Printing system and method of recording images

• US 6,089,691 A
• Filed: 07/18/1997
• Issued: 07/18/2000
• Est. Priority Date: 07/18/1996
• 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): BRASE, SANDRA L
• Application Number:
  US08/896,536
• Time in Patent Office: 1,096 Days
• Field of Search: 347/5, 347/9, 347/15, 347/40, 347/41, 347/43
• 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 1/52 Circuits or arrangements for halftone screening

Abstract

The present invention appropriately determines the on/off state of dots having different hues in a printer using at least two inks of different hues, thereby enhancing the quality of printing. The system of the present invention applies the systematic dither method to determine whether or not dots are to be formed by ink of a predetermined hue, for example, magenta. In the case of formation of dots by magenta ink, the system drives a piezoelectric element PE disposed on a head corresponding to the magenta ink to form magenta dots and calculates a resulting value MRST. In the case of non-formation of dots by the magenta ink, on the other hand, the resulting value MRST is set equal to zero. The system then applies the technique of error diffusion to determine whether or not dots are to be formed by cyan ink, based on the tone data of the cyan ink. The structure of the present invention enables a difference between density data M(x,y) of the magenta ink and its resulting value MRST to affect density data of the cyan ink. This makes it difficult to form dots of cyan ink in the vicinity of dots of magenta ink.

Claims

1. A printing system with a head for forming at least two types of dots having different hues on an object, said printing system recording a multi-tone image through a distribution of said dots, said printing system comprising:

input means for successively inputting multi-color tone signals regarding pixels included in an image to be printed;

first dot formation determination means for carrying out multi-valued coding with respect to one type of dots selected among said at least two types of dots having different hues, based on said input tone signal of a color corresponding to said one type of dots, and determining either one of formation and non-formation of said one type of dots;

second dot formation determination means for enabling the result of multi-valued coding carried out by said first dot formation determination means to affect a recording density to be realized by another type of dots having a different hue, carrying out multi-valued coding with respect to said another type of dots according to said recording density, and determining either one of formation and non-formation of said another type of dots; and

head drive means for driving said head based on the results of determination by said first dot formation determination means and said second dot formation determination means, thereby actually forming said at least two types of dots having different hues.

2. A printing system in accordance with claim 1, wherein said one type of dots selected among said at least two types of dots having different hues and processed by said first dot formation determination means are dots of a color having a greater visual effect.

3. A printing system in accordance with claim 1, wherein said one type of dots selected among said at least two types of dots having different hues are dots of one color component included in three primary colors that can express a full color, whereas said another type of dots having a different hue are dots of another color component included in said three primary colors.

4. A printing system in accordance with claim 1, wherein said one type of dots selected among said at least two types of dots having different hues are dots of one color component included in three primary colors that can express a full color, whereas said another type of dots having a different hue are dots of a color including said one color component and another color component.

5. A printing system in accordance with claim 1, wherein said first dot formation determination means comprises means for determining either one of formation and non-formation of said one type of dots, which has been selected among said at least two types of dots having different hues, based on said input tone signal of a color corresponding to said one type of dots, prior to said determination with respect to said another type of dots having a different hue,

said second dot formation determination means comprising means for determining either one of formation and non-formation of said another type of dots having a different hue, when said first dot formation determination means determines non-formation of said one type of dots.

6. A printing system in accordance with either one of claim 5, said printing system further comprising error diffusion means for calculating a difference between a first printing density, which corresponds to said input tone signal relating to said another type of dots and regarding a target pixel, and a second printing density, which is realized by said another type of dots in said target pixel, as a density error, based on said determination of either one of formation and non-formation of said another type of dots by said second dot formation determination means, and distributing said density error into peripheral pixels that are in proximity to said target pixel, in order to enable said density error to affect said determination of either one of formation and non-formation of said another type of dots by said second dot formation determination means with respect to said peripheral pixels.

7. A printing system in accordance with claim 6, wherein said error diffusion means comprises density difference calculation means for, when said first dot formation determination means determines formation of said one type of dots, calculating said difference between said first printing density corresponding to said input tone signal relating to said another type of dots and said second printing density realized by said another type of dots, as a value representing a degree of correlation of hues between said one type of dots and said another type of dots.

8. A printing system in accordance with claim 1, wherein said first dot formation determination means comprises means for determining either one of formation and non-formation of said one type of dots, which has been selected among said at least two types of dots having different hues, based on said input tone signal of a color corresponding to said one type of dots, prior to said determination with respect to said another type of dots having a different hue,

said second dot formation determination means comprising means for determining non-formation of said another type of dots having a different hue, when said first dot formation determination means determines formation of said one type of dots.

9. A printing system in accordance with either one of claim 8, said printing system further comprising error diffusion means for calculating a difference between a first printing density, which corresponds to said input tone signal relating to said another type of dots and regarding a target pixel, and a second printing density, which is realized by said another type of dots in said target pixel, as a density error, based on said determination of either one of formation and non-formation of said another type of dots by said second dot formation determination means, and distributing said density error into peripheral pixels that are in proximity to said target pixel, in order to enable said density error to affect said determination of either one of formation and non-formation of said another type of dots by said second dot formation determination means with respect to said peripheral pixels.

10. A printing system in accordance with claim 9, wherein said error diffusion means comprises density difference calculation means for, when said first dot formation determination means determines formation of said one type of dots, calculating said difference between said first printing density corresponding to said input tone signal relating to said another type of dots and said second printing density realized by said another type of dots, as a value representing a degree of correlation of hues between said one type of dots and said another type of dots.

11. A printing system in accordance with claim 1, wherein either one of said first dot formation determination means and said second dot formation determination means applies a dither method to determine either one of formation and non-formation of dots.

12. A printing system in accordance with claim 11, wherein said dither method applied by either one of said first dot formation determination means and said second dot formation determination means utilizes a threshold matrix of discrete dither.

13. A printing system in accordance with claim 1, wherein said head is able to discharge at least two types of inks having different densities, with respect to at least two color inks having different hues,

at least either one of said first dot formation determination means and said second dot formation determination means carrying out multi-valued coding for each type of dots selected among at least two types of dots having different densities per unit of area and formed by said at least two types of inks having different densities, and determining either one of formation and non-formation of said each type of dots.

14. A printing system in accordance with claim 13, wherein said at least two types of inks having different densities comprise a higher-density ink and a lower-density ink and a dye density of said lower-density ink is approximately one quarter a dye density of said higher-density ink.

15. A printing system in accordance with claim 1, wherein said head comprises a mechanism for discharging ink particles under a pressure applied to each ink running through an ink conduit by application of a voltage to a piezoelectric element arranged in said ink conduit.

16. A printing system in accordance with claim 1, wherein said head comprises a mechanism for discharging ink particles under a pressure applied to each ink running through an ink conduit by air bubbles that are produced by a supply of electricity to a heating body arranged in said ink conduit.

17. A printing system with a head for forming at least two types of dots having different hues on an object, said printing system recording a multi-tone image through a distribution of said dots, said printing system comprising:

input means for successively inputting multi-color tone signals regarding pixels included in an image to be printed;

first dot formation determination means for carrying out multi-valued coding with respect to one type of dots selected among said at least two types of dots having different hues, based on said input tone signal of a color corresponding to said one type of dots, and determining either one of formation and non-formation of said one type of dots;

local error calculation means for calculating a local difference between a first printing density, which corresponds to said input tone signal relating to said one type of dots and regarding a target pixel, and a second printing density, which is realized by said one type of dots in said target pixel, based on the result of multi-valued coding carried out by said first dot formation determination means;

second dot formation determination means for enabling the local difference to affect a recording density to be realized by another type of dots having a different hue, carrying out multi-valued coding with respect to said another type of dots according to said recording density, and determining either one of formation and non-formation of said another type of dots; and

head drive means for driving said head based on the results of determination by said first dot formation determination means and said second dot formation determination means, thereby actually forming said at least two types of dots having different hues.

18. A printing system in accordance with claim 17, wherein said local error calculation means comprises:

first degree of effect calculation means for calculating a first degree of effect of said first printing density, which corresponds to said input tone signal relating to said one type of dots and regarding said target pixel, upon a printing density by said another type of dots having a different hue;

second degree of effect calculation means for calculating a second degree of effect of said second printing density, which is realized by said one type of dots in said target pixel, upon said printing density by said another type of dots having a different hue;

third degree of effect calculation means for calculating a third degree of effect of a density error upon said printing density by said another type of dots having a different hue, based on said determination of either one of formation and non-formation of said another type of dots with respect to peripheral pixels that are in proximity to said target pixel, said density error representing a difference between a printing density corresponding to said input tone signals relating to said another type of dots and regarding said peripheral pixels and a printing density realized by said another type of dots in said peripheral pixels; and

means for calculating said local difference by taking into account said first degree of effect, said second degree of effect, and said third degree effect respectively calculated by said first, second and third degree of effect calculation means.

19. A printing system in accordance with claim 17, wherein said one type of dots selected among said at least two types of dots having different hues and processed by said first dot formation determination means are dots of a color having a greater visual effect.

20. A printing system in accordance with claim 17, wherein said one type of dots selected among said at least two types of dots having different hues are dots of one color component included in three primary colors that can express a full color, whereas said another type of dots having a different hue are dots of another color component included in said three primary colors.

21. A printing system in accordance with claim 17, wherein said one type of dots selected among said at least two types of dots having different hues are dots of one color component included in three primary colors that can express a full color, whereas said another type of dots having a different hue are dots of a color including said one color component and another color component.

22. A printing system in accordance with claim 17, said printing system further comprising error diffusion means for calculating a difference between a third printing density, which corresponds to said input tone signal relating to said another type of dots and regarding said target pixel, and a fourth printing density, which is realized by said another type of dots in said target pixel, as a density error, based on said determination of either one of formation and non-formation of said another type of dots by said second dot formation determination means, and distributing said density error into peripheral pixels that are in proximity to said target pixel, in order to enable said density error to affect said determination of either one of formation and non-formation of said another type of dots by said second dot formation determination means with respect to said peripheral pixels.

23. A printing system in accordance with claim 17, wherein either one of said first dot formation determination means and said second dot formation determination means applies a dither method to determine either one of formation and non-formation of dots.

24. A printing system in accordance with claim 23, wherein said dither method applied by either one of said first dot formation determination means and said second dot formation determination means utilizes a threshold matrix of discrete dither.

25. A printing system in accordance with claim 17, wherein said head is able to discharge at least two types of inks having different densities, with respect to at least two color inks having different hues,

at least either one of said first dot formation determination means and said second dot formation determination means carrying out multi-valued coding for each type of dots selected among at least two types of dots having different densities per unit of area and formed by said at least two types of inks having different densities, and determining either one of formation and non-formation of said each type of dots.

26. A printing system in accordance with claim 25, wherein said at least two types of inks having different densities comprise a higher-density ink and a lower-density ink and a dye density of said lower-density ink is approximately one quarter a dye density of said higher-density ink.

27. A printing system in accordance with claim 17, wherein said head comprises a mechanism for discharging ink particles under a pressure applied to each ink running through an ink conduit by application of a voltage to a piezoelectric element arranged in said ink conduit.

28. A printing system in accordance with claim 17, wherein said head comprises a mechanism for discharging ink particles under a pressure applied to each ink running through an ink conduit by air bubbles that are produced by a supply of electricity to a heating body arranged in said ink conduit.

29. A printing system with a head for forming at least two types of chromatic color dots of different hues by at least two chromatic color inks as well as achromatic color dots by an achromatic color ink on an object, said printing system recording a multi-tone image through a distribution of said dots, said printing system comprising:

input means for successively inputting tone signals regarding pixels included in an image to be printed;

density calculation means for calculating densities by said at least two chromatic color inks and a density by said achromatic color ink, based on said input tone signals;

achromatic color dot formation determination means for carrying out multi-valued coding with respect to said achromatic color ink based on said density by said achromatic color ink calculated by the density calculation means, and determining either one of formation and non-formation of achromatic color dots by said achromatic color ink;

density correction means for obtaining correction data, which are to reflect the densities by said at least two chromatic color inks, based on the result of multi-valued coding with respect to said achromatic color ink, and correcting the densities by said at least two chromatic color inks;

chromatic color dot formation determination means for carrying out multi-valued coding with respect to said at least two chromatic color dots of different hues, based on said corrected densities by said at least two chromatic color inks, and determining either one of formation and non-formation of said at least two chromatic color dots of different hues; and

head drive means for driving said head based on the results of determination by said achromatic color dot formation determination means and said chromatic color dot formation determination means, thereby actually forming said at least two chromatic color dots of different hues by said at least two chromatic color inks as well as said achromatic color dots by said achromatic color ink.

30. A printing system in accordance with claim 29, said printing system further comprising error diffusion means for calculating a difference between a first printing density, which corresponds to said input tone signals relating to said achromatic color dots and said at least two chromatic color dots and regarding a target pixel, and a second printing density, which is realized by said achromatic color dots and said at least two chromatic color dots in said target pixel, as a density error, based on said determination of either one of formation and non-formation of said achromatic color dots by said achromatic color dot formation determination means and of said at least two chromatic color dots by said chromatic color dot formation determination means, and distributing said density error into peripheral pixels that are in proximity to said target pixel, in order to enable said density error to affect said determination of either one of formation and non-formation of said at least two chromatic color dots by said chromatic color dot formation determination means with respect to said peripheral pixels.

31. A printing system in accordance with claim 29, wherein said head comprises a mechanism for discharging ink particles under a pressure applied to each ink running through an ink conduit by application of a voltage to a piezoelectric element arranged in said ink conduit.

32. A printing system in accordance with claim 29, wherein said head comprises a mechanism for discharging ink particles under a pressure applied to each ink running through an ink conduit by air bubbles that are produced by a supply of electricity to a heating body arranged in said ink conduit.

33. A method of controlling a head, which is able to form at least two types of dots having different hues on an object, and recording a multi-tone image through a distribution of said dots, said method comprising the steps of:

(a) successively inputting multi-color tone signals regarding pixels included in an image to be printed;

(b) carrying out multi-valued coding with respect to one type of dots selected among said at least two types of dots having different hues, based on said input tone signal of a color corresponding to said one type of dots, and determining either one of formation and non-formation of said one type of dots;

(c) enabling the result of multi-valued coding carried out in said step (b) to affect a recording density to be realized by another type of dots having a different hue, carrying out multi-valued coding with respect to said another type of dots according to said recording density, and determining either one of formation and non-formation of said another type of dots; and

(d) driving said head based on the results of determination in said step (b) and in said step (c), thereby actually forming said at least two types of dots having different hues.

34. A method of controlling a head, which is able to form at least two types of dots having different hues on an object, and recording a multi-tone image through a distribution of said dots, said method comprising the steps of:

(a) successively inputting multi-color tone signals regarding pixels included in an image to be printed;

(b) carrying out multi-valued coding with respect to one type of dots selected among said at least two types of dots having different hues, based on said input tone signal of a color corresponding to said one type of dots, and determining either one of formation and non-formation of said one type of dots;

(c) calculating a local difference between a first printing density, which corresponds to said input tone signal relating to said one type of dots and regarding a target pixel, and a second printing density, which is realized by said one type of dots in said target pixel, based on the result of multi-valued coding carried out in said step (b);

(d) enabling the local difference to affect a recording density to be realized by another type of dots having a different hue, carrying out multi-valued coding with respect to said another type of dots according to the recording density, and determining either one of formation and non-formation of said another type of dots; and

(e) driving said head based on the results of determination in said step (b) and said step (d), thereby actually forming said at least two types of dots having different hues.

35. A method of controlling a head, which is able to form at least two types of chromatic color dots of different hues by at least two chromatic color inks as well as achromatic color dots by an achromatic color ink on an object, and recording a multi-tone image through a distribution of said dots, said method comprising the steps of:

(a) successively inputting tone signals regarding pixels included in an image to be printed;

(b) calculating densities by said at least two chromatic color inks and a density by said achromatic color ink, based on said input tone signals;

(c) carrying out multi-valued coding with respect to said achromatic color ink based on the density by said achromatic color ink calculated in said step (b), and determining either one of formation and non-formation of achromatic color dots by said achromatic color ink;

(d) obtaining correction data, which are to reflect the densities by said at least two chromatic color inks, based on the result of multi-valued coding with respect to said achromatic color ink, and correcting the densities by said at least two chromatic color inks;

(e) carrying out multi-valued coding with respect to said at least two chromatic color dots of different hues, based on said corrected densities by said at least two chromatic color inks, and determining either one of formation and non-formation of said at least two chromatic color dots of different hues; and

(f) driving said head based on the results of determination in said step (c) and said step (e), thereby actually forming said at least two chromatic color dots of different hues by said at least two chromatic color inks as well as said achromatic color dots by said achromatic color ink.

36. An image display apparatus for forming at least two types of dots having different hues on an object and expressing a multi-tone image through a distribution of said dots, said image display apparatus comprising:

input means for successively inputting multi-color tone signals regarding pixels included in an image to be displayed;

first dot formation determination means for carrying out multi-valued coding with respect to one type of dots selected among said at least two types of dots having different hues, based on said input tone signal of a color corresponding to said one type of dots, and determining either one of formation and non-formation of said one type of dots;

second dot formation determination means for enabling the result of multi-valued coding carried out by said first dot formation determination means to affect a display density to be realized by another type of dots having a different hue, carrying out multi-valued coding with respect to said another type of dots according to the recording density, and determining either one of formation and non-formation of said another type of dots; and

dot formation means for actually forming said at least two types of dots having different hues, based on the results of determination by said first dot formation determination means and said second dot formation determination means.

37. A computer program product configured to store program instructions for execution on a computer system, which is connected to a printing system with a head for forming at least two types of dots having different hues on a printing object and recording a multi-tone image through a distribution of said dots, enabling the computer system to perform the steps of:

successively inputting multi-color tone signals regarding pixels included in an image to be printed;

carrying out multi-valued coding with respect to one type of dots selected among said at least two types of dots having different hues, based on said input tone signal of a color corresponding to said one type of dots, and determining either one of formation and non-formation of said one type of dots;

enabling the result of multi-valued coding with respect to said one type of dots to affect a recording density to be realized by another type of dots having a different hue, carrying out multi-valued coding with respect to said another type of dots according to said recording density, and determining either one of formation and non-formation of said another type of dots; and

driving said head based on the results of determination with respect to both said one type of dots and said another type of dots, thereby actually forming said at least two types of dots having different hues.

38. A computer program product configured to store program instructions for execution on a computer system, which is connected to a printing system with a head for forming at least two types of dots having different hues on a printing object and recording a multi-tone image through a distribution of said dots, enabling the computer system to perform the steps of:

successively inputting multi-color tone signals regarding pixels included in an image to be printed;

carrying out multi-valued coding with respect to one type of dots selected among said at least two types of dots having different hues, based on said input tone signal of a color corresponding to said one type of dots, and determining either one of formation and non-formation of said one type of dots;

calculating a local difference between a first printing density, which corresponds to said input tone signal relating to said one type of dots and regarding a target pixel, and a second printing density, which is realized by said one type of dots in said target pixel, based on the result of multi-valued coding with respect to said one type of dots;

enabling the local difference to affect a recording density to be realized by another type of dots having a different hue, carrying out multi-valued coding with respect to said another type of dots according to said recording density, and determining either one of formation and non-formation of said another type of dots; and

driving said head based on the results of determination with respect to both said one type of dots and said another type of dots, thereby actually forming said at least two types of dots having different hues.

39. A computer program product configured to store program instructions for execution on a computer system, which is connected to a printing system with a head for forming at least two types of chromatic color dots of different hues by at least two chromatic color inks as well as achromatic color dots by an achromatic color ink on a printing object and recording a multi-tone image through a distribution of said dots, enabling the computer system to perform the steps of:

successively inputting tone signals regarding pixels included in an image to be printed;

calculating densities by said at least two chromatic color inks and a density by said achromatic color ink, based on said input tone signals;

carrying out multi-valued coding with respect to said achromatic color ink based on the calculated density by said achromatic color ink, and determining either one of formation and non-formation of achromatic color dots by said achromatic color ink;

obtaining correction data, which are to reflect the densities by said at least two chromatic color inks, based on the result of multi-valued coding with respect to said achromatic color ink, and correcting the densities by said at least two chromatic color inks;

carrying out multi-valued coding with is respect to said at least two chromatic color dots of different hues, based on the corrected densities by said at least two chromatic color inks, and determining either one of formation and non-formation of said at least two chromatic color dots of different hues; and

driving said head based on the results of determination with respect to both said achromatic color dots and said at least two chromatic color dots, thereby actually forming said at least two chromatic color dots of different hues by said at least two chromatic color inks as well as said achromatic color dots by said achromatic color ink.