Neighborhood image processing stage for implementing filtering operations

Apparatus for performing filtering operations on an image matrix represented by a serial stream of multi-bit pixel values, said apparatus comprising:

• a master controller;
• a neighborhood transformation stage coupled to the controller, said stage having an array of temporary storage devices for sequentially accessing a neighborhood of pixels in the image matrix, said neighborhood consisting of a center pixel value and its surrounding neighbors in the image matrix;
• said stage including a transformation logic module connected to the neighborhood storage devices for generating a transformation output for each accessed neighborhood, said transformation logic module including:
• a series of comparators, each comparator having one input connected to the storage device containing the center pixel and another input connected to a storage device containing one of the neighbors, said comparators having outputs which are combined together to form a multi-bit address vector;
• random access memory means having a plurality of programmable locations addressable by the vector generated by the outputs of the comparators, the contents of the addressed location providing an output of the memory means, means for connecting the memory means to the master controller for programming said locations;
• sorting means having inputs connected to the storage devices containing the pixel values of the neighbors, said sorting means being operative to compare the values of the neighbors with each other and provide a series of outputs ranked in descending order according to the relative values of the neighbor pixels, a first subset of outputs containing the largest pixel values and a second subset containing the smallest pixel values of the neighbor pixels;
• programmable storage means connected to the master controller for providing an output for selecting a given output in each subset of the sorting means;
• selector means having inputs connected to said storage device containing the center pixel in the neighborhood and inputs connected to the ranked outputs of the sorting means, said selector means further including means for receiving the outputs from said memory means and said storage means, whereby said selector means is adapted to select as its output the value of the center pixel or one of the outputs from the sorting means as a function of the outputs from the memory and storage means;
• and
• whereby said stage can be used to perform a wide variety of filtering operations on the image matrix by appropriately programming the memory means and storage means.