Printing method, printing apparatus, and recording medium

• US 6,439,682 B1
• Filed: 03/01/1999
• Issued: 08/27/2002
• Est. Priority Date: 03/05/1998
• Status: Expired due to Term

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Kakutani, Toshiaki
• Primary Examiner(s): Barlow, Jr., John E.
• Assistant Examiner(s): Mouttet, Blaise
• Application Number:
  US09/259,326
• Time in Patent Office: 1,275 Days
• Field of Search: 347/15, 347/43, 358/1.8, 358/1.9, 358/298
• US Class Current: 347/15
• CPC Class Codes: H04N 1/40087 Multi-toning, i.e. converting a continuous-tone signal for reproduction with more than two discrete brightnesses or optical densities, e.g. dots of grey and black inks on white paper
• CPC Class Codes: H04N 1/4057 the pattern being a mixture of differently sized sub-patterns, e.g. spots having only a few different diameters multi-toning H04N1/40087

Abstract

In a printing apparatus that enables at least three different types of dots to be created in different ink weights by at least two different inks having an identical hue but different densities, the halftone processing is carried out in an appropriate sequence and according to an appropriate technique, which are determined by taking into account both the dispersibility of dots and the processing speed. The method of the present invention determines the on-off state of six different types of dots, which have different ink densities and ink weights, in the sequence of the large deep dot, the medium deep dot, the small deep dot, the large light dot, the medium light dot, and the small light dot. The dots created by an identical ink are subjected to the determination for the on-off state in a consecutive manner. A dither method that utilizes the recording ratio set for each type of dot according to the tone data is adopted in the determination for the on-off state of the dot. The method determines the on-off state of a target dot, based on a corrected recording ratio. The corrected recording ratio is obtained by adding the recording ratios of all the dots previously subjected to the determination for the on-off state to the recording ratio of the target dot. For example, the sum of the recording ratios of the large deep dot, the medium deep dot, and the small deep dot and the recording ratio of the large light dot is used in the determination for the on-off state of the large light dot. This arrangement of the present invention effectively prevents the different types of dots, especially the dots created by the identical ink, from being created in an identical pixel in an overlapping manner. One modified structure determines the on-off state of the small light dot by an error diffusion method. This improves the picture quality of the resulting printed image.

Claims

1. A method of printing a multi-tone image as a distribution of dots created with a head, said head handling at least two different inks that have an identical hue but different densities and creating at least three different types of dots, which include at least two different types of dots that have different ink weights and are created by at least one ink among the at least two different inks, to be created on a printing medium, said method comprising the steps of:

(a) inputting tone data of an image to be printed;

(b) successively determining on-off state of the at least three different types of dots with respect to each pixel in a preset sequence, the preset sequence comprising a specific order of ink weight in which the at least two different types of dots created by the identical ink are consecutively subjected to the determination for the on-off state; and

(c) driving said head based on results of the determination carried out in said step (b), so as to create the respective types of dots,

wherein said step (b) comprises the steps of;

(b1) setting a recording ratio regarding each of the at least three different types of dots, based on the tone data;

(b2) comparing the recording ratio set in said step (b1) for a specific dot, which is a first object of the determination, with a threshold value read from a dither matrix that has been provided in advance and determining on-off state of the specific dot based on a result of the comparison; and

(b3) comparing a corrected recording ratio with the threshold value and determining on-off state of another dot, which is a second or subsequent object of the determination, based on a result of the comparison with respect to pixels in which all the dots previously subjected to the determination for the on-off state are set in the off state, said corrected recording ratio being obtained by correcting the recording ratio set in said step (b1) for the another dot with the recording ratios of all the dots previously subjected to the determination for the on-off state.

2. A method in accordance with claim 1, wherein said step (b) successively determines the on-off state of the at least three different types of dots in a descending order of ink density.

3. A method in accordance with claim 1, wherein said head enables creation of at least four different types of dots, which include dots formed in at least two different ink weights respectively by a deep ink having a higher ink density and a light ink having a lower ink density, and

wherein said step (b) first determines the on-off state of the dots created by the deep ink in a descending order of ink weight and subsequently determines the on-off state of the dots created by the light ink in a descending order of ink weight.

4. A method of printing a multi-tone image as a distribution of dots created with a head, said head handling at least two different inks that have an identical hue but different densities and creating at least three different types of dots, which include at least two different types of dots that have different ink weights and are created by at least one identical ink among the at least two different inks, to be created on a printing medium, said method comprising the steps of:

(a) inputting tone data of an image to be printed;

(b) dividing the at least three different types of dots according to a preset classification into a first group including a plurality of different types of dots having higher density evaluation values and a second group including at least one type of dot having a lower density evaluation value;

(c) successively determining on-off state of the plurality of different types of dots in said first group with respect to each pixel in a preset sequence, the preset sequence comprising a specific order of ink weight in which the at least two different types of dots created by the identical ink are consecutively subjected to the determination for the on-off state;

(d) determining on-off state of the at least one type of dot in said second group by an error diffusion method based on correction data, the correction data being obtained by correcting the tone data with density errors occurring due to the on-off state of the plurality of dots in said first group; and

(e) driving said head based on results of the determinations carried out in said step (c) and said step (d), so as to create the respective types of dots,

wherein said step (c) comprises the steps of;

(c1) setting a recording ratio regarding each of the plurality of different types of dots in said first group, based on the tone data;

(c2) comparing the recording ratio set in said step (c1) for a specific dot, which is a first object of the determination, with a threshold value read from a dither matrix that has been provided in advance and determining on-off state of the specific dot based on a result of the comparison; and

(c3) comparing a corrected recording ratio with the threshold value and determining on-off state of another dot, which is a second or subsequent object of the determination, based on a result of the comparison with respect to pixels in which all the dots previously subjected to the determination for the on-off state are set in the off state, said corrected recording ratio being obtained by correcting the recording ratio set in said step (c1) for the another dot with the recording ratios of all the dots previously subjected to the determination for the on-off state.

5. A method in accordance with claim 4, wherein the at least one type of dot in said second group is a dot having a lowest density evaluation value among the at least three different types of dots created with said head.

6. A method in accordance with claim 4, wherein said step (c) carries out the determination for the on-off state of the respective dots with a single dither matrix, whether or not the respective dots are created by the identical ink.

7. A method in accordance with claim 4, wherein said step (c) further comprises the step of:

(c0) providing a new dither matrix, which includes threshold values in a different arrangement specified for each of the at least two different inks, from a dither matrix stored in advance, and

wherein said step (c) performs said step (c2) and said step (c3) to carry out the determination for the on-off state with the dither matrix corresponding to each of the at least two different inks, with respect to each dot created by the ink.

8. A method in accordance with claim 4, wherein said head enables creation of at least four different types of dots, which include dots formed in at least two different ink weights respectively by a deep ink having a higher ink density and a light ink having a lower ink density,

the at least one type of dot having the lower density evaluation value is a dot that has a lowest density evaluation value and is created by the light ink, and

wherein said step (c) excludes the dot that has the lowest density evaluation value and is created by the light ink, first determines the on-off state of the dots created by the deep ink in a descending order of ink weight, and subsequently determines the on-off state of the dots created by the light ink in a descending order of ink weight.

9. A printing apparatus that enables a multi-tone image to be printed as a distribution of dots created with a head, said head handling at least two different inks that have an identical hue but different densities and creating at least three different types of dots, which include at least two different types of dots that have different ink weights and are created by at least one ink among the at least two different inks, to be created on a printing medium, said printing apparatus comprising:

an input unit that inputs tone data of an image to be printed;

a dither determination unit that successively determines on-off state of the at least three different types of dots with respect to each pixel in a preset sequence, the preset sequence comprising a specific order of ink weight in which the at least two different types of dots created by the identical ink are consecutively subjected to the determination for the on-off state; and

a dot creation unit that drives said head based on results of the determination carried out by said dither determination unit, so as to create the respective types of dots,

wherein said dither determination unit comprises;

a memory unit in which a relationship between tone data and a recording ratio regarding each of the at least three different types of dots is stored;

a setting unit that refers to said memory unit and sets the recording ratio of each of the at least three different types of dots corresponding to the input tone data; and

a dot creation determination unit that compares a corrected recording ratio of a target dot with a threshold value stored in a dither matrix that has been provided in advance, said corrected recording ratio being obtained by correcting the recording ratio of the target dot set by said setting unit with the recording ratios of all the dots previously subjected to the determination for the on-off state, said dot creation determination unit then determining on-off state of the target dot with respect to pixels in which all the dots previously subjected to the determination for the on-off state are set in the off state, based on a result of the comparison.

10. A printing apparatus in accordance with claim 9, wherein said dither determination unit successively determines the on-off state of the at least three different types of dots in a descending order of ink density.

11. A printing apparatus in accordance with claim 9, wherein said head enables creation of at least four different types of dots, which include dots formed in at least two different ink weights respectively by a deep ink having a higher ink density and a light ink having a lower ink density, and

wherein said dither determination unit first determines the on-off state of the dots created by the deep ink in a descending order of ink weight and subsequently determines the on-off state of the dots created by the light ink in a descending order of ink weight.

12. A printing apparatus that enables a multi-tone image to be printed as a distribution of dots created with a head, said head handling at least two different inks that have an identical hue but different densities and creating at least three different types of dots, which include at least two different types of dots that have different ink weights and are created by at least one ink among the at least two different inks, to be created on a printing medium, said printing apparatus comprising:

a storage unit that stores divisions, which are obtained by dividing the at least three different types of dots according to a preset classification into a plurality of different types of dots having higher density evaluation values and at least one type of dot having a lower density evaluation value;

an input unit that inputs tone data of an image to be printed;

a dither determination unit that successively determines on-off state of the plurality of different types of dots having the higher density evaluation values with respect to each pixel in a preset sequence, the preset sequence comprising a specific order of ink weight in which the at least two different types of dots created by the identical ink are consecutively subjected to the determination for the on-off state;

an error diffusion determination unit that determines on-off state of the at least one type of dot having the lower density evaluation value by an error diffusion method based on correction data, the correction data being obtained by correcting the tone data with density errors occurring due to the on-off state of the plurality of dots having the higher density evaluation values; and

a dot creation unit that drives said head based on results of the determinations carried out by said dither determination unit and said error diffusion determination unit, so as to create the respective types of dots,

wherein said dither determination unit comprises;

a memory unit in which a relationship between tone data and a recording ratio regarding each of the plurality of different types of dots having the higher density evaluation values is stored;

a setting unit that refers to said memory unit and sets the recording ratio of each of the plurality of different types of dots having the higher density evaluation values corresponding to the input tone data; and

a dot creation determination unit that compares a corrected recording ratio of a target dot with a threshold value stored in a dither matrix that has been provided in advance, said corrected recording ratio being obtained by correcting the recording ratio of the target dot set by said setting unit with the recording ratios of all the dots previously subjected to the determination for the on-off state, said dot creation determination unit then determining on-off state of the target dot with respect to pixels in which all the dots previously subjected to the determination for the on-off state are set in the off state, based on a result of the comparison.

13. A printing apparatus in accordance with claim 12, wherein the at least one type of dot having the lower density evaluation value is a dot having a lowest density evaluation value among the at least three different types of dots created with said head.

14. A printing apparatus in accordance with claim 12, wherein said dither determination unit carries out the determination for the on-off state of the respective dots with a single dither matrix, whether or not the respective dots are created by the identical ink.

15. A printing apparatus in accordance with claim 12, wherein said dither determination unit further comprises:

a dither matrix generation unit that provides a new dither matrix, which includes threshold values in a different arrangement specified for each of the at least two different inks, from a dither matrix stored in advance; and

a decision unit that carries out the determination for the on-off state with the dither matrix corresponding to each of the at least two different inks, with respect to each dot created by the ink.

16. A printing apparatus in accordance with claim 12, wherein said head enables creation of at least four different types of dots, which include dots formed in at least two different ink weights respectively by a deep ink having a higher ink density and a light ink having a lower ink density,

the at least one type of dot having the lower density evaluation value is a dot that has a lowest density evaluation value and is created by the light ink, and

wherein said dither determination unit excludes the dot that has the lowest density evaluation value and is created by the light ink, first determines the on-off state of the dots created by the deep ink in a descending order of ink weight, and subsequently determines the on-off state of the dots created by the light ink in a descending order of ink weight.

17. A recording medium in which a program for enabling a multi-tone image to be printed by a printing apparatus is recorded in a computer readable manner, said printing apparatus comprising at least two different inks that have an identical hue but different densities and creating at least three different types of dots, which include at least two different types of dots that have different ink weights and are created by at least one ink among the at least two different inks, to be created on a printing medium,

said program comprising:

a program code that causes a computer to successively determine on-off state of the at least three different types of dots with respect to each pixel in a preset sequence, the preset sequence comprising a specific order of ink weight in which the at least two different types of dots created by the identical ink are consecutively subjected to the determination for the on-off state,

said program code causing the computer to actualize the functions of;

setting a recording ratio regarding each of the at least three different types of dots, based on tone data of an original image;

comparing the recording ratio of a specific dot, which is a first object of the determination, with a threshold value read from a dither matrix that has been provided in advance and determining on-off state of the specific dot based on a result of the comparison; and

comparing a corrected recording ratio with the threshold value and determining on-off state of another dot, which is a second or subsequent object of the determination, based on a result of the comparison with respect to pixels in which all the dots previously subjected to the determination for the on-off state are set in the off state, said corrected recording ratio being obtained by correcting the recording ratio of the another dot with the recording ratios of all the dots previously subjected to the determination for the on-off state.

18. A recording medium in accordance with claim 17, wherein said program code causes the computer to successively determine the on-off state of the at least three different types of dots in a descending order of ink density.

19. A recording medium in accordance with claim 17, wherein said printing apparatus enables creation of at least four different types of dots, which include dots formed in at least two different ink weights respectively by a deep ink having a higher ink density and a light ink having a lower ink density, and

wherein said program code causes the computer to first determine the on-off state of the dots created by the deep ink in a descending order of ink weight and subsequently determine the on-off state of the dots created by the light ink in a descending order of ink weight.

20. A recording medium in which a program for enabling a multi-tone image to be printed by a printing apparatus is recorded in a computer readable manner, said printing apparatus comprising at least two different inks that have an identical hue but different densities and creating at least three different types of dots, which include at least two different types of dots that have different ink weights and are created by at least one ink among the at least two different inks, to be created on a printing medium,

said program comprising:

a first program code that causes a computer to divide the at least three different types of dots according to a preset classification into a plurality of different types of dots having higher density evaluation values and at least one type of dot having a lower density evaluation value;

a second program code that causes the computer to successively determine on-off state of the plurality of different types of dots having the higher density evaluation values with respect to each pixel in a preset sequence, the preset sequence comprising a specific order of ink weight in which the at least two different types of dots created by the identical ink are consecutively subjected to the determination for the on-off state; and

a third program code that causes the computer to determine on-off state of the at least one type of dot having the lower density evaluation value by an error diffusion method based on correction data, the correction data being obtained by correcting the tone data with density errors occurring due to the on-off state of the plurality of dots having the higher density evaluation values,

said second program code causing the computer to actualize the functions of;

setting a recording ratio regarding each of the plurality of different types of dots having the higher density evaluation values, based on tone data of an original image;

comparing the recording ratio of a specific dot, which is a first object of the determination, with a threshold value read from a dither matrix that has been provided in advance and determining on-off state of the specific dot based on a result of the comparison; and

comparing a corrected recording ratio with the threshold value and determining on-off state of another dot, which is a second or subsequent object of the determination, based on a result of the comparison with respect to pixels in which all the dots previously subjected to the determination for the on-off state are set in the off state, said corrected recording ratio being obtained by correcting the recording ratio of the another dot with the recording ratios of all the dots previously subjected to the determination for the on-off state.

21. A recording medium in accordance with claim 20, wherein the at least one type of dot having the lower density evaluation value is a dot having a lowest density evaluation value among the at least three different types of dots created by said printing apparatus.

22. A recording medium in accordance with claim 20, wherein said second program code causes the computer to carry out the determination for the on-off state of the respective dots with a single dither matrix, whether or not the respective dots are created by the identical ink.

23. A recording medium in accordance with claim 20, wherein said second program code further causes the computer to actualize the functions of:

providing a new dither matrix, which includes threshold values in a different arrangement specified for each of the at least two different inks, from a dither matrix stored in advance; and

carrying out the determination for the on-off state with the dither matrix corresponding to each of the at least two different inks, with respect to each dot created by the ink.

24. A recording medium in accordance with claim 20, wherein said printing apparatus enables creation of at least four different types of dots, which include dots formed in at least two different ink weights respectively by a deep ink having a higher ink density and a light ink having a lower ink density,

the at least one type of dot having the lower density evaluation value is a dot that has a lowest density evaluation value and is created by the light ink, and

wherein said second program code causes the computer to exclude the dot that has the lowest density evaluation value and is created by the light ink, first determine the on-off state of the dots created by the deep ink in a descending order of ink weight, and subsequently determine the on-off state of the dots created by the light ink in a descending order of ink weight.