X-ray dark-field imaging enables a spatially-resolved visualization of
small-angle X-ray scattering. Using phantom measurements, we demonstrate that a
material's effective dark-field signal may be reduced by modification of the
visibility spectrum by other dark-field-active objects in the beam. This is the
dark-field equivalent of conventional beam-hardening, and is distinct from
related, known effects, where the dark-field signal is modified by attenuation
or phase shifts. We present a theoretical model for this group of effects and
verify it by comparison to the measurements. These findings have significant
implications for the interpretation of dark-field signal strength in
polychromatic measurements.Comment: 11 pages, 6 figures. Previously submitted to IEEE Transactions on
Medical Imagin