Method and apparatus for minimizing artifacts in images produced by error diffusion halftoning
AssigneeSeiko Epson Corporation
InventorJoseph S. Shu
Life of this patent
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Abstract
An image preprocessing method and apparatus processes image data line-by-line using an error diffusion process to generate a halftoned image. The method and apparatus varies the processing direction from line-to-line to minimize the presence of worm-type artifacts in a halftoned image where the processing direction of each line in the image is dependent on the content of the image. More particularly, the processing direction of each line in the image is dependent upon the grayscale value and/or the quantization error associated with one or more pixels of a previously processed line in the image.
Claims40
A method of converting a continuous-tone image, represented as an array of electronically encoded pixels each specifying a gray-scale value, into a binary raster suitable for electronic printing, the method comprising the steps of:
- A. identifying a series of pixels corresponding to a linear segment of the image;
- B. processing the identified pixels, in a sequence corresponding to movement along the segment in a selected one of a first direction and a second direction, to convert the pixels into binary raster values;
- and
- C. repeating the identification and processing steps until the image has been fully processed,
- wherein the selected one direction of a processing sequence is based on information from at least one previous processed pixel.
A method of converting a continuous-tone image, represented as an array of electrically encoded pixels each specifying a gray-scale value, into a binary raster suitable for electronic printing, the method comprising the steps of:
- A. identifying a series of pixels corresponding to a linear segment of the image;
- B. processing the identified pixels, in a sequence corresponding to movement along the segment in a predetermined direction, to convert the pixels into binary raster values;
- and
- C. repeating the identification and processing steps until the image has been fully processed,
- wherein the predetermined direction of a processing sequence is based on information from at least one previous processing sequence,
- wherein the direction-determining information comprises the gray-scale value of at least one previously processed pixel,
- wherein the gray-scale values of a plurality of previously processed pixels are combined, and the predetermined direction is obtained from the combination,
- wherein the previously processed pixels are selected from the immediately previous series of pixels, and
- wherein, for each processing sequence, the selected pixels occupy identical sequence locations in the immediately previous series of pixels.
A method of converting a continuous-tone image, represented as an array of electronically encoded pixels each specifying a gray-scale value, into a binary raster suitable for electronic printing, the method comprising the steps of:
- A. identifying a series of pixels corresponding to a linear segment of the image;
- B. processing the identified pixels, in a sequence corresponding to movement along the segment in a predetermined direction, to convert the pixels into binary raster values;
- and
- C. repeating the identification and processing steps until the image has been fully processed,
- wherein the predetermined direction of a processing sequence is based on information from at least one previous processing sequence,
- wherein step B comprises the steps of:
- B1. iteratively comparing the values of pixels with a threshold value;
- B2. selecting binary raster values based on the comparisons;
- and
- B3. electronically storing error values defining the differences between pixel values and the threshold values,
- wherein the direction-determining information comprises error values associated with at least one previously processed pixel.
An image-processing system for converting a continuous-tone image into a binary raster suitable for printing, the apparatus comprising:
- means for storing an array of electronically encoded pixels each representing a gray-scale value;
- and
- halftoning means for iteratively processing series of pixels each corresponding to a linear segment of the image, in a sequence representative of movement along the segment in a selected one of a first direction and a second direction, so as to produce binary raster values therefrom, wherein the selected one direction of the processing sequence is based on information from at least one previous processed pixel.
An image-processing system for converting a continuous-tone image into a binary raster suitable for printing, the apparatus comprising:
- means for storing an array of electronically encoded pixels each representing a gray-scale value;
- halftoning means for iteratively processing series of pixels each corresponding to a linear segment of the image, in a sequence representative of movement along the segment in a predetermined direction, so as to produce binary raster values therefrom, wherein the predetermined direction of the processing sequence is based on information from at least one previous processing sequence;
- and
- an image line buffer for storing the gray-scale values of the immediately previous series of pixels, and wherein the previously processed pixels are selected from the buffer,
- wherein, for each processing sequence, the selected pixels occupy identical memory locations in the buffer.
An image-processing system for converting a continuous-tone image into a binary raster suitable for printing, the apparatus comprising:
- means for storing an array of electronically encoded pixels each representing a gray-scale value;
- and
- halftoning means for iteratively processing series of pixels each corresponding to a linear segment of the image, in a sequence representative of movement along the segment in a predetermined direction, so as to produce binary raster values therefrom, wherein the predetermined direction of the processing sequence is based on information from at least one previous processing sequence;
- wherein the halftoning means comprises:
- a threshold circuit for iteratively comparing the values of pixels with a threshold value and generating, from the comparison, a binary raster value;
- an output buffer for storing the binary values;
- and
- an error buffer for storing error values defining the differences between pixel values and the threshold values, wherein the direction-determining information comprises error values associated with at least one previously processed pixel.
A printer for printing a continuous-tone image as patterns of monochrome dots on a print medium, the printer comprising:
- digitizing means responsive to the continuous-tone image for generating a stream of electronically encoded pixel values, each representing a gray-scale value of a portion of the continuous-tone image;
- means responsive to the stream of electronically encoded pixel values for storing the electronically encoded pixel values in a plurality of linear segments, each linear segment having a start and an end and comprising pixel values that represent contiguous portions of the continuous-tone image;
- and
- halftoning means controllable to process each pixel value in each of the plurality of linear segments in a selected one of a first direction and a second direction to generate output results;
- direction means responsive to the stored electronically coded pixel values for controlling the halftoning means in the selected one of the first direction and the second direction, the selected direction being based on information form at least one previous processed pixel;
- and
- a print mechanism responsive to the output results for generating the patterns of monochrome dots on the print medium.
A computer system comprising:
- a memory for storing data and programs;
- a central processing unit responsive to programs stored in the memory for controlling and coordinating the operation of the computer system;
- digitizing means responsive to the continuous-tone image for generating a stream of electronically encoded pixel values, each representing a gray-scale value of a portion of the continuous-tone image;
- means responsive to the stream of electronically encoded pixel values for storing the electronically encoded pixel values in a plurality of linear segments, each linear segment having a start and an end and comprising pixel values that represent contiguous portions of the continuous-tone image;
- halftoning means controllable to process each pixel value in each of the plurality of linear segments in a in a selected one of a first direction and a second direction to generate output results;
- direction means responsive to the stored electronically coded pixel values for controlling the halftoning means in the selected one of the first direction and the second direction, the selected direction being based on information from at least one previous halftoned pixel;
- and
- a printer responsive to the output results for printing patterns of monochrome dots on a print medium to generate a halftoned image.
Dependencies are inferred from the claim text.