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

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.

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.

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.