Radiographic Impulsive Noise removal (RaIN) filter - abstract
Digital radiographic images are corrupted by different kinds of noise. The major one has a Poisson statistic and it is associated with the photon counting process , , ; A/D conversion and data transmission constitute additional sources of noise; in particular, they can introduce impulsive noise , , . Although impulsive noise can be poorly visible in the raw image (Fig. 1), its effect becomes dramatic when the image is manipulated (for instance though gamma transformation or unsharp masking) to increase the constrast and the visibility of the anatomical details (Fig. 2).
To avoid this undesiderable effect, impulsive noise has to be removed
from the image before applying any processing algorithm. To this aim,
we have proposed a new filter (called RaIN), based on a switching scheme,
where all the pulses are first detected and then corrected through a
median filter , . The pulse detector is based on the hypothesis
that the major contribution to image noise is given by the photon counting
process, with only some pixels corrupted by impulsive noise. Such statistics
is described by an adequate mixture model, which is used to identify
the pixels corrupted by impusive noise (Fig. 3).