The X-axis of the radiographic histogram represents the

• A. Frequency of specific signal intensity values
• B. Number of line-pairs recorded by the receptor
• C. Specific signal intensity values from low to high
• D. Range of X-ray energies absorbed by the receptor

Answer: (C)

In radiographic histograms, the X-axis shows the grayscale levels, or signal intensity values, of the image pixels arranged from low to high. This means it tracks how the image’s pixel values span from dark to light. The height of the curve at each point on the Y-axis represents how many pixels have that specific gray level (the frequency). So the X-axis is about the actual gray values, not how often they occur. The frequency of those values is what the Y-axis shows. This setup helps assess exposure and image quality, since the distribution of gray levels reveals whether the image sits in an appropriate exposure range.