Image processing method and apparatus, threshold value matrix creating method, image forming apparatus, sub-matrix creating method and program

A computer readable medium having embodied thereon an image processing program for performing by a computer, the image processing program comprising:

• a first code segment for a recording failure position determination step of determining a recording failure position on an image corresponding to a malfunctioning recording element;
• a second code segment for a basic threshold value matrix storage step of storing a basic threshold value matrix set with threshold values used for halftoning of converting multiple-value input image data into dot data of a number of tonal graduations smaller than that of the multiple-value input image data by quantizing the multiple-value input image data;
• a third code segment for a sub-matrix storage step of storing a plurality of sub-matrices in association with recording failure positions in the basic threshold value matrix, each of the sub-matrices being set with threshold values which are substituted for the threshold values in a partial region of the basic threshold value matrix, the partial region including a pixel position corresponding to the recording failure position and having a width of a prescribed number of pixels;
• a fourth code segment for a replacement region determination step of determining a corresponding region with the width of the prescribed number of pixels including the recording failure position in the basic threshold value matrix, according to the pixel position in the input image data and the recording failure position determined in the recording failure position determination step;
• a fifth code segment for a sub-matrix selection step of selecting one of the sub-matrices stored in the sub-matrix storage step to use for substituting for the corresponding region determined in the replacement region determination step;
• a sixth code segment for a threshold value replacement step of creating a reformed threshold value matrix by replacing the threshold values of the corresponding region including the recording failure position in the basic threshold value matrix, with the one of the sub-matrices selected in the sub-matrix selection step;
• and
• a seventh code segment for a quantization processing step of quantizing the input image data by selectively using the basic threshold value matrix and the reformed threshold value matrix.

An image processing apparatus, comprising:

• a recording failure position determination device which determines a recording failure position on an image corresponding to a malfunctioning recording element;
• a basic threshold value matrix storage device which stores a basic threshold value matrix set with threshold values used for halftoning of converting multiple-value input image data into dot data of a number of tonal graduations smaller than that of the multiple-value input image data by quantizing the multiple-value input image data;
• a sub-matrix storage device which stores a plurality of sub-matrices in association with recording failure positions in the basic threshold value matrix, each of the sub-matrices being set with threshold values which are substituted for the threshold values in a partial region of the basic threshold value matrix, the partial region including a pixel position corresponding to the recording failure position and having a width of a prescribed number of pixels;
• a replacement region determination device which determines a corresponding region with the width of the prescribed number of pixels including the recording failure position in the basic threshold value matrix, according to the pixel position in the input image data and the recording failure position determined by the recording failure position determination device;
• a sub-matrix selection device which selects one of the sub-matrices to use for substituting for the corresponding region determined by the replacement region determination device;
• a threshold value replacement device which creates a reformed threshold value matrix by replacing the threshold values of the corresponding region including the recording failure position in the basic threshold value matrix, with the one of the sub-matrices selected by the sub-matrix selection device;
• and
• a quantization processing device which quantizes the input image data by selectively using the basic threshold value matrix and the reformed threshold value matrix.

A threshold value matrix creating method, comprising:

• a basic threshold value matrix storage step of storing a basic threshold value matrix set with threshold values used for halftoning of converting multiple-value input image data into dot data of a number of tonal graduations smaller than that of the multiple-value input image data by quantizing the multiple-value input image data;
• a sub-matrix storage step of storing a plurality of sub-matrices in association with recording failure positions in the basic threshold value matrix, each of the sub-matrices being set with threshold values which are substituted for the threshold values in a partial region of the basic threshold value matrix having a width of a prescribed number of pixels including a pixel position corresponding to a position of a malfunctioning recording element;
• a sub-matrix selection step of selecting at least one of the sub-matrices stored in the sub-matrix storage step;
• and
• a threshold value replacement step of creating a reformed threshold value matrix by replacing the threshold values of a partial region of the basic threshold value matrix with the sub-matrix selected in the sub-matrix selection step, the partial region including the recording failure position and having a width of a prescribed number of pixels.

A computer readable medium having embodied thereon a threshold value matrix creating program for performing by a computer, the threshold value matrix creating program comprising:

• a first code segment for a basic threshold value matrix storage step of storing a basic threshold value matrix set with threshold values used for halftoning of converting multiple-value input image data into dot data of a number of tonal graduations smaller than that of the multiple-value input image data by quantizing the multiple-value input image data;
• a second code segment for a sub-matrix storage step of storing a plurality of sub-matrices in association with recording failure positions in the basic threshold value matrix, each of the sub-matrices being set with threshold values which are substituted for the threshold values in a partial region of the basic threshold value matrix having a width of a prescribed number of pixels including a pixel position corresponding to a position of a malfunctioning recording element;
• a third code segment for a sub-matrix selection step of selecting at least one of the sub-matrices stored in the sub-matrix storage step;
• and
• a fourth code segment for a threshold value replacement step of creating a reformed threshold value matrix by replacing the threshold values of a partial region of the basic threshold value matrix with the sub-matrix selected in the sub-matrix selection step, the partial region including the recording failure position and having a width of a prescribed number of pixels.

An image forming apparatus, comprising:

• a recording head in which a plurality of recording elements are arranged;
• a conveyance device which causes the recording head and a recording medium to move relatively to each other by conveying at least one of the recording head and the recording medium;
• a recording failure position determination device which determines a recording failure position on an image corresponding to at least one of the recording elements that is malfunctioning in the recording head;
• a basic threshold value matrix storage device which stores a basic threshold value matrix set with threshold values used for halftoning of converting multiple-value input image data into dot data of a number of tonal graduations smaller than that of the multiple-value input image data by quantizing the multiple-value input image data;
• a sub-matrix storage device which stores a plurality of sub-matrices in association with recording failure positions in the basic threshold value matrix, each of the sub-matrices being set with threshold values which are substituted for the threshold values in a partial region of the basic threshold value matrix, the partial region including a pixel position corresponding to the recording failure position and having a width of a prescribed number of pixels;
• a replacement region determination device which determines a corresponding region with the width of the prescribed number of pixels including the recording failure position in the basic threshold value matrix, according to the pixel position in the input image data and the recording failure position determined by the recording failure position determination device;
• a sub-matrix selection device which selects one of the sub-matrices to use for substituting for the corresponding region determined by the replacement region determination device;
• a threshold value replacement device which creates a reformed threshold value matrix by replacing the threshold values of the corresponding region including the recording failure position in the basic threshold value matrix, with the one of the sub-matrices selected by the sub-matrix selection device;
• a quantization processing device which generates the dot data by quantizing the input image data by selectively using the basic threshold value matrix and the reformed threshold value matrix;
• and
• a recording control device which controls driving of the recording elements in the recording head, according to the dot data generated by the quantization processing device.