JPH0983798A - Image recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable recording of high quality with superior gradations by thresholding and setting recording density with matrix patterns prepared by the density values of recording materials, and combining the binary and set density values of selected recording materials and reproducing the gradations of an image. SOLUTION: In a distribution table 12, input image data stored in an image memory 11 are sorted by referring to the density at the time of recording. Matrix generating circuits 13A-13C form matrixes of the input image data sorted by the distribution table 12. Thresholding circuits 14A-14C process the input image data according to the matrixes formed by the matrix generating circuits 13A-13C. After the data are distributed by those circuits, image data by distribution destinations are threshold processed according to the matrixes and recording heads of colors corresponding to ink by density are driven to perform gradational recording without a skip and connection stripes according to their combination.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording method, and more particularly to an image recording method for performing gradation recording by using at least two kinds of ink having different densities for similar colors.

[0002]

2. Description of the Related Art As a device for recording an image input from an image scanner or the like according to its gradation, a device such as an inkjet, electrophotographic, silver halide photograph, or printing machine has been put into practical use. Several methods have been proposed as a method of reproducing the gray scale in.

For example, a dither method in which one pixel of an input image is made to correspond to one recording dot of binary recording, and the shade of the input image is divided into a plurality of recording dots (for example, m ×
The density pattern method of recording in correspondence with the (n matrix) is known.

The threshold matrix used in these methods is a dot concentration type in which the center is the nucleus and the recording dots are successively thickened according to the gradation, and the spatial frequency corresponding to the density of the recording dots is as high as possible. There is known a dot-dispersion type in which the above-mentioned dispersion is performed.

On the other hand, a color image is recorded by superimposing inks and toners of respective colors (generally yellow, magenta, cyan and black), and moire fringes of colors that may occur at this time. Has been performed, and a method of providing screen angles with different angles for each color has been performed in order to obtain the color uniformity by randomly making the overlapping state of the recording dots due to the color overlapping.

By the way, the above-described gradation reproduction method enables excellent gradation recording when the resolution of the recording apparatus is sufficiently high (about 1000 dots / inch or more). However, when the resolution of the recording device is low (about 360 to 720 dots / inch), the recorded dots in the highlight portion are conspicuous, and the discontinuity of the pixels easily causes the image to be rough.

Therefore, in order to further increase the number of gradations, a method of making the recording dots themselves multi-valued is performed.

For example, a method is known in which the diameter of a recording dot attached to a recording material is changed to obtain gradation by controlling the voltage or pulse width applied to the recording head. However, this method is limited in that the diameter of the recording dots is not stable and the size of the smallest recordable dot that can be recorded.

Therefore, in order to improve the gradation characteristics, a recording method has been proposed in which a plurality of inks having different densities are used and the gradation is reproduced by at least two kinds of recording dots having different densities for the same color.

[0010]

However, when the data of the grayscale image is divided into a plurality of density regions corresponding to a plurality of inks having different densities as described above and binarized by a plurality of threshold matrixes, respectively. In some cases, the gradation loses smoothness at the boundary of each of the divided density regions (hereinafter referred to as “gradation jump”), and pseudo contours are generated, which deteriorates the image quality.

Furthermore, when a recording material is scanned by using a head in which a plurality of ejection ports are arranged and recording is performed in units of a plurality of lines, uneven sheet feeding of the recording material and manufacturing of a multi-nozzle head are performed. Streak-like noise (hereinafter referred to as a "joint streak") is apt to occur in a plurality of line units due to unevenness in the line, and thus image quality is likely to be deteriorated.

The present invention aims to solve such a problem.

[0013]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention is directed to image recording in which pixels are formed on a recording material by a plurality of recording materials having different densities to reproduce the gradation of an image. In the halftone processing of the method, the density to be used is selected from the recording materials according to the gradation value for each pixel of the input image, and the recording density according to the selected recording material is further prepared for each density of the recording material. The selected recording material is binarized and set according to the matrix pattern
It is characterized in that the gradation of the image is reproduced by the combination of the densities set by the value setting.

That is, the image recording method according to the present invention is an ink jet recording method in which at least two different kinds of plural inks are ejected to reproduce gradation, and when recording with recording dots having different densities, the gradation of recording data is changed. According to each of the images distributed according to three or more, the pseudo-halftone processing is performed on each of the distributed images.
Select the threshold matrix corresponding to each, increase the number of recording dots according to the order of the threshold matrix corresponding to the increase of the density value, and prioritize from the non-recording dot part of the matrix prepared for the image whose density is one step lower. It will be filled up.

According to the image recording method of the present invention, the recording data for recording pixels by density is divided into, for example, three, and the threshold matrix corresponding to the recording material (ink) of each density is selected to obtain an input image. In the lowest density area, low density recording dots are recorded, and in the higher density area, low density recording dots and one-step higher middle density recording dots are recorded. Further, in a region of higher density, recording is performed with medium-density recording dots and high-density recording dots one step higher.

In the threshold matrix, the order of increase of the recording dots in the threshold matrix is set in correspondence with the increase of the density value, and the non-recording dot portion of the matrix for the image having the density one step lower is given priority. And set to fill.

For that purpose, in particular, two dots are used for recording dots of each density.
The coarseness of graininess due to the isolated dots when recording the binarized data is higher than that when the isolated dots with high density are directly recorded on the background color of the recording material. Is less likely to occur and can be eliminated.

Further, since the pixels of the recording areas are different in the pixels having different densities of one-step gradation, it is possible to avoid the dot overlap on the recording material. Contributes to the prevention of problems such as ink bleeding that cannot be absorbed by the recording material, and wrinkles and wrinkles on the recording material, even when multiple times are applied to the same location on the recording material. it can.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows the construction of an ink jet printer to which the present invention is applied. In this example, four types of color inks, namely, yellow (Y), magenta (M), cyan (C) and black ( For the four colors of K), it is possible to hold four types of ink having different densities, and it is possible to eject ink independently of each other for recording. That is, reference numeral 1 denotes a carriage, and the 16 recording heads 2 and the ink tanks 3 that are connected to these recording heads 2 and that supply inks of different colors and densities to the respective recording heads 2 are provided on the carriage 1. It is installed. Reference numeral 4 is a flexible wiring board for sending recording signals to each recording head 2, reference numeral 5 is a guide rail for guiding the carriage 1, reference numeral 6 is connected to the carriage 1, and timing for moving and scanning the carriage 1 along the guide rail 5 is provided. A belt, 7 is a motor for driving the timing belt 6.

Further, P is a recording material (hereinafter referred to as a recording sheet), which is held at a position facing each ink ejection port surface of the recording head 2 and ejects each ink during reciprocating scanning in the X direction by the carriage 1. Recording is performed with ink that is selectively ejected from an outlet (not shown) according to a recording signal. Thus, the sheet feeding is repeated in the Y direction by the conveying unit (not shown) every time the printing for one scanning is performed. In the case of this example, each recording head 2 has an ejection port array that is composed of 64 ink ejection ports and is arranged in the Y direction.
In the first embodiment described below, among the 16 recording heads 2, the first density ink (D1), the second density ink (D2), and the third density ink for the above four colors are arranged in ascending order.
Twelve inks having different densities of the density ink (D3) are ejected.

[First Embodiment] FIG. 2 shows the arrangement of an image processing circuit according to the first embodiment. Here, reference numeral 11 is an image memory for inputting image data (input image data) from the host device side, and 12 is referred to the density when the input image data stored in the image memory 11 is recorded. Sorting tables for sorting, 13A, 13B, 13C are matrixing circuits for matrixing the input image data sorted by the sorting table 12, 14A,
14B and 14C are matrixing circuits 13A, 13B and 1
It is a binarization circuit that binarizes input image data based on a matrix of 3C. Thus, in the case of this example, the above-described circuit sorts the image data as described in detail below, and the image data for each sorting is binarized based on the matrix, and the density-based inks D1 to D
By driving the recording heads 2 of the respective colors corresponding to No. 3 and combining them, it is possible to carry out gradation recording without jumps or connecting lines.

When sorting the input image data by the sorting table 12, as shown in FIG. 3, in the input image data of the original document, the brightest (high density) portion is 0, and the darkest (low density). The gradation is represented by an 8-bit digital value in which the part) is 255. Further, the distribution table 12 has different densities D1 and D.
The recording densities on the recording sheet P with the inks 2 and D3 were measured in advance, and LUT (based on a look-up table) correction was performed on the recording density. Furthermore,
In this embodiment, matrix forming circuits 13A, 13B, 13C
As the matrix used for
As shown in (C), 16 steps of 4 × 4 are displayed so that recorded dots can be obtained as an output image in the order of numbers according to the gradation of the input image data. However,
In these threshold matrices, when dots are recorded on the recording sheet P, the inks D1 and D1 having the same color but different densities are formed.
It goes without saying that it is desirable to set so that the ink of No. 2 or the inks of D2 and D3 do not overlap each other, and especially the isolated dots do not overlap.

FIG. 5 shows an example of formation of recording dots for each gradation value by binarized output image data through the circuit shown in FIG. 2 according to this embodiment. Here, a black square portion is a portion where recording dots are output, and a white square portion is a portion where recording dots are not output. In FIG. 5, (A) is assigned for recording a pixel having a gradation of 121 or more in the input image data in the distribution table shown in FIG.
It is shown that the input image data up to 1 is printed by the combination of the ink having the density D1 and the ink having the density D2. Since the matrix has 16 stages, the output image data is also divided into 16 stages. Similarly, in FIG. 5B, the gradation of the input image data is 120 to 0 in the distribution table shown in FIG.
The recording is performed by the combination of the ink having the density of D2 and the ink having the density of D3.

What should be noted here is that the ink of the density D2 involved in the halftone process is continuous from (A) to (B) of FIG. 5 according to the matrix shown in (B) of FIG. is there. In this way, by providing continuity in the gradation of the recording dots with the ink having the density D2, it is possible to carry out the conventional gradation inconvenience, that is, smooth gradation recording in which the roughness of graininess is not noticeable.

[Second Embodiment] This embodiment is an example in which the inkjet print shown in FIG. 1 is fully used.
The first density ink D1, the second density ink D2, the third density ink D3, and the fourth density ink D4 are 16 in order from the lowest density with respect to the four color inks of Y, M, C, and K, respectively. The recording heads 2 are individually ejected. Therefore, in the case of this example, a distribution table as shown in FIG. 6 and four threshold matrixes as shown in FIG. 7 are prepared. In FIG. 6, the dotted line indicates recording with ink D1, the double-dotted line indicates recording with ink D2, the broken line indicates recording with ink D3, and the solid line indicates recording with ink D4. Further, in FIG. 7, (A), (B), (C), and (D) are threshold matrices prepared for the inks D1, D2, D3, and D4, and also in this case, the inks used simultaneously In, the numerical values of the respective threshold values are set so that the dots do not overlap each other.

Further, in the case of this example, as shown in FIG. 6, the ink used for forming the output image is divided into four stages according to the gradation value of the recorded image. With respect to the inks D2 and D3 relating to the above, the same effect as described in the first embodiment can be obtained by providing the gradation of the output image with continuity by combining with the matrix. Since the circuit configuration and the operation procedure of the halftone processing are the same as those described above, the description thereof will be omitted.

In the embodiment described above, the printer in which the recording dots are formed by ejecting and landing the liquid ink has been described. However, the ink is an ink which solidifies at room temperature or lower and softens at room temperature or You may use what is liquefied.

The present invention is not limited to ink jet recording but can be applied to recording methods such as a thermal transfer recording method and an electrophotographic method.

Further, in the above-mentioned embodiment, the distribution table was only briefly described, but regarding the density of the recording dots on the recording material at the time of recording,
Needless to say, the gradation value is controlled by adding a LUT correction after forming a matrix.

Furthermore, in the above embodiment, the systematic dither method is used as the pseudo halftone processing, but another method such as the density pattern method may be used. Also, the threshold matrix is shown as a 4 × 4 matrix for easy understanding, but it may be increased depending on the resolution of the printing apparatus used depending on the purpose of printing. Although the method has been described above, it goes without saying that other methods such as a dot concentration type may be used.

[0032]

As described above, according to the present invention, in the halftone processing, the density to be used is selected and selected from the recording materials according to the gradation value for each pixel of the input image. The recording density of the recording material is further binarized and set by a matrix pattern prepared for each density of the recording material, and the gradation of the image is obtained by a combination of the binarized densities of the selected recording material. Is reproduced, recording is performed with a recording material suitable for the density in the recording area of the input image, and the corresponding gradation is output by properly combining the recording materials used for the halftone processing. Since the image is obtained on the image, noise and graininess on the recorded image due to the isolation of pixels can be made inconspicuous, and high-quality recording with excellent gradation can be performed.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an inkjet printer to which the present invention is applied.

FIG. 2 is a block diagram showing a configuration of an image processing circuit according to the present invention.

FIG. 3 is an explanatory diagram of a distribution table according to the first embodiment of this invention.

FIG. 4 is an explanatory diagram showing a threshold matrix according to the first embodiment of the present invention as (A), (B), and (C) according to ink densities.

FIG. 5 is an explanatory diagram showing recording dots output according to the first embodiment of the present invention divided into (A) and (B) according to the gradation of input image data.

FIG. 6 is an explanatory diagram of a distribution table according to a second embodiment of the present invention.

FIG. 7 shows (A), (B), (C), (D) the threshold matrix according to the second embodiment of the present invention according to the density of ink.
FIG.

[Explanation of symbols]

 1 Carriage 2 Recording Head 3 Ink Tank 11 Image Memory 12 Sorting Table 13A, 13B, 13C Matrixing Circuit 14A, 14B, 14C Binarization Circuit P Recording Material (Recording Sheet) D1, D2, D3 Ink Density (or by Density) ink)

Front Page Continuation (72) Inventor Akihiro Mohri 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (4)

[Claims] 1. A gradation value for each pixel of an input image in a halftone process of an image recording method for reproducing a gradation of an image by forming pixels on a recording material with a plurality of recording materials having different densities. The density to be used is selected from among the recording materials according to the above, and the recording density of the selected recording material is further binarized and set by a matrix pattern prepared for each density of the recording material. The image recording method, wherein the gradation of the image is reproduced by a combination of the binarized and set densities of. 2. A matrix pattern prepared for each density of the recording material shows an order of binarization corresponding to an increase of the density value, and the order is the order shown in the matrix pattern of the lower density. The image recording method according to claim 1, wherein the image recording method is set so as not to overlap. 3. A plurality of recording materials having different densities for different colors, and pixels for each color can be formed on the recording material by the plurality of recording materials. Alternatively, the image recording method described in 2. 4. The recording material is ink, and the pixels are formed by ink dots by ejecting ink onto the recording material. Image recording method.