초록 ▼

In an image processor, a data corrector corrects input image data, a determining unit determines an output tone value of a target pixel from the corrected image data and threshold, and a calculator calculates a difference between the output tone value and the corrected image data as an error value.

In an image processor, a data corrector corrects input image data, a determining unit determines an output tone value of a target pixel from the corrected image data and threshold, and a calculator calculates a difference between the output tone value and the corrected image data as an error value. The threshold is set in such manner that a rate of change of the mean error of the error values with respect to a change in the input tone value is within a predetermined range.

대표청구항 ▼

What is claimed is: 1. An image processor, comprising: an input data corrector that corrects image data of a target pixel by giving a weight to error values in the neighborhood of the target pixel and adding weighted error values to a tone value of the target pixel; an output tone value determining

What is claimed is: 1. An image processor, comprising: an input data corrector that corrects image data of a target pixel by giving a weight to error values in the neighborhood of the target pixel and adding weighted error values to a tone value of the target pixel; an output tone value determining unit that determines an output tone data of the target pixel based on corrected image data, and based on a threshold corresponding to a position of the target pixel; and an error value calculator that calculates a difference between the output tone data and the corrected image data as an error value, wherein the output tone value determining unit sets the threshold corresponding to the position of the target pixel to be within a numerical threshold range determined by a process that includes obtaining corrected image data when an output dot pattern output as an output tone value is in a steady state, and determining the numerical threshold range from the obtained corrected image data, wherein, in the steady state, a same output dot pattern is stably generated repeatedly as a result of repeated tone processing of a solid image having a certain input tone value, wherein the process of obtaining corrected image data is repeated for a plurality of different output dot patterns. 2. The image processor according to claim 1, wherein the output tone value determining unit sets the threshold from the numerical threshold range without excluding any of the plurality of output dot patterns. 3. The image processor according to claim 2, wherein the output tone value determining unit sets the threshold from a neighborhood of a median, including the median, in the numerical threshold range as a predetermined threshold. 4. The image processor according to claim 1, wherein the output tone value determining unit sets the threshold from the numerical threshold range, when a mean error value is specified respectively with respect to the plurality of output dot patterns. 5. The image processor according to claim 1, wherein the output tone value determining unit sets the threshold by excluding an output dot pattern having a small mean output tone value in neighborhood of a pixel having the output tone value in a predetermined range, from the plurality of output dot patterns, when the setting is such that as the pixel value becomes larger, the density becomes higher. 6. The image processor according to claim 5, wherein the output tone value determining unit set the threshold from the range of small output tone values, excluding the lowest density from the predetermined range. 7. The image processor according to claim 5, wherein the output tone value determining unit sets the threshold by changing the predetermined range corresponding to the output tone value in the neighborhood. 8. The image processor according to claim 5, wherein the output tone value determining unit sets the threshold by assuming that neighboring pixels are adjacent to the target pixel. 9. The image processor according to claim 5, wherein the output tone value determining unit sets the threshold by assuming that neighboring pixels are neighboring pixels of the target pixel in the horizontal scanning direction. 10. The image processor according to claim 5, wherein the output tone value determining unit includes a phase controller that controls a phase of the pixels. 11. The image processor according to claim 10, wherein the phase controller determines a phase of the target pixel based on values of pixels that are adjacent to the target pixel in the horizontal scanning direction. 12. The image processor according to claim 1, wherein the output tone value determining unit sets the threshold by excluding an output dot pattern in which there is no pixel having a large output tone value in neighborhood of a pixel having the output tone value in a predetermined range, from the plurality of output dot patterns, when the setting is such that as the pixel value becomes larger, the density becomes higher. 13. The image processor according to claim 1, wherein the output tone value determining unit sets the threshold by excluding an output dot pattern having a large mean output tone value in neighborhood of a pixel having the output tone value in a predetermined range, from the plurality of output dot patterns. 14. The image processor according to claim 13, wherein the output tone value determining unit sets the threshold from the range of large output tone values, excluding the highest density from the predetermined range. 15. The image processor according to claim 1, wherein the output tone value determining unit sets the threshold by excluding an output dot pattern in which there is no pixel having a small output tone value in neighborhood of a pixel having the output tone value in a predetermined range, from the plurality of output dot patterns. 16. The image processor of claim 1, wherein the output tone determining unit is configured to determine a plurality of thresholds corresponding to the position of the target pixel, the thresholds being chosen from a corresponding plurality of numerical threshold ranges determined by the process that includes obtaining corrected image data for the plurality of different output dot patterns. 17. A method of image processing, comprising: correcting image data of a target pixel by giving a weight to error values in the neighborhood of the target pixel and adding weighted error values to a tone value of the target pixel; determining an output tone data of the target pixel based on corrected image data, and a threshold corresponding to a position of the target pixel; and calculating a difference between the output tone data and the corrected image data as an error value, wherein the determining includes setting the threshold corresponding to the position of the target pixel to be within a numerical threshold range determined by a process that includes obtaining corrected image data when an output dot pattern output as an output tone value is in a steady state, and determining the numerical threshold range from the obtained corrected image data, wherein, in the steady state, a same output dot pattern is stably generated repeatedly as a result of repeated tone processing of a solid image having a certain input tone value, wherein the process of obtaining correcting image data is repeated for a plurality of different output dot patterns. 18. The method according to claim 17, wherein the determining includes setting the threshold from neighborhood of a median, including the median, in the obtained numerical threshold range. 19. The method according to claim 17, wherein the determining includes setting the numerical threshold from the threshold range, when a mean error value is specified respectively with respect to the plurality of output dot patterns. 20. The method according to claim 17, wherein the determining includes setting the threshold by excluding an output dot pattern having a small mean output tone value in neighborhood of a pixel having the output tone value in a predetermined range, from the plurality of output dot patterns, when the setting is such that as the pixel value becomes larger, the density becomes higher. 21. The method according to claim 20, wherein the determining includes setting the threshold from the range of small output tone values, excluding the lowest density from the predetermined range. 22. The method according to claim 20, wherein the determining includes setting the threshold by changing the predetermined range corresponding to the output tone value in the neighborhood. 23. The method according to claim 20, wherein the determining includes setting the threshold by assuming that neighboring pixels are adjacent to the target pixel. 24. The method according to claim 20, wherein the determining includes setting the threshold by assuming that neighboring pixels are neighboring pixels of the target pixel in the horizontal scanning direction. 25. The method according to claim 17, wherein the determining includes setting the threshold by excluding an output dot pattern in which there is no pixel having a large output tone value in neighborhood of a pixel having the output tone value in a predetermined range, from the plurality of output dot patterns, when the setting is such that as the pixel value becomes larger, the density becomes higher. 26. The method according to claim 17, wherein the determining includes setting the threshold by excluding an output dot pattern having a large mean output tone value in neighborhood of a pixel having the output tone value in a predetermined range, from the plurality of output dot patterns. 27. The method according to claim 26, wherein the determining includes setting the threshold from the range of large output tone values, excluding the highest density from the predetermined range. 28. The method according to claim 17, wherein the determining includes setting the threshold by excluding an output dot pattern in which there is no pixel having a small output tone value in neighborhood of a pixel having the output tone value in a predetermined range, from the plurality of output dot patterns. 29. The method according to claim 17, wherein the determining includes controlling a phase of the pixels. 30. The method according to claim 17, wherein the controlling includes determining a phase of the target pixel based on values of pixels that are adjacent to the target pixel in the horizontal scanning direction.