What does the term "high subject contrast" indicate in radiographic testing?

The term "high subject contrast" in radiographic testing indicates large variations in thickness. When there are significant differences in thickness or density between different areas of the material being examined, this results in more noticeable differences in the resulting radiograph, making it easier to distinguish features, defects, or boundaries within the material. High subject contrast contributes to the visibility of details in the image, as areas with varied composition or thickness will either absorb or transmit more radiation, creating a stark contrast in the radiographic image.

This high level of contrast is essential for detecting flaws such as cracks, voids, or weld defects, since these inconsistencies typically create variations in density that enhance the clarity of the radiograph. In contrast, textures or compositions that are uniform or similar in thickness may not present enough difference to produce a clear image, leading to low subject contrast. Thus, the presence of large variations in thickness is key to achieving a high subject contrast outcome in radiographic inspections.