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Median Filtering of Shot and Speckle Noise in Images
When the pixels in a neighborhood are ranked into order from brightest to darkest, the median value (in the middle of the ranked list) is placed in the central pixel location. This operation is applied to each pixel in the original image, to produce a new image in which the extreme pixel values are discarded. This interactive tutorial shows the application of a median filter with different neighborhood sizes to shot and speckle noise. Because no averaging is applied, the method does not blur edges. The median filter can, however, remove details that are smaller than the radius of the neighborhood. This offers a selective way to remove shot noise, dust and scratches, for instance.
The tutorial initializes with a randomly selected specimen appearing in the Specimen Image window. The Choose A Specimen pull-down menu provides a selection of specimen images, in addition to the initial randomly chosen one. The Noise Level slider controls the amount of noise that is added, while the Noise Type radio buttons select either Shot or Speckle noise. The Choose an Operation pull-down menu determines the size of the neighborhood used for the median filtering operation that will be performed. The result of the filtering operation appears in the Filtered Image window.
Contributing Authors
John C. Russ - Materials Science and Engineering Dept., North Carolina State University, Raleigh, North Carolina, 27695.
Matthew Parry-Hill, and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.
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