Generation method, storage medium, and image forming apparatus that generate a threshold matrix by using determined thresholds

A non-transitory storage medium storing a program for causing a computer to execute each step of a method of generating a threshold matrix that includes a plurality of submatrices divided into a lattice form and is for converting multi-tone image data into image data of a lower number of tones, the method comprising:

• determining, in accordance with rising density in an extreme density range, a threshold for setting each pixel of the threshold matrix so as to consecutively grow an isolated dot corresponding to a halftone dot in a low density range to a first dot size for each submatrix;
• setting, when the size of isolated dots in a predetermined number of submatrices is grown to the first dot size, an intermediate position between the isolated dots in the predetermined number of submatrices;
• determining, for each of one or more submatrices including the set intermediate position, a threshold to set for each pixel of the threshold matrix so that the isolated dot is consecutively grown until a second dot size is smaller than the first dot size;
• and
• generating the threshold matrix by using the determined thresholds.

A non-transitory storage medium storing a program for causing a computer to execute each step of a method of generating a threshold matrix that includes a plurality of submatrices divided into a lattice form and is for converting multi-tone image data into image data of a lower number of tones, the method comprising:

• determining, in accordance with falling density in an extreme density range, a threshold for setting each pixel of the threshold matrix so as to consecutively grow an isolated blank dot corresponding to a blank area hole in a high density range to a first dot size for each submatrix;
• setting, when the size of the isolated blank dots in a predetermined number of submatrices is grown to the first dot size, an intermediate position between the isolated blank dots in the predetermined number of submatrices;
• determining, for each of one or more submatrices including the set intermediate position, a threshold to set for each pixel of the threshold matrix so that the isolated blank dot is consecutively grown until a second dot size is smaller than the first dot size;
• and
• generating the threshold matrix by using the determined thresholds.

An image forming apparatus comprising:

• (A) a memory configured to store a threshold matrix for executing halftone processing for converting a multi-tone input image data into output image data of a lower number of tones;
• (B) a controller unit comprising a processor for executing a program or a hardware circuit;
• and
• (C) a printing device,
• wherein the controller unit:
• (a) uses the threshold matrix stored in the memory to execute halftone processing in relation to the input image data, and to generate output image data;
• (b) controls the printing device to cause the printing device to print on a sheet an image based on the output image data,
• wherein the threshold matrix has a plurality of submatrices,
• and, in a case when screen processing is executed in relation to input image data configured by a first density:
• (1) for a first submatrix, thresholds are arranged so that a dot of a first size is outputted;
• (2) for a second submatrix, thresholds are arranged so that, in a case when screen processing is executed in relation to a region of the first density, a dot of a second size smaller than the first size is outputted;
• and (3) for a third submatrix and a fourth submatrix, thresholds are arranged so that, in a case when screen processing is executed in relation to a region of the first density, a dot is not outputted, and, in a case when screen processing is executed in relation to input image data configured by a second density that is higher than a first density:
• (4) for the first submatrix and the second submatrix, thresholds are arranged so that a dot of the first size is outputted;
• (5) for a third submatrix, thresholds are arranged so that a dot of the second size is outputted;
• and (6) for a fourth submatrix, thresholds are arranged so that a dot is not outputted, (7) in a case when screen processing is executed in relation to input image data configured by a third density that is higher than the second density, for the plurality of submatrices, thresholds are arranged so that a dot of the first size is outputted, and (8) in a case when screen processing is executed in relation to input image data configured by a density higher than the third density, in accordance with the density of the input image data becoming higher, thresholds are arranged so that the size of a configured dot becomes larger.