Method, apparatus and computer program for halftoning digital images
First Claim
1. A method for generating a halftone image having output pixels from an input image comprising input pixels having input pixel values, said method comprising the steps of:
- for each input pixel, adding an error term to the input pixel value in a halftone unit to obtain a modified input pixel value, wherein the error term is a weighted sum of error values of previous pixels to be directed to the input pixel;
determining an error diffusion threshold level based on the input pixel value;
applying a quantization operation to the modified input pixel value using the determined error diffusion threshold level for obtaining an output pixel value; and
determining an error value of the input pixel that is a difference between the output pixel value and the modified input pixel value,wherein the error diffusion threshold level depends on a result of a comparison operation performed between the input pixel value and a threshold value selected from a set of threshold values, the selection of the threshold value being based on the position of the input pixel in the input image.
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Abstract
A method for generating a halftone image includes the steps of, for each input pixel, adding a previously determined error term to the input pixel value to obtain a modified input pixel value; determining an error diffusion threshold level based on the input pixel value; applying a quantization operation to the modified input pixel value using the determined error diffusion threshold level for obtaining an output pixel value; and determining an error contribution. The error diffusion threshold level depends on a result of a comparison operation performed between the input pixel value and a threshold value selected from a set of threshold values, the selection of the threshold value being based on the position of the input pixel in the input image.
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Citations
14 Claims
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1. A method for generating a halftone image having output pixels from an input image comprising input pixels having input pixel values, said method comprising the steps of:
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for each input pixel, adding an error term to the input pixel value in a halftone unit to obtain a modified input pixel value, wherein the error term is a weighted sum of error values of previous pixels to be directed to the input pixel; determining an error diffusion threshold level based on the input pixel value; applying a quantization operation to the modified input pixel value using the determined error diffusion threshold level for obtaining an output pixel value; and determining an error value of the input pixel that is a difference between the output pixel value and the modified input pixel value, wherein the error diffusion threshold level depends on a result of a comparison operation performed between the input pixel value and a threshold value selected from a set of threshold values, the selection of the threshold value being based on the position of the input pixel in the input image. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An apparatus for generating a halftone image having output pixels from an input image comprising input pixels having input pixels values, said apparatus comprising:
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an error diffusion module that adds an error term to the input pixel value to obtain a modified input pixel value, wherein the error term is a weighted sum of error values of previous pixels to be directed to the input pixel, and determines an error value of the input pixel that is a difference between the output pixel value and the modified input pixel value; a threshold calculator that determines an error diffusion threshold level based on the input pixel value; and a quantizer that applies a quantization operation to the modified input pixel value using the determined error diffusion threshold level to obtain an output pixel value, wherein the threshold calculator is suited to determine the error diffusion threshold level based on a result of a comparison operation performed between the input pixel value and a threshold value selected from a set of threshold values according to the position of the input pixel in the input image. - View Dependent Claims (8)
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9. A computer program product residing on a nontransitory computer readable recording medium comprising instructions for causing at least one process unit to perform a method for generating a halftone image having output pixels from an input image comprising input pixels having input pixels values, said method comprising the steps of:
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for each input pixel, adding an error term to the input pixel value to obtain a modified input pixel value, wherein the error term is a weighted sum of error values of previous pixels to be directed to the input pixel; determining an error diffusion threshold level based on the input pixel value; applying a quantization operation to the modified input pixel value using the determined error diffusion threshold level for obtaining an output pixel value; and determining an error value of the input pixel that is a difference between the output pixel value and the modified input pixel value, wherein the error diffusion threshold level depends on a result of a comparison operation performed between the input pixel value and a threshold value selected from a set of threshold values, the selection of the threshold value being based on the position of the input pixel in the input image. - View Dependent Claims (10, 11, 12, 13, 14)
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Specification