The CT gray value, also known as the gray level, is a numerical value assigned to each voxel in a CT image. It corresponds to the degree of X-ray attenuation (absorption and scattering) caused by the material at that specific location.
Since attenuation depends on both the material's density and atomic composition, the gray value serves as a digital indicator of internal characteristics. In a typical CT image, materials with high attenuation (such as metal) result in higher gray values and appear brighter, while low-attenuation areas (such as air or resin) appear darker. This contrast allows operators to distinguish internal structures and detect defects non-destructively.
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