JP4229671B2 - Image recording device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an image recording apparatus provided with recording head means having a plurality of recording elements capable of multi-value recording.
[0002]
[Prior art]
  Conventionally, many image recording apparatuses such as printers and facsimiles employ a recording head such as a thermal head or an inkjet head having a plurality of recording elements. When the recording width is wide, if a recording head having a length longer than the recording width is used, recording with the wide recording width is possible. However, such a recording head with a wide recording width is generally a good product at the time of manufacture. Since the yield is poor, there is a problem that the cost increases.
[0003]
  Therefore, it has been proposed to perform recording with a wide recording width by using a large number of recording heads with a short recording width that are relatively inexpensive to manufacture. For example, in Japanese Patent Laid-Open No. 2000-79707 (Prior Art 1), short recording heads capable of recording a plurality of multi-value image data are arranged adjacent to each other so as to partially overlap, and pixels in the overlapping region are arranged adjacent to this. A recording method for joint printing with two recording elements corresponding to the head is disclosed. In this case, in order to maintain the continuity of the recorded image in the overlapping area, when recording by one adjacent recording head, the input signal of each pixel is multiplied by a coefficient that gradually decreases from the beginning to the end of the overlapping area. The image recording is performed, and at the time of recording by the other adjacent recording head, the image signal is recorded by multiplying the input signal of the pixel by a coefficient that gradually increases from the beginning to the end of the overlapping area.
[0004]
  Japanese Laid-Open Patent Publication No. 2002-144542 (Prior Art 2) discloses white streaks and blacks that occur due to misalignment of recording elements in overlapping regions of adjacent heads when a plurality of recording heads are arranged to increase the recording width. In order to eliminate the streaks, an image recording apparatus is disclosed in which the recording elements used for recording the overlapping region are selected according to the arrangement pitch of the elements of the recording head and the interval between the adjacent recording elements of the adjacent recording head, and image recording is performed. ing.
[0005]
[Problems to be solved by the invention]
  However, in the conventional technique 1 described above, it is necessary to accurately align the positions of the adjacent recording elements of the adjacent recording heads in the overlapping region, which is difficult to manufacture and increases the cost. Even if the recording elements can be accurately aligned, the pixels in the overlapping area are printed jointly by the two corresponding recording elements of the adjacent recording heads, so that the input multivalued image data is printed by one recording element. The print density at this time is not necessarily the same as the density when printing is distributed to the two recording elements, so even if the density of the overlap area and other areas can be prevented from changing suddenly, The uneven density of the area cannot be eliminated.
[0006]
  Furthermore, when the alignment of the recording elements is not accurate, or when the position of the combined recording elements is shifted due to changes over time, the position of the recording elements is shifted at the portion where the print areas of the adjacent recording heads overlap, thereby causing a joint. No solution is disclosed for the problem that the density of the portion changes and the density becomes uneven.
[0007]
  Further, in the above-described prior art 2, when there is a shift in the position of the adjacent recording element of the adjacent recording head, the black and white stripes are not noticeable by selecting the recording element used for recording the pixels in the overlapping area. Even if it can be done, it is not possible to eliminate non-uniformity in the density of the overlapping region. Further, even if the density non-uniformity can be eliminated, the density may be high or low depending on the location of the printed dots, so that the printed image becomes dense in the overlapping area. As a result, a difference in dot pattern occurs between the overlapping region and the other region, resulting in degradation of image quality.
[0008]
  The present invention has been made paying attention to such a problem, and the object thereof is to perform accurate alignment of a recording head having a plurality of recording elements capable of multi-value recording, and An image recording apparatus capable of obtaining a high-quality image even when the position of the recording element of the recording head changes due to a change with time is provided.
[0009]
  Another object of the present invention is to provide an image recording apparatus capable of obtaining optimum correction data corresponding to a case where the recording head is not accurately aligned or a change in the position of the recording element due to a change with time. There is to do.
[0010]
[Means for Solving the Problems]
  In order to achieve the above object, an image recording apparatus according to the first aspect of the present invention includes a plurality of recording heads that are capable of multi-value recording and have a row of recording elements arranged linearly. A plurality of input image signals corresponding to predetermined pixels in the overlapping portion, and a line-type recording head in which the recording element arrays are arranged in the arrangement direction of the recording elements. An image signal distribution unit that divides the input image signal into each of the adjacent recording elements of the plurality of recording heads, and performs recording of a predetermined pixel in an overlapping portion of the plurality of recording heads, and the plurality of adjacent recording elements The input image signal before being input to the plurality of adjacent recording elements is converted into the plurality of adjacent recording elements so that the density of the image corresponding to the predetermined pixel recorded by Anda image signal correcting means for correcting in accordance with the distance betweenIn the image recording apparatus, the image signal correction unit corrects the input image signal before being divided by the image signal distribution unit..
[0011]
  Also,The image recording apparatus according to the second aspect of the present invention is the first aspect of the present invention.In the image recording apparatus according toThe image signal correcting unit selects, from the correction coefficient storage unit, a correction coefficient storage unit in which a plurality of different correction coefficients are stored in advance and a correction coefficient corresponding to the distance between the plurality of adjacent recording elements. The input image signal is corrected based on a selection unit and a correction coefficient selected by the selection unit..
[0015]
DETAILED DESCRIPTION OF THE INVENTION
  First, a technique that is a premise for describing the embodiment of the present invention will be described as a reference example.
(FirstReference example)
  FIG. 1 shows the first of the present invention.Reference example2 is a diagram showing a configuration of a line type recording head (hereinafter referred to as a line head) 1 of a high-speed printer. FIG. 1 shows a configuration in which the line type recording head 1 is composed of two short recording heads for the sake of simplicity. In the following description, the term “recording” will be described as equivalent to “printing”. The short recording head 11 has nozzles as a plurality of recording elements, and the short recording head 12 similarly has nozzles as a plurality of recording elements. These two recording heads 11 and 12 are arranged in the nozzle arrangement direction ( They are arranged adjacent to each other in a partially overlapping manner when viewed from the paper feed direction (second direction) which is a direction orthogonal to the first direction. Details of the arrangement of the recording heads 11 and 12 will be described later. As described above, since the recording width is increased by arranging the two short heads 11 and 12 so as to overlap each other, the width is wider than that when printing is performed using the single short head 11 or 12. Printing can be realized.
[0016]
  When printing, the line head 1 is controlled to carry out printing while conveying the recording paper in the second direction (paper feeding direction).
[0017]
  Note that the nozzles of the recording head 11 and the recording head 12 described above are capable of multi-value image recording. Ie bookReference exampleThen, ink droplets from 1 drop to 7 drops can be ejected from each nozzle. Therefore, gradations from 0 to 8 can be expressed. Here, the drop represents a unit amount of the ejected ink.
[0018]
  The image data to be printed is subjected to various types of image processing, and an 8-value input image signal is supplied to the nozzle as a control signal to be printed. Although only a single line head 1 is shown here, color printing can be performed by arranging a plurality of similar line heads in the second direction and printing different colors for each line head. In addition, the number of overlapping nozzles, that is, the width of the overlapping region is appropriately set as necessary.
[0019]
  FIG. 2 is an enlarged view of the portion of the line head 1 shown in FIG. As shown in FIG. 2, the recording head 11 has nozzles 11-1 to 11-8, and the recording head 12 has nozzles 12-1 to 12-8. The recording heads 11 and 12 are partially overlapped when viewed from the direction orthogonal to the nozzle arrangement direction. In this case, the nozzles 11-5 to 11-8 of the recording head 11 and the nozzles 12-1 to 12-4 of the recording head 12 are arranged in an overlapping manner. Therefore, the nozzle 11-5 and the nozzle 12-1, the nozzle 11-6 and the nozzle 12-2, the nozzle 11-7 and the nozzle 12-3, and the nozzle 11-8 and the nozzle 12-4 are arranged adjacent to each other. The nozzles are precisely aligned.
[0020]
  In order to perform printing using the line head having such an arrangement, the technique disclosed in the above-described prior art 1 can be used. For example, when the image data of gradation 7 is input to the line head 1, the image on the left side of the overlapping portion is subjected to 7-drop printing using the nozzles 11-1 to 11-4 of the recording head 11 and the overlapping portion. For the image on the right side, 7-drop printing is performed using the nozzles 12-5 to 12-8 of the recording head 12. And about an overlapping area, while making nozzles 11-5, 11-6, 11-7, and 11-8 perform 5, 4, 3, and 2 drop printing, respectively, nozzles 12-1, 12-2, and 12 are used. -3, 12-4 perform 2, 3, 4, 5 drop printing, respectively, so that the total print drop of adjacent nozzles is the same as the input image gradation.
[0021]
  However, it is actually difficult to accurately arrange the positions of adjacent nozzles as shown in FIG. 2, and increasing the alignment accuracy leads to an increase in manufacturing cost. Even if accurate positioning is performed at the time of shipment of the product, there is a possibility that the position of the nozzle may be shifted due to a change with time.
[0022]
  3 shows an adjacent nozzle 11-5 of the recording head 11 and an adjacent nozzle 12-1 of the recording head 12, an adjacent nozzle 11-6 and an adjacent nozzle 12-2, an adjacent nozzle 11-7 and an adjacent nozzle 12-3, and an adjacent nozzle. It is a figure which shows the state which 11-8 and the position of the adjacent nozzle 12-4 have each shifted | deviated by (delta). In such a state, even if one pixel is jointly printed using the adjacent nozzles 11-5 to 11-8 and 12-1 to 12-4, the print density of the joint print pixel is increased due to the shift δ. Or thin.
[0023]
  FIG. 4 illustrates the present invention for solving the above-described problems.First reference example1 is a diagram illustrating a configuration of an image recording apparatus according to FIG. When the image signal is input to the joint print control unit 100, the joint print control unit 100 determines whether the input pixel is in the overlap region from the address signal of the input image signal (not shown) and the address data of the overlap region. . When it is determined that the input image signal is an input image signal to a pixel that is not an overlapping region, the input image signal is directly sent to the recording heads 11 and 12 as an input image signal to a pixel that is not jointly printed, and is output from the nozzle to the recording paper 2. Then, a predetermined drop of ink is ejected.
[0024]
  If it is determined that the input image signal is a pixel belonging to the overlapping area, the input image signal is input to the image signal correction unit 101 as an input image signal to the pixels to be jointly printed and stored in the correction coefficient storage. Correction is performed by selecting a correction coefficient stored in the means 102 such that the density of the image corresponding to the pixel becomes a predetermined density from a plurality of different correction coefficients. Details of the correction will be described later.
[0025]
  The corrected image signal is input to the image signal distribution unit 103. The image signal distribution unit 103 divides the corrected image signal at a predetermined ratio, and distributes the divided image signals to the adjacent nozzles of the adjacent recording heads 11 and 12 for joint printing. Drop ink corresponding to the distributed signal is ejected from each of the adjacent nozzles onto the recording paper 2.
[0026]
  FIG. 5A is a diagram illustrating an example in which all the pixels in the overlapping area are jointly printed by the adjacent nozzles of the recording head 11 and the recording head 12. In FIG. 5A, hatched portions as shown in FIG. 5B are pixels printed only by the nozzles of the recording head 11, and among FIG. 5A, FIG. The hatched portions as shown in () are pixels printed only by the nozzles of the recording head 12. Further, hatched portions as shown in FIG. 5D are pixels on which the nozzles of the recording head 11 and the nozzles of the recording head 12 print jointly, and the image signal input to this pixel is adjacent to two adjacent pixels. Distributed to the nozzle. For example, the distribution ratio may be 50%. Statistically, as long as the distribution ratio of the two adjacent heads to the adjacent nozzles is 50%, the individual joint print nozzles may be distributed randomly. For example, if the input image signal to the joint print pixel is 6 drops, it is distributed to 3 drops and 3 drops for each nozzle.
[0027]
  FIG. 6A is a diagram illustrating an example in which only one pixel is jointly printed by adjacent nozzles of the recording head 11 and the recording head 12 in one row of the overlapping region. In FIG. 6A, the hatched portions as shown in FIG. 6B are pixels printed only by the nozzles of the recording head 11, and FIG. The hatched portions as shown in () are pixels printed only by the nozzles of the recording head 12. Further, hatched portions as shown in FIG. 6D are pixels on which the nozzles of the recording head 11 and the nozzles of the recording head 12 jointly print, and image signals input to this pixel are adjacent to each other. Distributed to the nozzle. Here, as shown in FIG. 6, only one pixel indicated by A to H is jointly printed in each row. Pixels to the left of the pixels to be jointly printed are printed by the nozzles of the left recording head 11, and pixels to the right of the pixels to be jointly printed are printed by the nozzles of the right recording head 12.
[0028]
  Note that the position of the pixels to be jointly printed may be a predetermined position or may be randomly determined in the overlapping area. BookReference exampleIn the overlap region of 4 pixels, pixels to be jointly printed at random are determined.
[0029]
  FIG. 7 is a diagram for explaining the relationship between input pixels and nozzles. The recording head 11 includes a plurality of nozzles 11-1 to 11-8, and the recording head 12 includes a plurality of nozzles 12-1 to 12-8. The nozzles 11-5 to 11-8 of the recording head 11 and the portions corresponding to the nozzles 12-1 to 12-4 of the recording head 12 are arranged overlappingly, and the nozzle 11-5 is the nozzle 12-1. The nozzle 11-6 is adjacent to the nozzle 12-2, the nozzle 11-7 is adjacent to the nozzle 12-3, and the nozzle 11-8 is adjacent to the nozzle 12-4. Overlapping parts are pixels that are jointly printed.
[0030]
  It is determined whether the image signals input to the recording heads 11 and 12 belong to the pixels to be jointly printed. If the image signals do not belong to the pixels to be jointly printed, the input image signals are directly sent to the corresponding nozzles. Let them enter. On the other hand, when the input image signal belongs to a pixel to be jointly printed, the input image signal is corrected to a new input image signal, and then is applied to the nozzles corresponding to the recording heads 11 and 12 at a predetermined ratio. Distributed and input.
[0031]
  FIG. 7 shows that among the input image signals 200 to 211 having the pixel value s, the input image signal 206 is corrected to an input image signal having a new pixel value s ′ and then distributed to a and b, respectively. 7 and 12-3 are shown.
[0032]
  In the distribution, the distribution ratio may be determined with reference to a lookup table (LUT) created in advance.
[0033]
  8A and 8B are diagrams for explaining an example of a method for calculating the pixel value S of the target pixel. In general, the density of a pixel of interest is determined not only by the ink area of that pixel, but also by the relationship with pixels around the pixel of interest. Therefore, here, as shown in FIG. 8A, when there is an input image signal to the target pixel to be jointly printed, the pixel value s and the pixels of the 3 × 3 block pixels around the target pixel The weighted average of the values s1 to s8 is taken, and the obtained value is set as a new pixel value S. The coefficient for each pixel when obtaining the weighted average is as shown in FIG. Therefore, the new pixel value S is
  S = (1/36) × s1 +,..., + (6/9) × s +,..., + (1/36) × s8. Then, signal correction is performed on the newly calculated pixel value S to obtain S ′.
[0034]
  FIG. 9 is a diagram illustrating a configuration example that realizes correction of an input image signal to a joint print pixel. BookReference exampleThis image recording apparatus can perform multi-value printing of 1 to 7 drops. Therefore, the input pixel value s of the pixels to be jointly printed takes a value in the range of 0 ≦ s ≦ 7. The correction coefficient storage unit 102 stores correction coefficients k1 to k7 corresponding to 1 to 7 drop input image signals.
[0035]
  The adder 301 adds the quantization error err to the input image signal (pixel value s) of the pixels to be jointly printed, and outputs a new pixel value S = s + err. The quantization error err here is a quantization error after correction of the previous joint print pixel. The initial value of err is 0.0. Based on the interpolation of S and k1... K7, the correction coefficient selection unit 303 uses K = F (S, k1, k2,..., K7) (where F is a linear interpolation or spline interpolation function), A correction coefficient K corresponding to S = s + err is selected from the correction coefficient storage means 102.
[0036]
  In the multiplier 302, the pixel value S is multiplied by the correction coefficient K, and the corrected pixel value S ′ = (s + err) × K is input to the image signal distribution unit 103. The image signal distribution unit 103 rounds S ′ to an integer (ie, [S ′]), and then distributes it to A and B. Here, A = [S ′] / 2 and B = [S ′] − A. Of course, any combination of integer values satisfying A + B = [S ′] and 0 ≦ A ≦ 7 and 0 ≦ B ≦ 7 may be adopted.
[0037]
  On the other hand, the quantization error calculation unit 304 calculates a quantization error err = S ′ − (A + B) based on S ′, A, and B, and inputs the calculation error to the addition unit 301. This is used when the next input pixel value is corrected.
[0038]
  The above processing is performed for all the joint print pixels in the overlapping area.
[0039]
  FIG. 10 is a diagram showing a modification of the configuration shown in FIG. It is a figure which shows the modification of the structure for correct | amending the input image signal to the pixel by which joint printing is carried out. Here, the correction coefficient selection unit 303 ′ simply applies the correction coefficient K multiplied by the input pixel value S = s + err output from the addition unit 301 to K = ks (1), not by linear interpolation of k1. ≦ s ≦ 7). Since the operation of other parts is as described with reference to FIG. 9, the description thereof is omitted here.
[0040]
  FIG. 11 is a diagram showing a modification of the configuration shown in FIG. As explained in FIG.Reference exampleIn this example, the quantization error err is added to the input pixel value S before the input pixel value S is corrected. Here, the quantization error err is added to the pixel value S after the input pixel value S is corrected. It was made to do. The image signal distribution unit 103 distributes an integer obtained by rounding off [S ′ + err], that is, a value S ′ + err obtained by adding the quantization error err to the corrected input image signal S ′ to A and B.
[0041]
(SecondReference example)
  FIG. 12 shows the second of the present invention.Reference exampleIt is a figure for demonstrating the outline of this. As shown in FIG. 12, the two recording heads 11 and 12 are partially overlapped when viewed from the paper feed direction (second direction) which is a direction orthogonal to the nozzle arrangement direction (first direction). Has been. Further, a CCD sensor 110 for reading an image recorded by the recording heads 11 and 12 is disposed immediately after the line head 1.
[0042]
  BookReference exampleThen, a predetermined input image signal is supplied to the recording heads 11 and 12 of the line head 1 to record a test chart, and the recorded test chart 111 is read by the CCD sensor 110. Based on the read image, the density distribution of the overlapping area 111a of the test chart is calculated. Details will be described later.
[0043]
  FIG. 13 is a diagram illustrating a configuration for determining an optimum correction coefficient using a test chart. First, the test chart data generated by the test chart generating means 120 is the firstReference exampleAre input to the joint printing control means 100 of the image recording apparatus described in the above. The joint printing control unit 100 determines whether or not the input pixel is in the overlapping area from the address signal of the input image signal (not shown) and the address data of the overlapping area. When it is determined that the input image signal is an input image signal of a pixel that is not an overlapping region, the input image signal is directly sent to the recording heads 11 and 12 as an input image signal to a pixel that is not jointly printed, and from the nozzle to the recording paper 2 A predetermined drop of ink is ejected.
[0044]
  If it is determined that the input image signal is a pixel belonging to the overlapping area, the input image signal is input to the image signal correction unit 101 as an input image signal to the pixels to be jointly printed and stored in the correction coefficient storage. Correction is performed by selecting a correction coefficient stored in the means 102 such that the density of the image corresponding to the pixel becomes a predetermined density from a plurality of different correction coefficients.
[0045]
  The corrected image signal is input to the image signal distribution unit 103. The image signal distribution unit 103 divides the corrected image signal at a predetermined ratio, and distributes the divided image signals to the adjacent nozzles of the adjacent recording heads 11 and 12 for joint printing. Drop ink corresponding to the distributed signal is ejected from each of the adjacent nozzles onto the recording paper 2.
[0046]
  Next, the recorded portion of the recording paper 2 is read by the CCD sensor 110, and the density distribution of the overlapping region is obtained. Next, the determination unit 121 compares the obtained density distribution of the overlapping region with a predetermined density distribution to determine whether or not the predetermined density distribution substantially matches, and if not, determines the next candidate. The input image signal is corrected using the correction coefficient, and recording is performed on the recording paper 2 by the method described above. Then, the recorded portion is read by the CCD sensor 110, and the determination unit 121 determines again whether or not the density distribution of the overlapping portion substantially matches the above-described predetermined density distribution. In this way, the correction coefficient when the density distribution substantially matching the predetermined density distribution is obtained is stored as the optimum correction coefficient.
[0047]
  FIG. 14 is a diagram for explaining the correction method described in FIG. 13 using a specific example. BookReference exampleThe line head 1 in the image recording apparatus can eject ink droplets of 0 to 7 drops, so that 8-level multi-gradation recording is possible. However, an optimum correction coefficient corresponding to the number of drops must be obtained. Accordingly, in order to obtain the optimum correction coefficient corresponding to the number of drops, a test chart as shown in FIG. 14 was created.
[0048]
  FIG. 14 shows a printed image formed by ejecting a predetermined number of drops of ink, and the input image signal of the overlapping area in each block is corrected using a plurality of different correction coefficients as candidates and printed. Test charts 111-1 to 111-6 are shown. For example, in block 1, the correction coefficient k = 1.6 is used. However, in the test chart 111-1 formed in this case, it can be seen that the print density in the overlapping region is too high and the joint is conspicuous. On the contrary, the correction coefficient k = 0.6 is used in the block 6, but in the test chart 111-6 formed in this case, the print density is too low and the joints are conspicuous as well.
[0049]
  On the other hand, the correction coefficient k = 1.2 or k = 1.0 is used in the block 3 or 4, but the joint is almost conspicuous in the overlapping area of the test charts 111-3 and 111-4 formed in this case. Therefore, it can be determined that there is an optimum correction coefficient.
[0050]
  The test chart image of each block is read by the CCD sensor 110 and integrated in the paper feed direction, thereby obtaining a density distribution in the head joint direction of each block.
[0051]
  FIG. 15 is a graph obtained by integrating the read signals obtained by reading with the CCD sensor 110 described above. The horizontal axis indicates the nozzle arrangement direction, and the vertical axis indicates the integrated value of the CCD read signal in the paper feed direction. As shown in FIG. 15, two threshold values 1 and 2 of a predetermined density are set in advance, and it is determined whether or not the density distribution falls within the range (allowable range) of the two threshold values 1 and 2. If it is within the range, the density of the overlapping region is almost the same as that outside the overlapping region, so that it is determined to be flat. In FIG. 15, since the density distributions of the block 3 and the block 4 are within the allowable range, one of the correction coefficients 1.0 and 1.2 is selected as the optimum correction coefficient.
[0052]
  BookReference exampleThen, all the test charts corrected using the six correction coefficients from 0.6 to 1.6 were printed, but the present invention is not limited to this. For example, by using a technique called a bisection method, it is possible to obtain an optimum correction coefficient with a smaller number of test charts. As an example, when it is known in advance that the target correction coefficient belongs between two correction coefficients, for example, the correction coefficient is as low as the higher (maximum) correction coefficient 2.0. If it is known that the correction coefficient is between 0.8 (minimum), the correction coefficient 1.4 intermediate between 0.8 and 2.0 is first corrected as a temporary optimal correction coefficient, Print a test chart to obtain the density distribution. In the case of the correction coefficient 1.4, the density distribution of the block 2 corresponds. However, as shown in FIG. 11, the density distribution of the block 2 does not fall within the allowable range, so that the optimum correction coefficient cannot be obtained. . Therefore, the next candidate is an intermediate value between 0.8 and 1.4, 1.1. Correction is performed using this value, a test chart is printed, a density distribution is obtained, and it is determined whether or not it is within the allowable range. This procedure is repeated until the concentration distribution falls within the allowable range. According to such a method, an optimum correction coefficient can be obtained with fewer test charts printed.
[0053]
  Note that whether or not the obtained density distribution is within a predetermined allowable range may be determined mechanically, but a human can easily determine visually by looking at a graph as shown in FIG.
[0054]
  FIG. 16 is a flowchart for explaining the procedure for detecting the optimum correction coefficient by the bisection method. First, the maximum correction coefficient that can be a candidate is Kmax, the minimum correction coefficient is Kmin, and the optimum correction coefficient is K = (Kmax + Kmin) / 2 (step S1). Next, test chart data is generated by the test chart generating means 120 and input to the joint printing control means 100. In the joint printing control means 100, an input image signal to the pixels to be jointly printed is selected and input to the image signal correction means 101. The image signal correcting unit 101 corrects the input image signal to the pixels to be jointly printed with the correction coefficient K. Next, the corrected input image signal is distributed at a predetermined ratio by the image signal distribution means 103 and printed on the recording paper 2 by the recording heads 11 and 12 (step S2).
[0055]
  Next, the printed test chart is read by the CCD sensor 110, and the density distribution in the nozzle array direction is calculated from the read image (step S3). Next, the calculated density distribution is compared with a predetermined threshold (thresholds 1 and 2 in FIG. 15), and the calculated density distribution is within an allowable range of the predetermined threshold (a range between the thresholds 1 and 2 in FIG. 15). (NO in step S4), if NO, it is determined whether the density of the overlapping region is lower than the lower limit of the threshold (step S5). In the case of NO, K is set as the maximum correction coefficient Kmax, the same Kmin is set as the minimum correction coefficient Kmin (step S6), and then the process returns to step S1 and the above processing is repeated. If the determination in step S5 is YES, the same Kmax is set as the maximum correction coefficient Kmax, K is set as the minimum correction coefficient Kmin (step S7), and then the process returns to step S1 and the above processing is repeated.
[0056]
  The density distribution is calculated by performing printing while changing the correction coefficient K in the above process, and when it is determined in step S4 that the calculated density distribution is within the allowable range of the threshold value, K is the optimum correction coefficient. (Step S8), and the process ends.
[0057]
(FirstEmbodiment)
  FIG.As explained in the first and second reference examplesAbout the timing of image recording device correctionFirst embodimentIt is a figure for demonstrating. AboveReference exampleThen, after the input image signal to the pixels to be jointly printed is corrected by the image signal correction unit 101, the image signal distribution unit 103 distributes the corrected input image signal and supplies it to the recording head 11 and the recording head 12. ButIn the first embodimentAs shown in FIG. 17, first, the image signal distribution means 103 first distributes the input image signal to the pixels to be jointly printed, and the distributed input image signal is converted into the image signal correction means 101-1 and 101-, respectively. 2 to be corrected and sent to the recording heads 11 and 12Do.
[0058]
(Second Embodiment)
  FIG.As explained in the first and second reference examplesAbout selection method of correction coefficient of image recording deviceSecond embodimentIt is a figure for demonstrating. Although the correction coefficients k1 to k7 vary depending on the distance between adjacent nozzles, the distance measured in advance and the correction coefficient are stored in a lookup table (LUT), and the distance between adjacent nozzles of the image recording apparatus that is actually used. The correction coefficients k1 to k7 are selected according to the above. This will be described in detail below.
[0059]
  Here, the distance between adjacent nozzles is defined as δ. When δ changes, the print density of the joint print pixel changes. In the present invention, since the nozzle position is not adjusted, it is not possible to know the value of the distance δ between adjacent nozzles in a certain state. So above mentionedReference exampleAt that time, the optimum correction coefficient was obtained.
[0060]
  However, if an appropriate correction coefficient is set for each number of δ obtained by measurement in advance in the lookup table (LUT) in the form shown in FIG. Even when δ changes due to fluctuations, the correction coefficient closest to δ measured can be immediately extracted from the LUT simply by measuring δ at that time. According to such a method, the series of processing described with reference to FIG. 16 is not required, and the time for detecting the optimum correction coefficient can be greatly shortened.
[0061]
  Further, it is necessary to change the correction coefficient depending on the type of recording paper and ink used. When these conditions are also taken into consideration, the type of recording paper and the type of ink are further added to the LUT items in FIG. 18 and the corresponding correction coefficients are stored, so that when the apparatus is actually used. A correction coefficient can be selected and used according to various conditions.
[0062]
(Third embodiment)
  FIG.First and second reference examplesThe configuration of the image recording deviceThird embodimentIt is a figure for demonstrating. The present invention has been described above.First and second reference examplesThe recording head is not limited to a line head in which a plurality of recording heads are partially overlapped and connected, and image recording is performed by repeating main scanning and sub-scanning using one recording head. The present invention can also be applied to a so-called serial scan type recording apparatus. That is, as shown in FIG. 19, first, the first printing corresponding to the head width is performed in the main scanning of the recording head 20, and the second printing partially overlapped with the first printing in the sub-scanning of the recording head 20. By performing the printing with the same recording width, it is possible to perform the printing with the recording width expanded while partially providing an overlapping area. Therefore, the aboveFirst and second reference examplesIt can be seen that the various methods described in the above can be applied to a serial scan type recording apparatus. Furthermore, it goes without saying that the present invention can be applied to a multi-scan type recording apparatus in which one pixel is formed by a plurality of scans.
[0063]
【The invention's effect】
  According to the present invention, even when accurate positioning of a recording head having a plurality of recording elements capable of multi-value recording is not performed, and even when the position of the recording element of the recording head changes due to aging, Thus, it becomes possible to obtain a high-quality image.
[0064]
  Further, it is possible to obtain optimum correction data corresponding to a case where the print head is not accurately aligned or a change in the position of the print element due to a change with time.
[Brief description of the drawings]
FIG. 1 shows the first of the present invention.Reference example2 is a diagram showing a configuration of a line type recording head (hereinafter referred to as a line head) 1 of a high-speed printer.
FIG. 2 is an enlarged view showing a portion of the line head 1 of FIG.
FIG. 3 is a diagram illustrating a state where the positions of the adjacent nozzles of the recording head 11 and the adjacent nozzles of the recording head 12 are shifted by δ.
FIG. 4 of the present inventionFirst reference example1 is a diagram illustrating a configuration of an image recording apparatus according to FIG.
FIG. 5 is a diagram illustrating an example in which all pixels in an overlapping region are jointly printed by adjacent nozzles of the recording head 11 and the recording head 12;
6 is a diagram illustrating an example in which only one pixel is jointly printed by adjacent nozzles of the recording head 11 and the recording head 12 in one row of the overlapping region. FIG.
FIG. 7 is a diagram for explaining a relationship between an input pixel and a nozzle.
FIG. 8 is a diagram for explaining an example of a method of calculating a pixel value of a target pixel.
FIG. 9 is a diagram illustrating a configuration example that realizes correction of an input image signal to a joint print pixel.
10 is a diagram showing a modification of the configuration shown in FIG.
11 is a diagram showing a modification of the configuration shown in FIG.
FIG. 12 shows the second of the present invention.Reference exampleIt is a figure for demonstrating the outline of this.
FIG. 13 is a diagram showing a configuration for determining an optimum correction coefficient using a test chart.
FIG. 14 is a diagram for describing the correction method described in FIG. 13 using a specific example;
15 is a graph obtained by integrating reading signals obtained by reading by the CCD sensor 110. FIG.
FIG. 16 is a flowchart for explaining a procedure for detecting an optimum correction coefficient by a bisection method.
FIG. 17 shows first and second.Reference exampleThe timing of image recording device correctionFirst embodimentIt is a figure for demonstrating.
FIG. 18 shows first and second.Reference exampleThe correction coefficient selection method of the image recording deviceSecond embodimentIt is a figure for demonstrating.
FIG. 19 shows first and second.Reference exampleThe configuration of the image recording deviceThird embodimentIt is a figure for demonstrating.
[Explanation of symbols]
1 Line type recording head (line head)
2 Recording paper
11 Recording head
11-1 to 11-8 nozzle
12 Recording head
12-1 to 12-8 nozzle
100 Joint printing control means
101 Image signal correction means
102 Correction coefficient storage means
103 Image signal distribution means

Claims (2)

Overlapping portion having a plurality of recording heads capable of multi-value recording having a row of recording elements arranged in a straight line, and the plurality of recording heads overlapping each other along the arrangement direction of the recording elements A line type recording head formed by arranging
An input image signal corresponding to a predetermined pixel in the overlapping portion is divided into a plurality of input image signals, and distributed to each adjacent recording element of the plurality of recording heads that performs recording of the predetermined pixel in the overlapping portion of the plurality of recording heads. Image signal distribution means for
An input image signal before being input to the plurality of adjacent recording elements is input to the plurality of adjacent recording elements so that the density of an image corresponding to the predetermined pixel recorded by the plurality of adjacent recording elements is a predetermined density. Image signal correcting means for correcting according to the distance between the recording elements;
In an image recording apparatus comprising :
The image recording apparatus, wherein the image signal correcting unit corrects an input image signal before being divided by the image signal distributing unit . The image signal correcting means includes
A correction coefficient storage unit in which a plurality of different correction coefficients are stored in advance;
A selection unit that selects a correction coefficient from the correction coefficient storage unit according to a distance between the plurality of adjacent recording elements;
The image recording apparatus according to claim 1, wherein the input image signal is corrected based on a correction coefficient selected by the selection unit.

Images