Printer, dither matrix generation method, and recording medium

1. An inkjet printer for printing a halftone image generated by comparing a grayscale original image with a dither matrix, comprising:

a head having a plurality of outlets arranged in a width direction perpendicular to a predetermined scan direction each of which ejects droplets of ink onto a printing medium;

a scanning mechanism for moving said printing medium relatively to said head in said scan direction;

a matrix memory for storing a modified dither matrix which is a two-dimensional array where a plurality of element values are arranged in a column direction corresponding to said scan direction and a row direction corresponding to said width direction, a plurality of positions in said row direction as many as said plurality of outlets are associated with said plurality of outlets, respectively, and said plurality of element values are modified on the basis of variation in print densities with respect to said width direction caused by ejection from said plurality of outlets; and

an ejection controller for controlling ejection of ink from said plurality of outlets, in accordance with comparison results between pixel values of said original image at positions of said plurality of outlets relative to said printing medium and element values of said modified dither matrix corresponding to said pixel values, in synchronization with movement of said printing medium relative to said head.

2. The printer according to claim 1 , wherein

said plurality of outlets in said head are arranged so as to cover an entire printing area on said printing medium with respect to said width direction.

3. The printer according to claim 1 , further comprising:

a density measurement part for measuring densities of regions corresponding to said plurality of outlets in a predetermined pattern on said printing medium which is printed by said head with using an unmodified dither matrix; and

an operation part for obtaining said modified dither matrix on the basis of said unmodified dither matrix and measurement results acquired by said density measurement part.

4. The printer according to claim 3 , wherein

said predetermined pattern includes a plurality of pattern elements corresponding to a plurality of density levels, respectively, and

said measurement results are acquired through measurement of said plurality of pattern elements by said density measurement part.

5. The printer according to claim 1 , wherein

said head comprises a plurality of ejection modules in each of which outlets are arranged at a regular ejection pitch in said width direction, and

a center-to-center distance in said width direction of adjacent outlets between each combination of adjacent two of said plurality of ejection modules is equal to or longer than 0 and shorter than said ejection pitch.

6. The printer according to claim 5 , further comprising:

a density measurement part for measuring densities of regions corresponding to said plurality of outlets in a predetermined pattern on said printing medium which is printed by said head with using an unmodified dither matrix; and

an operation part for obtaining said modified dither matrix on the basis of said unmodified dither matrix and measurement results acquired by said density measurement part.

7. The printer according to claim 6 , wherein

said predetermined pattern includes position indicating parts each of which is located away in said scan direction from a portion used for measurement of densities and associated with positions of said adjacent outlets.

8. The printer according to claim 7 , wherein

said density measurement part detects said position indicating parts, whereby a level of smoothing of measurement results is reduced in measuring densities of regions corresponding to said adjacent outlets in said predetermined pattern.

9. The printer according to claim 5 , further comprising:

a density measurement part for measuring densities of regions corresponding to said adjacent outlets in a predetermined pattern on said printing medium which is printed by said head with using an unmodified dither matrix; and

an operation part for obtaining said modified dither matrix on the basis of said unmodified dither matrix and measurement results acquired by said density measurement part.

10. The printer according to claim 1 , wherein

each of said plurality of outlets can form a plurality of dots having different sizes by ejecting different amounts of droplets, and

each element value of said modified dither matrix is a set of sub-element values used for determination of a size of a dot.

11. A dither matrix generation method for generating a dither matrix compared with a grayscale original image when generating a halftone image from said original image in printing in an inkjet printer which comprises a head having a plurality of outlets arranged in a width direction perpendicular to a predetermined scan direction each of which ejects droplets of ink onto a printing medium, and a scanning mechanism for moving said printing medium relatively to said head in said scan direction, said method comprising the steps of:

a) preparing a basic dither matrix which is a two-dimensional array where a plurality of element values are arranged in a column direction corresponding to said scan direction and a row direction corresponding to said width direction, and a plurality of positions in said row direction as many as said plurality of outlets are associated with said plurality of outlets, respectively; and

b) acquiring a modified dither matrix by modifying said plurality of element values on the basis of variation in print densities with respect to said width direction caused by ejection from said plurality of outlets.

12. The dither matrix generation method according to claim 11 , wherein

said plurality of outlets in said head are arranged so as to cover an entire printing area on said printing medium with respect to said width direction.

13. The dither matrix generation method according to claim 11 , wherein

said step b) comprises the steps of:

b1) measuring densities of regions corresponding to said plurality of outlets in a predetermined pattern on said printing medium which is printed by said head with using said basic dither matrix; and

b2) obtaining said modified dither matrix on the basis of said basic dither matrix and measurement results acquired in said step b1).

14. The dither matrix generation method according to claim 13 , wherein

said predetermined pattern includes a plurality of pattern elements corresponding to a plurality of density levels, respectively, and

said measurement results are acquired through measurement of said plurality of pattern elements in said step b1).

15. The dither matrix generation method according to claim 11 , wherein

said head comprises a plurality of ejection modules in each of which outlets are arranged at a regular ejection pitch in said width direction, and

a center-to-center distance in said width direction of adjacent outlets between each combination of adjacent two of said plurality of ejection modules is equal to or longer than 0 and shorter than said ejection pitch.

16. The dither matrix generation method according to claim 15 , wherein

said step b) comprises the steps of:

b1) measuring densities of regions corresponding to said plurality of outlets in a predetermined pattern on said printing medium which is printed by said head with using said basic dither matrix; and

b2) obtaining said modified dither matrix on the basis of said basic dither matrix and measurement results acquired in said step b1).

17. The dither matrix generation method according to claim 16 , wherein

said predetermined pattern includes position indicating parts each of which is located away in said scan direction from a portion used for measurement of densities and associated with positions of said adjacent outlets.

18. The dither matrix generation method according to claim 17 , wherein

in said step b1), said position indicating parts are detected, whereby a level of smoothing of measurement results is reduced in measuring densities of regions corresponding to said adjacent outlets in said predetermined pattern.

19. The dither matrix generation method according to claim 15 , wherein

said step b) comprises the steps of:

b1) measuring densities of regions corresponding to said adjacent outlets in a predetermined pattern on said printing medium which is printed by said head with using said basic dither matrix; and

b2) obtaining said modified dither matrix on the basis of said basic dither matrix and measurement results acquired in said step b1).

20. The dither matrix generation method according to claim 11 , wherein

each of said plurality of outlets can form a plurality of dots having different sizes by ejecting different amounts of droplets, and

each element value of said modified dither matrix is a set of sub-element values used for determination of a size of a dot.

21. An electronic apparatus-readable recording medium in which data of a dither matrix is recorded, said dither matrix being compared with a grayscale original image when generating a halftone image from said original image in printing in an inkjet printer which comprises a head having a plurality of outlets arranged in a width direction perpendicular to a predetermined scan direction each of which ejects droplets of ink onto a printing medium, and a scanning mechanism for moving said printing medium relatively to said head in said scan direction, said data being generated by executing steps including the steps of:

a) preparing a basic dither matrix which is a two-dimensional array where a plurality of element values are arranged in a column direction corresponding to said scan direction and a row direction corresponding to said width direction, and a plurality of positions in said row direction as many as said plurality of outlets are associated with said plurality of outlets, respectively; and

b) acquiring a modified dither matrix by modifying said plurality of element values on the basis of variation in print densities with respect to said width direction caused by ejection from said plurality of outlets.

22. The recording medium according to claim 21 , wherein

said plurality of outlets in said head are arranged so as to cover an entire printing area on said printing medium with respect to said width direction.

23. The recording medium according to claim 21 , wherein

said step b) comprises the steps of:

b1) measuring densities of regions corresponding to said plurality of outlets in a predetermined pattern on said printing medium which is printed by said head with using said basic dither matrix; and

b2) obtaining said modified dither matrix on the basis of said basic dither matrix and measurement results acquired in said step b1).

24. The recording medium according to claim 23 , wherein

said predetermined pattern includes a plurality of pattern elements corresponding to a plurality of density levels, respectively, and

said measurement results are acquired through measurement of said plurality of pattern elements in said step b1).

25. The recording medium according to claim 21 , wherein

said head comprises a plurality of ejection modules in each of which outlets are arranged at a regular ejection pitch in said width direction, and

a center-to-center distance in said width direction of adjacent outlets between each combination of adjacent two of said plurality of ejection modules is equal to or longer than 0 and shorter than said ejection pitch.

26. The recording medium according to claim 25 , wherein

said step b) comprises the steps of:

b1) measuring densities of regions corresponding to said plurality of outlets in a predetermined pattern on said printing medium which is printed by said head with using said basic dither matrix; and

b2) obtaining said modified dither matrix on the basis of said basic dither matrix and measurement results acquired in said step b1).

27. The recording medium according to claim 26 , wherein

said predetermined pattern includes position indicating parts each of which is located away in said scan direction from a portion used for measurement of densities and associated with positions of said adjacent outlets.

28. The recording medium according to claim 27 , wherein

in said step b1), said position indicating parts are detected, whereby a level of smoothing of measurement results is reduced in measuring densities of regions corresponding to said adjacent outlets in said predetermined pattern.

29. The recording medium according to claim 25 , wherein

said step b) comprises the steps of:

b1) measuring densities of regions corresponding to said adjacent outlets in a predetermined pattern on said printing medium which is printed by said head with using said basic dither matrix; and

b2) obtaining said modified dither matrix on the basis of said basic dither matrix and measurement results acquired in said step b1).

30. The recording medium according to claim 21 , wherein

each of said plurality of outlets can form a plurality of dots having different sizes by ejecting different amounts of droplets, and

each element value of said modified dither matrix is a set of sub-element values used for determination of a size of a dot.

31. An electronic apparatus-readable recording medium in which data of a dither matrix is recorded, said dither matrix being a two-dimensional array where a plurality of element values are arranged in a column direction and a row direction and being compared with a grayscale original image when generating a halftone image from said original image in recording dots in a dot recording apparatus which comprises a head having a plurality of dot output elements for recording dots in a plurality of writing element regions, respectively, arranged in a width direction perpendicular to a predetermined scan direction on an object, said width direction corresponding to said row direction and said scan direction corresponding to said column direction, and a scanning mechanism for moving said plurality of writing element regions on said object relatively to said object in said scan direction, wherein

in said dither matrix, a plurality of positions in said row direction as many as said plurality of dot output elements are associated with said plurality of dot output elements, respectively, said plurality of element values have a directional property in said column direction by modifying said plurality of element values on the basis of variation in outputs of said plurality of dot output elements.