Threshold matrix, a method of generating the same, and a method of reproducing color image
View Patent ↗A dot pattern with a plurality of pixels representing a two-dimensional image is formed on a printing plate material by applying laser beams, which are turned on and off for each pixel depending on dot pattern data, to the printing plate material in a main scanning direction, while the laser beams are moved in an auxiliary scanning direction that is orthogonal to the main scanning direction. A threshold matrix having an array of thresholds is obtained for generating a dot where the degree of a variation of the dot periphery length in a main scanning direction is smaller, i.e., a dot where the dot periphery length in the main scanning direction has a smaller standard deviation.
1. A method of generating a threshold matrix for converting a continuous-tone image into a dot pattern representing a binary image, the method comprising the steps of:
defining a reference periphery length proportion per unit area of the dot pattern as Ref_sur=(4×r×Q 1/2 )/R where r represents a pattern frequency, Q represents a blackened ratio, and R represents an output resolution;
determining a periphery length proportion per unit area for the dot pattern generated by the threshold matrix corresponding to the blackened ratio Q as Mes_sur;
defining a dot pattern periphery length evaluation index as Mes_sur/Ref_sur; and
determining a threshold array of the threshold matrix such that the dot pattern periphery length evaluation index is small.
2. A method according to claim 1 , wherein the threshold array of the threshold matrix is determined such that the dot pattern periphery length evaluation index is less than 1.085 for all blackened ratios Q ranging from 0 to 1.
3. A method of generating a threshold matrix for converting a continuous-tone image into a dot pattern representing a binary image, the method comprising the step of:
determining a threshold array of the threshold matrix such that a variation of periphery length ratios of a dot pattern in a main scanning direction is small.
4. A method according to claim 3 , wherein the threshold array of the threshold matrix is determined such that a standard deviation of the peripheral length ratios of the dot pattern in the main scanning direction is less than 0.019 for all blackened ratios Q ranging from 0 to 1.
5. A computer readable medium having stored therein a threshold matrix, said computer readable medium containing computer executable instructions for:
causing the threshold matrix to convert a continuous-tone image into a dot pattern representing a binary image,
wherein when a reference periphery length proportion per unit area of the dot pattern is defined as Ref_sur=(4×r×Q 1/2 )/R where r represents a pattern frequency, Q represents a blackened ratio, and R represents an output resolution, a periphery length proportion determined per unit area for the dot pattern generated by the threshold matrix corresponding to the blackened ratio Q is represented by Mes_sur,
a threshold array of the threshold matrix is determined such that a dot pattern periphery length evaluation index defined as Mes_sur/Ref_sur is less than 1.085 for all blackened ratios Q ranging from 0 to 1.
6. A computer readable medium having stored therein a threshold matrix, said computer readable medium containing computer executable instructions for:
causing the threshold matrix to convert a continuous-tone image into a dot pattern representing a binary image,
wherein a threshold array of the threshold matrix is determined such that a standard deviation of peripheral length ratios of the dot pattern in the main scanning direction is less than 0.019 for all blackened ratios Q ranging from 0 to 1.
7. A method of generating a threshold matrix for converting a continuous-tone image into a dot pattern representing a binary image, the method comprising the steps of:
defining a reference periphery length proportion per unit area of the dot pattern as Ref_sur=(4×r×Q 1/2 )/R where r represents a pattern frequency, Q represents a blackened ratio, and R represents an output resolution;
determining a periphery length proportion per unit area for the dot pattern generated by the threshold matrix corresponding to the blackened ratio Q as Mes_sur;
defining a dot pattern periphery length evaluation index as Mes_sur/Ref_sur; and
determining a threshold array of the threshold matrix such that the dot pattern periphery length evaluation index is small and that a variation of periphery length ratios of the dot pattern in a main scanning direction is small.
8. A method of reproducing a color image by at least four dot patterns, each of the dot patterns comprising a binary image, at least one of the dot patterns being obtained by using a threshold matrix to convert a continuous-tone image into a dot pattern representative of a binary image, wherein
when a reference periphery length proportion per unit area of the dot pattern is defined as Ref_sur=(4×r×Q 1/2 )/R where r represents a pattern frequency, Q represents a blackened ratio, and R represents an output resolution, a periphery length proportion determined per unit area for the dot pattern generated by the threshold matrix corresponding to the blackened ratio Q is represented by Mes_sur, and
a threshold array of the threshold matrix is determined such that a dot pattern periphery length evaluation index defined as Mes_sur/Ref_sur is less than 1.085 for all blackened ratios Q ranging from 0 to 1.
9. A method of reproducing a color image by at least four dot patterns, each of the dot patterns comprising a binary image, at least one of the dot patterns being obtained by using a threshold matrix to convert a continuous-tone image into a dot pattern representative of a binary image, wherein
a threshold array of the threshold matrix is determined such that a standard deviation of peripheral length ratios of the dot pattern in a main scanning direction is less than 0.019 for all blackened ratios Q ranging from 0 to 1.
10. A threshold matrix generating system, comprising:
a threshold matrix generating apparatus which generates a threshold matrix for converting a continuous-tone image into a dot pattern representing a binary image, wherein
when a reference periphery length proportion per unit area of the dot pattern is defined as Ref_sur=(4×r×Q1/2)/R where r represents a pattern frequency, Q represents a blackened ratio, and R represents an output resolution, a periphery length proportion determined per unit area for the dot pattern generated by the threshold matrix corresponding to the blackened ratio Q is represented by Mes_sur,
a threshold array of the threshold matrix is determined such that a dot pattern periphery length evaluation index defined as Mes_sur/Ref_sur is less than 1.085 for all blackened ratios Q ranging from 0 to 1; and
an output system.
11. A threshold matrix generating system, comprising:
a threshold matrix generating apparatus which generates a threshold matrix for converting a continuous-tone image into a dot pattern representing a binary image, wherein a threshold array of the threshold matrix is determined such that a standard deviation of peripheral length ratios of the dot pattern in the main scanning direction is less than 0.019 for all blackened ratios Q ranging from 0 to 1; and
an output system.