Dither matrix creating device

A dither matrix creating device comprising:

• a processor configured to function as:
• an acquiring unit configured to acquire a basic dither matrix including a plurality of threshold values corresponding to a plurality of input values that can be inputted, respectively, the basic dither matrix being divided into a plurality of cells to which the plurality of threshold values are allocated, respectively, a threshold value that is allocated in each of the plurality of cells in the basic dither matrix being predetermined;
• a modifying unit configured to modify the basic dither matrix to provide a modified dither matrix, the modified dither matrix including a plurality of sets of threshold value, each threshold value set including N number of threshold values, N being an integer greater than 1, the modified dither matrix being used by an image processing device for converting an input image into an output image according to a dither method, the image processing device being capable of converting an input image into an output image according to an error diffusion method, the input image including a plurality of input pixels each having a multi-level input density value, the output image including a plurality of output pixels each corresponding to respective one of the plurality of input pixels, each output pixel having an (N+1)-level output value, each output value indicating one of (a) that no dot is formed and (b) that one of N types of dots is formed, a dot DJ indicating J-th dot of the N types of dots, a density represented by a dot DJ being greater as J gets greater, J being an integer greater than or equal to 1 and smaller than or equal to N, the N threshold values including threshold values DTJ indicating J-th threshold value;
• wherein when the image processing device converts an input image into an output image according to the dither method, the image processing device converts each input density value into an output value in such a manner that:
• the image processing device converts an input density value of an input pixel into an output value indicating that the dot DN is formed if the input density value is greater than or equal to the threshold value DTN;
• the image processing device converts an input value into an output value indicating that a dot DJ-1 is formed if the input density value is smaller than the threshold value DTJ and greater than or equal to the threshold value DTJ-1 where J is greater than 1 and smaller than or equal to N;
• and
• the image processing device converts an input value into an output value indicating that no dot is formed if the input density value is smaller than the threshold value DT1;
• wherein the modifying unit modifies the basic dither matrix by adjusting at least one of N number of threshold values such that the image processing device can produce a first output image by using the modified dither matrix according to the dither method, the first output image being more similar to an output image produced based on the input image according to the error diffusion method than an output image to be produced by using the basic dither matrix according to the dither method,
• wherein when the image processing device converts an input image into an output image according to the error diffusion method, the image processing device converts an input density value of a pixel included in the input image into an output value according to a predetermined relationship between the input density value and an usage rate of dot DK, the usage rate of dot DK indicating a ratio of a pixel number of reference output pixels having an output value that the dot DK is formed to a total number of the reference output pixels when the image processing device converts a reference input image into a reference output image including the reference output values according to the error diffusion method, the reference input image including a plurality of reference input values having a single input density value, the reference output image including the reference output pixels, K being an integer greater than or equal to 1 and smaller than or equal to N;
• wherein the processor is further configured to function as a correcting unit configured to correct, if the predetermined relationship includes a range of input density value in which a sum of usage rates for all dots D1 through DN decreases as the input density value increases, the predetermined relationship to a corrected relationship such that the sum of usage rates fails to decrease in the range of input density value as the input density value increases;
• wherein the modifying unit modifies the basic dither matrix to the modified dither matrix by adjusting a threshold value DTK of N number of threshold values based on the corrected relationship.

A non-transitory computer readable storage medium storing a set of program instructions installed on and executed by a computer, the program instructions comprising:

• acquiring a basic dither matrix including a plurality of threshold values corresponding to a plurality of input values that can be inputted, respectively, the basic dither matrix being divided into a plurality of cells to which the plurality of threshold values are allocated, respectively, a threshold value that is allocated in each of the plurality of cells in the basic dither matrix being predetermined;
• and
• modifying the basic dither matrix to provide a modified dither matrix, the modified dither matrix including a plurality of sets of threshold value, each threshold value set including N number of threshold values, N being an integer greater than 1, the modified dither matrix being used by an image processing device for converting an input image into an output image according to a dither method, the image processing device being capable of converting an input image into an output image according to an error diffusion method, the input image including a plurality of input pixels each having a multi-level input density value, the output image including a plurality of output pixels each corresponding to respective one of the plurality of input pixels, each output pixel having an (N+1)-level output value, each output value indicating one of (a) that no dot is formed and (b) that one of N types of dots is formed, a dot DJ indicating J-th dot of the N types of dots, a density represented by a dot DJ being greater as J gets greater, J being an integer greater than or equal to 1 and smaller than or equal to N, the N threshold values including threshold values DTJ indicating J-th threshold value;
• wherein when the image processing device converts an input image into an output image according to the dither method, the image processing device converts each input density value into an output value in such a manner that:
• the image processing device converts an input density value of an input pixel into an output value indicating that the dot DN is formed if the input density value is greater than or equal to the threshold value DTN;
• the image processing device converts an input value into an output value indicating that a dot DJ-1 is formed if the input density value is smaller than the threshold value DTJ and greater than or equal to the threshold value DTJ-1 where J is greater than 1 and smaller than or equal to N;
• and
• the image processing device converts an input value into an output value indicating that no dot is formed if the input density value is smaller than the threshold value DT1;
• wherein the basic dither matrix is modified to the modified dither matrix by adjusting at least one of N number of threshold values such that the image processing device can produce a first output image by using the modified dither matrix according to the dither method, the first output image being more similar to an output image produced based on the input image according to the error diffusion method than an output image to be produced by using the basic dither matrix according to the dither method,
• wherein when the image processing device converts an input image into an output image according to the error diffusion method, the image processing device converts an input density value of a pixel included in the input image into an output value by using a single set of N number of threshold values ET1 through ETN, a threshold value ET1 indicating J-th threshold value of the N number of threshold values ET1 through ETN;
• wherein when the image processing device converts an input image into an output image according to the error diffusion method, the image processing device converts each input density value into an output value in such a manner that:
• the image processing device corrects, for each of input pixels included in the input image, the threshold values ET1 through ETN to provide a corrected threshold values CT1 through CTN by adding a variation value respective threshold values ET1 through ETN;
• the image processing device converts an input density value of an input pixel into an output value indicating that the dot DN is formed if the input density value is greater than or equal to the corrected threshold value CTN;
• the image processing device converts an input value into an output value indicating that the dot DJ-1 is formed if the input density value is smaller than the corrected threshold value CTJ and greater than or equal to the corrected threshold value CTJ-1 where J is greater than 1 and smaller than or equal to N;
• and
• the image processing device converts an input value into an output value indicating that no dot is formed if the input density value is smaller than the corrected threshold value CT1;
• wherein each of the plurality of threshold value sets included in the modified dither matrix corresponds to respective one of the plurality of threshold values included in the basic matrix, a threshold value set included in the modified dither matrix that corresponds to a minimum threshold value smallest among the plurality of threshold values included in the basic dither matrix including N number of minimum threshold values MDT1 through MDTN, a minimum threshold value MDTJ indicating a minimum threshold value among the threshold values DTJ included in the plurality of threshold value sets, the minimum threshold value MDT1 through MDTN calculated by multiplying the threshold values ET1 through ETN by a volatility of variation values.

A dither matrix creating method comprising:

• acquiring a basic dither matrix including a plurality of threshold values corresponding to a plurality of input values that can be inputted, respectively, the basic dither matrix being divided into a plurality of cells to which the plurality of threshold values are allocated, respectively, a threshold value that is allocated in each of the plurality of cells in the basic dither matrix being predetermined;
• and
• modifying the basic dither matrix to provide a modified dither matrix, the modified dither matrix including a plurality of sets of threshold value, each threshold value set including N number of threshold values, N being an integer greater than 1, the modified dither matrix being used by an image processing device for converting an input image into an output image according to a dither method, the image processing device being capable of converting an input image into an output image according to an error diffusion method, the input image including a plurality of input pixels each having a multi-level input density value, the output image including a plurality of output pixels each corresponding to respective one of the plurality of input pixels, each output pixel having an (N+1)-level output value, each output value indicating one of (a) that no dot is formed and (b) that one of N types of dots is formed, a dot DJ indicating J-th dot of the N types of dots, a density represented by a dot DJ being greater as J gets greater, J being an integer greater than or equal to 1 and smaller than or equal to N, the N threshold values including threshold values DTJ indicating J-th threshold value;
• wherein when the image processing device converts an input image into an output image according to the dither method, the image processing device converts each input density value into an output value in such a manner that:
• the image processing device converts an input density value of an input pixel into an output value indicating that the dot DN is formed if the input density value is greater than or equal to the threshold value DTN;
• the image processing device converts an input value into an output value indicating that a dot DJ-1 is formed if the input density value is smaller than the threshold value DTJ and greater than or equal to the threshold value DTJ-1 where J is greater than 1 and smaller than or equal to N;
• and
• the image processing device converts an input value into an output value indicating that no dot is formed if the input density value is smaller than the threshold value DT1;
• wherein the basic dither matrix is modified to the modified dither matrix by adjusting at least one of N number of threshold values such that the image processing device can produce a first output image by using the modified dither matrix according to the dither method, the first output image being more similar to an output image produced based on the input image according to the error diffusion method than an output image to be produced by using the basic dither matrix according to the dither method,
• wherein when the image processing device converts an input image into an output image according to the error diffusion method, the image processing device converts an input density value of a pixel included in the input image into an output value by using a single set of N number of threshold values ET1 through ETN, a threshold value ETJ indicating J-th threshold value of the N number of threshold values ET1 through ETN;
• wherein when the image processing device converts an input image into an output image according to the error diffusion method, the image processing device converts each input density value into an output value in such a manner that:
• the image processing device corrects, for each of input pixels included in the input image, the threshold values ET1 through ETN to provide a corrected threshold values CT1 through CTN by adding a variation value respective threshold values ET1 through ETN;
• the image processing device converts an input density value of an input pixel into an output value indicating that the dot DN is formed if the input density value is greater than or equal to the corrected threshold value CTN;
• the image processing device converts an input value into an output value indicating that the dot DJ-1 is formed if the input density value is smaller than the corrected threshold value CTJ and greater than or equal to the corrected threshold value CTJ-1 where J is greater than 1 and smaller than or equal to N;
• and
• the image processing device converts an input value into an output value indicating that no dot is formed if the input density value is smaller than the corrected threshold value CT1;
• wherein each of the plurality of threshold value sets included in the modified dither matrix corresponds to respective one of the plurality of threshold values included in the basic matrix, a threshold value set included in the modified dither matrix that corresponds to a minimum threshold value smallest among the plurality of threshold values included in the basic dither matrix including N number of minimum threshold values MDT1 through MDTN, a minimum threshold value MDTJ indicating a minimum threshold value among the threshold values DTJ included in the plurality of threshold value sets, the minimum threshold value MDT1 through MDTN calculated by multiplying the threshold values ET1 through ETN by a volatility of variation values.