Dither matrix, image processing method, storage medium, image processing apparatus, image forming apparatus, and image forming system

An image processing method of performing image processing on image data of an image, wherein the image processing includes halftone processing that is performed using a dither mask made of a dither matrix used in halftone processing for converting input image data having M input halftone levels into output image data having N>N>2) output halftone levels, wherein

• multiple submatrices are arranged in the dither matrix at a screen angle without overlap and without leaving space in the dither matrix so that output pixels form a halftone dot pattern or screen lines;
• concentration type submatrices are used as the submatrices when an input halftone level is within a range of input halftone levels corresponding to an output halftone level that is lower than a predetermined threshold level T (N>T>1);
• and
• dispersion type submatrices are used as the submatrices when the input halftone level is within a range of input halftone levels corresponding to an output halftone level that is equal to or higher than the predetermined threshold level T;
• the image is to be formed by an image forming apparatus including a recording head that jets drops of a recording liquid;
• the image is formed on such a recording medium that the drops of the recording liquid do not spread smoothly but clump together thereon;
• the recording medium is composed of a base material and at least one coating layer formed on a side of the base material;
• when the recording medium is brought into contact with the recording liquid for 100 ms in an environment of 23° C. and 50% RH, between 2 and 40 ml/m2 of the recording liquid is transferred onto the recording medium;
• and
• when the recording medium is brought into contact with the recording liquid for 400 ms in the environment of 23° C. and 50% RH, between 3 and 50 ml/m2 of the recording liquid is transferred onto the recording medium.

An image processing method of performing image processing on image data of an image, wherein the image processing includes halftone processing that is performed using a dither mask made of a dither matrix used in halftone processing for converting input image data having M input halftone levels into output image data having N (M>N>2) output halftone levels, wherein

• multiple submatrices are arranged in the dither matrix at a screen angle without overlap and without leaving space in the dither matrix so that output pixels form a halftone dot pattern or screen lines;
• concentration type submatrices are used as the submatrices when an input halftone level is within a range of input halftone levels corresponding to an output halftone level that is lower than a predetermined threshold level T (N>T>1);
• and
• dispersion type submatrices are used as the submatrices when the input halftone level is within a range of input halftone levels corresponding to an output halftone level that is equal to or higher than the predetermined threshold level T;
• the image is to be formed by an image forming apparatus including a recording head that jets drops of a recording liquid;
• the image is formed on such a recording medium that the drops of the recording liquid do not spread smoothly but clump together thereon;
• the recording medium is composed of a base material and at least one coating layer formed on a side of the base material;
• when the recording medium is brought into contact with pure water for 100 ms in an environment of 23° C. and 50% RH,. between 2 and 45 ml/m2 of the pure water is transferred onto the recording medium;
• and
• when the recording medium is brought into contact with the pure water for 400 ms in the environment of 23° C. and 50% RH, between 3 and 50 ml/m2 of the pure water is transferred onto the recording medium.