What step in digital image processing identifies the useful exposure values ('values of interest') in raw image data?

• A. Histogram analysis
• B. Rescaling
• C. Lookup table (LUT) adjustments
• D. Digitization

Answer: (A)

Analyzing the histogram of the raw pixel values is how we find the useful exposure values. The histogram shows how often each gray level occurs across the image. The portion that contains the actual anatomical signal—separated from background noise on the low end and from clipped data on the high end—defines the values of interest. Identifying this region tells us which pixel values should be preserved and emphasized during display, guiding how the data will be mapped to display gray levels. After the VOI is established, operations like windowing and scaling adjust how that range is shown. The other steps don’t identify the useful data themselves: rescaling changes the overall range, LUT adjustments map values after the VOI is known, and digitization is the conversion step from analog to digital.