JP6171289B2 - Image processing method, image processing apparatus, and program - Google Patents

Description

  The present invention relates to a method of processing image data used for image formation in an image processing apparatus capable of forming an image by drawing each dot (pixel) for each color in a matrix system with several colors of ink. An image processing method for performing processing for reducing color misregistration appearing in an ink image due to variations or the like occurring in the configuration of image forming means for drawing dots of each color, an image processing apparatus and a computer having means for performing the processing, and the processing means Related to the program to function as.

Today, most of the printers using electrophotography and ink jet systems that form images on paper and other media based on image data use a method of drawing dots in a matrix system to form ink images. ing.
Hereinafter, the background of the printing technology will be described by taking an inkjet printer as an example.
An ink jet printer has a relatively simple configuration, a small size, low cost, and low power consumption, as compared with other image forming methods such as an electrophotographic method. In addition, since it can be printed in a non-contact manner, it can be used for a variety of media, and it has the advantage of being able to form high-definition images because of its high resolution and good dot reproducibility. A wide variety of products have been developed.

Inkjet printers can be broadly divided into serial and line types. The serial method is a method of ejecting ink while reciprocating an inkjet head (hereinafter referred to as “recording head” or simply “head”) a plurality of times in a direction orthogonal to the recording sheet conveyance direction. This method is inferior in printing speed to the line method described later, but can form an image by reciprocating the head a plurality of times, so that it is easy to improve the recording resolution and to improve the image quality. In addition, there is an advantage that the configuration is simple and the apparatus can be easily reduced in size and cost.
In the other line type printer, a recording head having nozzles arranged in a line perpendicular to the sub-scanning direction is arranged almost across the paper width, and the paper is placed in a direction perpendicular to the longitudinal direction (line direction) of the head. This is a printer that forms an image at high speed by discharging ink while being conveyed (see the description of FIG. 1 below).

By the way, in the image formation by the dot matrix method, various conditions relating to image formation may change for each dot, and color unevenness occurs in the formed ink image because it is difficult to keep the conditions constant. There's a problem.
In particular, in an ink jet printer, there are various factors of color unevenness, and the influence of variations in a plurality of recording heads is large. Since the recording head usually uses a plurality of heads and nozzles, the characteristics of the ink droplets ejected from the individual nozzles (dot size, shape, landing position, presence / absence of satellite droplets) also vary. This appears as uneven color on the image (see the description of FIGS. 2 to 5 below).

  In the case of a line-type printer, forming a single long head over the entire width of the paper has a high technical difficulty and a poor manufacturing yield. Therefore, as shown in FIG. It is common to adopt a configuration arranged side by side in the scale direction (see the description of FIG. 2 below), which corresponds to an example in which the above-described head having a plurality of configurations is employed. Therefore, band-like color unevenness occurs in the image due to variations in individual heads. In addition, since the line-type printer completes the output image by carrying the paper once, color unevenness due to this variation directly leads to deterioration of the image quality, which is a particularly important issue.

As one of the methods for solving the above-mentioned color unevenness problem, the color unevenness is corrected by controlling the driving voltage applied to the head and nozzle so as to draw the color component dots in the target color and correcting the variation in the ejection characteristics. A technique for reducing the above is known (for example, see Patent Document 1). The above correction controls the ink droplet characteristics such as the size of the dots ejected from the nozzles by changing the drive voltage value applied to the head and nozzle for drawing the color component dots, and aims at the size of each color component dot. The color (density) is adjusted to reduce variations in ejection characteristics. That is, the color unevenness that occurs is eliminated.
However, in order to control the image color depending on the characteristics of the ejected ink droplet to the target color with high accuracy, a drive voltage control system with a high-accuracy circuit configuration is required.
In addition, in order to reduce color unevenness with high accuracy by such drive voltage control, it is actually not necessary to deal with each head unit, and in response to the difference in ejection characteristics of each nozzle provided in one head, it is fine. Unit correction is required.
Therefore, the configuration of the device that performs the above-described drive control that is necessary for reducing the color unevenness with high accuracy becomes complicated, resulting in high cost.

Another method known as a method for solving the above-mentioned color unevenness problem is a method of correcting the density to obtain an output image by changing ejection characteristics by γ correction for each nozzle (for example, Patent Documents). 2, see). In this correction, a predetermined γ correction coefficient that changes the input-to-output relationship prepared for each nozzle is applied to the input image data to adjust the image data to be used for output, thereby correcting the density to obtain the density of the output image. To do.
The method using γ correction is simpler in configuration than the above method using drive voltage control, and is more advantageous in terms of cost.

However, in the method by γ correction, the density of each ink color is adjusted by changing the gradation characteristics of the input versus output. That is, even if the density unevenness for a single color can be corrected, two or more color component dots are removed. The color unevenness of the color (hereinafter referred to as “multi-order color”) represented by the image formed by superimposing and drawing is not taken into consideration, and the effect of reducing the color unevenness of the multi-order color is not guaranteed. This is because the color of the multi-order color changes depending on the overlapping state of the plurality of color component dots, and the color changes if the overlapping state is different even if the color unevenness of the single color is adjusted.
Note that the above-described conventional technique for reducing color unevenness by driving voltage control is basically a technique applied to a single color, and in this prior art, means for reducing the color unevenness of multi-order colors has been proposed. Absent.

  An object of the present invention is to reduce color unevenness generated in an ink image not only in a single color but also in a multiple order when performing processing for forming an image by overlapping each color dot drawn in a matrix system for each color with a plurality of colors of ink. It is to be able to do with colors.

The present invention includes a color information acquisition step acquire the color gamut of each divided element groups obtained by dividing a dot drawing elements of several to a predetermined group of elements forming a multi-color ink image, for each divided element group color a color conversion processing step of performing color conversion into the drawing image reproducible region from the original image based on the target color defined in the color gamut overlapping respectively the image processing method having.

Based on the drawing image color-converted by the image processing method according to the present invention, the ink image is formed by superimposing each color dot drawn by a matrix method for each color with a plurality of colors of ink, thereby forming an image In addition to a single color, it is possible to reduce the color unevenness that occurs in the multi-order color .

1 is a diagram illustrating a schematic configuration of an image forming unit of a printer according to an embodiment of the present invention. FIG. 3 is a diagram illustrating a schematic configuration of a head array in which short recording heads are connected and color unevenness that occurs in an image drawn by the head array. It is a figure explaining the example of a change of the array structure in a head array. It is a figure explaining the example of a structure change of the head array of a multiple head structure. It is a figure explaining the structural example of the head array which connected the recording head to the line direction. FIG. 2 is a diagram illustrating a schematic configuration of a control unit of a printer according to an embodiment of the present invention. It is a figure explaining the division | segmentation unit of a correction group, and the color reproduction range of each correction group. It is a flowchart which shows the process sequence which produces the color conversion table which sets the color conversion parameter which correct | amends a color shift. It is a figure explaining the mapping of the color target (target color) according to the color reproduction range of a correction group. It is a flowchart which shows the process sequence of the data for image output including the color conversion process process using the color conversion table produced in FIG. It is a figure explaining an example of the setting method of the color target with respect to a correction group. It is a figure explaining the other example of the setting method of the color target with respect to a correction group. It is a figure explaining the process of the boundary part between the images formed by the correction group.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
Here, as an embodiment of the image processing method and the image processing apparatus of the present invention, a single color or a multi-order color by a matrix method by a inkjet method on a medium such as paper (hereinafter referred to as “recording paper”) based on image data. A printer (hereinafter also referred to as “inkjet printer”) that draws the dots to form an ink image will be described as an example.

The ink jet printer of this embodiment is roughly composed of a mechanism unit and a control unit.
The mechanism unit has means for transporting the recording paper and means for recording ink dots on the surface of the recording paper being transported by an ink jet method.
The recording paper needs to be transported in the predetermined sub-scanning direction required for each of the serial method and the line method as described in [Background Art] when dots are drawn by the matrix method. For this reason, a recording paper conveying belt driven by a motor and its drive control means are provided as recording paper conveying means.

In addition, the dot recording by the ink jet method performs a predetermined recording operation required in accordance with the conveyance of the recording paper in the serial method or the line method.
Since the serial method involves main scanning of the recording head, the recording head includes a recording head supported by a carriage that is driven by a motor and moves in the main scanning direction, and drive control means for the carriage.
Since the recording head is driven in synchronism with the movement of the carriage that supports it in the main scanning direction and the movement of the recording paper in the sub-scanning direction to draw ink dots, it has control means necessary for this driving.
On the other hand, in the line system, the recording head is fixed and no moving means for the serial system is required, but the recording head is driven in synchronism with the movement of the recording paper in the sub-scanning direction to draw dots. And control means necessary for this drive.
The configuration of the mechanism unit of the present ink jet printer described above is basically an existing technology, and thus detailed description of the configuration is omitted.

However, the configuration of the recording head according to the image processing process peculiar to the present invention that can reduce color unevenness generated in an ink image formed by superimposing color dots drawn by a plurality of rows of nozzles provided in the recording head. Details of the configuration of the control unit that performs image processing will be described below.
In the following, an embodiment taking the line method as an example will be mainly described.

<Recording head>
FIG. 1 is a diagram illustrating a schematic configuration of an image forming unit of a printer according to an embodiment of the present invention.
The image forming unit in FIG. 1 shows the relationship between a line type recording head (shown as “line head” in the figure) and the recording paper P.
In the line system, as shown in FIG. 1, recording heads 71K, 71C, 71M, and 71Y for each color component (here, four colors of K: black, C: cyan, M: magenta, and Y: yellow) are provided over the paper width. Be placed. The recording head for each color component has a nozzle that is elongated in its entirety and arranged in an array in the longitudinal direction (in FIG. 1, the nozzle outlets are indicated by black circles), and this nozzle arrangement direction (also referred to as “line direction”). Ink images are formed by ejecting ink at regular intervals while transporting the recording paper P in the sub-scanning direction orthogonal to (). According to the line system having the configuration shown in FIG. 1, the recording head is fixed, and the printing is completed by passing the recording paper P once at a constant speed, so that the productivity is high.

Further, since a long recording head over the entire width of the recording paper as shown in FIG. 1 is difficult to produce a product with high accuracy guaranteed, and the cost is high, a long recording head is formed by connecting a plurality of short recording heads. A head array (a nozzle array arranged in a fixed direction constituted by one or a plurality of recording heads) can be used.
FIG. 2 is a diagram illustrating a schematic configuration of a head array in which short recording heads are connected and color unevenness that occurs in an image drawn by the head array. The “line head array” of A in the figure constitutes a long head array by connecting a plurality of short recording heads 71A to 71E in which nozzles are arranged in a direction orthogonal to the paper transport direction. The recording heads 71 </ b> A to 71 </ b> E are installed with their mutual positions so that the nozzles in the respective joints are arranged so as not to overlap (refer to the description of FIGS. 4B and 5A). The “color unevenness image” in B in the figure shows the color unevenness that can occur in the ink images formed by the recording heads 71A to 71E (details will be described later).

By the way, in the recording head used in this embodiment, the ink droplet ejection operation method can be implemented by an existing operation method such as PZT (lead zirconate titanate) method, thermal method, electrostatic method, etc. The method is not particularly limited.
In general, four colors of the color component KCMY are used as ink colors used in the present embodiment. Examples of using these are shown, but other colors may be used. Regarding the number, the number of colors of four or more may be used, or the number of colors of four or less may be used. Note that the present invention is particularly effective for correcting color misregistration occurring in an image of a secondary color or higher, so that the greater the number of colors, the more effective.

The following description will focus on an example of a printer that constitutes a head array in which a plurality of recording heads shown in FIG.
The present invention is also applicable to the case where a long line head (see FIG. 1) extending over the entire width of the recording paper is used, but a plurality of heads (hereinafter, the recording head is also simply referred to as “head”) as described above. In the case of connection, the problem of uneven color is more likely to occur unless there is variation in ejection of individual heads or positional accuracy when the heads are arranged side by side.
Further, for convenience of explanation, only one color / one head array is illustrated and described. Actually, a head array having the same configuration is provided for a predetermined plurality of colors used by the printer.

The head shown in FIG. 2A has a plurality of nozzle rows in one head, and here, a head that improves the recording resolution per head by arranging two nozzle rows on a staggered pattern. Used.
FIG. 3 is a diagram for explaining a modification example of the array configuration in the head array. The structure shown in each modification example of A to E in FIG. 3 can be adopted as a unit head in a head array having a multi-head configuration.
The head 70 of FIG. 3A has a configuration in which one (single) row of nozzles 70n is provided.
3B and 3C, each of the nozzles 71n and 72n is provided in two (plural) rows, and the first nozzle row and the second nozzle row of the head 71 do not overlap each other (dots from both nozzles are lined). In contrast, the first row and the second row of the head 72 overlap each other (the heads 71A to 71E in FIG. 2 correspond to this arrangement). In this configuration, dots from both nozzles occupy the same position in the line direction and can overlap.

The heads 73 and 74 in FIGS. 3D and 3E are provided with 4 (plural) rows of nozzles 73n and 74n, and the first to fourth nozzle rows of the head 73 are configured to be non-overlapping with each other. The first row and the second row, the third row and the fourth row of the head 74 are arranged in a non-overlapping manner, and the first row and the third row, and the second row and the fourth row are arranged in an overlapping manner. It is the composition which takes.
As described above, when overlapping nozzles are arranged, dots from two or more nozzles exist in the same position in the line direction. Therefore, this operation performance can be used to improve the ink ejection frequency. In addition, the recording resolution can be improved. In addition, it is possible to take a configuration that compensates for the poor landing characteristics of each other by performing ink ejection by sharing these nozzles.
Note that the nozzles in one head are usually used for a single color, and can be implemented by dealing with existing design techniques. Although described as a condition, the present invention is not limited to this, and when two or more nozzle rows are provided in one head, another ink may be assigned to each row.

FIG. 4 is a diagram for explaining a configuration change example of a head array having a multi-head configuration, and the configuration shown in each of the change examples A to C in FIG. 4 can be adopted as a head array.
The head array of FIG. 4A has a configuration in which two heads 71 (FIG. 3B) are provided in an overlapping arrangement as a double head. The head array in FIG. 4A is configured with two heads in the same nozzle arrangement as the head array in FIG. 3E.
The head array shown in FIG. 4B has a configuration in which a head 71 (FIG. 3B) and two heads 71 ′ having a non-overlapping relationship with the head are combined as a double head. The head array of FIG. 4B is configured with two heads in the same nozzle arrangement as the head array of FIG. 3D.
The head array of FIG. 4C is a configuration in which the two head arrays of FIG. 4B having a multiple head configuration are further combined in an overlapping relationship.
The head array having a multi-head configuration makes it easier to manufacture a head array having a multi-nozzle array configuration that can improve the above-described ejection frequency and recording resolution than that having a single head configuration.

Here, the configuration of a head array in which a plurality of recording heads are connected in the line direction (head length direction) will be further described.
FIG. 5 is a diagram illustrating a configuration example of a head array in which recording heads are connected in the line direction.
When the short recording heads 71A to 71C are connected to each other in the line direction, that is, the head long direction, the nozzles at the ends connecting the adjacent recording heads 71A to 71C do not overlap as shown in FIG. Either of the two forms of the form (A in the figure) and the form in which the nozzles overlap (B in the figure) can be adopted. Note that the head array composed of the recording heads 71A to 71E described above with reference to FIG. 2 as the line type recording head has a configuration in which the nozzles at the ends connecting the heads do not overlap, and the head array of FIG. It corresponds to.

  As shown in FIG. 5A or 2, when the nozzles of the ends connecting the heads are not overlapped, when the heads 71 </ b> A to C and A to E are arranged in the line direction, due to the positional deviation at the joint of each head. This is because image streaks and color unevenness due to head characteristic differences are particularly conspicuous. For example, if the positional relationship between the assembled heads is too close, black streaks occur at the joints, and if they are too far apart, white streaks occur, and if there is a density difference between the heads, Since a step-like rapid density change occurs, this is easily noticeable as an image defect portion. This black streak or white streak is a phenomenon corresponding to the “landing deviation” in FIG. 2B showing the cause of color unevenness and the appearance of color unevenness corresponding to the cause in FIG. 2B. The difference in density generated between the heads corresponds to the color unevenness due to “variation of dot diameter” in FIG. 2B.

  Therefore, as shown in FIG. 5B, the nozzles of the ends connecting the heads are configured to overlap. By overlapping the nozzles, this part has a higher nozzle density than the other parts, and by controlling the dot recording amount of this part, it is possible to correct color unevenness that may occur at the joints. become. For example, in the case of black lines, the ink adhesion amount is decreased, and in the case of white lines, the ink adhesion amount is increased. In the case of a level difference, correction can be made by taking a technique such as changing the ink adhesion amount step by step so that the density gradually changes. The method of changing the ink adhesion amount is to change the gradation data input as a drive signal to each overlapping nozzle, or to drive the nozzles that overlap the data input to the overlapping part with a mask pattern etc. It is possible to adopt a method of discharging the ink after sorting.

<Control part>
The configuration of the control unit of the printer will be described with reference to FIG.
FIG. 6 is a diagram illustrating a schematic configuration of a control unit of the printer according to the embodiment of the present invention.
The control unit 200 in FIG. 6 is configured by a computer having a function of controlling the entire printer. A control unit 200 configured by a computer includes a CPU 201, a program executed by the CPU 201, a ROM (Read Only Memory) 202 that stores other fixed data, a RAM (Random Access Memory) 203 that temporarily stores image data, and the like. A rewritable non-volatile memory (NVRAM) 204 for maintaining data even while the power of the printer is shut off, image processing for performing various signal processing and rearrangement on image data, and other overall devices are controlled. ASIC (Application Specific Integrated Circuit) 205 for processing input / output signals for the purpose.

  The control unit 200 also includes a host I / F 206 for transmitting and receiving data and signals to and from the host side, a data transfer unit for driving and controlling the recording head 7, and a drive waveform generating unit for generating a drive waveform. A printing control unit 207 including the head driver (driver IC) 208 for driving the recording head 7, a motor driving unit 210 for driving the sub-scanning motor 31, and an AC bias for supplying an AC bias to the charging roller 26. A supply unit 212, an I / O 213 for inputting detection signals from the encoder sensor 35, detection signals from various sensors such as a temperature sensor 215 for detecting the environmental temperature, and the like are provided. The control unit 200 is connected to an operation panel 214 for inputting information such as operating conditions set in the printer and displaying information on the apparatus side such as the printer status via the I / O 213. .

  Further, the control unit 200 is connected to a host device such as an image (information) processing device such as a personal computer, an image reading device such as an image scanner, an imaging device such as a digital camera, etc., connected via a cable or a network. Data exchange such as image data is performed through F206.

  Further, the CPU 201 of the control unit 200 reads and analyzes the print data in the reception buffer in the host I / F 206, performs necessary image processing, data rearrangement processing, and the like in the ASIC 205, and performs print control on the image data. The data is transferred from the unit 207 to the head driver 208.

  Further, the CPU 201 is based on a speed detection value and a position detection value obtained by sampling a detection pulse from the encoder sensor 35 of the rotary encoder, and a speed target value and a position target value obtained from a previously stored speed / position profile. Then, a drive output value (control value) for the sub-scanning motor 31 that drives the recording paper conveyance belt 21 is calculated, and the sub-scanning motor 31 is driven via the motor driving unit 210 and the motor driver.

  The print control unit 207 transfers the image data received from the ASIC 205 to the head driver 208 as serial data, and also transfers a transfer clock, a latch signal, a droplet control signal (mask signal), and the like necessary to transfer the image data and confirm the transfer. Is output to the head driver 208.

  Further, the print control unit 207 includes a drive waveform generation unit and a head driver 208 configured by a D / A converter, a voltage amplifier, a current amplifier, and the like that perform D / A conversion on the drive signal pattern data stored in the ROM 202. A drive waveform selection unit is provided, and a drive waveform composed of one or a plurality of drive pulses (drive signals) is generated and output to the head driver 208.

  The head driver 208 ejects droplets of the selected recording head 7 by selecting a driving signal constituting a driving waveform provided from the print control unit 207 based on image data corresponding to one row of the recording head 7 input serially. The recording head 7 is driven by applying it to a driving element such as a PZT piezoelectric element that generates energy. At this time, by selecting a driving pulse constituting the driving waveform, for example, dots having different sizes such as large droplets (large dots), medium droplets (medium dots), and small droplets (small dots) can be distinguished. it can.

[Reduction of uneven color]
The head array in which the line type printer configured as described above has a plurality of recording heads connected in the line direction shown in FIG. 5A has a plurality of dots arranged in line with the dot arrangement to be drawn in the head. Since the nozzle is provided as a drawing element, in addition to the head unit, the variation in the ink ejection characteristics between the nozzles arranged in the head causes the ink image to be formed while the image is formed on the recording paper in one scan in the sub-scanning direction. This will cause a problem that appears as uneven color in the line direction in the image.
This color unevenness occurs in the line direction, and as shown in FIG. 2B, “variation in dot diameter” appears as a difference in image density (the figure shows a case where the dot diameter changes in units of heads). , Dot “landing deviation” appears as black streaks and white streaks in a uniform density image (the figure shows the case where the deviation of the dot landing position changes in units of nozzles), and is an abnormality that occurs in ink droplets. A certain “occurrence of satellite” appears as an image stripe of an unintended color (in the figure, a case where satellite is generated in units of nozzles) is shown.

Although this problem can be solved by means of correcting color misregistration by a signal such as a voltage for driving the nozzle, as described in [Background Art], the apparatus configuration required for high accuracy becomes complicated, and It also leads to high costs. Note that the drive control for correcting the color misregistration basically controls the diameter of the dots ejected from the nozzles. In the case of a multi-order color, it is expressed by superposition of a plurality of colors, so that depending on how the colors overlap, the color may change even if the same dot diameter is output. For this reason, in the method of controlling individual nozzles with the drive voltage corresponding to the dot diameter, the correction cannot be completed, and the color unevenness of the multi-order color cannot be sufficiently reduced.
Further, although there is a solution method by γ correction, this method cannot cope with correction of multi-color misregistration as described in [Background Art].

<Basic processing for color misregistration correction>
Therefore, in this printer, color conversion that divides a head array consisting of a plurality of dot drawing elements (here, nozzles) into predetermined element groups and corrects color misregistration for each group in units of the divided groups. By applying the processing, color unevenness is reduced by adjusting the color tone between the groups (hereinafter, the above element group is referred to as “correction group”).
Note that the division of the plurality of slurs constituting the head array into correction groups is based on the premise that the ink image formed by the dots drawn by the nozzles of the correction group to be divided forms a group of image portions. In other words, since a predetermined area of the ink image formed by the drawing of dots is a target for color misregistration evaluation of each correction group, the group of nozzles corresponding to the image area to be evaluated is corrected as a correction group based on the evaluation result. In the basic processing described here, a recording head unit in which the divided correction group units are connected in the line direction is taken as an example.

Hereinafter, a basic process of color misregistration correction will be described.
The color misregistration correction processing can be broadly divided into a color conversion table creation process applied to each of the above-described correction groups, and a print process for an output target original image, that is, a color conversion process using a color conversion table created for each correction group. And a process of outputting a corrected ink image using the drawing image obtained through the above process. The process of outputting the ink image is different in that a color conversion process to be applied for each correction group is assigned. Except for this point, the process of outputting the ink image is basically the same as the process conventionally performed as the output process of the ink image. There is no difference.

  In the color conversion table creation process, a plurality of image forming units are determined based on the color measurement results of the ink image formed when the image forming unit is operated based on the color gamut detection data (color patch creation data described later). A color gamut for each correction group obtained by dividing the dot drawing element (nozzle arrangement) of the configuration into predetermined correction groups is acquired, and a color gamut that can be reproduced by any of the correction groups is determined based on the acquired result. In addition, by changing the color conversion parameter for converting the original image to the drawing image, the change is made so that there is no deviation in the color of each correction group when the ink image is formed with the target color setting within the defined color gamut. A color conversion table having the converted color conversion parameters is created for each correction group.

  As a rough flow of this process, first, as shown in FIG. 7A, the head array is divided into a plurality of correction groups A, B, and C (in the figure, the unit of the group is one head), and color reproduction is performed. Measure the color of the color patch corresponding to each correction group when the area detection data is set and draw a dot, obtain the color reproduction area for each correction group, and based on the obtained color reproduction area Color conversion correction of each correction group is applied so that there is no color shift (difference) between the correction groups.

In the correction group, finer color unevenness is corrected as the unit is finer, but on the other hand, the number of parameters, the number of measurement patches, parameter creation time, and the like necessary for correction increase. Practically, it may be adapted by changing the number of heads and the number of nozzles for each group according to the actual ejection performance of the heads, the size of the printer, and the cost.
The size of the correction group to be divided does not have to be the same, and the size and the division position may be changed depending on the location and the color. It is better to adapt the method by finely dividing the group. For example, when there is a nozzle overlap portion at the head joint as shown in FIG. 5B, the nozzle overlap portion may be set as at least one correction group.

FIG. 8 is a flowchart showing a processing procedure for creating a color conversion table for setting color conversion parameters for correcting color misregistration.
This processing flow is performed by the correction unit 240 included in the control unit 200.
The start of processing according to this processing flow is when the control unit 200 receives an execution instruction from the outside through the operation panel 214 or the like, or when the control unit itself has a function of determining when correction is necessary. Follow the judgment of this function.
When the processing flow of FIG. 8 is started, the correction unit 240 first prints and prints an image pattern for color gamut detection (hereinafter referred to as “color patch”) such as a color patch in each correction group. The color of the pattern is measured, and color information used for color gamut detection is acquired (step S101).
At this time, the color patch to be printed is a color patch (in the case of four colors, primary to quaternary colors) so that a color reproduction range can be acquired. It is possible to grasp the color gamut more accurately as the number of colors in the color patch increases. However, since the image to be printed, the amount of ink consumed, and the measurement time increase, the color information is narrowed down and the color information of the color gamut that is not measured. May be supplemented by calculation.

  The printed color patch is measured by detecting the color using a sensor, scanner, spectral densitometer, or the like. Although the printer does not include such a measuring unit, the image processing apparatus according to the present invention is configured by using an external device that provides the measuring unit via the I / O 213 or the host I / F 206. can do. For example, in the case of a scanner, there is already a processing system that realizes a copy function by connecting to a printer. By using this system, a color patch output to a medium such as recording paper by the printer can be read by the scanner. Thus, the transmission of the obtained image can be easily performed. The image processing apparatus according to the present invention can be implemented by connecting to the printer with a cable or a network.

In step S101, the detection amount of the color patch detected by a sensor or the like is expressed as color information expressed by a color value of the color system.
As the color information obtained here, information such as RGB may be used as it is, or may be handled after being converted into the CIELAB color system. In terms of quantitatively dealing with color, it is better to use the CIELAB color system, etc., such as spectral densitometers that can directly acquire L * a * B * values, such as sensors and scanners. In this case, it is desirable to perform conversion to the CIELAB color system. As a conversion method, for example, a calibration plate for calibration whose L * a * B * value is known is read, and the RGB value read by the above-described sensor or scanner and the nominal La * B * value of this calibration plate are obtained. What is necessary is just to convert by matching.

In step S101, the correction unit 240 measures the color patch for each correction group, acquires color information representing each color gamut (hereinafter described as La * B *), and then performs this processing. Then, a target color (hereinafter, also referred to as “color target”) is determined in the shift correction performed to correct the color shift generated between the correction groups.
Each correction group has different ink ejection characteristics and landing positions, and therefore has a different color reproduction range, and was obtained as color information in the previous step. The obtained color information is expressed as each color reproduction area (FIG. 7C) in association with the image (FIG. 7B) formed by each correction group A, B, C in FIG. As shown in the figure, there is a region that does not overlap with each other, and this portion corresponds to a color gamut that can express one but not the other. For this reason, even if an attempt is made to correct a color by setting a color target aiming at this area, one correction group cannot express the color gamut, and thus color misregistration cannot be corrected.

Therefore, a target color (target color) is determined in the color gamut (FIG. 7C) of each correction group.
As a procedure in the processing flow of FIG. 8, the color gamut obtained for each correction group by measuring the color patch in step S101 is searched, the color gamut overlapping between the groups is obtained, and the obtained color gamut range is set as the target color. Is provided to the next step (step S102).
In the case of correction groups A, B, and C in FIG. 7, A∩B∩C is an overlapping portion of the color reproduction gamuts of these three groups, that is, a color gamut range that can be reproduced in common with these three groups. Define the target color within the color gamut.

For the target color, when printing is instructed by a drawing image that designates the target color, a color conversion process suitable for each correction group is applied so that dots forming an ink image of the same color are drawn in each correction group. Determine for. Accordingly, if a large number of target colors are set as color targets, the color shift can be reduced accordingly.
The target color thus determined is set according to the created color target by creating a color target in which the color is mapped.
As a procedure in the processing flow of FIG. 8, the target color obtained in step S102 is determined within the provided color gamut range, and a color target in which the determined target color is mapped is created (step S103).

  The color target is determined in advance by a method of mapping a target color targeted as a printer onto the reference color gamut. The target color prepared in this way is reduced or enlarged to an overlapping color gamut that can be reproduced by each correction group. Each target color of the color target may be defined by L * a * B *, for example.

FIG. 9 is a diagram illustrating mapping of color targets (target colors) according to the color gamut of the correction group. The figure shows the concept of processing for re-mapping primary color targets mapped on the reference color gamut to target colors within the correction group A, B, and C color gamut ranges.
In the example of FIG. 7, it is the color gamut of the correction group A (color gamut A in FIG. 9) that reduces the gamut of the primary color target and falls within the color gamut range and becomes the minimum. Then, the image is reduced and mapped again so as to be within this color reproduction region. Although the color target of FIG. 9 is represented by a two-dimensional schematic diagram, L * a * B * is three-dimensional data.

As another embodiment, for example, three processing modes are applied by re-mapping color targets in the color gamuts A, B, and C having different ranges corresponding to the respective correction groups and applying them to each correction group. The color conversion processing is performed in the processing mode corresponding to the correction color targets A, B, and C in FIG.
As described above, since the correction color target is reduced or enlarged based on the color target, it is possible to correct color misregistration while preserving the original color tone of the printer. Therefore, it is difficult to produce a strange appearance.
When the three processing modes corresponding to the correction groups A, B, and C are used as described above, not only the color unevenness between the correction groups is reduced in each processing mode, but also the difference from the color originally intended as the printer is eliminated. Therefore, it is difficult to cause a sense of incongruity in the corrected image.

As described above, when mapping is performed again from the primary color target and the correction color target is obtained, the color of the color conversion process to the drawing image used by each correction group so as to aim at the obtained correction color target next. A conversion table is created (step S104).
The color conversion table created here reduces the color difference (deviation) between groups by applying the original image to color conversion processing to an image used by each correction group for drawing.

The color conversion table used for the color conversion processing of the printer is originally a table for converting RGB data of the original image color into KCMY data of the ink color. Here, the RGB value of the original image color is converted in accordance with the correction color target. For this purpose, the table data describes the conversion parameters for associating the KCMY values of the ink colors.
These conversion data, color target, and color correction target are stored in the apparatus main body or the ROM or RAM of the equipment connected to the apparatus main body, and are used for processing by referring to them appropriately.
Also in this processing flow, the created color conversion table is stored in the ROM 202 or the NVRAM 204, and the processing is terminated.

FIG. 10 is a flowchart showing a processing procedure of image output data including a color conversion process using the created color conversion table after performing the processing according to the flow of FIG.
This processing flow relates to a print output process performed on an original image input by the control unit 200 that has received a print request.
When the processing flow of FIG. 10 is started, the control unit 200 first inputs image data to be processed (step S201). The input image data is usually scanner input or PDL (page description language) data, and is represented by RGB data.

The RGB input image data is processed into image data used for print output.
In this image processing, first, RGB input image data is converted from input RGB data to CMYK data for drawing each color version of an ink image by color conversion processing using the color conversion table created by the processing flow of FIG. 8 for each correction group. Conversion is performed (step S202).

Next, the color-converted drawing CMYK data of each color plate is converted into multi-value (binary or higher) dot pattern data that can be handled by the inkjet head by halftone processing (step S203).
Thereafter, a rendering process is performed in which the pattern data obtained in the preceding stage is associated with the nozzles provided in the printer head and the conveyance of the recording paper performed in the sub-scanning direction (step S204).
Next, the head (nozzle) is driven by the output image data obtained in the preceding rendering process to print out on a medium such as recording paper (step S205), and the process of this flow is terminated.

By performing the color conversion process for correcting the color misregistration in accordance with the process flow of FIGS. 8 and 10 described above, it is possible to realize a process of reducing the color unevenness of the image in not only a single color but also a multi-color. In addition, since the correction unit is divided into groups composed of a plurality of dot drawing elements (nozzles), it is possible to obtain good image quality while suppressing the time required for correction and the increase in the configuration scale of the printer.
In addition, by setting a color target within the color reproduction gamut of each correction group, it is possible to unify the color gamut used between the correction groups and correct color misregistration while maintaining the target color of the printer.

<Support for drawing objects>
The original image to be output by the printer includes an image generated based on PDL data. The PDL data is composed of a plurality of types of drawing objects for one image. A plurality of types of drawing objects, such as characters, images, and graphics, are used and have different image characteristics.
This characteristic is related to how the human recognizes the image. That is, the human eye has a feature that it is easy to recognize a color difference with respect to a large area, but it is difficult to recognize a color difference with a small area. For this reason, when a color difference occurs in an image such as a photograph, the difference is noticeable, but in a picture such as a character or a thin line, the color difference is difficult to recognize. The deterioration of the visibility of the shape (pattern) is more likely to be a problem.

Therefore, with regard to color conversion processing for an original image composed of multiple types of drawing objects, the effect of reducing color unevenness by correcting color misregistration can be maintained by changing the method of color conversion processing depending on the type of drawing object in the image. However, it is possible to perform a process for preventing the image quality from being deteriorated.
Specifically, as described above, since an image object can easily recognize a difference in color, a correction color target is created in an overlapping color reproduction range in order to obtain a unified color among correction groups (see FIG. (Refer to 7,) Color conversion is performed, and character / line (graphic) objects reduce or enlarge the color target in each correction group color gamut, and create correction color targets using the full color gamut for each correction group. Then (see FIG. 9) color conversion processing is performed.
By doing so, image objects that tend to have noticeable color differences reduce color differences, and character / line objects that emphasize visibility over color differences maximize the color gamut that each correction group can represent. Visibility can be improved by performing color conversion processing to be used.

<Instruction of color target by user>
The color target that sets the target color to be targeted as a printer is adjusted according to the mapped target color, and at least the output of that color is guaranteed. The color is determined based on. For this reason, the output of the color which a user wants to express is not necessarily guaranteed.
Therefore, a function is provided that allows the target color value of the color target to be designated so that the user can obtain the desired color.

In the basic process of color misregistration correction described above, a configuration having a preset color target has been described. However, here, a color that the user wants to express can be configured by allowing the user to change the preset color target. And color correction based on it.
When changing the color target and re-creating it, the color patch is output in a color gamut that can be expressed uniformly by each correction group in the print mode in which the color target is created, recording paper, temperature, humidity, etc. The procedure is to recreate the color target based on this patch. This is because if a color target is created based on the color information output by some correction groups, the color target may not be expressed by another correction group.

FIG. 11 is a diagram illustrating an example of a method for setting a color target for a correction group.
The example shown in FIG. 11 is an example in which the above-described problem occurs. Here, the color target created to be changed does not fit in the overlapping color reproduction range where the colors can be unified in each correction group.
In such a case, the color target may be created first, and the created color target may not fit in the overlapping color reproduction area, and then reduced or enlarged to fit in the overlapping color reproduction area. In this case, since the color space is reduced or enlarged, the pattern shape of the color target is preserved, but the absolute value of the color is different from the one originally created by the user and is not desired by the user. Color expression may occur.

In order to improve this point, as shown in FIG. 12, first, each correction group searches for a color gamut that can be expressed without color difference, that is, can be expressed in a unified manner, and creates a color target indicated by the user in the obtained overlapping color gamut. If it is set as the structure which carries out, the color which the user aimed can be expressed without a color difference.
As a method for allowing the user to designate a target color of the color target as a desired color, an existing method using an ICC (International Color Consortium) profile or the like can be applied, and the operation panel 214 is used. In addition, processing according to the above method can be executed by an external instruction via the host I / F 206.

  In addition, the case where the color conversion is changed depending on the drawing object described in <Support for drawing objects> above is applied, and the image object is color-converted with the correction color target (color target specified by the user) specified in the overlapping color gamut. , Characters and lines are created according to the color gamut of each correction group, and the color target specified by the user is mapped to the color gamut of each correction group to create a correction color target for each correction group. Correction group color conversion may be performed. In this case, as the image object is specified by the user, the character or line object is expressed in a color expanded to a range that can be reproduced by each correction group while preserving the color of the color specified by the user. .

<Change of processing mode, color target, etc.>
It is desirable that the processing mode for color misregistration correction and the change of the color target can be set according to the print mode, the recording paper, the ambient environment of the printer, and the like.
For example, the print mode may be changed depending on factors such as print resolution, nozzle drive waveform, recording paper conveyance speed, and recording paper type. If the print mode changes, the color of the ink image naturally changes.
Even in the same print mode, when the recording paper to be used changes, the color changes because the ink penetration method and the color of the paper itself change.
Also, even when the ambient environment of the printer such as temperature and humidity changes, the color can change because the landing characteristics of the head and the ink penetration conditions change.

Therefore, the above-described color misregistration correction and color target change can be performed in accordance with changes in each of the elements that affect the color of the output image.
Also in the case of the above-described change in the print mode, the correction color target is reduced or enlarged according to the color gamut that can be reproduced by each correction group by the method described with reference to FIG. 9 in the above embodiment. By creating and correcting color misregistration, not only the color difference between correction groups, but also the color difference that occurs between different processing modes, between different recording papers, and between different ambient environments can be corrected. The color shift can also be corrected by a method in which the user resets the color target in accordance with changes in each element that affects the color of the output image. When each correction group corresponds to each processing mode (see FIG. 9), a correction color target that meets each condition is created in the same manner as described above, and color conversion based on the created color target is performed. I do.

<Processing system configuration>
A configuration of a system that performs the color misregistration correction process will be described.
It is more desirable that the above-described series of color misregistration correction processes can be performed by a single image processing apparatus to be corrected. This is because some image processing devices do not have means such as sensors, scanners, and colorimeters that detect color patches, so these systems are configured as external units and corrected using data measured by the external units. It may be configured to perform processing.

However, if the device is equipped with a means to detect color patches and a program that performs a series of correction processes can be built into the main unit, an independent process can be performed without the need for an external device. It becomes possible.
For example, in the case of an image forming apparatus such as an MFP (multi-function peripheral) having functions such as a scanner and a facsimile, this color misregistration correction is performed by using a scanner mounted as an external device and a unit mounted alone without using a PC. This can be implemented by adding the processing function. If implemented with such a configuration, the color misregistration correction processing can be performed without assistance from an external function in image output processing performed in the MFP such as copying and fax images, and convenience can be improved.

Further, a part of the processing function of the color misregistration correction may be installed in the host computer and executed. In general, the host computer has higher memory and CPU specifications than the main unit, and the processing performance is good. By performing the color misregistration correction process using the resources of the host computer, correction can be performed faster and with higher accuracy. Is possible.
In addition, a configuration in which both the processing performed by the image processing apparatus alone and the processing using the host computer can be adopted, and they may be used properly.
In addition, there is an existing means for generating image output data of an image processing apparatus using a hardware or software configuration tool called RIP (raster image processor). A means for creating a color patch for acquiring color information such as the color gamut in the RIP, color information built-in, or based on color information measured by an independent scanner, sensor, colorimeter or the like. If an image processing apparatus that does not have a color misregistration correction processing function can output an image without color unevenness, the color conversion table and the function for creating image output data reflecting the color conversion can be output. it can.

<Execution timing of color misregistration correction>
Next, the timing for acquiring color information such as a color gamut or creating color conversion table data in the color misregistration correction process will be described.
For the above color information, when the print mode is changed, the recording paper is changed, the temperature and humidity conditions are changed, the predetermined number of sheets are printed, the predetermined job is printed, the predetermined time has elapsed, the head is replaced, It is preferable to execute this acquisition process at the timing of startup or at least at the time of the execution instruction of the user or prompt the acquisition.

The above execution timings are timings at which changes in the color gamut and nozzle discharge conditions are predicted. The color information is acquired at this timing, and a correction color target is created, a color conversion table is created, and application to image output is performed.
However, the processing after the creation of the correction color target may be performed together with the acquisition of the color information. However, depending on the conditions specific to the apparatus, there is little change in the cause of color misregistration, and the correction effect is almost zero. It may not come out.
Therefore, when the deviation between the acquired color information and the target color (predetermined color target) is out of the predetermined allowable range, the processing after the creation of the correction color target is performed. Therefore, the processing efficiency is improved by omitting the processing regarded as invalid.

For this reason, it is determined whether or not the deviation between the acquired color information and the target color is within a predetermined allowable range, and when the predetermined color is out of the predetermined allowable range, processing after the creation of the correction color target is performed, or execution of this processing is performed. A notification that prompts
Note that when acquiring color information for the above determination, a method of creating a color patch with a smaller number of colors than when actually performing color misregistration correction at a later stage may be employed. To obtain color information for actual color misregistration correction, it is necessary to create a very large number of color patches and measure the color. In the case where correction is performed by dividing nozzles, the number of points increases even more.
For this reason, when used for the above-described allowance determination, it is more effective to measure the color patch output by focusing on a representative color and estimate the overall color change based on the color change at that point. The man-hours for output and measurement can be suppressed, and the merit is great.

In addition, it is possible to reduce the number of points as described above, and use a method to print color patches between images being printed, between print jobs, outside the frame, or a method to directly use the color of the image being printed. In addition, if the processing by this method is performed in real time, the correction processing can be executed only when necessary without reducing productivity.
The color change may be determined by the luminance or RGB value, but when converted to La * B *, it can be determined by the size using ΔE representing the color difference, which is advantageous. It is a technique. There are several versions of ΔE. You can use any of them, but in the new version, corrections such as differences in color difference perception by color gamut (difficulty in color differences when saturation is high) have been made. It is recommended to make corrections.

Regarding the color difference, there are two viewpoints of the color difference between the correction groups and the target color (target color). Either of these may be managed, or both may be managed, and the allowable color difference may be different between the two.
In general, the difference between the absolute values of colors is not noticeable, and the relative difference is noticeable. For this reason, it is better that the color difference between the correction groups is stricter than the color difference with respect to the target color.
Further, regarding the color difference between correction groups, the color difference between adjacent correction groups is more conspicuous than the color difference between remote correction groups. Therefore, the color difference between adjacent correction groups should be stricter than the color difference between remote correction groups. By doing so, it is possible to prevent color correction from being performed more than necessary.
In addition, it is better that the user can specify the allowable color difference.

<Create color patch>
In order to obtain color information such as the color gamut, a color patch of the ink image formed by the dots drawn by the nozzles of each correction group is created. When this color patch is output, the nozzle drive voltage and ejection Items that affect the landing state, such as adjustment and recording paper conveyance speed, must be configured on the assumption that the conditions are adjusted first.
This means that if image output, color information acquisition, and color conversion data are created and applied with insufficient adjustment, correction will be performed under conditions that deviate from the original appropriate image output conditions. Because it ends up.

  For this reason, it is necessary to perform image output after performing or confirming various adjustments before outputting the color information acquisition image. For example, a configuration may be adopted in which an adjustment state such as position adjustment can be automatically detected using a sensor or the like, and when adjustment is appropriate, a configuration in which the process proceeds to image output processing of a color patch may be employed.

<Check device status>
The printer may change its output color characteristics with time. For example, it is conceivable that the ejection characteristics of the ink jet head are changed. This may occur when the nozzle state is temporarily deteriorated or may deteriorate due to a change with time.
In these cases, the color gamut that can be reproduced is widened, but may be narrowed, and the original ability of the printer may not be exhibited. Therefore, when the color gamut is narrowed to a predetermined value or less, it is desirable to perform maintenance, contact user support, or promote such a response.
Therefore, a processing function is provided for confirming the apparatus status as to whether or not such an output abnormality of the printer has occurred, and dealing with the output abnormality.

Here, the management function for acquiring the color gamut of each correction group and storing the color gamut acquired in the past, the color gamut of the correction group and the color gamut of the target color, or the color gamut acquired in the past And a function for notifying that the apparatus is in an abnormal state on the condition that the determination result is determined to be out of the predetermined allowable range. To do.
The determination of the allowance based on the color gamut may be performed with respect to the color gamut of the original target color (color target) of the printer, or the difference between the initial color gamut of the printer and the past correction color target may be compared. The color difference may be determined by threshold processing for determining an allowable range based on the volume and area of the color space, the La * B * value, brightness, density, and saturation of the specific color.

<Reduction of uneven color at the boundary>
Regarding the grouping into correction groups, the grouping in large units can simplify the correction processing load and device configuration, but this correction processing method can control only the average value of each group's color. Changes in characteristics cannot be corrected. For example, when correction is performed by grouping as shown in FIG. 7, color unevenness generated within the group cannot be corrected. For this reason, even if the average values between the groups are combined, the color change at the boundary where the groups are switched may be conspicuous.

Therefore, as a process for reducing color unevenness at the boundary portion between adjacent correction groups, image data used for drawing by drawing dots drawn by the dot drawing elements (nozzles) of both groups is generated.
FIG. 13 is a diagram for explaining the processing of the boundary portion between images formed by the correction group, and shows each of the images of FIGS. 13B to 13E subjected to the reduction processing with respect to FIG. 13A where this processing is not performed. In FIG. 13B, as an example of an output image drawn by interposing dots with adjacent correction groups, FIG. 13B shows “strip division”, FIG. 13C shows “wave division”, FIG. 13D shows “block division”, FIG. Indicates each image of “gradation division”.

In the example of FIGS. 13B to 13E, the boundary portion between the correction group A and the correction group B has a shape in which the place where the correction parameter of the group A is applied and the portion where the correction parameter of the group B is applied are two-dimensionally complicated. With such a configuration, even when the correction group is divided in large units, it is possible to make the sudden color change in the switching portion inconspicuous.
Note that in order to enable the above-described dot drawing, the boundary portion of the ink image drawn by the correction group can be overlapped by the dots drawn by the nozzles of both groups (see FIG. 5B). Become a premise.

<Development for serial printers>
Although the above embodiment has been described with respect to an example of a line printer in which color unevenness is a particular problem, it is possible to reduce color unevenness in individual heads and improve image quality by performing similar processing in a serial printer. Can do.
Even in a serial type printer, there is a device that increases the productivity by increasing the width of an image that can be formed in one scan by connecting the head in the longitudinal direction. In this case, the internal and external variations of the heads become a problem as in the above-described line head array. Therefore, by applying the present invention to a printer having such a configuration, a good image quality without color unevenness can be obtained. It becomes possible to obtain.

  In each of the above embodiments, the embodiment of the present invention has been described by taking an inkjet printer as an example. However, a printer that can superimpose color dots drawn in a matrix system, that is, can form a multi-order color ink image. In that case, the present invention can be carried out in the same manner in other types of printers such as an electrophotographic printer.

  7, 70 to 74, 71A to E..., Print head, 200... Control unit, 201... CPU, 202... ROM, 203. Host I / F, 207... Print control unit, 208... Head driver, 210 .. Motor drive unit, 213... I / O, 214.

Japanese Patent No. 4650005 Japanese Patent Laid-Open No. 10-795

Claims (12)

A color information acquisition step of acquiring a color reproduction area of each divided element group obtained by dividing a plurality of dot drawing elements forming a multi-color ink image into predetermined element groups;
A color conversion processing step for performing color conversion from an original image to an image for drawing based on a target color determined within a color gamut range in which the color gamuts of the respective divided element groups overlap;
An image processing method. The image processing method according to claim 1,
At least one of the divided element groups is an image processing method including a plurality of dot drawing elements. The image processing method according to claim 1 or 2,
A target color setting step for setting the target color, wherein the target color setting step is a step of setting a value for another object occupying a larger image area than the character / line object among the drawing objects as the target color. There is an image processing method. The image processing method according to claim 1 or 2 ,
Has a target color setting step of setting the target color, the target color setting step, step der Ru image processing method to set to increase or decrease the target color in advance mapped on a reference color gamut. The image processing method according to any one of claims 1 to 4,
An image processing method in which the target color is generated based on a color value designated from outside . The image processing method according to any one of claims 1 to 5,
A dot image data generation step of generating image data used in the image forming unit to draw each color dot based on the drawing image processed in the color conversion processing step;
Image processing method. The image processing method according to claim 6 .
On the premise that the boundary portion between the ink images drawn by the divided element group can be drawn with dots drawn by the dot drawing elements of both groups, the dot image data generation step An image processing method for generating image data used for drawing by interposing dots to be drawn by dot drawing elements of the group . The image processing method according to claim 4 ,
Deviation between the target color previously mapped on the reference color gamut with respect to the color gamut acquired in the color information acquisition step or deviation between the color gamuts of the respective divided element groups is within a predetermined allowable range. A deviation amount determination step for determining whether or not there is,
An image processing method for performing color conversion from the original image to a drawing image by using an existing color conversion parameter on the condition that it is determined in the deviation amount determination step that the image is within a predetermined allowable range . The image processing method according to claim 8, wherein
The predetermined allowable range is an image processing method for setting a different range adapted to a target color to be determined or a combination of each of the divided element groups . The image processing method according to any one of claims 1 to 9,
A color gamut management step of acquiring the color gamut of each of the divided element groups and storing the color gamut acquired in the past;
A color gamut determination step for determining whether a difference between the acquired color gamut and the target color gamut or a previously acquired color gamut is within a predetermined allowable range;
And an abnormality notification step of notifying that the image processing apparatus is in an abnormal state on the condition that it is determined that the color reproduction range determination step is out of a predetermined allowable range.
Image processing method . Color information acquisition means for acquiring a color reproduction range of each divided element group obtained by dividing a plurality of dot drawing elements forming a multi-color ink image into predetermined element groups;
Color conversion processing means for performing color conversion from an original image to a drawing image based on a target color defined within a color gamut range where the color reproduction ranges of the respective divided element groups overlap,
An image processing apparatus. A program for causing a computer to function as the color information acquisition unit and the color conversion processing unit in the image processing apparatus according to claim 11.

Images