An Expectation Maximization Approach to impulsive Noise Removal in digital Radiography

Objective Impulsive noise constitutes a serious disturbing
factor in digital radiography. The aim of this paper is to propose
a new filter which is capable of eliminating efficiently
this kind of noise.
Method The filter is based on the classical switching scheme:
the pulses are first detected and then corrected through a
median filter. The novelty element is a pulse detector based
on an adequate statistical model of the image noise. This
model is constituted of a mixture of photon counting and
impulsive noise.
Results The filter operation has been verified and compared
with existing algorithms on both synthetic and real images.
The filter is capable to remove, on the average, more than
94% of the pulses, with a positive predictive value higher than
80%. The computational time required to filter a radiograph
of 4.5 Mpixels is just above 2 s.
Conclusion Thanks to the accurate description of the noise
statistics and the efficient computational scheme implemented,
the filter can be used to reliably and quickly remove
impulsive noise from digital radiographs. The experimental
results demonstrate the superiority of the proposed filter with
respect to traditional methods.