Image processing apparatus for generating dot data for image data, printing apparatus for generating dot data for image data, and image processing method for generating dot data for image data

• US 8,681,378 B2
• Filed: 03/23/2012
• Issued: 03/25/2014
• Est. Priority Date: 03/24/2011
• Status: Active Grant

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Kakutani, Toshiaki
• Primary Examiner(s): BRYAR, JEREMIAH A
• Application Number:
  US13/428,462
• Publication Number:
  US 20120243012A1
• Time in Patent Office: 732 Days
• Field of Search: None
• US Class Current: 358/1.9
• CPC Class Codes: H04N 1/4051 producing a dispersed dots halftone pattern, the dots having substantially the same size different sizes H04N1/4057
• CPC Class Codes: H04N 1/4092 Edge or detail enhancement

Abstract

An image is divided into first a second regions on the basis of inputted image data, and a comparison is made between the gradation values of pixels in the first region and threshold values corresponding to the pixels of the first region of a dither mask. The results of the comparison are referenced to determine whether or not dots are formed in the pixels of the first region. Errors are calculated based on the results of determining the first boundary pixels, which are in the first region near the boundary between the first region second regions. Some of the errors are distributed as diffusion errors to pixels in the second region near the boundary. The diffusion errors distributed from the first boundary pixels are added, and it is determined whether or not dots are formed by the error diffusion method in the pixels of the second region.

Claims

1. An image processing apparatus for processing image data having a plurality of pixels and expressing an image using a gradation value for each pixel, the image processing apparatus comprising:

an input unit configured to input the image data;

a region-dividing processor configured to divide the image into at least a first region and a second region on the basis of the inputted image data;

a comparator configured to compare gradation values of pixels in the first region and threshold values corresponding to the pixels of the first region of a dither mask having a plurality of threshold values;

a first dot-decision processor configured to decide whether or not dots are formed in pixels of the first region among first boundary pixels, which are pixels in the first region near the boundary between the first region and the second region, using information on pixels included in the first region and not using information on pixels included in the second region;

a second dot-decision processor configured to decide whether or not dots are formed in some of the pixels in the second region, using information on pixels included in the first region and information on pixels included in the second region; and

a dot data generator configured to generate dot data for the image data using formation or non-formation of dots as decided by the first and second dot-decision processors.

2. The image processing apparatus of claim 1, wherein

the first dot-decision processor adds diffusion errors distributed from processed pixels near the first boundary pixels to the gradation values of the first boundary pixels to calculate a first corrected gradation values, and references at least comparison results of the comparator to make decisions on whether or not dots are formed in pixels of the first region, and then calculates errors between the first corrected gradation values and a first decision result values with respect to the first boundary pixels, the first decision result values corresponding to density expressed by the pixels in results of the decisions on whether or not dots are formed in pixels of the first region, and distributes the errors as diffusion errors to unprocessed pixels near the first boundary pixels.

3. The image processing apparatus of claim 1, wherein

the second dot-decision processor calculates, with respect to some of the pixels in the second region, second corrected gradation values in which diffusion errors distributed from processed pixels in an adjacent area that includes the first boundary pixels have been added to the gradation values of the pixels, compares the second corrected gradation values and a predetermined threshold value to make decisions on whether or not dots are formed in some of the pixels in the second region, calculates errors between the second corrected gradation values and second decision result values, the second decision result values corresponding to density expressed by the pixels in results of the decisions on whether or not dots are formed in some of the pixels in the second region, and distributes the errors as diffusion errors to pixels in an adjacent area.

4. The image processing apparatus of claim 1, wherein

the region-dividing processor divides the image that comprises the plurality of pixels so that the region that satisfies predetermined conditions for a region suitable for processing by a dither method becomes the first region, and the region that satisfies predetermined conditions for a region suitable for processing by an error diffusion method becomes the second region.

5. The image processing apparatus of claim 1, wherein

the first dot-decision processor decides, as a result of the comparison, that dots are formed in cases in which the gradation value of a pixel in the first region is greater than the threshold value corresponding to a pixel in the first region of the dither mask, and that dots have not been formed in cases in which the gradation value is less than the threshold value.

6. The image processing apparatus of claim 1, wherein

the first dot-decision processor compares a predetermined determination value and third corrected gradation values in which diffusion errors distributed from processed pixels among some of the pixels in an area adjacent to the first region have been added to the gradation values of the pixels, and decides whether or not dots are formed, and, as a result of the comparison by the comparator, adjusts the determination values within a predetermined width so that the determination value applied in cases in which the gradation value of a pixel in the first region is greater than the threshold value corresponding to a pixel in the first region of the dither mask does not exceed the determination value applied in cases in which the gradation value of a pixel in the first region is equal to or less than the threshold value corresponding to a pixel in the first region of the dither mask.

7. The image processing apparatus of claim 1, wherein

the second dot-decision processor decides whether or not dots are formed by an error diffusion method, using an error diffusion threshold value prepared in advance as a threshold value used in the error diffusion method.

8. The image processing apparatus of claim 1, wherein

the first region is a region composed of pixels without edge pixels, edge pixels being pixels constituting an edge having gradation value whose difference with respect to an adjacent pixel is equal to or greater than a predetermined value, and wherein the second region is a region composed of the edge pixels.

9. The image processing apparatus of claim 1, wherein

the second region is a thin-line or character region included in an image.

10. The image processing apparatus of claim 1, wherein

the first region is a region composed of inner pixels, which are pixels other than outer edge pixels constituting an outer edge of a line drawing, among pixels constituting the line drawing included in the image, and wherein the second region is a region composed of the outer edge pixels.

11. The image processing apparatus of claim 1, wherein

the first region is a region having less noise in high-frequency components than a predetermined value, and wherein the second region is a region having more noise in the high-frequency components than the predetermined value.

12. A printing apparatus for performing a printing operation on the basis of image data having a plurality of pixels and expressing an image using a gradation value for each pixel, the printing apparatus comprising:

an input unit configured to input the image data;

a region-dividing processor configured to divide the image into at least a first region and a second region on the basis of the inputted image data;

a comparator configured to compare gradation values of pixels in the first region and threshold values corresponding to the pixels of the first region of a dither mask having a plurality of threshold values;

a first dot-decision processor configured to add diffusion errors distributed from processed pixels near the first boundary pixels to the gradation values of the first boundary pixels in the first boundary pixels, which are pixels in the first region near the boundary between the first region and the second region to calculate a first corrected gradation values, and configured to reference at least comparison results of the comparator to make decisions on whether or not dots are formed in pixels of the first region, and then calculating errors between the first corrected gradation values and first decision result values with respect to the first boundary pixels, the first decision result values corresponding to density expressed by the pixels in results of the decisions whether or not dots are formed in pixels of the first region, and configured to distribute the errors as diffusion errors to unprocessed pixels near the first boundary pixels;

a second dot-decision processor configured to calculate, with respect to some of pixels in the second region, second corrected gradation values in which diffusion errors distributed from processed pixels in an adjacent area that includes the first boundary pixels have been added to the gradation values of the pixels, configured to compare the second corrected gradation values and a predetermined threshold value to make decisions on whether or not dots are formed in some of the pixels in the second region, configured to calculate errors between the second corrected gradation values and second decision result values, the second decision result values corresponding to density expressed by the pixels in results of the decisions on whether or not dots are formed in some of the pixels in the second region, and configured to distribute the errors as diffusion errors to pixels in an adjacent area;

a dot data generator configured to generate dot data for the image data using formation or non-formation of dots as decided by the first and second dot-decision processors; and

a printing unit configured to perform a printing operation on the basis of the dot data.

13. An image processing method for processing image data having a plurality of pixels and expressing an image using a gradation value for each pixel, the image processing method comprising:

inputting the image data;

dividing the image into at least a first region and a second region on the basis of the inputted image data;

comparing gradation values of pixels in the first region and threshold values corresponding to the pixels of the first region of a dither mask having a plurality of threshold values;

adding diffusion errors distributed from processed pixels near the first boundary pixels to the gradation values of the first boundary pixels, the first boundary pixels being pixels in the first region near the boundary between the first region and the second region to calculate a first corrected gradation values, and referencing at least comparison results of the comparing of the gradation values and the threshold values to make decisions on whether or not dots are formed in pixels of the first region, and then calculating errors between the first corrected gradation values and first decision result values with respect to the first boundary pixels, the first decision result values corresponding to density expressed by the pixels in results of decisions on whether or not dots are formed in pixels of the first region, and distributing the errors as diffusion errors to unprocessed pixels near the first boundary pixels;

calculating, with respect to some of pixels in the second region, second corrected gradation values in which diffusion errors distributed from processed pixels in an adjacent area that includes the first boundary pixels have been added to the gradation values of the pixels, comparing the second corrected gradation values and a predetermined threshold value to make decisions on whether or not dots are formed in some of the pixels in the second region, calculating errors between the second corrected gradation values and second decision result values, the second decision result values corresponding to density expressed by the pixels in results of the decisions on whether or not dots are formed in some of the pixels in the second region, and distributing the errors as diffusion errors to pixels in an adjacent area; and

generating dot data for the image data using formation or non-formation of dots as decided by the first and second dot-decision processors.