Halftone images using special filters
AssigneeHewlett-Packard Company
InventorQian Lin
Life of this patent
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Abstract
A method of generating a halftone image from a grey scale image by means of a dither matrix. The matrix includes many patterns Each pattern corresponds to one grey level of the grey scale image. The value of each element in each pattern depends on a special positive filter with a single peak and a region-of-support. The peak is approximately at the center of the region-of-support. One preferred filter is a guassian filter. For a given pattern, the region-of-support of the filter depends on the average separation of the elements with values equal to one in that pattern; and the elements with values equal to one are substantially uniformly distributed across the pattern.
Claims19
A method of generating a halftone image from a grey scale image by means of a dither matrix,
- the halftone image, the grey scale image and the dither matrix each occupying an area, the three areas being substantially equal to each other,
- the halftone image and the grey scale image each having a plurality of pixels, each pixel having a value, and
- the dither matrix having a plurality of elements that are generated by a plurality of patterns, each pattern also having a plurality of elements, each element in each pattern occupying a position in the pattern, each element having a value,
- the method comprising the steps of comparing the value of each pixel of the grey scale image with the value of an element in the dither matrix and, based on the result of the comparison, determining the value of a corresponding pixel of the halftone image, and
- the value of each element in each pattern of the dither matrix being determined by a single-peaked and positive filter with a region-of-support, the peak being approximately at the center of the region-of-support, and
- for a given pattern, the region-of-support being dependent on the average separation of a pre-selected value in that pattern, such that all elements with the preselected values are substantially uniformly distributed across the pattern.
A method of generating a halftone image as recited in claim wherein the filter is a guassian filter.
A method of generating a halftone image as recited in claim wherein the filter is a triangular filter.
A method of generating a halftone image as recited in claim wherein the image is in black-and-white.
Dependencies are inferred from the claim text.