Geometrically reducing mask error diffusion
First Claim
Patent Images
1. A method of error diffusing an image, the image having a plurality of scan lines each having a plurality of pixels, said method comprising, for each of said pixels, the steps of:
- applying an error diffusion mask to an output error value of previously processed pixels to determine an input error value for said pixel wherein the error diffusion mask comprises error diffusion coefficients corresponding to all previously error diffused pixels of said image; and
determining an output value and an output error value of said pixel, both said output pixel value and said output error value being dependent upon the input error value and an input pixel value of said pixel.
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Abstract
An image processing system in which a computer image is halftoned by halftoning a current pixel using error diffusion, with a halftoned output value of the current pixel being determined using errors derived from substantially all previously halftoned pixels of the image. Output error values are determined for each pixel, and are acted upon by an error diffusion mask of geometrically reducing values. In certain instances, previously halftoned pixels are divided into two or more groups to obtain a desired contribution from previously halftoned pixels.
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Citations
14 Claims
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1. A method of error diffusing an image, the image having a plurality of scan lines each having a plurality of pixels, said method comprising, for each of said pixels, the steps of:
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applying an error diffusion mask to an output error value of previously processed pixels to determine an input error value for said pixel wherein the error diffusion mask comprises error diffusion coefficients corresponding to all previously error diffused pixels of said image; and determining an output value and an output error value of said pixel, both said output pixel value and said output error value being dependent upon the input error value and an input pixel value of said pixel. - View Dependent Claims (2, 3, 4)
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- 5. A method of halftoning an image, said image comprising a plurality of pixels arranged in scan lines, said method comprising the step of error diffusing each pixel of said image characterized in that a halftoned output value and an output error value of said pixel are determined from error values obtained from all previously halftoned pixels of said image, both said output pixel value and said output error value being defendant upon an input error value and an input pixel value of said pixel.
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12. Apparatus for halftoning an image, said apparatus comprising:
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receiving means for receiving input pixels of said image intended for display in raster scan order, and error diffusing means for error diffusing said input pixels to provide error diffused halftoned output pixels for display and an output error value associated with each output pixel, wherein a halftoned output value of a current pixel of said image is determined from input error values obtained from all previously halftoned pixels of said image, and further wherein both said output pixel value and said output error value are dependent upon the input error values and an output pixel value of said pixel.
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13. A computer software system for executing instructions on a general purpose computer, wherein said instructions comprise a plurality of process modules for halftoning an image, said image comprising a plurality of pixels arranged in a plurality of scan lines, said modules comprising:
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a first module for determining a derived input value of a current pixel of said image by summing an input pixel value of said current pixel with an input error value; a second module for determining said input error value from output error values of all pixels of said image preceding said current pixel; a third module for determining a halftoned output value for said current pixel from said derived input value; and a fourth module for determining an output error value, both said output value and said output error value being dependent upon the input error value and an input pixel value of said current pixel. - View Dependent Claims (14)
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Specification