US 6,608,941 B1Granted

Image processing apparatus

AssigneeSharp Kabushiki Kaisha

InventorsMichiyuki Suzuki, Yoshinori Hayashi

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Abstract

An object of the present invention is to avoid such a problem that white dropouts and the Moire phenomenon occur in a filter-processed image. A filter unit employed in an image processing apparatus provided within a copying machine first selects as a pixel of interest any one of a plurality of reversed density pixels which constitute an image to be processed. Next, the filter unit uses density of this interest pixel before being corrected, density of pixels located at peripheral portions of this interest pixel, and a predetermined filter coefficient so as to calculate a weighted average value for each of the density. Finally, the filter unit compares the density of this interest pixel before being corrected with the weighted average values to output as a corrected density of this interest pixel, such a value approximated to a density equivalent to a black level. Furthermore, the filter unit compares the density of the interest pixel before being corrected with the predetermined reference density and, only when the density before being corrected is less than the reference density, it outputs the above-described weighted average value as the corrected density of this interest pixel irrespect to such a large/small relationship between the density before being corrected and the weighted average value.

Claims18

Dependent claims

An image processing apparatus comprising:

area designating means for selecting any one of pixels as a pixel of interest, which are contained in an image composed of a plurality of reversed density pixels, to thereby designate as an area to be processed, an area contained in said image which is composed of a predetermined number of pixels including the pixel of interest;
average value calculating means for performing a weighted average calculation of densities of all of the pixels within the area to be processed by employing a plurality of weighting coefficients corresponding to a positional relationship between each of the all pixels and the pixel of interest so as to thereby calculate weighted average values of the densities of all of the pixels;
limiting means for limiting the weighted average values to be smaller than, or equal to a predetermined upper limit density and to be larger than, or equal to a predetermined lower limit density;
first comparing means for comparing the weighted average value limited by the limiting means with the density of the interest pixel;
and
density replacing means for replacing the density of the interest pixel by the weighted average value when the density of the interest pixel is less than the limited weighted average value, and also for maintaining the density of the interest pixel when the density of the interest pixel is more than, or equal to the limited weighted average value, in response to the comparison result of the first comparing means.

3 more elements

Dependencies are inferred from the claim text.