Physical and chemical changes can degrade the visual color appearance of old paintings. Five digital color restoration techniques, which can be used to simulate the original appearance of paintings, are presented. Although a small number of color samples is employed in the restoration procedure, simulation results indicate that good restoration quality can be attained.
A nonlinear multichannel digital filter is presented in this correspondence. The output is a weighted sum of all samples in the filter window, with a single parameter controlling the filter nonlinearity. Although input data ordering is not required, performance can surpass the performance of other ordering-based multichannel filters.
Digital implementations of sorting networks that rely on a digital signal processor core are not as efficient as their analog counterparts. This paper builds on the comparators for which efficient analog implementations exist that employ operational amplifiers. From a statistical point of view, comparators are based on nonlinear means. Their probability density function and the first-and second-order moments are derived for independent uniformly distributed inputs. comparators provide estimates of the minimum and maximum of their inputs. A proper approach to compensate for the estimation errors is proposed. Applications of the comparators in odd-even transposition networks, median approximation networks, and min/max networks are presented.
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