WO2000019704A1 - Dispositif et procede de traitement d'images, et imprimante - Google Patents

Dispositif et procede de traitement d'images, et imprimante Download PDF

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Publication number
WO2000019704A1
WO2000019704A1 PCT/JP1999/005241 JP9905241W WO0019704A1 WO 2000019704 A1 WO2000019704 A1 WO 2000019704A1 JP 9905241 W JP9905241 W JP 9905241W WO 0019704 A1 WO0019704 A1 WO 0019704A1
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Prior art keywords
matrix
pixel
dot
value
image
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PCT/JP1999/005241
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English (en)
Japanese (ja)
Inventor
Toshiaki Kakutani
Saburo Yosho
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Seiko Epson Corporation
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Publication of WO2000019704A1 publication Critical patent/WO2000019704A1/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/40—Picture signal circuits
    • H04N1/405—Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels
    • H04N1/4051—Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels producing a dispersed dots halftone pattern, the dots having substantially the same size
    • H04N1/4052—Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels producing a dispersed dots halftone pattern, the dots having substantially the same size by error diffusion, i.e. transferring the binarising error to neighbouring dot decisions
    • H04N1/4053—Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels producing a dispersed dots halftone pattern, the dots having substantially the same size by error diffusion, i.e. transferring the binarising error to neighbouring dot decisions with threshold modulated relative to input image data or vice versa
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/40—Picture signal circuits
    • H04N1/405—Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels
    • H04N1/4051—Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels producing a dispersed dots halftone pattern, the dots having substantially the same size

Definitions

  • Image processing apparatus and method, and printing apparatus are Image processing apparatus and method, and printing apparatus
  • the present invention provides a technique for performing halftone processing on an image having a gradation value for each pixel, a technique for printing an image using the image processing technique, and designing a matrix used in the image processing.
  • a technique for performing halftone processing on an image having a gradation value for each pixel a technique for printing an image using the image processing technique, and designing a matrix used in the image processing.
  • an ink jet printer that forms a dot with several colors of ink ejected from a plurality of nozzles provided in a head and records an image has been proposed. It is widely used to print processed images in multiple colors and multiple tones. In such printing, usually, only two gradations of dot on / off can be taken for each pixel. Therefore, an image is printed after image processing for expressing the gradation of the original image data by the dispersibility of dots, that is, so-called halftone processing.
  • an ink jet printing which is a so-called multi-value printing, capable of expressing more than two levels of ON / OFF for each dot. For example, by changing the dot diameter divided by the ink density, three or more types of density can be expressed for each pixel. Multi-tones can be formed by superimposing multiple dots for each pixel. It is a pudding evening that can be expressed. Even in such printing, halftone processing is required because the gradation of the original image data cannot be sufficiently expressed in each pixel unit.
  • a dither method is one of the typical methods.
  • a preset ⁇ value is used for each component.
  • a matrix called Bayer type is shown in Fig. 25.
  • a 4 ⁇ 4 Bayer matrix has 16 thresholds from 0 to 15.
  • the on / off determination of the dot of each pixel is performed in accordance with the dither matrix.
  • Figure 26 shows the correspondence between the dither matrix and the image data.
  • the components shown in (a, b) in Fig. 26 represent the components of the dither matrix in Fig. 25, respectively.
  • the image data has pixels that are many times the size of the dither matrix in each of the vertical and horizontal directions. Therefore, in the dither method, the dither matrix shown in FIG. 25 is repeatedly arranged and arranged in a grid in each of the vertical and horizontal directions.
  • the matrix repetition direction has a certain angle with respect to the two-dimensional pixel array direction in order to generate a screen angle that simulates halftone printing.
  • a dither matrix may be arranged as described above, in the dot-dispersion type dither method, the dither matrix is usually arranged in a grid because it is not related to the halftone dot printing.
  • FIG. 27 shows the concept of dot on / off determination in the dither method.
  • FIG. 27 shows the result of dot on / off determination for an image having a constant gradation value 8 for each pixel.
  • the tone value of the image data is compared with the threshold value of the dither matrix corresponding to each pixel, and it is determined that a dot is to be formed in a pixel having a larger tone value of the image data.
  • the dots are turned on in a pine pattern.
  • the pixel for turning on the dot changes according to the gradation value of the image data and the dither matrix used in the halftone processing.
  • FIG. 28 shows a state in which the result of the on / off determination shown in FIG. Figure 28 shows the result of using the dither matrix in the correspondence shown in Figure 26. This shows the result of the dot on / off determination of the dot obtained by the above.
  • the hatched portions in FIG. 28 are the pixels for which the dots should be turned on. As shown in the figure, the pixels on which dots are to be formed are widely distributed in a pine pattern. If the dither matrix used for halftone processing changes, the dots will turn on in a different pattern from that in FIG. In the ink jet printing, dots are formed in each pixel according to the result of the halftone means such as the dither method described above.
  • an ink jet printer if there is a mechanical manufacturing error or the like in a nozzle that discharges ink, the amount of ink to be discharged and the position of dots to be formed vary from nozzle to nozzle. If the ink discharge amount of a specific nozzle is large or the dot formation position shifts, the gap between adjacent laths and evenings becomes large or small, causing uneven density in the printed image at that part. Particularly in printers that form dots while scanning the head in the main direction, similar unevenness is likely to occur continuously in the main scanning direction, so that streak-like density unevenness called banding may appear in the main scanning direction. .
  • the dot generation rate may be biased every day according to the threshold of the dither matrix and the gradation value of the image.
  • the occurrence of dots in the entire image is determined by arranging the dither matrix in a grid pattern, such a biased pattern is repeatedly generated, which promotes a bias in the dot generation rate for each raster.
  • a raster having a large number of dots is formed by nozzles formed by shifting the positions of the dots, remarkable banding may occur and image quality may be degraded.
  • each raster is formed using two or more different nozzles.
  • each nozzle is formed by two main scans using two nozzles. In the first main scan, only odd-numbered dots of each raster are formed intermittently. Sub-scanning is performed thereafter, and in the second main scanning, only even-numbered dots are intermittently formed using nozzles different from those in the first scanning. If such a recording method is adopted, since each raster is formed by two or more different nozzles, a shift in dot formation position caused by nozzle characteristics or the like can be dispersed on each raster.
  • Image quality can be improved.
  • the halftone processing is performed by using the dither method, the above-described effect of the overlap may not be sufficiently obtained.
  • the pixels whose dots should be turned on are arranged in a checkered pattern. This means that the dot of either the odd-numbered pixel or the even-numbered pixel is turned on when viewed at each raster.
  • the dots of the odd-numbered pixels of each raster are formed in the first main scan, and the dots of the even-numbered pixels of each raster are formed in the second main scan. .
  • each raster is eventually formed only by the first or second main scanning.
  • the advantage of the overlap method obtained by forming the dots on each lath using different nozzles could not be used, and the advantage of improving the image quality could not be sufficiently obtained.
  • the Bayer type dither matrix used in the above-described example is a matrix that is relatively frequently used in halftone processing by the dither method. It has been found that when such a matrix is used, the problem that the advantage of the overlap method cannot be obtained sufficiently occurs.
  • the Bayer-type dither matrix is taken as an example.However, when other dither matrices are used, the dot generation rate for each raster and the even and odd pixels Since it is difficult to make the dot generation rates almost equal, a similar problem has occurred. If a dither matrix different from the bayer type is used, the dots are formed in a pattern different from the pattern shown in FIG. However, even in this case, the same pattern is repeatedly displayed in the vertical and horizontal directions of the image in a diagonal matrix. Therefore, if there is a bias in the number of dots formed in each evening, banding may occur based on variations in the ink ejection direction. In addition, if there is a raster in which a relatively small threshold value is biased in odd-numbered pixels, the effect of recording by the overlap method cannot be sufficiently obtained.
  • a similar problem occurred in halftone means other than the dither method.
  • a halftone processing method other than the dither method for example, there is a method called an error diffusion method.
  • Such a method originally performs halftone processing without using a matrix.
  • a predetermined noise is intentionally added to the image data before halftone processing. Processing may be performed.
  • a matrix with predetermined noise data is used as the noise data in the correspondence shown in Fig. 26, a fixed repetition pattern
  • the same problem as the above-described problem described with the dither method as an example may occur due to the addition of noise. Disclosure of the invention
  • the present invention has been made to solve the above-mentioned problem.
  • a halftone means using a dot dispersion type matrix
  • a pattern in which dots are formed is periodically arranged in a vertical and horizontal direction in an image area.
  • the purpose of the present invention is to provide a technology for avoiding the appearance of an image and improving image quality.
  • the present invention employs the following configurations.
  • the image processing apparatus includes:
  • the image data is determined for each pixel according to the magnitude relationship between the gradation value and a predetermined threshold value.
  • An image processing device that determines whether a dot is on or off and generates an output data corresponding to a predetermined image output device,
  • Storage means for storing a dot-dispersion type two-dimensional matrix having a size smaller than the size of the image data composed of the two-dimensional pixel array and having a predetermined value as a component;
  • the matrix is shifted with respect to the image data from a grid in a range in which deterioration of image quality caused by interference between on / off of dots and a fluctuation cycle of dot forming characteristics of the image output device can be avoided.
  • the gist of the invention is to include a halftone means for judging on / off of a dot by reflecting the components of the matrix in the gradation value or the threshold value of the image data.
  • the grid means that the arrangement on the image data is grid-shaped when the matrix is captured as one unit as shown in Fig. 26, for example.
  • the matrix is associated with a state deviating from the grid, it is possible to prevent the dots from being repeatedly formed in a fixed pattern in the X direction and the y direction.
  • the number of formed dots tends to be biased for each arrangement in the X direction or y direction. For example, if there is a bias in the number of dots formed for each arrangement in the X direction, and if the recording position of the arrangement having a large number of dots is displaced, on / off of the dots and the dot formation of the image output device will occur. Remarkable banding occurs due to interference with the characteristic fluctuation cycle, and the image quality is reduced.
  • the image processing apparatus of the present invention by preventing the dots from being repeatedly formed in a fixed pattern, it is possible to avoid a bias in the number of dots formed for each row. Therefore, it is possible to suppress the occurrence of banding and perform half-tone processing with excellent image quality.
  • the present application intends to avoid deterioration of image quality caused by interference between on / off of dots and a fluctuation cycle of dot forming characteristics of the image output device when dots are formed in a dispersed manner. It is a thing.
  • the present application has found that in an image output device that forms dots in this manner, image quality is degraded due to interference between the on / off of the dots and the fluctuation cycle of the dot formation characteristics of the image output device. This has great technical significance in that it has been found that such interference can be mitigated by a simple method of shifting the arrangement of the matrix from the grid.
  • the size of the matrix In terms of avoiding repeated formation of dots in a certain pattern, for simplicity, it is possible to set the size of the matrix to be very large. According to such means, the memory for storing the matrix data becomes enormous. In addition, it takes a long time to read data from the memory. According to the image processing apparatus and the image processing method of the present invention, the above effects can be obtained without increasing the size of the matrix. That is, according to the image processing apparatus and the image processing method of the present invention, there is also an advantage that the image quality can be improved without increasing the memory and the processing time.
  • FIG. 1 is an explanatory diagram showing the correspondence between image data and matrices.
  • Each square in FIG. 1 indicates a pixel.
  • the bold line in FIG. 1 indicates an area corresponding to a matrix as a unit.
  • the matrices were associated in a grid as shown in FIG. 26, but in the image processing apparatus of the present invention, for example, as shown in FIG. 1, the matrices are sequentially shifted in the y direction in a stepwise manner. It is.
  • FIG. 1 shows an example in which it is shifted in the y direction, it may be made to correspond while being shifted in the X direction, or both may be made to correspond.
  • the amount of shift in each direction can be set to various values. Further, it is not necessary to shift the matrix in all the regions of the image data, and it is also possible to shift the matrix in some regions from the grid shape.
  • n XX ny pixels consisting of nx in the X direction and ny in the y direction (nx and ny are integers of 2 or more), and each pixel has a predetermined range of gradation values
  • the on / off state of the dot is determined for each pixel according to the magnitude relationship between the gradation value and a predetermined threshold, and the output data corresponding to the predetermined image output device is determined.
  • Mxxmy (1 ⁇ mx ⁇ nx, 1 ⁇ my ⁇ n storage means for storing a dot-dispersion type matrix of (integer y); and halftone for judging dot on / off by reflecting the matrix component to the gradation value or the threshold value for each pixel.
  • the matrix component reflected on the kx-th pixel in the X direction (kX is an integer satisfying 0 ⁇ kx ⁇ nX) and the ky-th pixel in the y direction (ky is an integer satisfying 0 ⁇ ky ⁇ ny) is provided.
  • the image processing device is given by (Xt, yt) (0 ⁇ xt ⁇ mx, 0 ⁇ yt ⁇ my) given by the following equation (1).
  • a d i v b is an operator that calculates the quotient of a / b as an integer
  • a% b is the remainder operator to find the remainder of aZb
  • dxl, dx2, dyl, and dy2 are integers equal to or greater than 0, and at least one of dxl, dx2, dy1, and dy2 is a value other than 0.
  • this image processing apparatus similarly to the above-described image processing apparatus, it is possible to reduce the occurrence of the dot formation pattern being repeated in one direction in the matrix unit, and to improve the image quality.
  • the correspondence between the image data and the matrix in the above invention will be specifically described with reference to FIG.
  • image data is composed of pixels arranged two-dimensionally in the X and y directions, and n X pixels from 0 to n X—1 in the X direction, y direction Has ny pixels from 0 to ny- 1.
  • An arbitrary pixel of this image data is represented as (kx, ky) by using a number in the X direction and the y direction (hereinafter referred to as a pixel number).
  • Matrix is also a two-dimensional array of data It has mx components from 0 to mx-1 in the X direction, and my components from 0 to my-1 in the y direction.
  • An arbitrary component of the matrix is represented as (xt, yt).
  • FIG. 1 shows the relationship between the matrix and the image data in such a state.
  • the matrices are associated with the portions indicated by the thick lines and broken lines in FIG.
  • the matrix can be associated with the image data in other image areas.
  • d y 1 1
  • the matrices are associated as shown by the thick lines in FIG. In other words, as the pixel numbers in the X direction increase, the corresponding matrices are gradually shifted in the negative direction in the y direction. If d y 1 is greater than 1, the amount of matrix shift will be even greater.
  • FIG. 1 shows a case where d y 1 is a constant value, for example, d y 1 may be changed every time the value of r X or r y changes.
  • d y 1 may be changed every time the value of r X or r y changes.
  • the way the matrix shifts in the y direction changes in various ways.
  • the other values d X 1, d X 2, and dy 2 may take different values each time the value of r X or ry changes.
  • a matrix is associated and has a certain gradation value.
  • the halftoning results will naturally be different.
  • the image processing apparatus of the present invention can perform halftone processing with excellent image quality by suppressing the repetition of the dot formation pattern. Naturally, such an effect is not limited to an image having a constant gradation value.
  • the present invention is also applicable to a case where a plurality of types of such matrices are provided.
  • a different matrix may be used for the other area including the area A2 in FIG. 1 and the area A1.
  • the halftone means may be a means for performing halftone processing after reflecting the components of the matrix as noise data in the image data.
  • the halftone means may include any one of the matrices as the threshold. It can be a means for performing a halftone process by a dither method using a minute.
  • the dither method since halftone processing is performed according to the magnitude relationship between the tone value of image data and the threshold value of the matrix, a fixed dot formation pattern is likely to occur repeatedly according to the correspondence relationship between image data and matrix . According to the above-described image processing apparatus, such repetition can be avoided and the image quality can be improved by shifting the matrix to correspond. Moreover, the image quality can be improved without impairing the advantage of the dither method that the processing time required for the halftone processing is short.
  • the dot dispersion type dither matrix in the present invention is a matrix in which threshold values are set so that the positions of dots formed according to gradation values are dispersed as much as possible in the matrix.
  • Various matrices are known as such a dot dispersion type dither matrix. For example,
  • the matrix can be a Bayer-type dither matrix.
  • Figure 2 shows an example of a 4x4 matrix as a bayer-type dither matrix. This is a matrix having 16 types of thresholds from thresholds 0 to 15. Looking at the 3X3 portion shown in the area P1 in FIG. 2, the components at the four corners are assigned values from 0 to 3 in order. Similarly, the four corners of the 3 ⁇ 3 portion shown in area P 4 are assigned values 4-7, the four corners of area P 2 are assigned values 8-11, and the four corners of area P 3 are assigned the value 1 2 to 15 are assigned.
  • a plurality of small matrices each of which has four thresholds assigned in a predetermined pattern to four corners having a predetermined size smaller than the dither matrix size, are prepared, and a dither matrix is generated by combining these with a Bayer type.
  • FIG. 2 illustrates the case of 4 ⁇ 4 as an example, matrices of other sizes are similarly defined.
  • the Bayer type matrix is generated by the above-described method, it is characterized in that the assignment of the threshold to each component in the matrix is regular. Therefore, the dots formed according to the gradation values have a regular pattern over the entire image area, and banding is likely to occur. According to the image processing apparatus of the present invention, since the occurrence of such regular patterns can be reduced, the image quality can be greatly improved.
  • the matrix may be a blue noise mask type matrix.
  • Fig. 3 shows an example of a 64 x 64 matrix as a blue noise mask type matrix. Only a part is shown for convenience of illustration.
  • a threshold is set so that the appearance of the threshold (0 to 255) is not biased in any 16 x 16 area inside a matrix of size 64 x 64. Has been assigned.
  • a matrix having such properties is called a bull noise mask type matrix.
  • Blue noise mask type matrices are configurable for various sizes and threshold ranges.
  • the matrix may be a matrix capable of performing halftone processing with high dot dispersibility in an image area wider than an area corresponding to the size of the matrix.
  • n XX ny pixels consisting of nx in the X direction and ny in the y direction (nx and ny are integers of 2 or more), and each pixel has a predetermined range of gradation values
  • a dot is formed by driving a head according to the on / off of a dot specified according to the magnitude relationship between the gradation value and a predetermined threshold value for each pixel.
  • Halftone means for judging on / off of dots by reflecting any component of the matrix in one of the gradation value and the threshold value for each of the pixels
  • the halftone processing is performed after the matrices are shifted to correspond to each other, and dots are formed in accordance with the results of the half-toning processing. High quality printing becomes possible.
  • various correspondences can be made between the matrix and the image data.
  • Main scanning means for reciprocating the head relative to the print medium in the X direction, wherein the head comprises a plurality of nozzles arranged in the y direction;
  • a sub-scanning unit that relatively moves the head and the print medium in the y-direction; and a main scanning unit, a sub-scanning unit, and a drive of the head are controlled to form each dot row aligned in the X-direction by 2 It is preferable that a drive control unit formed by using the above nozzles is provided, and at least the dy 1 ⁇ 0.
  • each dot row arranged in the X direction is formed using two or more nozzles.
  • By forming dot rows using different nozzles it is possible to improve the image quality by dispersing the shift of the dot formation position due to the characteristics of the nozzles. Wear.
  • dots are formed after halftone processing is performed while the matrix is sequentially shifted in the y-direction with respect to the image data. Therefore, in the above-described printing apparatus, the effect of forming each dot row using different nozzles can be sufficiently exhibited, and high-quality printing can be performed. The effect will be described with a specific example.
  • a dot row recording method a method of recording odd-numbered dots in the X direction with nozzle A and recording an even-numbered dot with nozzle B can be considered.
  • the matrix is made to correspond to the image data in a grid pattern, the pixels in which dots are formed are biased toward the odd-numbered pixels in the X direction depending on the relationship between the gradation value of the image data and the threshold value of the matrix.
  • the threshold value of the matrix There are cases.
  • most of the dot rows are formed by the nozzles A, and the effect of forming the dot rows using different nozzles cannot be sufficiently obtained.
  • “at least d y 1 ⁇ ⁇ 0” is set. This is because the effect of improving the image quality is large when the matrices are correspondingly shifted in the y direction. Needless to say, the matrix may be shifted only in the X direction to correspond, or may be shifted in both the X direction and the y direction.
  • the present invention can be configured as an image processing method.
  • an image processing method for an image composed of a two-dimensional array of pixels and having a gradation value in a predetermined range for each pixel, the difference between the gradation value and a predetermined threshold value for each pixel is determined.
  • a dot dispersion type two-dimensional matrix having a predetermined value as a component is applied to the image data to reduce image quality degradation caused by interference between dot on / off and a fluctuation cycle of dot forming characteristics of the image output device.
  • This is an image processing method in which dots are arranged so as to be deviated from a grid in an avoidable range, and the on / off state of dots is determined by reflecting the components of the matrix in the gradation values or the threshold value of the image data.
  • an existing matrix such as the above-described bayer type matrix or bull noise mask type matrix may be used. It is also possible to use a designed matrix.
  • the matrix design method of the present invention is:
  • n XX ny pixels consisting of nx in the X direction and ny in the y direction (nx and ny are integers of 2 or more), and each pixel has a predetermined range of gradation values
  • mx Xmy an integer of 1 ⁇ mx ⁇ n, 1 ⁇ my ⁇ ny
  • a value to be reflected in the gradation value or a predetermined threshold value when the dot on / off is determined is stored in advance.
  • the first n (n is an integer of 1 or more) values are determined by taking into account the dispersibility of the threshold value and the arbitrary components of the matrix.
  • the step (c) comprises:
  • (c-12) a step of setting a leading value in a case where the remaining values are arranged in accordance with the magnitude relation to a component evaluated to be the longest from a component for which a value has already been set; and
  • the gist consists of
  • the matrix designed by the above design method is composed of a component whose threshold is set by the designer's intention and a component whose threshold is set by calculation.
  • Step (a) in the above-described design method is a step of setting the arrangement of the matrix in the image data.
  • Various arrangements are conceivable, such as a square arrangement as shown in FIG. 26 and an arrangement in which the matrix is sequentially shifted in the y direction as shown in FIG.
  • n thresholds are assigned to the components of the matrix.
  • Fig. 4 shows an example in which the thresholds are arranged in ascending order and n thresholds are assigned in ascending order.
  • FIG. 5 shows an example of the evaluation.
  • Fig. 5 shows the matrices in the image This shows a state in which the boxes are associated with each other.
  • the part shown by the thick line in FIG. 5 corresponds to the matrix.
  • the components shown in FIG. 4 have thresholds of values 0 to n ⁇ 1
  • the thresholds of values 0 to n ⁇ 1 are set at the locations shown in FIG. 5, respectively.
  • the distance is evaluated for a component whose value is undefined, for example, (2, my-1).
  • FIG. 1 consider the case where the distance is evaluated for a component whose value is undefined, for example, (2, my-1).
  • mp which is one of the pixels to which this component corresponds, is hatched.
  • dl to d4 are distances from pixels corresponding to a matrix different from pixel mp. “Across a plurality of matrices” means that the distances to the pixels on the different matrices are also evaluated.
  • One of the distances d1 to d4 calculated in this way is selected as an evaluation value for the threshold 0. In FIG.
  • the distance is calculated for a part of the pixels to which the threshold value 0 is assigned. However, all the pixels may be calculated. In the same way, the evaluation values for all the threshold values from the already set values 0 to n-1 are calculated. Further, such an evaluation value is calculated not only for the pixel mp but also for all components whose thresholds are not defined.
  • a component that is evaluated as being farthest from the component for which the threshold value has already been set is obtained based on the evaluation value calculated in the step (c-1).
  • Such a component corresponds to the component having the highest dispersibility.
  • the n-th threshold value is set for such a component.
  • the set threshold is the nth smallest value.
  • the matrix designing method of the present invention by repeating the above-described steps (c-11) and (c-2) sequentially, emphasis is placed on dot dispersibility in consideration of the arrangement of the matrix in the image data. To set the threshold.
  • halftone processing is performed using a matrix designed by the design method of the present invention, high-quality halftone processing can be performed.
  • the threshold value may be set in order from the larger threshold value.
  • the thresholds may be set in order from a larger threshold.
  • the above-described distance may be evaluated in consideration of factors other than the dispersibility of the dots, and the threshold value of the matrix may be set.
  • Matrix components to be reflected on the first pixel in the X direction (X 1 is an integer of 0 ⁇ x 1 ⁇ n X) and on the first pixel in the y direction (y 1 is an integer of 0 ⁇ y 1 ⁇ ny) May correspond to (xt, yt) (0 ⁇ xt ⁇ mx, 0 ⁇ yt ⁇ my) given by the above equation (1).
  • This correspondence corresponds to the case where the matrix is made to correspond to the image data in a state shifted from the grid, as described in the image processing apparatus above.
  • the above-described design method it is possible to generate a matrix in which the dispersibility of dots is sufficiently ensured over the entire image region, while assuming that the matrix is displaced from the grid shape. Therefore, if a matrix designed by the above design method is used, high-quality image processing can be performed.
  • the above-described image device of the present invention can also be configured by realizing the above-described halftone processing by a computer. Therefore, the present invention adopts an aspect as a recording medium on which such a program is recorded. You can also.
  • the recording medium of the present invention is a recording medium of the present invention.
  • nxxny pixels consisting of nx pixels in the X direction and ny pixels in the y direction (nx and ny are integers of 2 or more), and each pixel has a predetermined range of gradation values.
  • a computer-readable recording medium for storing a program for determining dot on / off in accordance with a magnitude relationship between the gradation value and a predetermined threshold value for each of the pixels.
  • the grayscale value or the threshold value of the kx-th pixel (kX is an integer satisfying 0 ⁇ kx ⁇ nX) in the X direction and the ky-th pixel (ky is an integer satisfying 0 ⁇ ky ⁇ ny) in the y direction are as described above.
  • the above-described image processing apparatus of the present invention can be realized by executing the program recorded on each of the recording media by the computer.
  • the storage medium include a flexible disk, a CD-R ⁇ M, a magneto-optical disk, an IC card, a ROM cartridge, a punched card, a printed matter on which a code such as a barcode is printed, and a computer internal storage device (RAM or RAM).
  • RAM or RAM Various computer-readable media such as a memory such as a ROM) and an external storage device can be used.
  • It also includes a storage device of a program supply device that supplies a computer program for realizing the halftone processing function of the image processing device to a computer via a communication path.
  • the present invention can be configured as a program itself for realizing the above functions or various signals that can be regarded as the same.
  • FIG. 1 is an explanatory diagram showing the correspondence between image data and matrices.
  • FIG. 2 is an explanatory diagram showing the contents of the Bayer matrix.
  • FIG. 3 is an explanatory diagram showing an example of a blue noise mask type matrix.
  • FIG. 4 is an explanatory diagram showing the arrangement of thresholds in a matrix.
  • FIG. 5 is an explanatory diagram showing the calculation of the distance to each component.
  • FIG. 6 is a schematic configuration diagram of a printing apparatus as an embodiment.
  • FIG. 7 is an explanatory diagram showing the configuration of the software.
  • FIG. 8 is a schematic configuration diagram of the printer according to the embodiment.
  • FIG. 9 is an explanatory diagram showing a schematic configuration of a dot recording head for printing in the embodiment.
  • FIG. 10 is an explanatory diagram illustrating the principle of dot formation during printing in the example.
  • FIG. 11 is an explanatory diagram showing the internal configuration of the controller of the printer.
  • FIG. 12 is an explanatory diagram showing the driving waveforms of the nozzles during printing and the state of the dots formed by the driving waveforms in the embodiment.
  • FIG. 13 is a flowchart showing the flow of the dot formation control routine.
  • FIG. 14 is a flowchart showing a flow of the halftone process by the dither method.
  • FIG. 15 is an explanatory diagram showing the correspondence between the matrix and the image data in the embodiment.
  • FIG. 16 is an explanatory diagram showing a result of forming a dot according to the example.
  • FIG. 17 is an explanatory diagram showing how dots are formed by the overlap method.
  • FIG. 18 is a flowchart showing the flow of the halftone process by the error diffusion method.
  • FIG. 19 is an explanatory diagram showing weights when diffusing an error.
  • FIG. 20 is a flowchart illustrating the procedure of the design method according to the embodiment.
  • FIG. 21 is an explanatory diagram illustrating setting of thresholds in the design method according to the embodiment.
  • FIG. 22 is an explanatory diagram illustrating the calculation of the distance in the design method according to the embodiment.
  • FIG. 23 is an explanatory diagram illustrating an evaluation value of the distance in the design method of the example.
  • FIG. 24 is an explanatory diagram showing a matrix designed by the design method of the embodiment.
  • FIG. 25 is an explanatory diagram showing a bayer type matrix.
  • FIG. 26 is an explanatory diagram showing the correspondence between a matrix and image data in the conventional technology.
  • FIG. 27 is an explanatory diagram showing the concept of dot on / off determination by the dither method.
  • FIG. 28 is an explanatory diagram showing a dot formation result in the conventional technique.
  • FIG. 6 is a block diagram illustrating a configuration of an image processing apparatus and a printing apparatus as one embodiment of the present invention.
  • the scanner 90 and the color printer 22 are connected to the computer 90.
  • the computer 90 functions not only as an image processing apparatus but also as a printing apparatus in combination with the printer 22.
  • This computer 90 includes the following units interconnected by a bus 80, centering on a CPU 81 that executes various arithmetic processes for controlling operations related to image processing according to a program.
  • the ROM 82 stores in advance the program data necessary for executing various arithmetic processing by the CPU 81, and the RAM 83 stores the program data required for executing various arithmetic processing by the CPU 81 similarly.
  • the input interface 8 4 is connected to the scanner 1 2
  • the output interface 85 controls the input of signals, and controls the output of data to the printer 22.
  • the CRTC 86 controls the signal output to the CRT 21 capable of displaying color
  • the disk controller (DDC) 87 exchanges data with the hard disk 16, the flexible drive 15 or a CD-ROM drive (not shown). Control.
  • the hard disk 16 stores various programs loaded into the RAM 83 and executed, various programs provided in the form of device drivers, and the like.
  • a serial input / output interface (SIO) 88 is connected to the bus 80.
  • This SI ⁇ 88 is connected to a modem 18, and is connected to a public telephone line PNT via the modem 18.
  • the computer 90 is connected to an external network via the SIO 88 and the modem 18, and by connecting to a specific server-SV, a program required for image processing can be downloaded to the hard disk 16. Is also possible. It is also possible to load the necessary programs on a floppy disk FD or CD-ROM, and have the program run on the convenience store 90.
  • FIG. 7 is a block diagram illustrating a software configuration of the printing apparatus.
  • Comb At evening 90, the application program 95 is running under the given operating system.
  • the operating system incorporates a video driver 91 and a printer driver 96, and the application program 95 outputs image data FNL to be transferred to the printer 22 via these drivers. Will be done.
  • An application program 95 for performing image retouching and the like reads an image from the scanner 12, and displays the image on the CRT display 21 via the video driver 91 while performing predetermined processing on the image.
  • the data ORG supplied from the scanner 12 is read from the color manuscript and the three color components of red (R), green (G) and blue (B) are read. This is the original color image data ORG consisting of the components.
  • the printer driver 96 of the combination 90 receives image information from the application program 95, and receives a signal that can be processed by the printer 22 (here, a signal that can be processed by the printer 22).
  • Halftoned signals for cyan, magenta, yellow, and black are provided inside the printer driver 96.
  • the resolution conversion module 97 serves to convert the resolution of the color image data provided by the application program 95, that is, the number of pixels per unit length into a resolution that can be handled by the printer driver 96. .
  • the color correction module 98 refers to the color correction table LUT and uses the cyan (C) used by the printer 22 for each pixel. ), Magenta (M), yellow (Y), and black ( ⁇ ).
  • the data subjected to the color correction in this way has a gradation value with a width of, for example, 256 gradations.
  • the halftone module 99 executes a halftone process for expressing the gradation value in the printer 22 by forming dots in a dispersed manner.
  • the halftone module of the present embodiment is included in at least the image processing apparatus of the present invention.
  • the image data processed in this way is rearranged by the rasterizer 100 in the order of data to be transferred to the printer 22, and output as final image data FNL.
  • the printer 22 only plays a role of forming dots in accordance with the image data FNL, and does not perform image processing. However, it is a matter of course that these processes may be performed by the printer 22.
  • the printer 22 has a mechanism for transporting the paper P by the paper feed motor 23, a mechanism for reciprocating the carriage 31 in the axial direction of the platen 26 by the carriage motor 24, and a carriage 31.
  • a control circuit 40 that controls the exchange of data.
  • the mechanism for reciprocating the carriage 31 in the axial direction of the platen 26 includes a sliding shaft 3 4, which is installed in parallel with the platen 26 axis, and holds the carriage 31 slidably, and a carriage motor 24. It comprises a pulley 38 on which an endless drive belt 36 is stretched, and a position detection sensor 39 for detecting the origin position of the carriage 31.
  • the carriage 31 has a cartridge 71 for black ink (Bk) and a cartridge 72 for color ink containing three color inks of cyan (C), magenta (M) and yellow (Y). Can be mounted.
  • a total of four ink discharge heads 6 1 to 6 4 are formed on the print head 2 8 below the carriage 3 1, and the bottom of the carriage 3 1 has a head for each color.
  • An inlet pipe 67 (see Fig. 9) for guiding the ink from the ink tank is provided upright.
  • FIG. 9 is an explanatory diagram showing a schematic configuration inside the ink ejection head 28.
  • the ink cartridges 7 1 and 7 2 are mounted on the carriage 31, the ink in the ink cartridge is sucked out through the introduction pipe 67 by utilizing the capillary phenomenon as shown in FIG.
  • the printing head 28 is provided at the lower portion of the carriage 31 and is guided to the heads 6 1 to 64 of the respective colors.
  • the operation of sucking ink into the heads 61 to 64 of each color is performed by a dedicated pump.In this embodiment, the pump for suction and the print head 28 at the time of suction are operated.
  • the illustration and description of the configuration of the covering cap and the like are omitted.
  • FIG. 10 shows the structure of the piezo element PE and the nozzle Nz in detail. As shown in the upper part of FIG. 10, the piezo element PE is installed at a position in contact with the ink passage 68 that guides the ink to the nozzle Nz. As is well known, the piezo element PE is an element that distorts the crystal structure due to the application of a voltage, and performs electro-mechanical energy conversion at extremely high speed.
  • the piezo element PE is extended by the voltage application time as shown in the lower part of Fig. 10. Then, one side wall of the ink passage 68 is deformed. As a result, the volume of the ink passage 68 contracts in accordance with the expansion of the piezo element PE, and the ink corresponding to the contraction becomes particles Ip and is discharged at high speed from the tip of the nozzle Nz. Printing is performed by the ink particles Ip penetrating into the paper P mounted on the platen 26.
  • FIG. 11 is an explanatory diagram showing the internal configuration of the control circuit 40.
  • a PC interface 44 for exchanging data with the computer 90, a paper feeder 23, a carriage motor 24 And signals with operation panel 32, etc.
  • Peripheral input / output unit (PI ⁇ ) 45 that exchanges data
  • timer 46 that measures time
  • drive buffer 47 that outputs dot on / off signals to heads 6 1 to 66
  • the control circuit 40 also includes a transmitter 51 for outputting a driving waveform for driving the piezo element at a predetermined frequency, and outputs from the transmitter 51 to the heads 61 to 64 at a predetermined timing.
  • a distributor 55 for distributing is also provided.
  • the control circuit 40 receives the dot data processed by the computer 90, temporarily stores it in the RAM 43, and outputs it to the driving buffer 47 at a predetermined timing.
  • FIG. 12 is an explanatory diagram showing the arrangement and connection of one nozzle row of the heads 61 to 64 as an example.
  • 48 nozzles Nz are arranged in a staggered manner at a constant nozzle pitch k.
  • the state of dots formed by the nozzle row of the present embodiment is shown on the right side of FIG.
  • the circle shown by the solid line is a dot that can be formed by one main scan.
  • the dashed line is shown as an indicator of the interval between the dots.
  • the nozzle pitch k corresponds to two dots.
  • each nozzle array need not be arranged in a staggered manner, and may be arranged on a straight line. However, if they are arranged in a staggered pattern as shown in FIG. 12, there is an advantage that the nozzle pitch k can be easily set small in manufacturing.
  • Each of the nozzle arrays of the heads 6 1 to 6 4 is interposed in a circuit in which the driving buffer 47 is used as a source and the distribution output unit 55 is used as a sink.
  • One of the electrodes is connected to each output terminal of the driving buffer 47, and the other electrode is connected to the output terminal of the distribution output device 55 collectively.
  • the drive waveform of the oscillator 51 is output from the distribution output device 55.
  • On / off for each nozzle is determined from CPU 81 and each terminal of drive buffer 47 When the signal is output to the, only the piezo element PE that has received the ON signal from the driving buffer 47 is driven according to the driving waveform.
  • the ink particles Ip are simultaneously discharged from the nozzles of the piezo element PE that have received the ON signal from the transfer buffer 47.
  • the nozzle rows are formed in a staggered manner, so when forming dots while transporting the carriage 31, in order to form dots arranged in one row in the main scanning direction, It is necessary to shift the ink ejection timing of each nozzle row. In addition, it is necessary to similarly shift the ink ejection timing for each of the heads 61 to 64.
  • the CPU 81 outputs on / off signals of the respective dots via the driving buffer 47 in consideration of such a timing shift to form dots of each color.
  • the printer 22 of this embodiment transports the paper P by the paper feed mode 23 (hereinafter referred to as “sub-scan”), and controls the carriage 31 by the carriage motor 24. It is reciprocated (hereinafter referred to as main scanning), and at the same time, the piezo elements PE of the heads 6 1 to 6 4 of the print head 28 are driven to eject ink of each color to form dots. To form a multi-color image on paper P.
  • the printer 22 having the head that discharges ink using the piezo element PE is used, but a printer that discharges ink by another method may be used.
  • the present invention may be applied to a pudding type in which ink is discharged by bubbles generated in the ink passage by energizing a heater disposed in the ink passage.
  • FIG. 13 shows the flow of the dot formation control processing routine.
  • This is a process executed by the CPU 81 of the computer 90.
  • the CPU 81 inputs image data (step S100).
  • This image data is the data passed from the application program 95 shown in FIG. 2 and has a value of 0 to 15 for each of the R, G, and B colors for each pixel constituting the image. This is data having 16 gradation values.
  • the resolution of this image data changes according to the resolution of the original image data ORG.
  • the CPU 81 converts the resolution of the input image data into a resolution for printing by the printer 22 (step S105). If the image data is lower than the printing resolution, resolution conversion is performed by generating new data between adjacent original image data by linear interpolation. Conversely, if the image data is higher than the print resolution, resolution conversion is performed by thinning out the data at a fixed rate.
  • the resolution conversion processing is not essential in the present embodiment, and printing may be executed without performing such processing.
  • the color correction process is a process of converting image data consisting of R, G, and B gradation values into a decimation of gradation values of C, M, Y, and ⁇ colors used in the printer 22.
  • This processing is performed by using a color correction table LUT (see Fig. 7) that stores the combination of:, M, Y, and ⁇ to represent the color composed of each combination of R, G, and B in the print area 22.
  • Various known techniques can be applied to the processing itself for performing color correction using the color correction table LUT, and for example, processing by interpolation (such as the technique described in Japanese Patent Application Laid-Open No. 4-144481) can be applied.
  • the CPU 81 performs halftone processing on the color-corrected image data (step S200).
  • the halftone process means that the printer 22 converts the tone value of the original image (16 tones in the present embodiment) into a tone value that can be expressed by the printer 22 for each pixel.
  • halftone processing is performed for two gradations of dot on / off, but halftone processing for more gradations is performed. It may be performed.
  • halftone processing is performed by the dither method.
  • Fig. 14 shows the flow of halftone processing by the dither method.
  • the CPU 81 inputs an image data CD (step S202).
  • the input image data CD is a color image that has been subjected to color correction processing (step S110 in FIG. 13) and has 16 gradations for each color of C, ⁇ , ⁇ , and K.
  • initialization is performed by assigning a value of 0 to each pixel number (kx, ky) constituting the image data (step S204).
  • the image data is composed of nx two-dimensionally arranged pixels in the main scanning direction and ny in the sub-scanning direction.
  • Figure 1 shows the relationship between image data and pixels.
  • Each pixel has a pixel number kx assigned in the main scanning direction (X direction in FIG. 1) from the left side in FIG. 1 and a pixel number assigned in the sub scanning direction (y direction in FIG. 1) from the upper side in FIG. Expressed using ky.
  • the upper left pixel shown in FIG. 1 is set as the pixel to start processing.
  • the CPU 81 calculates the component number (Xt, yt) of the dither matrix used for the halftone processing (step S206).
  • the dither matrix is composed of mx two-dimensionally arranged components in the main scanning direction and my in the sub-scanning direction.
  • each component is represented by an integer component number (Xt, yt) such that 0 ⁇ xt ⁇ mx and 0 ⁇ ytmy.
  • each component number is calculated by the following equation (2).
  • yt ((kxdiv mx) xdy + ky)% my;... (2)
  • % is the remainder operator, for example, kX% mx means the remainder of kxZmx.
  • Kxdivmx means the quotient of kxZmx.
  • Figure 15 shows the correspondence between dither matrix components and each pixel. For convenience of illustration, only the-part of the image data is shown. The components of the dither matrix corresponding to each pixel are shown in Fig. 15 in the form of (xt, yt). The values from 0 to 9 at the top of Fig. 15 indicate the pixel numbers in the main scanning direction, and the values from 0 to 5 on the left indicate the pixel numbers in the sub-scanning direction. ing.
  • Pixels (5, 0) to (7, 0) Components (1, 1) to (3, 1); Pixels (4, 1) to (7, 1) —Components (0, 2) to (3, 2); Pixels (4, 2) to (7, 2) —Components (0, 3) to (3, 3) );
  • the shift amount dy in the sub-scanning direction is also a constant value in the entire image area, but the shift amount dy is changed each time the matrix is used repeatedly in the main scanning direction or the sub-scanning direction. Can also.
  • the CPU 81 compares the gradation value CD (kx, ky) of the image data with the threshold value DM (xt, yt) of the dither matrix (step S208). .
  • the gradation value is larger than the threshold value, that is, when CD (kX, ky)> DM (xt, yt)
  • Substitute the value that indicates the ON of the dot into the value CDR (kx, ky) (step S212).
  • step S210 it is determined that the dot should be turned off, and a value indicating that the dot is turned off is substituted into the result value CDR (kx, ky) (step S210).
  • the result value CDR is transferred to the driving buffer 47 (see FIG. 12) through processing such as rasterizing, which will be described later, and determines ON / OFF of each nozzle.
  • the CPU 81 increases the pixel number kx by the value 1 (step S214). That is, the pixel to be processed is shifted by one in the main scanning direction. Further, it is determined whether or not the pixel number kX set in this way is equal to or more than the value nX (step S216). As described above, the image data has nx pixels in the main scanning direction, and the pixel number kX can take a value from 0 to nX-1.
  • the CPU 81 initializes the pixel number kX in the main scanning direction by substituting the value 0, and increases the pixel number ky in the sub-scanning direction by the value 1 (step S218). This means that processing of the next raster will begin.
  • the image data has ny pixels in the sub-scanning direction, and the pixel number ky can take a value from 0 to ny-1.
  • the CPU 81 increases the pixel number ky in the above step S218, compares the pixel number ky with the value ny (step S220), and when ky is greater than or equal to the value ny. Ends the halftone process.
  • Fig. 16 shows an example of the result of performing the above processing.
  • FIG. 16 shows the result of performing halftone processing on image data having a constant gradation value 8 using the Bayer matrix shown in FIG. The correspondence between the matrix and the image data is as shown in Fig.15. Comparing the Bayer type matrix shown in Fig.
  • the gradation value 8 is larger than the threshold values set as the components (2, 2), (1, 3), and (3, 3). Therefore, a dot is turned on at a pixel corresponding to such a component.
  • the hatched pixels indicate pixels whose dots are turned on. Looking at the unit of each matrix, the dots are formed in a checkered pattern, but since the matrix is shifted from the image data in the sub-scanning direction, the dots in the entire image data are in a checkered pattern. No.
  • the CPU 81 performs a rasterization on the result value CDR subjected to the halftone processing by the above processing (step S300 in FIG. 13). This means that one raster's worth of data is sorted in the order that the evening is transferred to the head of the pudding.
  • a recording method is used in which every other dot is formed, for example, every other dot, and the second main scan forms the remaining dots.
  • each raster is formed by two main scans.
  • step S240 creates the data to be transferred to the head according to the recording method performed by the printer 22.
  • the CPU 81 outputs the data and transfers it to the printer 22 (step S310).
  • Fig. 17 shows an example of dot recording by the overlap method.
  • the nozzle pitch in the sub-scanning direction is 2 dots.
  • the position of the head in the sub-scanning direction is shown corresponding to the first to fifth main scanning.
  • the position of each nozzle is indicated by “ ⁇ ”.
  • the number enclosed by a circle indicates the nozzle number.
  • the right side of FIG. 17 shows the state of the dots formed in each main scan.
  • the sub-scan is performed with a feed amount equivalent to three dots, and then the dots are formed while the second main scan is performed. Also in this case, for the above-mentioned reason, dots are formed using only the nozzles No. 4 to No. 6. Further, after performing sub-scanning corresponding to three dots, dots are formed while performing third main scanning.
  • the position of No. 2 nozzle in the third main scan coincides with the position of No. 5 nozzle in the first main scan. Therefore, the second nozzle records a pixel in which no dot is formed in the first main scan, that is, an even-numbered pixel.
  • dots can be formed in the area indicated by PA in FIG. 17 without gaps.
  • odd-numbered pixels and even-numbered pixels are formed by different nozzles.
  • the dither matrix is By shifting the pattern in a stepwise manner from the grid, the dots can be suppressed from being formed in a regular pattern in units of a matrix.
  • dots are completely formed in a checkered pattern as shown in FIG. 28 for image data having a constant gradation value of 8. Will be.
  • the regularity of dots is broken as shown in FIG.
  • the printing apparatus of the present embodiment it is possible to suppress the occurrence of unevenness in the number of dots for each raster due to the loss of dot regularity. Therefore, when there is a nozzle in which the dot formation position is shifted based on a mechanical manufacturing error, it is possible to avoid an increase in the number of dots formed by such a nozzle. As a result, it is possible to avoid occurrence of remarkable banding in a lasing portion formed by the nozzle, and to improve image quality. This effect can be obtained both in the case of performing the overlap recording and in the case of completing each raster in one main scan.
  • the image quality can be improved even when performing recording by the overlap method for the following reason.
  • dots are formed in a regular pattern as shown in FIG. 28, the pixels on which dots are formed are often biased to odd-numbered pixels or even-numbered pixels when viewed from each raster. In the case where such deviation occurs, even if the recording by the overlap method is adopted, most of each lath is substantially formed by a single nozzle. I can't get enough.
  • the printing apparatus of the present embodiment as a result of suppressing the above-mentioned regular pattern, it is possible to suppress the pixels in which dots are formed from being biased to odd-numbered or even-numbered. Therefore, the effect of improving the image quality by the overlap method can be sufficiently obtained.
  • the hardware configuration of the printing apparatus according to the second embodiment is the same as that of the printing apparatus according to the first embodiment (see FIGS. 6 to 12).
  • the dot formation control process is the same as in the first embodiment (see FIG. 13).
  • the content of the halftone process (step S200 in FIG. 13) is different from that of the first embodiment.
  • a halftone process is performed using an error diffusion method.
  • FIG. 18 shows the contents of the halftone process in the second embodiment, that is, the halftone process by the error diffusion method.
  • the CPU 81 reads the image data CD (step S250), and performs initialization by substituting the value 0 into both the pixel numbers (kx, ky) (step S252).
  • These processing contents are the same as the halftone processing (steps S202 and S204 in FIG. 14) in the first embodiment.
  • the CPU 81 generates the diffusion error correction data CDX based on the initialized image data of the pixel number (0, 0) (step S254).
  • an error in the gradation expression generated for the processed pixel is assigned in advance to pixels surrounding the pixel with a predetermined weight, so that in step S254, the corresponding error is read out. This is reflected in the pixel of interest to be processed now.
  • Fig. 19 shows an example of how to assign this error to which pixel in the surrounding area and to what degree of weighting the pixel PP of interest.
  • a predetermined weight (1Z4, 1Z8, 1/16). The error diffusion processing will be described later in detail.
  • the CPU 81 calculates a component number (Xt, yt) of the matrix (step S256).
  • the calculation of the component number (X t, y t) is performed using the equation (2) described in the first embodiment.
  • the size and displacement d y of the matrix used in this embodiment are the same as those in the first embodiment. Therefore, the correspondence between the matrix and the image data is the same as in the first embodiment. In other words, the correspondence is such that the matrix is displaced stepwise from the grid by one pixel in the sub-scanning direction.
  • the matrix component DM (xt, yt) thus set is added as noise to the diffusion error correction data CDX (kx, ky) obtained in step S254.
  • the image data after the noise is added is the noise added data C DN (kX, ky)
  • the following equation (3) is calculated. The reason for adding noise in this way will be described later.
  • CDN (k X, ky) CDX (kx, ky) + DM (xt, yt)... (3) Compare the magnitude of the noise-added CDN generated in this way with a predetermined threshold TH (step S 260), if the data CDN is greater than the threshold value TH, substitute a value indicating that the dot is on into the result value CDR (kx, ky) . If the data CDN is less than the threshold value TH, the result value CDR (kx, ky) Substitute a value indicating that the dot is off into ky) (step S240).
  • the threshold value TH is a value that serves as a reference for judging on / off of a dot as described above. This threshold value TH can be set to any value. In this embodiment, the threshold value TH is set to a value 7 which is an intermediate value between 16 gradation values of 0 to 15 which can be taken by the image data CD.
  • step S266 the CPU 81 calculates an error generated by the halftone process, and executes a process of diffusing the error to peripheral pixels (step S266). Error and Is the original image data from the evaluation value of the density represented by each dot after halftone processing.
  • the error calculated in this way is diffused to peripheral pixels at the rate shown in FIG.
  • the error corresponding to the gradation value 4 is calculated at the pixel PP of interest
  • the error corresponding to the gradation value 1 which is the error 14 is diffused to the adjacent pixel P1. Will be.
  • the errors are similarly diffused for the other pixels at the rate shown in FIG.
  • the error thus diffused is reflected on the image data CD in step S254 described above, and diffusion error correction data CDX is generated.
  • the CPU 81 increases the pixel number kx by the value 1 (step S268) and compares the magnitude relationship with the number nX of pixels in the main scanning direction (step S270) ). If the pixel number kx is equal to or larger than the pixel number nx, the value 0 is substituted into, and the pixel number kx in the sub-scanning direction is increased by the value 1 (step S2722), and the pixel number ny in the sub-scanning direction (Step S2744) The pixels to be processed are sequentially moved until the processing for all the pixels is completed by these processes. When the processing has been completed for all the pixels, the halftone processing routine ends, and the process returns to the dot formation control processing routine (FIG.
  • the subsequent processing is the same as in the first embodiment.
  • noise is added to the diffusion error correction data CDX in step S258.
  • the error diffusion method can originally perform halftone processing without adding noise.
  • the dot generation rate may suddenly change according to the change in the gradation value. For example, in the case of image data having a uniform gradation value of 8, a large error occurs when the dot is turned on and when the dot is turned off. Therefore, it is very difficult to determine whether the dot is on or off. It is easy to be stable. If the occurrence rate of dots changes rapidly, false contours may occur and the image quality may decrease. In this embodiment, noise is added to avoid such a phenomenon. By adding noise to the image data, it is possible to prevent the above-mentioned unstable gradation values from being present over a wide range, and thus it is possible to suppress a sudden change in the incidence of dots.
  • a matrix set so that the average value of each component value is 0 is used. If the average value is a value other than 0, the density expressed as a whole will change.
  • a matrix in which each component of the bayer type matrix was shifted so as to fall within the range of -7 to 7 was used.
  • various matrices such as a blue noise mask type matrix can be used by shifting them so that the average value of the threshold value becomes zero.
  • high-quality halftone processing and printing can be performed by adding noise based on a matrix.
  • the matrix is made to correspond to the image data in a grid pattern, the added noise will be a repetition of a regular pattern, so that the dots may be formed in a regular pattern.
  • the matrix is shifted stepwise with respect to the image data so that the formation of such a regular pattern can be avoided, and high-quality printing can be performed. I can. Such an effect can be obtained regardless of whether printing is performed by completing each raster in one main scan or printing by the overlap method.
  • the matrix is made to correspond to the matrix while being shifted stepwise in the sub-scanning direction. However, the matrix may be shifted in the main scanning direction, or may be shifted to both. Absent.
  • the embodiment can be adopted as a recording medium on which a program for realizing such processing is recorded.
  • recording media include flexible disks, CD-ROMs, magneto-optical disks, IC cards, ROM cartridges, punched cards, printed materials on which codes such as barcodes are printed, and internal storage devices (such as RAM and Various computer-readable media can be used, such as a memory such as a ROM) and an external storage device.
  • a program supply device that supplies a computer program for performing the above-described image processing and the like at the time of combination via a communication path is also possible.
  • a generally well-known bayer type matrix is used for halftone processing.
  • a blue noise mask type matrix can also be used.
  • a matrix designed for the image processing device and the printing device can also be used.
  • FIG. 20 is a flowchart showing the procedure of a matrix design method according to an embodiment of the present invention.
  • FIGS. 21 to 24 show specific design examples. The matrix design method in this embodiment will be described with reference to these drawings.
  • step S10 set the size of the matrix and the threshold stored in the matrix Is set.
  • the matrix size is set according to the gradation value to be expressed by halftone processing and the memory capacity for storing the matrix.
  • the threshold is set according to the gradation value to be expressed by the halftone processing.
  • the matrix size is set to 4 ⁇ 4, and the threshold value is set in a range of values 0 to 15.
  • the threshold value is a continuous integer in the range of values 0 to 15.
  • a discrete threshold value may be stored.
  • overlapping thresholds may exist.
  • the arrangement of the matrix refers to the correspondence of the matrix to the image data.
  • the matrix may be arranged in a grid pattern with respect to the image data, or may be arranged in a stair-like manner. In the present embodiment, as described later, they are arranged stepwise.
  • thresholds 0 and 1 are assigned to components in the matrix (step S14).
  • FIG. 21 shows the assignment of thresholds in the present embodiment.
  • the value 0 was assigned to component (0, 0) and the value 1 was assigned to component (2, 1). This means that two thresholds are assigned from the smaller of all thresholds arranged in the matrix. Three or more thresholds may be assigned in ascending order, or only the smallest ⁇ value may be assigned.
  • the threshold value can be assigned to an arbitrary component, but is desirably assigned in consideration of the dispersibility of dots.
  • FIG. 20 shows the step of substituting the value 2 for the threshold value nc to be set in this sense.
  • step S18 select one component in the matrix for which the threshold has not yet been set.
  • step S20 the evaluation value of the distance from this component to the component for which the threshold has already been set is calculated (step S20).
  • the component (3, 0) is selected first.
  • FIG. 22 shows the position of this component on the image data.
  • FIG. 22 shows the correspondence between the matrix and the image data in the present embodiment.
  • the component (3, 0) corresponds to the pixel DD in FIG.
  • the matrix is arranged stepwise in FIG. 22, there are many pixels corresponding to the component (3, 0), but one of them may be selected.
  • the distance evaluation value is calculated for each.
  • the evaluation value of the distance is calculated through a step of calculating a distance to a pixel for which a threshold has already been set, as described later, and a step of obtaining an evaluation value of the distance based on the distance.
  • the calculation of the distance is performed in the following manner.
  • the pixels DD with undefined thresholds there are many pixels to which threshold 0 is assigned according to the arrangement of the matrix.
  • the distance is calculated by selecting the pixel with the shortest distance from among such a large number of pixels.
  • the pixel adjacent to the upper right of the pixel DD is the closest pixel.
  • the distance between the pixel to which threshold value 1 is assigned and the pixel DD is calculated.
  • a distance evaluation value e vl is obtained by the following equation (4). Where "-" is a power operator.
  • the component having the smallest evaluation value is selected (step S24).
  • the evaluation value e V A component having a minimum value of 1 corresponds to a pixel that is farther from any pixel for which a threshold has already been set, so if halftone processing is performed using a matrix designed by assigning a threshold to such a component, In this embodiment, it is possible to secure the dispersibility of the dots in the entire image data.In this embodiment, taking into account the arrangement of the matrix on the image data, the pixels for which the threshold is already set and the pixels which are not defined are used. Is calculated for the reason This is to ensure dot dispersibility throughout the image data.
  • the next threshold is set as the target.
  • the threshold nc is increased by 1 (step S26).
  • Figure 24 shows the result of the threshold assignment.
  • the matrix shown in Fig. 24 has a different matrix from both the bayer type and the blue noise mask type.
  • the matrix obtained in this manner may be corrected according to the relationship with the image data to be processed. For example, if the image data has gradation values from 0 to 255, the correction of multiplying each threshold by a factor is performed so that the matrix in Fig. 24 adopts a maximum of 255 thresholds. It may be applied.
  • the noise matrix is used as the noise matrix in the halftone processing shown in FIG. 18, correction for shifting the value of each component so that the average value becomes 0 may be performed.
  • various corrections can be made according to the relationship with the image data.
  • the matrix design method described above it is possible to obtain a matrix with high dot dispersibility in consideration of the arrangement of the matrix with respect to the image data. If halftone processing is performed using the matrix designed in this way, high-quality halftone processing with high dot dispersibility in the entire image data becomes possible. Further, according to the above design method, it is possible to obtain a matrix on the premise that the matrix is arranged in a stepwise manner as shown in FIG. 22 with respect to the image data. As a result, it is possible to obtain a matrix most suitable for the image processing apparatus and the printing apparatus of the present embodiment described above.
  • the present invention is applicable to an image processing apparatus that generates output data to be supplied to various image output apparatuses that output images using dots, such as an ink jet printer.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Color, Gradation (AREA)
  • Facsimile Image Signal Circuits (AREA)
  • Image Processing (AREA)

Abstract

Des matrices de juxtaposition sont disposées pas à pas dans des données images afin de permettre un traitement demi-teinte. En d'autres termes, ces matrices de juxtaposition sont décalées l'une après l'autre dans le sens de balayage horizontal ou vertical, ou dans les deux, la répétition régulière d'une suite de points dans ces sens de balayage horizontal ou vertical pouvant ainsi être prévenue et la formations de bandes dans l'image limitée, ce qui permet d'améliorer la qualité de l'image. Cette technique peut être appliquée au procédé de dispersion d'erreur selon lequel les données matricielles sont ajoutées comme bruit, ladite matrice pouvant être une matrice connue ou une matrice répartie par points conçue en fonction d'une disposition pas à pas.
PCT/JP1999/005241 1998-09-25 1999-09-24 Dispositif et procede de traitement d'images, et imprimante WO2000019704A1 (fr)

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JP28874898A JP3767209B2 (ja) 1998-09-25 1998-09-25 画像処理装置および方法並びに印刷装置
JP10/288748 1998-09-25

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US7251060B2 (en) 2000-12-12 2007-07-31 Ricoh Company, Ltd. Image-processing device using quantization threshold values produced according to a dither threshold matrix and arranging dot-on pixels in a plural-pixel field according to the dither threshold matrix
JP4779510B2 (ja) * 2005-08-30 2011-09-28 セイコーエプソン株式会社 画像形成方法および画像形成装置
JP2007062099A (ja) * 2005-08-30 2007-03-15 Seiko Epson Corp 画像形成方法および画像形成装置
JP4779509B2 (ja) * 2005-08-30 2011-09-28 セイコーエプソン株式会社 画像形成方法および画像形成装置
JP5077138B2 (ja) * 2008-08-13 2012-11-21 カシオ電子工業株式会社 画像形成装置
JP5515987B2 (ja) * 2010-04-05 2014-06-11 株式会社リコー 画像形成装置
JP5832350B2 (ja) * 2012-03-28 2015-12-16 株式会社Ｓｃｒｅｅｎホールディングス 閾値マトリクス生成方法、画像データ生成方法、画像データ生成装置、画像記録装置および閾値マトリクス
US9064202B2 (en) * 2012-06-06 2015-06-23 Canon Kabushiki Kaisha Data processing apparatus and print data generating method
JP2018012278A (ja) * 2016-07-21 2018-01-25 株式会社ミマキエンジニアリング 立体物造形方法及び立体物造形装置

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WO2008028406A1 (fr) * 2006-08-22 2008-03-13 Peking University Founder Group Co., Ltd Procédé et système de lecture et de traitement d'images par suspension réticulaire de l'image à diffusion d'erreur
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US12001900B2 (en) 2019-10-11 2024-06-04 3M Innovative Properties Company Inkjet printing method and inkjet printing device

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