Dither pattern generation method, dither pattern and image processing apparatus

A dither pattern generation method for generating plural dither patterns that include a first dither pattern and a second dither pattern in which threshold values 1 to MAX are arranged, comprising:

• a first dot pattern generation process of generating a first dot pattern in which S×N (S and N are integers that satisfy 1≦S<MAX, and 1≦N) dots are arranged in a specified dither pattern area so as to have a blue noise characteristic;
• a second dot pattern generation process of generating a second dot pattern so that a dot pattern that combines the first dot pattern and the second dot pattern and the second dot pattern each have a blue noise characteristic;
• a process of generating the combined dot pattern that combines the first dot pattern and the second dot pattern;
• a first threshold value setting process of setting threshold values for the first dither pattern by setting each of threshold values 1 to S for every N pixels that are correlated with the first dot pattern so that threshold values having a high value are set for positions having a high dot concentration ratio in the combined dot pattern and the first dot pattern;
• and
• a second threshold value setting process of setting threshold values for the second dither pattern by setting each of threshold values 1 to S for every N pixels that are correlated with the second dot pattern so that threshold values having a high value are set for positions having a high dot concentration ratio in the combined dot pattern and the second dot pattern.

A dither pattern generation method for generating plural dither patterns that include a first dither pattern and a second dither pattern in which threshold values 1 to MAX are arranged, comprising:

• a first dot pattern generation process of generating a first dot pattern in which S×N (S and N are integers that satisfy 1≦S<MAX, and 1≦N) dots are arranged in a specified dither pattern area so as to have a blue noise characteristic;
• a second dot pattern generation process of generating a second dot pattern in which S×N (S and N are integers that satisfy 1≦S<MAX, and 1≦N) dots are arranged in a specified dither pattern area so as to have a blue noise characteristic, and so that a combination with the first dot pattern has a blue noise characteristic;
• a first threshold value setting process of setting threshold values for the first dither pattern by setting each of threshold values 1 to S for every N pixels that are correlated with the first dot pattern so that threshold values having a high value are set for positions having a high dot concentration ratio in the first dot pattern and the second dot pattern;
• and
• a second threshold value setting process of setting threshold values for the second dither pattern by setting each of threshold values 1 to S for every N pixels that are correlated with the second dot pattern so that threshold values having a high value are set for positions having a high dot concentration ratio in the first dot pattern and the second dot pattern.