transformation. Histogram analysis is a diagnostic/analytical step that helps determine how to set or choose a LUT, but it is not the operation that directly increases contrast itself.