Image processing apparatus for converting image data by unit of multiple pixels

• US 7,375,855 B2
• Filed: 03/14/2003
• Issued: 05/20/2008
• Est. Priority Date: 03/20/2002
• Status: Expired due to Fees

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Kakutani, Toshiaki
• Primary Examiner(s): Rogers; Scott A.
• Application Number:
  US10/390,090
• Publication Number:
  US 20040001549A1
• Time in Patent Office: 1,894 Days
• Field of Search: 358/1.9, 358/3.06, 358/3.21, 358/3.23, 358/534, 358 303- 305, 382/252
• US Class Current: 358/3.03
• CPC Class Codes: G06K 15/02 using printers
• CPC Class Codes: H04N 1/52 Circuits or arrangements for halftone screening
• CPC Class Codes: H04N 1/58 Edge or detail enhancement; Noise or error suppression, e.g. colour misregistration correction H04N1/62 takes precedence

Abstract

The technique of the invention joins a preset number of adjacent pixels into a unit and collectively converts input image data of each unit into dot data. Here the image data is expressed by tone values of respective pixels constituting an image, and the dot data represents dot on-off state. The technique stores dot on-off state determined with regard to at least part of pixels included in a processed unit, which has been subjected to the data conversion, in such a manner that a pixel position in the processed unit is identifiable. The procedure of the data conversion by units specifies a target pixel, in which a dot on-off state is to be determined, in a unit, detects a dot creation status with regard to an object pixel that is located at a specific position relative to the target pixel, and determines the dot on-off state in the target pixel based on the detection result. This arrangement effectively prevents the picture quality of a resulting image from being worsened by conversion of the image data into the dot data by units.

Claims

1. An image processing apparatus that converts image data expressed by tone values of respective pixels constituting an image into dot data representing dot on-off state, said image processing apparatus comprising:

a dot data conversion module that joins a preset number of adjacent pixels into a unit and collectively converts the image data of each unit into the dot data; and

a dot on-off state storage module that stores dot on-off state determined with regard to at least part of pixels included in a processed unit, which has been subjected to the data conversion, in such a manner that a pixel position in the processed unit is identifiable,

wherein said dot data conversion module comprises;

a target pixel specification sub-module that successively specifies a target pixel, in which a dot on-off state is to be determined, in each unit;

a dot creation status detection sub-module that detects a dot creation status with regard to an object pixel that is located at a specific position relative to the target pixel, among the at least part of the pixels included in the processed unit, for which the dot on-off state is stored; and

a dot on-off state determination sub-module that determines the dot on-off state in the target pixel, based on a tone value of the image data at the target pixel and the dot creation status detected with regard to the object pixel at the specific position.

2. An image processing apparatus in accordance with claim 1, wherein said dot on-off state determination sub-module comprises:

a dot formation prohibition sub-module that prohibits formation of a dot in the target pixel, when the detected dot creation status shows presence of a dot in the object pixel at the specific position.

3. An image processing apparatus in accordance with claim 2, wherein said dot creation status detection sub-module detects dot creation status with regard to multiple object pixels that are located at the specific position relative to the target pixel, and

said dot formation prohibition sub-module prohibits formation of a dot in the target pixel, when the detected dot creation status shows presence of a dot in any of the multiple object pixels at the specific position.

4. An image processing apparatus in accordance with claim 2, wherein said dot creation status detection sub-module detects dot creation status with regard to multiple object pixels that are located at a specific position relative to the target pixel, and

said dot formation prohibition sub-module prohibits formation of a dot in the target pixel, when the detected dot creation status shows presence of a dot in all of the multiple object pixels at the specific position.

5. An image processing apparatus in accordance with claim 1, wherein said dot on-off state determination sub-module comprises:

a dot formation recommendation sub-module that recommends formation of a dot in the target pixel, when the detected dot creation status shows presence of a dot in the object pixel at the specific position.

6. An image processing apparatus in accordance with claim 1, wherein said dot data conversion module further comprises:

a summation calculation sub-module that calculates a summation of tone values of the respective pixels included in each unit, and

said dot on-off state determination sub-module determines the dot on-off state in the target pixel, based on the calculated summation as well as the tone value of the image data at the target pixel and the dot creation status detected with regard to the object pixel at the specific position.

7. An image processing apparatus in accordance with claim 6, wherein said dot on-off state determination sub-module comprises:

a suppression sub-module that suppresses formation of a dot in the target pixel, when the calculated summation is not greater than a predetermined value.

8. An image processing apparatus in accordance with claim 6, wherein said dot on-off state determination sub-module comprises:

a promotion sub-module that promotes formation of a dot in the target pixel, when the calculated summation is not less than a preset value.

9. An image processing apparatus in accordance with claim 6, wherein said dot data conversion module further comprises:

a pixel position storage sub-module that stores a mapping of an object pixel position for detection of the dot creation status to a tone value, and

said dot creation status detection sub-module detects the dot creation status with regard to an object pixel position mapped to the calculated summation of the tone values.

10. An image processing apparatus in accordance with claim 9, wherein said pixel position storage sub-module stores a mapping, such that a pixel position mapped to a first tone value that is smaller than a predetermined value is farther from the target pixel than a pixel position mapped to a second tone value that is greater than the predetermined value.

11. An image processing apparatus in accordance with claim 1, wherein said dot data conversion module further comprises:

a pixel position storage sub-module that stores a mapping of an object pixel position for detection of the dot creation status to a tone value, and

said dot creation status detection sub-module detects the dot creation status with regard to an object pixel position mapped to the tone value of the target pixel.

12. An image processing apparatus in accordance with any one of claims 1, 2, 5, and 6, wherein said dot on-off state determination sub-module applies an error diffusion method to determine the dot on-off state in the target pixel, and varies a threshold value of the error diffusion method, which is referred to for the determination, according to the dot creation status detected by said dot creation status detection sub-module.

13. An image processing apparatus in accordance with claim 1, wherein said dot on-off state determination sub-module applies an error diffusion method to determine the dot on-off state in the target pixel, and decides that no dot is to be created in the target pixel when the detected dot creation status shows the presence of a dot in the object pixel at the specific position relative to the target pixel.

14. An image processing apparatus in accordance with claim 1, wherein said dot on-off state storage module stores a data array of multiple consecutive data, which represent the dot on-off state of multiple pixels and are arranged in a specific order that allows for identification of the processed unit to which each pixel belongs and a position of the pixel in the processed unit.

15. An image processing apparatus in accordance with claim 1, wherein said dot on-off state storage module stores a data array of multiple consecutive data, which represent the dot on-off state of multiple pixels, are classified into each pixel position in the processed unit, and are arranged in a specific order that allows for identification of the processed unit to which each pixel belongs, corresponding to each pixel position in the processed unit.

16. A printing apparatus that receives image data expressed by tone values of respective pixels constituting an image and creates dots on a printing medium based on the input image data, said printing apparatus comprising:

a unit definition module that joins a preset number of adjacent pixels into a unit;

a dot data conversion module that collectively converts image data of multiple pixels constituting each unit into dot data representing dot on-off state of the respective pixels;

a dot creation module that creates dots in specified pixels, based on the converted dot data; and

a dot on-off state storage module that stores dot on-off state determined with regard to at least part of pixels included in a processed unit, which has been subjected to the data conversion, in such a manner that a pixel position in the processed unit is identifiable,

wherein said dot data conversion module comprises;

a target pixel specification sub-module that successively specifies a target pixel, in which a dot on-off state is to be determined, in each unit;

a dot creation status detection sub-module that detects a dot creation status with regard to an object pixel that is located at a specific position relative to the target pixel, among the at least part of the pixels included in the processed unit, for which the dot on-off state is stored; and

a dot on-off state determination sub-module that determines the dot on-off state in the target pixel, based on a tone value of the image data at the target pixel and the dot creation status detected with regard to the object pixel at the specific position.

17. An image processing method of converting image data expressed by tone values of respective pixels constituting an image into dot data representing dot on-off state, said image processing method comprising the steps of:

joining a preset number of adjacent pixels into a unit and collectively converting the image data of each unit into the dot data; and

storing dot on-off state determined with regard to at least part of pixels included in a processed unit, which has been subjected to the data conversion, in such a manner that a pixel position in the processed unit is identifiable,

wherein said converting step comprises the sub-steps of;

successively specifying a target pixel, in which a dot on-off state is to be determined, in each unit;

detecting a dot creation status with regard to an object pixel that is located at a specific position relative to the target pixel, among the at least part of the pixels included in the processed unit, for which the dot on-off state is stored; and

determining the dot on-off state in the target pixel, based on a tone value of the image data at the target pixel and the dot creation status detected with regard to the object pixel at the specific position.

18. A computer program product that attains a method of converting image data expressed by tone values of respective pixels constituting an image into dot data representing dot on-off state, said computer program product comprising:

a computer readable recording medium; and

a computer program that is stored in said recording medium,

said computer program causing a computer to attain the functions of;

joining a preset number of adjacent pixels into a unit and collectively converting the image data of each unit into the dot data; and

storing dot on-off state determined with regard to at least part of pixels included in a processed unit, which has been subjected to the data conversion, in such a manner that a pixel position in the processed unit is identifiable,

wherein said converting function comprises the sub-functions of;

successively specifying a target pixel, in which a dot on-off state is to be determined, in each unit;

detecting a dot creation status with regard to an object pixel that is located at a specific position relative to the target pixel, among the at least part of the pixels included in the processed unit, for which the dot on-off state is stored; and

determining the dot on-off state in the target pixel, based on a tone value of the image data at the target pixel and the dot creation status detected with regard to the object pixel at the specific position.