JP4996314B2 - Correction table determination method and image processing method - Google Patents

Description

  The present invention relates to an image processing method and an image processing apparatus, and more particularly to an image processing method and an image processing apparatus that perform calibration. The present invention can also be applied to a recording apparatus and a recording method for performing calibration.

  An ink jet recording apparatus is a non-impact printer, has low noise, and can be easily printed in color.

  A general ink jet recording apparatus ejects ink droplets onto a recording medium while a carriage carriage mounted with a recording head scans in a main scanning direction. When one main scan is completed, the recording medium is sent in a predetermined amount in the sub-scanning direction. By repeating the sub-scanning and main scanning, an image is formed on the recording medium.

  In such a recording apparatus, the width of the sub-scanning region is determined by the number of ejection ports of the recording head, the recording density, and the number of scans. In recent years, there are recording apparatuses that realize high-speed recording by reducing the number of scans as much as possible. In addition, there is a recording apparatus that increases the recording density in order to increase the density and number of ejection ports of the head to achieve high image quality. For example, the nozzle interval is 20 microns, and the number of discharge ports may exceed 1000 per row.

  In a recording apparatus that performs color recording, a plurality of recording heads having inks such as yellow, magenta, cyan, and black are provided, and a color image is formed by mixing these inks.

  By the way, if there are variations in the size of the ink droplets ejected from these recording heads, it may be impossible to perform high-quality recording. That is, an image with a larger color of ink droplets is stronger than a color of smaller ink droplets, and a good color balance may not be maintained.

  In addition, with higher image quality of printers, more accurate gray balance like monochrome photographs is required, and gray gradations are colored, or only certain gradations are colored, So-called color shift may occur. In order to eliminate the gray tone granularity in the low density range, recording is performed using a light-type low density ink.In the middle to high density range, recording is performed using dark ink. This is for recording in a high density region.

  The cause of this color shift is also the variation in the size of the ink droplets ejected from the recording head. Although the recording head is precisely manufactured, the size of the ink droplets varies about ± 10% of the size of the main droplets. At this time, the density difference due to the variation in the size of the ink droplets may occur up to about 7%. For this reason, when different recording heads are used, such as when the recording head is replaced, the color development tendency changes, and the whole may become bluish or reddish. In addition, good gray may not be reproduced.

  In order to correct these color balances, for example, Patent Document 1 discloses a method of creating a new density correction table when the recording head is replaced. For example, Patent Document 2 discloses a method of correcting the color balance by measuring the ejection characteristics of the recording head.

  However, the correction method disclosed in Patent Document 1 requires a measuring instrument such as a scanner. Further, in the correction method disclosed in Patent Document 2, when the number of ink colors increases, the number of patterns increases, so that adjustment by the user may be difficult.

Japanese Patent Publication No. 2004-50431 Japanese Patent Publication No. 2004-160970

  On the other hand, there is also a method that has a plurality of tables set in advance by a printer, records several types of calibration patches, selects the one that looks the most gray, and corrects the variation in ejection amount.

  However, in order to perform highly accurate correction by these correction methods, the number of patches becomes enormous. In addition, if the amount of change is reduced in order to perform highly accurate correction, the difference in color tone becomes small, and it may be difficult for the user to understand the change in color tone.

  The present invention has been made from such a viewpoint, and an object of the present invention is to provide an image processing method and an image processing apparatus that can perform high-precision output correction with a small number of patches.

Therefore, the present invention provides a correction table determination method for determining a correction table for use in a recording apparatus that records an image on a recording medium using a plurality of colors of ink, and includes a plurality of correction tables corresponding to one ink color. A plurality of combinations of patches corresponding to values obtained by correcting predetermined input values corresponding to the plurality of colors of ink using a combination of correction tables each including a correction table selected from one of the correction tables. A plurality of recording tables corresponding to each of the correction tables included in a combination corresponding to a patch selected from the plurality of patches among the plurality of types of combinations. And a determination step of determining as a correction table for correcting corresponding image data .

The present invention is also a correction table determination method for determining a correction table for use in a recording apparatus that records an image on a recording medium using a plurality of colors of ink, and a plurality of correction tables corresponding to one ink color. A plurality of combinations of patches corresponding to values obtained by correcting predetermined input values corresponding to the plurality of colors of ink using a combination of correction tables each including a correction table selected from one of the correction tables. A plurality of patches selected from the plurality of patches recorded in the first recording step and each of the plurality of patches recorded in the first recording step. A plurality of patches in a density range smaller than the density range, and the predetermined input value using a plurality of types of correction tables of the combinations A second recording step for recording a plurality of patches corresponding to each corrected value, and the correction included in a combination corresponding to a patch selected from the plurality of patches recorded in the second recording step A determination step of determining each table as a correction table for correcting image data corresponding to the plurality of colors of ink .

  According to the above configuration, a patch close to gray is selected from patches with different ink mixing ratios, and coarse adjustment is performed, and a patch close to gray from a patch with a gradation value at a finer interval around the selected patch. You can select and make fine adjustments.

  As a result, it is possible to provide an image processing method in which the number of patches is small and output correction can be performed with high accuracy.

  Next, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic diagram showing an outline of the ink jet recording apparatus of the present embodiment. Reference numeral 101 denotes a paper feed roller, 102 denotes a recording medium such as plain paper, 103 denotes a main scanning guide, 104 denotes a carriage, 105 denotes a recording bed, and 106 denotes a platen.

  The recording medium 102 is sandwiched between a pair of paper feed rollers 101. As the roller 101 rotates, the recording medium 102 is conveyed in the sub-scanning direction X. The platen 106 is provided below the recording head 105. The recording head 105 has an ejection port on the surface facing the platen 106. During recording (printing), the recording medium 102 is located between the platen 106 and the recording head 105. Further, the recording medium 102 is held by the platen 106 so that the interval between the recording medium 102 and the recording head 105 is appropriate.

  The recording head 105 is detachably attached to the carriage 104, and the carriage is moved along the main scanning guide 103 by carriage driving means (not shown) while scanning the recording medium in the Y direction (main scanning direction). Ink droplets are ejected. Note that the recording head 105 is supplied with ink from an ink supply device (not shown). By ejecting a plurality of colors of ink from the recording head 105, an image according to the image data can be recorded on the recording medium.

  In addition, this ink jet recording apparatus takes out a recording medium supply means for supplying the recording medium 102 to the paper feed roller 101, a recovery means for maintaining the state around the ejection port of the recording head 105 properly, and a recording medium 102 that has finished recording. A recording medium discharge means is provided.

  When a recording start command signal is input to the ink jet recording apparatus, the recording medium supply unit supplies the recording medium 102 until the leading end of the recording medium 102 reaches the position of the paper feed roller 101. Thereafter, according to the recording signal, the recording medium 102 is fed by the paper feed roller 101 so that the recording head 105 is positioned at the recording start position on the recording medium 102. Subsequently, recording is performed by ejecting ink droplets onto the recording medium 102 while the carriage and the recording head 105 perform main scanning. When the recording head 105 finishes one main scan, the paper feed roller 101 feeds the recording medium 102 by a predetermined amount in the sub-scanning direction. Then, the recording head 105 again ejects ink droplets onto the recording medium 102 while performing main scanning. After recording is performed on the recording medium 102 by repeating the sub-scanning and main scanning, the recording medium 102 is discharged.

  As a means for ejecting ink from the recording head 105 to the recording medium 102, a heating element (electrothermal conversion element) is provided in the vicinity of the ejection opening formed in the recording head 105, and an ink is applied by applying an electrical signal to the heating element. Is heated locally to generate bubbles. There is a method of ejecting ink by the pressure of the bubbles. In addition, there is a method of ejecting ink by pressure similarly using mechanical deformation using an electromechanical conversion element such as a piezoelectric element.

  Further, the recording apparatus stores a control unit (CPU) that controls the above-described carriage recording scan, recording medium conveyance operation, recording head drive, and the like, parameters, image data, and recording data necessary for each control. It has a memory. Furthermore, the recording apparatus includes an operation panel for setting various conditions for the recovery of the recording head, the type of the recording medium, and various maintenance by the user.

  FIG. 2 is a diagram showing a flow of image processing until recording data is generated from image data in the first embodiment of the present invention. When an image signal (image data) based on RGB signals is input to the host computer (201), the input RGB signals are converted into R'G'B 'signals in a conversion table for photographs or graphics according to the recording mode. (202). After that, it is converted into four colors C (cyan), M (magenta), Y (yellow), and K (black), which are the number of output colors of the printer (203). Next, an output correction table for each color of CMYK is selected (204). Then, it is converted into C'M'Y'K 'by the table selected for each color (205). The selection for each color is selected from an output correction table selected and set in advance as will be described later with reference to FIG. Thereafter, resolution conversion is performed on C "M" Y "K" (206), and binarization processing is performed (207). Ink is ejected from the recording head based on the recording data generated in this way, and an image according to the image data is recorded on the recording medium.

  Next, the description of the output correction table and the method of selecting the output correction table in 204 of FIG. 2 will be described.

  FIG. 3 is a table showing an output correction table prepared in advance in the present embodiment. FIG. 4 is a graph showing the relationship (γ characteristics) between the input and output of the output correction table shown in FIG. Note that the number of correction tables in the present embodiment is nine, but the number of tables in the present invention is not limited to this, and the number and type of tables are determined by variations in density, correction accuracy, and the like. May be. Similarly, the γ characteristics of the respective tables are not limited to the γ characteristics shown in FIG. This output correction table is stored in a storage means such as a memory (ROM, RAM) of the host computer or recording device.

  The calibration (color adjustment) of the present embodiment is performed by selecting one correction table from nine types of correction tables corresponding to the ejection amount. In this embodiment, in order to select one correction table from nine types of correction tables, the steps are divided into first-stage printhead calibration (coarse adjustment) and second-stage printhead calibration (fine adjustment). To do. In the first stage print head calibration, a table group is determined as to which correction table to use among the group 1, group 2 and group 3 among the tables shown in FIG. In the second stage print head calibration, it is determined which table to use among the correction tables of the table group determined in the first print head calibration. As shown in FIG. 3, the plurality of tables 0 to 8 are classified into a plurality of groups 1 to 3, respectively. Each of the groups 1 to 3 includes a plurality of tables.

  In the present embodiment, in the first print head calibration, any one of group 1, group 2, and group 3 is determined in consideration of a deviation of the ejection amount of ± 10% due to the print head difference. These groups are centered on Table 1, Table 4, and Table 7 having correction factors of + 7%, 0%, and -7%, respectively, by dividing the range of deviation of the discharge amount of ± 10% into three equal parts. . If 7% is corrected by the correction table, the density is corrected by about 5%.

In the second recording head calibration, an appropriate correction table is determined from three tables further provided in each table group. The correction table in each table group is composed of tables that can correct the density difference of 1.5% by changing the correction coefficient by 2%. That is, in group 1, a table 0 with a correction coefficient of −9% and a correction table 2 with a correction coefficient of −5% are provided centering on table 1 with a correction coefficient of −7%. In group 2, a table 3 with a correction coefficient of -2% and a correction table 5 with a correction coefficient of + 2% are provided centering on a table 4 with a correction coefficient of 0%. Similarly, in the group 3, a table 6 having a correction coefficient of + 5% and a correction table 8 having a correction coefficient of + 9% are provided centering on a table 7 having a correction coefficient of + 7%.
Hereinafter, a procedure for selecting an output correction table will be described.

  FIG. 5 is a flowchart showing a procedure for selecting an output correction table in the present embodiment. The procedure for selecting the output correction table starts when the user selects the “color adjustment” function using the operation panel set in the printer main body. The printer of this embodiment is a printer that uses CMYK four color inks, but the present invention is not limited to these color materials. That is, even if these color materials use inks of three colors or less, or other color materials such as light cyan (Lc) and light magenta (Lm) are further used. Good. Further, the procedure for selecting the output correction table may be operated from the menu screen of the printer driver installed in the host computer in addition to the operation panel of the printer main body.

  First, the user selects “color adjustment” on the operation panel (501). When “color adjustment” is selected (501), first-stage recording head calibration (coarse adjustment) is started.

  In the first stage recording head calibration, first, the fixed pattern A is printed (502, first recording step).

  FIG. 6 is a diagram showing the fixed pattern A. In the fixed pattern A, the recording duty is distributed so that the central patch 9 has a density of about 0.6% gray when three colors of cyan, magenta, and yellow are recorded on the coated paper. Centering on this patch 9, a plurality of patches having relatively different CMY ink mixing ratios are arranged assuming a density difference of 5% that occurs when the ink discharge amount of the recording head is around 7%.

  FIG. 7 is a table showing CMY ink mixing ratios of patches 0 to 18 arranged in the fixed pattern shown in FIG. In the patch, three types of density are set for each of CMY. That is, for C ink, the densities of 37.6%, 40.4%, and 43.2% are set. In M ink, the densities of 46.3%, 49.8%, and 53.3% are set. For Y ink, densities of 27.0%, 29.0%, and 31.1% are set. Nineteen patches with patch numbers 0 to 18 have a pattern mixture ratio set by a combination of these densities. And as described above, the patch of patch number 9 is mixed so that the density is about 0.6%. In addition, the mixing ratio is such that the density difference between the patches is about 5%.

  In the fixed pattern A shown in FIG. 6, the arrangement of the patches is such that the yellow image ratio is relatively higher as it goes upward, the cyan relative ratio is higher as it goes lower left, and magenta as it goes lower right. The arrangement is such that the relative ratio is high.

  In this embodiment, the gray patch is printed as a sample in order to make it easy to select a patch, that is, to determine a patch close to the sample gray. The sample patch is printed in halftone using black ink.

  Note that the arrangement of the patches and the pattern mixture ratio of the present invention are not limited to those shown in FIGS. 6 and 7, and may be any arrangement that can be compared with the sample gray. It may be determined appropriately according to the nature and purpose.

  Next, the user visually evaluates the patch of the fixed pattern A closest to the sample gray, selects the patch number, and inputs the patch number information (503). If there is a difference in the amount of ink discharged due to variations in the recording head, the color balance changes. The patch shown in FIG. 6 has an apparent color change, so that an optimum gray color appears in any of patch numbers 0 to 18. That is, a patch that can balance the discharge amount is the same gray as the sample gray. The user inputs information on the number or position of the selected patch from the operation unit. The printer stores the value in the internal memory. In addition to the patch number and position information selected by the user, the printer can also store recording conditions (ink ejection amount, head driving conditions) when the selected patch is recorded, in the memory. .

  When a patch is selected, a correction table number corresponding to the selected patch number is determined (first selection step). In the coarse adjustment, which is the first stage print head calibration, three types of tables are prepared for each color.

  FIG. 8 is a table showing the correspondence between patch numbers and correction table numbers. For each color of CMY, 1, 4 or 7 is determined in the correction table. Correction table 1 is a correction coefficient of −7%, correction table 4 is a correction coefficient of 0%, and correction table 7 is a correction table of correction coefficient + 7%. For example, when a patch with patch number 0 is selected, C is the correction table number 1 of group 1, M is the correction table number 1 of group 1, and Y is the table of correction table number 7 of group 3.

  Next, the second stage print head calibration (fine adjustment) is performed. In the second-stage recording head configuration, first, the fixed pattern B is printed (504, second recording step). The arrangement of the fixed pattern B patches is the same as the arrangement of the fixed pattern A patches shown in FIG.

  FIG. 9 is a table showing the relationship of CMY ink mixing ratios of patches 0 to 18 arranged in the fixed pattern B. The plurality of patches arranged in the fixed pattern B are patches having a mixing ratio difference smaller than the mixing ratio difference of the plurality of patches recorded by the fixed pattern A patch. By making the mixing ratio difference (density difference) smaller than that of the fixed pattern A patch, fine adjustment is possible with the fixed pattern B patch. That is, the patch corresponds to the correction table determined by the print head calibration in the second stage.

  In the table shown in FIG. 9, “0” indicates the same mixing ratio as the patch selected in the coarse adjustment (first-stage recording head calibration). Further, “+” and “−” are a ratio that is slightly higher and a slightly lower ratio than the mixing ratio of the patch selected in the coarse adjustment. That is, a value obtained by adding or subtracting a value obtained by halving the value of the difference between the three types of mixing ratios determined by the mixing ratio of the patches of the fixed pattern A to the ratio of “0”.

  For example, in the coarse adjustment, when a patch with patch number 0 is selected, table 1 is selected for C. Therefore, in this case, the mixture ratio of patches C arranged in the fixed pattern B is 37.6% for the patch “0” in the table of FIG. Further, the “+” patch in the table of FIG. 9 is 39.0%. The “-” patch is 36.7%.

  Similarly, for M, Table 1 is selected. Therefore, in this case, the M mixing ratio of patches arranged in the fixed pattern B is 46.3% for the patch “0” in the table of FIG. Further, the patch “+” in the table of FIG. 9 is 48.1%. The “-” patch is 44.6%.

  Further, for Y, the table 7 is selected. Therefore, in this case, the Y mixing ratio of the patches arranged in the fixed pattern B is 31.1% for the patch “0” in the table of FIG. Further, the patch “+” in the table of FIG. 9 is 32.2%. The “−” patch is 30.0%.

  Then, from among the patches of the fixed pattern B, the user visually evaluates the one closest to the sample gray and selects the patch number (505). Then, information on the selected number is input from the operation unit. The printer stores the value in the internal memory.

  When the selected patch information is input, a correction table is selected based on the selected patch (506, second selection step). That is, in the table shown in FIG. 9, when the patch with patch number 0 is selected, C, M, and Y are “+”, “+”, and “−”, respectively. Similarly, in the case of patch number 1, “0”, “+”, “−”, and in the case of patch number 2, “−”, “+”, “−”. Based on this result and the result of the first stage print head calibration, the correction table is selected.

  Specifically, since the table 1 is selected in the coarse adjustment for C, when “+” is set, the correction table 2 having a correction coefficient of 2% plus that of the table 1 is selected. Become. When “−” is set, the correction table 0 having a correction coefficient 2% minus that of the table 1 is selected.

  Similarly, since the table 1 is selected in the coarse adjustment for M, when “+” is set, the correction table 2 having a correction coefficient 2% higher than that of the table 1 is selected. When “−” is set, the correction table 0 having a correction coefficient 2% minus that of the table 1 is selected.

  Since the table 7 is selected in the rough adjustment for Y, when “+” is set, the correction table 8 having a correction coefficient 2% greater than that of the table 7 is selected. When “−” is set, the correction table 6 having a correction coefficient 2% minus that of the table 7 is selected.

  FIG. 10 is a table summarizing the relationship between the selected patch and the correction table. The correction table number finally selected is described by the table group selected by the coarse adjustment and the code of the table selected by the fine adjustment.

  For example, when group 1 is selected by coarse adjustment and a patch with patch number 8 (C, M, Y = “0”, “−”, “−”) is selected by fine adjustment, C is table 1, M Table 0 is selected for Y, and Table 6 is selected for Y.

  When the correction table is selected, the printer stores the correction table in a memory inside the main body. After the recording signal reaches the printer, when the image is converted and recorded, the table selector switches the correction table for each color based on the value stored in the main body memory. Then, the image signal is converted by applying a correction table to correct the color of the image.

  With this calibration, it is possible to calibrate a density having a density difference of ± 5% due to recording head variation to about ± 1.5%.

  As described above, when the calibration is performed, the first recording head calibration and the second recording head calibration are performed. In the first recording head calibration, first, rough adjustment is performed in a range in which the ink discharge amount difference ± 10% is divided into three equal parts. Thereafter, fine adjustment is performed in a range obtained by further dividing the range selected by the first print head calibration into three equal parts by the second print head calibration. Thus, the number of patches can be reduced by performing calibration in two stages. In addition, the user can easily perform highly accurate correction.

1 is a schematic diagram illustrating an outline of an ink jet recording apparatus according to a first embodiment of the present invention. It is a figure which shows the flow of the image processing in the 1st Embodiment of this invention. It is a table | surface which shows the correction table prepared in advance in the 1st Embodiment of this invention. It is a graph which shows the (gamma) characteristic of the output correction table shown in FIG. It is a flowchart which shows the procedure which selects the output correction table in the 1st Embodiment of this invention. It is a figure which shows the fixed pattern A in the 1st Embodiment of this invention. It is a table | surface which shows the mixing ratio of the CMY ink of the patch from 0 to 18 arrange | positioned at the fixed pattern shown in FIG. It is the table | surface which showed the response | compatibility of the patch number and correction table number in the 1st Embodiment of this invention. It is a table | surface which shows the relationship of the mixing ratio of the CMY ink of the patch of 0-18 arrange | positioned at the fixed pattern B in the 1st Embodiment of this invention. It is the table | surface which put together the relationship of the selected patch and correction table in the 1st Embodiment of this invention.

Explanation of symbols

101 Paper Feeding Roller 102 Recording Medium 103 Main Scanning Guide 104 Carriage 105 Recording Head 106 Platen

Claims (3)

A correction table determination method for determining a correction table for use in a recording apparatus that records an image on a recording medium using a plurality of colors of ink ,
A value obtained by correcting each of the predetermined input values corresponding to the plurality of colors of ink using a combination of correction tables including a correction table selected from a plurality of correction tables corresponding to one ink color for each ink color. A recording step for recording a plurality of patches corresponding to the plurality of types of the combinations,
A correction table for correcting each of the correction tables included in a combination corresponding to a patch selected from the plurality of patches among the plurality of types of combinations, for correcting image data corresponding to the plurality of colors of ink. A decision step to decide as
A correction table determination method comprising: A correction table determination method for determining a correction table for use in a recording apparatus for recording an image on a recording medium using ink of a plurality of colors,
  A value obtained by correcting each of the predetermined input values corresponding to the plurality of colors of ink using a combination of correction tables including a correction table selected from a plurality of correction tables corresponding to one ink color for each ink color. A first recording step of recording a plurality of patches corresponding to a plurality of types of the combinations,
A plurality of patches including a patch selected from a plurality of patches recorded in the first recording step and having a density range smaller than a density range of each of the plurality of patches recorded in the first recording step A second recording step of recording a plurality of patches corresponding to values obtained by correcting each of the predetermined input values using a plurality of types of correction tables of the combinations;
Each of the correction tables included in a combination corresponding to a patch selected from the plurality of patches recorded in the second recording step is used as a correction table for correcting image data corresponding to the plurality of colors of ink. A decision process to decide;
A correction table determination method comprising: The image data for recording the image is corrected using a plurality of correction tables corresponding to the plurality of colors of ink determined in the correction table determination method according to claim 1 or 2. Processing method.

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