Method and apparatus for effecting spot/void filtering of image data

Claim 1

Apparatus for filtering digital image data in the form of an array of multi-bit pixels each having one of a plurality of gray-scale values, said apparatus comprising: threshold means for storing a predetermined threshold and for converting said gray-scale value of each of said pixels to an array of binary signals in which each pixel has a binary signal associated therewith, one value of said binary signal being associated with said gray-scale value being greater than said predetermined threshold and a second value of said binary signal being associated with said gray-scale value being less than said predetermined threshold; means for detecting a pattern of neighboring binary pixels in a window containing a center pixel being analyzed and its neighbors; and transforming means for changing the gray-scale value of the center pixel in the window as a function of the detected pattern, the transforming means comprising averager means for averaging the gray-scale values of the pixels in the window, and selector means having a first input connected to the averager means, a second input connected to a predetermined gray-scale value associated with background, a third input connected to a predetermined gray-scale value associated with image formation data, a fourth input providing a gray-scale value of the center pixel being analyzed, and selection input means coupled to the means for detecting, operative to couple one of the inputs to the selector means to an output of the selector means as a function of a detected pattern of neighboring binary pixel values.

Claim 8

A method of filtering digital image data in the form of a first array of pixels each having one of a plurality of gray-scale values, said method comprising: converting each gray-scale value in the first array into one of two binary values in accordance with a predetermined threshold gray-scale value; placing each binary signal value into a second array of binary pixels, each binary pixel corresponding to one of the gray-scale pixels in the first array; generating a control signal as a function of a pattern of binary signals in the second array; and selecting one of a plurality of predetermined gray-scale values in accordance with the control signal and replacing a gray-scale value of a preselected pixel in the first array with the selected one predetermined gray-scale value.

Claim 9

A method of filtering digital image data in the form of a first array of pixels each having one of a plurality of gray-scale values, said method comprising: converting each gray-scale value in the first array into one of two binary values in accordance with a predetermined threshold gray-scale value; placing each binary signal value into a second array of binary pixels, each binary pixel corresponding to one of the gray-scale pixels in the first array; generating a control signal as a function of a pattern of binary signals in the second array; and selecting one of a plurality of predetermined gray-scale values in accordance with the control signal and replacing a gray-scale value of a preselected pixel in the first array with the selected one predetermined gray-scale value.