System and method for converting continuous half tone image into pseudo half tone image
AssigneeKabushiki Kaisha Toshiba
InventorsMasayoshi Murayama, Fumitaka Sato
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Abstract
In processing of a minimizer average error method (or an error diffusion method), a threshold value for determining whether a point (pixel) as an object to be processed is a black or white dot is changed in accordance with the pixel position using a threshold value matrix having a two-dimensional repetitive pattern. When a one-dot size in an output apparatus which can only perform binary expression in units of pixels is larger than a logical size, a continuous tone image is converted into a pseudo half tone image in consideration of an increase in size of a dot into other dots (projecting portions).
Claims14
A system for converting continuous tone image into a pseudo half tone image, which converts input image data expressed by a plurality of bits per pixel into output image data expressed by one bit per pixel, comprising:
- error storage means for storing errors generated when input image data of pixels are converted into output image data expressed by one bit per pixel;
- correction means for multiplying errors, stored in said error storage means, at pixels adjacent to a pixel to be converted with weighting coefficients so as to correct the density of an input image data value of the pixel to be converted;
- threshold value storage means for storing threshold values having different values according to a position of the pixel to be converted, and used for determining a value of output image data;
- and
- comparison means for comparing the input image data value corrected by said correction means, and the threshold value stored in said threshold value storage means corresponding to the position of the pixel to be converted to provide an output binary image data value of the pixel to be converted.
A system for converting a continuous tone image into a pseudo half tone image, which converts input image data expressed by a plurality of bits per pixel into output image data expressed by one bit per pixel, comprising:
- error storage means for storing errors generated when input image data of pixels are converted into output image data expressed by one bit per pixel;
- image storage means for storing the output image data obtained by converting the input image data of the pixels;
- correction value calculation means for multiplying errors, stored in said error storage means, at pixels adjacent to a pixel to be converted with weighting coefficients so as to calculate a correction value of input image data of the pixel to be converted;
- first determination means for determining a value of the output image data on the basis of the image data value corrected by said correction value calculation means;
- second determination means for determining an error evaluation value at the pixel to be converted on the basis of output image data values at pixels adjacent to the pixel to be converted stored in said image storage means, and the output image data value at the pixel to be converted determined by said first determination means;
- and
- error calculation means for calculating an error generated upon conversion of the input image data at the pixel to be converted on the basis of the error evaluation value determined by said second determination means, and the correction value obtained by said correction value calculation means.
A system for converting a continuous tone image into a pseudo half tone image, which converts input image data expressed by a plurality of bits per pixel into output image data expressed by one bit per pixel, comprising:
- error storage means for storing errors generated when input image data of pixels are converted into output image data expressed by one bit per pixel;
- image storage means for storing the output image data obtained by converting the input image data of the pixels;
- correction value calculation means for multiplying errors, stored in said error storage means, at pixels adjacent to a pixel to be converted with weighting coefficients so as to calculate a correction value of input image data of the pixel to be converted;
- first determination means for determining a value of the output image data on the basis of the image data value corrected by said correction value calculation means, and the threshold value stored in said threshold value storage means corresponding to a position of the pixel to be converted;
- second determination means for determining an error evaluation value at the pixel to be converted on the basis of output image data values at pixels adjacent to the pixel to be converted stored in said image storage means, and the output image data value at the pixel to be converted determined by said first determination means;
- and
- error calculation means for calculating an error generated upon conversion of the input image data at the pixel to be converted on the basis of the error evaluation value determined by said second determination means, and the correction value obtained by said correction value calculation means.
A method for converting a continuous tone image into a pseudo half tone image, which converts input image data expressed by a plurality of bits per pixel into output image data expressed by one bit per pixel, comprising the steps of:
- a) dividing an input image into n.times.n submatrices (n is a positive integer not less than 2);
- b) assigning different threshold values to the divided submatrices, respectively;
- c) multiplying errors generated upon digitization of adjacent points corresponding to an objective point of the input image with predetermined weighting coefficients so as to obtain a correction density of the objective point;
- and
- d) comparing the correction density with the threshold value corresponding to the objective point, and determining according to a comparison result whether the objective point is a black dot or a white dot.
A method for converting a continuous tone image into a pseudo half tone image, which converts input image data expressed by a plurality of bits per pixel into output image data expressed by one bit per pixel, comprising the steps of:
- a) storing errors generated upon conversion of the input image data of the pixels;
- b) storing output image data obtained upon conversion of the input image data of the pixels;
- c) multiplying the errors, stored in the step a), at pixels adjacent to a pixel to be converted with weighting coefficients so as to calculate a correction value of input image data of the pixel to be converted;
- d) determining an output image data value on the basis of the input image data value corrected in the step c);
- e) determining an error evaluation value at the pixel to be converted on the basis of the output image data values at the pixels adjacent to the pixel to be converted stored in the step b), and the output image data value at the pixel to be converted determined in the step d);
- and
- f) calculating an error generated upon conversion of the input image data at the pixel to be converted on the basis of the error evaluation value determined in the step e), and the correction value obtained in the step c).
A method for converting a continuous tone image into a pseudo half tone image, which converts input image data expressed by a plurality of bits per pixel into output image data expressed by one bit per pixel, comprising the steps of:
- a) storing errors generated upon conversion of the input image data of the pixels;
- b) storing output image data obtained upon conversion of the input image data of the pixels;
- c) multiplying the errors, stored in the step a), at pixels adjacent to a pixel to be converted with weighting coefficients so as to calculate a correction value of input image data of the pixel to be converted;
- d) determining an output image data value on the basis of the input image data value corrected in the step c), and the threshold value corresponding to a position of the pixel to be converted;
- e) determining an error evaluation value at the pixel to be converted on the basis of the output image data values at the pixels adjacent to the pixel to be converted stored in the step b), and the output image data value at the pixel to be converted determined in the step d);
- and
- f) calculating an error generated upon conversion of the input image data at the pixel to be converted on the basis of the error evaluation value determined in the step e), and the correction value obtained in the step c).
Dependencies are inferred from the claim text.