JP5843532B2 - Image processing apparatus and control method thereof - Google Patents

Description

  The present invention relates to a process for forming an image on a recording medium using a black color material and a plurality of chromatic color materials.

The following techniques are known as techniques for realizing high color development by expanding the color gamut (color reproduction area) of a printer.
Patent Document 1 describes that, in addition to basic color inks of cyan, magenta, yellow, and black, a special color ink that expands the color gamut of basic colors such as red, green, and blue is used. Specifically, it is described that the red region of the color gamut is expanded by further using red ink that can reproduce red with higher saturation than red formed by overlapping magenta dots and yellow dots.
In Patent Document 2, when yellow dots and cyan dots are formed in an overlapping manner, the color development is different between the case where yellow dots are formed in the order of cyan and the case where cyan dots are formed in the order of cyan. Is described. Colors that can only be reproduced when layered in the order of yellow and cyan are formed in the order of cyan and yellow. It is described to expand.
Patent Document 3 describes that when red dots and yellow and magenta dots overlap, the color developability is reduced as compared with the case where they do not overlap. When the quantized color material amount data is converted into binary data representing dot formation / non-formation in association with a predetermined dot arrangement pattern, a dot arrangement pattern different from other colors is used for red. Thus, it is described that the probability of overlapping is reduced and the color gamut is expanded.

JP-A-6-233126 JP 2004-155181 A JP 2005-88579 A

  Here, there is a problem that the color gamut of a dark part (low brightness part) is lowered as a problem that occurs particularly noticeably in a printed matter printed with an ink jet printer mainly using a pigment as a colorant (pigment ink). FIG. 1 is a schematic diagram showing the color gamut shape of a yellow hue of a printed matter printed by a pigment ink jet printer. The horizontal axis in the figure is the saturation C * of the CIE Ch color space, the vertical axis is the lightness L *, the points A, B, C, and D are the colors of the outermost color gamut near white, yellow, black, and black, respectively. It is a point to show. As shown in the figure, the color gamut shape of the dark portion (low lightness portion) from yellow to black is greatly recessed inward compared to the straight line connecting yellow and black. Particularly in the vicinity of black, as can be seen from the position of the point D with respect to the point C, the saturation does not change so much even if the brightness changes greatly. Such a color gamut shape causes a gradation failure (collapse) in color mapping.

  However, since the techniques described in Patent Document 1 and Patent Document 3 require new ink, the structure of the printer becomes more complicated and larger.

  In the technique disclosed in Patent Document 2, the color gamut of intermediate brightness is expanded in the hue from yellow to green via cyan, but the color gamut of the dark part (low brightness area) from yellow to black is not expanded. .

  Accordingly, an object of the present invention is to expand the color gamut of the low brightness portion without adding a new recording material.

In order to solve the above problems, an image processing apparatus according to the present invention includes an image having black color material data corresponding to a black color material and a plurality of chromatic color material data corresponding to each of the plurality of chromatic color materials. Quantization means for quantizing data for each pixel; acquisition means for obtaining a maximum recording color material having a maximum pixel value in a target pixel among the black color material and the chromatic color material; and the maximum recording color Determining means for deciding whether or not to exclusively form dots in the target pixel of each of the black color material and the chromatic color material according to a material and a quantization result by the quantization means It is characterized by.

  According to the present invention, it is possible to expand the color gamut of the low brightness portion without adding a new recording material.

It is a schematic diagram which shows the color gamut shape of the yellow hue of the printed matter printed with the pigment inkjet printer. It is a graph which shows the example of the spectral reflectance of paper and an ink. It is a schematic diagram which shows arrangement | positioning on the recording medium of black ink and yellow ink. It is a graph which shows the spectral reflectance by arrangement | positioning of FIG. It is a graph which shows the color development by arrangement | positioning of FIG. 3 in the L * -b * plane of CIELab color space. It is a schematic diagram which shows arrangement | positioning on the recording medium of black ink and color ink. It is a graph which shows the spectral reflectance of the color ink area | region by arrangement | positioning of FIG. It is a graph which shows the spectral reflectance by arrangement | positioning of FIG. FIG. 7 is a graph showing color development by the arrangement of FIG. 6 on the L * -a * plane of the CIELab color space. It is a graph which shows the relationship between the overlapping state of an ink and the chromaticity of an image in the a * -b * plane of CIELab color space. It is a schematic diagram showing the arrangement of cyan ink and yellow ink on a recording medium. It is a graph which shows the spectral reflectance by arrangement | positioning of FIG. It is a graph which shows the color development by arrangement | positioning of FIG. 11 in the L * -a * plane of CIELab color space. 2 is a schematic diagram illustrating a schematic configuration of an image forming apparatus 1501. FIG. 1 is a block diagram illustrating a schematic configuration of an image forming system. It is a block diagram explaining the schematic structure of an image process. 5 is a schematic diagram illustrating an example of a color separation table stored in a color separation table storage unit 1608. FIG. It is a schematic diagram which shows color space (R ', G', B '). It is a schematic diagram which shows the color separation table of a black-color line. It is the block diagram which showed typically the halftone process by an error diffusion method. It is a figure which shows the mode of a process scan. 10 is a flowchart for explaining an operation performed by a halftone processing unit 1606. 6 is a diagram for explaining data stored in an accumulated error memory 2007. FIG. FIG. 3 is a schematic diagram of an image after performing a halftone process according to the first exemplary embodiment. FIG. 6 is a diagram schematically illustrating a recording head and a recording pattern in a multipass recording method.

  In this specification, ink that is a recording agent is expressed in katakana notation such as cyan, magenta, yellow, and black. The black ink is referred to as a black color material or black ink. Cyan ink, magenta ink, and yellow ink are collectively referred to as chromatic color material, chromatic color ink, or color ink. Cyan, magenta, and yellow are collectively referred to as color or chromatic color, and black is referred to as black or achromatic color. In addition, the color or its data and hue are represented by one uppercase letter such as C, M, Y, K. That is, C represents cyan or its data or hue, M represents magenta or its data or hue, Y represents yellow or its data or hue, and K represents black or its data or hue. .

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the structure shown in the following Examples is only an example, and this invention is not limited to the structure shown in figure. In addition, the same components are described with the same reference numerals.

<Relationship between image structure and color development>
A relationship between the spatial arrangement (hereinafter also referred to as an image structure) of color materials on a recording medium (for example, paper) and color development will be described with reference to the drawings.

  FIG. 2 is a schematic diagram showing the spectral reflectance of each of paper as a recording medium and ink as a color material, in which the horizontal axis represents wavelength and the vertical axis represents reflectance. A waveform 201 indicates the spectral reflectance of paper, a waveform 202 indicates the spectral reflectance of black ink, a waveform 203 indicates the spectral reflectance of cyan ink, and a waveform 204 indicates the spectral reflectance of yellow ink.

  Each color development when the ink having the reflection characteristics shown in FIG. 2 is arranged differently on the paper surface as shown in FIG. 3 will be described. Arrangement 301 shows a case where black ink and yellow ink are arranged side by side without overlapping each other (hereinafter also referred to as juxtaposed color mixing). On the paper surface, there is no area where the paper itself is exposed, and all areas are filled with any ink. The color development in the arrangement 301 is calculated from the weighted average based on the area ratio of each ink, that is, from the following equation (1), as can be seen from a generally known Murray-Davis equation.

R (λ) = S_K × R_K (λ) + S_Y × R_Y (λ) (1)
Here, R (λ), R_K (λ), and R_Y (λ) represent the reflectance at the wavelength λ of the black ink and the yellow ink, respectively, at the time of color mixing, and S_K and S_Y represent the paper surfaces of the black ink and the yellow ink, respectively. The area ratio (value of 0 to 1) on the upper side. An arrangement 302 shows a case where the black ink and the yellow ink overlap each other and are arranged in a layered manner (when a color material layer is formed). As with the arrangement 301, it is assumed that there is no area where the paper itself is exposed on the paper surface, and that all areas are filled with ink. Here, the color development in the arrangement 302 is calculated from the following equation (2).

R (λ) = R_Y (λ) + {T_Y (λ) ² × R_K (λ)} / {1−R_K (λ) × R_Y (λ)} (2)
Here, R (λ), R_K (λ), and R_Y (λ) represent the reflectance at the wavelength λ of the black ink and the yellow ink, respectively, and T_Y (λ) represents the transmittance of the yellow ink.

<Combination of black ink and one colored ink>
In particular, in the case of an ink having a larger amount of light scattering component than pigment ink, such as pigment ink, the reflectance and transmittance need to consider not only the light absorbing component but also the scattering component. As for the spectral reflectance characteristics shown in FIG. 2, a spectral reflectance model calculated from the above formulas (1) and (2) when an ink whose light scattering component cannot be ignored, such as a pigment ink, is used. The figure is shown in FIG. A waveform 401 corresponds to the arrangement 301, and a waveform 402 corresponds to the arrangement 302. For easy comparison, S_K and S_Y are adjusted so that the waveform 401 and the waveform 402 have the same brightness, but this does not affect which of the waveforms is sharp. It can be seen that the waveform 401 is the spectral reflectance of the waveform showing a steep change compared to the waveform 402.

  In other words, between the black ink that absorbs a large amount of light in the entire visible wavelength region and the colored ink that absorbs a small amount of light in some visible wavelength regions (hereinafter, the color inks other than the black ink are also called color inks) I can say that. When the inks are arranged side by side without overlapping each other as in the arrangement 301 (that is, the inks are mutually exclusive), the wavelength region where the absorption by the color ink is large (the short wavelength side in FIG. 4). Then, the reflectance is low. On the other hand, the reflectance increases in the wavelength region where absorption by the color ink is small (in FIG. 4, the long wavelength side). Therefore, the spectral reflectance shows a steep change as shown by the waveform 401. On the other hand, when the inks overlap each other as in the arrangement 302 and are arranged in layers above and below, if the absorption by one of the inks is large, the ink is absorbed more and the reflectance is low. Therefore, when an ink having a large absorption at all wavelengths such as black ink overlaps with another ink, the reflectance becomes low at all wavelengths.

  By the way, paying attention only to the light absorption, and assuming that the reflectance of the black ink is constant at all wavelengths, the spectral reflectance of the yellow ink arranged in layers above and below the black ink is It is only a constant multiple when placed. That is, since a steep waveform is maintained, even if the black ink and the yellow ink are arranged to overlap, the spectral reflectance is not low at all wavelengths.

  However, as described above, the scattering component cannot be ignored in the pigment ink. The absorption component lowers the reflectance as the absorption is higher, while the scattering component is added to the reflectance as a bias. In addition, since the scattering component is generally large at a wavelength with much absorption, the change in the spectral reflectance for each wavelength is moderated by the scattering component.

  Here, FIG. 5 shows the difference in coloring due to the difference between the arrangement 301 and the arrangement 302 on the L * -b * plane of the CIELab color space. This figure is the L * -b * plane in the yellow hue, the horizontal axis is b *, and the vertical axis is the lightness L *. A point 501 indicates yellow, a point 502 indicates black, a point 503 indicates the chromaticity in the case of the arrangement 301, and a point 504 indicates the chromaticity in the case of the arrangement 302. It can be seen that the greater the distance from the lightness L * axis, the higher the saturation, so that the point 503 has higher saturation than the point 504. Although yellow and black have been described as examples, the same applies to cyan and black, and magenta and black.

<Combination of black ink and two colored inks>
In the above, the combination of black ink and one colored ink has been described. Next, for the combination of black ink and two colored inks, the relationship between the spatial arrangement of the color material layer on the paper and the color development will be described.

  The description will be made assuming that the spectral reflectance of the ink is the same as that in FIG. The color development when the ink having the reflection characteristics shown in FIG. 2 is arranged on the paper as shown in FIG. 6 will be described. As described above, the black ink and the color ink are more highly colored when they are arranged side by side without overlapping each other, rather than being arranged in layers above and below each other. Here, a case where black ink and color ink are arranged exclusively without overlapping will be described as an example. The case where cyan ink and yellow ink are arranged side by side without overlapping each other as in arrangement 601 is compared with the case where cyan ink and yellow ink overlap each other and arranged in layers above and below as in arrangement 602. .

  In the case of the arrangement 601, the reflectance of the area on the paper surface where only the color ink excluding the black ink is arranged (hereinafter also referred to as the color ink area) is expressed by the waveform 203 in FIG. It is represented by a weighted average with the waveform 204. On the other hand, in the case of the arrangement 602, the reflectance of the color ink region excluding the black ink is obtained from the waveform 203 and the waveform 204 and the transmittance of each ink (not shown) using the above-described equation (2). FIG. 7 shows the spectral reflectances of the color ink regions of the arrangement 601 and the arrangement 602 obtained as described above. A waveform 701 corresponds to the arrangement 601, and a waveform 702 corresponds to the arrangement 602. As shown in the figure, it can be seen that the waveform 702 has a steeper spectral reflectance characteristic, that is, higher saturation than the waveform 701. In other words, the color inks are more highly colored when they are arranged one above the other in layers, rather than being arranged side by side without overlapping each other.

  Further, FIG. 8 shows the spectral reflectance of the entire region in which arbitrary ink including black ink is arranged in the case of the arrangement 601 and the arrangement 602. A waveform 801 corresponds to the arrangement 601, and a waveform 802 corresponds to the arrangement 602. This spectral reflectance is calculated using Equation (1) from the reflectance of the black ink and the reflectance of the color ink region. For easy comparison, the area ratio of the black ink and the color ink region is adjusted so that the brightness of the arrangement 601 and the arrangement 602 is the same, but the waveform is not affected.

  Here, FIG. 9 shows the difference in coloring due to the difference in arrangement between the arrangement 601 and the arrangement 602 on the L * -a * plane of the CIELab color space. This figure is the L * -a * plane in the green hue, the horizontal axis is a *, and the vertical axis is lightness L *. A point 901 indicates green, a point 902 indicates black, a point 903 indicates the arrangement 602, and a point 904 indicates the arrangement 301. It can be seen that the greater the distance from the lightness L * axis, the higher the saturation, so that the point 903 has higher saturation than the point 904. In addition, although the description has been given by taking an example of the dark color gamut from green (mixed color of cyan and yellow) to black, the same applies to red (mixed color of yellow and magenta) to black, and blue (mixed color of magenta and cyan) to black. .

<Combination of color ink and color ink>
Up to this point, the L * -a * plane and the L * -b * plane have been described. However, the chromatic color (hereinafter also referred to as exclusive color) that is recorded exclusively without overlapping with other dots is reduced to one color or less. The fact that a color with higher saturation can be reproduced will be described on the a * -b * plane of the CIELab color space. FIG. 10 is a schematic diagram for explaining the relationship between the ink overlap state and the chromaticity of the image, where the horizontal axis indicates a * in the CIELab color space and the vertical axis indicates b *. In the figure, point A indicates a color when all pixels are formed only by Y dots, point B indicates a color when all pixels are formed by overlapping Y dots and C dots, point C Indicates a color when all the pixels are formed by only C dots, and point O indicates an achromatic color. Here, the color of the first image including the first pixel formed only by Y dots and the second pixel formed by Y dots and C dots is indicated by a point on the line segment AB. Similarly, the color of the second image including the second pixel and the third pixel formed by only C dots is indicated by a point on the line segment BC. The color of the third image including the first pixel, the second pixel, and the third pixel is indicated by a point inside the triangle ABC.

  By the way, since the saturation of each point is given by the distance to the point O, the point P0 is closer to the point O than the point P1 at the point P0 inside the triangle ABC and the point P1 on the line segment AB. The color indicated by the point P0 is lower in saturation than the color indicated by the point P1. On the other hand, the hue angle of the color indicated by the point P0 and the color indicated by the point P1 are the same. That is, the color of the third image has lower saturation than the color of the first image having the same hue angle. The same applies to the relationship between the color of the third image and the color of the second image, and the color of the third image has lower saturation than the color of the second image having the same hue angle. .

  Here, the third image includes a plurality of exclusive colors (for example, two colors of Y dots and C dots). On the other hand, the first image and the second image include only one exclusive color. That is, by arranging dots of the chromatic color material so that the exclusive color is one color or less, a color having higher saturation than an image including a plurality of chromatic colors such as the third image can be reproduced.

  As described above, in order to expand the color gamut in a dark part where black ink is used, the following conditions contribute to the outermost color gamut. The condition is that the black ink and the color ink are exclusive, the color inks are arranged in an exclusive manner without overlapping each other, and the paper white is almost covered with any ink. It is three points of being done. Here, exclusion can also be said to mean that the centers of the dots do not overlap each other.

  Except for the outermost color gamut of the dark part, the color gamut does not change even if the color inks are excluded or overlapped. However, since the area where the color inks are overlapped is synonymous with the arrangement of dots with low brightness, the dots are visually noticeable, which causes a decrease in graininess. Therefore, it is possible to obtain a better image by forming different inks as much as possible except for the outermost color gamut of the dark part.

  Further, although the expansion of the color gamut is not so large, the exclusive color may be one color or less, and the color ink may be overlapped with the black ink.

  Here, the ink arrangement will be described for the bright color gamut that does not use black ink. The description will be made assuming that the spectral reflectance of the ink is the same as in FIG. When arranged on the paper as in the arrangement 1101 and the arrangement 1102 in FIG. 11, as described above, the spectral reflectance of each color ink region is as shown in FIG. On the other hand, the spectral reflectances of the arrangement 1101 and the arrangement 1102 including the area where the paper white is exposed are the weighted average with the paper white reflectance 201, and thus have the characteristics shown in FIG. In other words, if there is a region where paper white is exposed without being covered with ink, the change in spectral reflectance of the entire region becomes gradual. Therefore, by replacing Y in Equation (1) with W, the image It turns out that the whole saturation falls.

  However, as can be seen from the waveform 1201 and the waveform 1202, the spectral reflectances of the arrangement 1101 and the arrangement 1102 are substantially the same. Note that the area ratio of the paper white exposure area and each color ink area is adjusted so that the brightness is the same in the case of the arrangement 1101 and the arrangement 1102, but to determine which waveform is steep. Has no effect.

  FIG. 13 shows the color development in the arrangement 1101 and the arrangement 1102 on the L * -a * plane of the CIELab color space. This figure is the L * -a * plane in the green hue, the horizontal axis is a *, and the vertical axis is lightness L *. A point 1301 indicates green, a point 1302 indicates paper white, and a point 1303 indicates chromaticity in the case of the arrangement 1101 and the arrangement 1102. Naturally, from the spectral reflectance shown in FIG. 12, in the bright part where the black ink is not used, the color inks may overlap each other and be arranged in layers in the vertical direction, or may be arranged side by side without overlapping each other. The degree does not change. Note that the bright color gamut from paper white to green (mixed color of cyan and yellow) has been explained as an example, but paper white to red (mixed color of yellow and magenta), paper white to blue (mixed color of magenta and cyan) Is the same. The same applies to the light color gamut from paper white to cyan, magenta, and yellow.

  Therefore, when the color inks are arranged in layers in the upper and lower directions by overlapping the color inks, it is preferable to arrange them side by side without overlapping each other in the bright part where the black ink is not used.

[Example 1]
<Configuration of image forming system>
(Configuration of image forming apparatus)
First, the configuration of the image forming apparatus of this embodiment will be described. FIG. 14 is a schematic diagram illustrating the configuration of the image forming apparatus 1501 according to the present exemplary embodiment. The head cartridge 1401 includes a recording head and an ink tank that are integrally formed, and is mounted on the carriage 1402 in a replaceable manner. The head cartridge 1401 has a recording head composed of a plurality of ejection openings and an ink tank that supplies ink to the recording head, and is provided with a connector for transmitting and receiving signals for driving the ejection openings of the recording head. It has been. The carriage 1402 is provided with a connector holder for transmitting signals to the head cartridge 1401 via the connector. The carriage 1402 can reciprocate along the guide shaft 1403. Specifically, the carriage 1402 is driven by a main scanning motor 1404 as a driving source through a driving mechanism such as a motor pulley 1405, a driven pulley 1406, and a timing belt 1407, and its position and movement are controlled. The head cartridge 1401 mounted on the carriage 1402 is held so that the ejection port surface protrudes downward from the carriage 1402 and is parallel to the recording medium 1408. The movement of the carriage 1402 along the guide shaft 1403 is referred to as “main scanning”, and the movement direction is referred to as “main scanning direction”.

  A recording medium 1408 such as a print sheet is mounted on an auto sheet feeder (hereinafter referred to as ASF) 1410. When an image is formed, a pickup roller 1412 is rotated via a gear by driving a sheet feed motor 1411, and is separated and fed one by one from the ASF 1410. The Then, by the rotation of the transport roller 1409, the transport roller 1409 is transported to a recording start position facing the ejection port surface of the head cartridge 1401 on the carriage 1402. The conveyance roller 1409 is rotated through a gear by the rotation of the LF motor 1413. Whether or not the recording medium 1408 has been conveyed to the recording start position is determined by the paper end sensor 1414 detecting the passage of the recording medium 1408.

  The image forming operation is performed as follows. First, the recording medium 1408 is conveyed to a predetermined recording start position. Thereafter, the carriage 1402 moves on the recording medium 1408 along the guide shaft 1403, and ink is ejected from the ejection ports in accordance with a signal for driving each ejection port of the recording head during the movement. When the carriage 1402 moves to one end of the guide shaft 1403, the conveyance roller 1409 conveys the recording medium 1408 by a predetermined amount in a direction perpendicular to the scanning direction of the carriage 1402. Hereinafter, this is referred to as “paper feeding” or “sub-scanning”, and this transport direction is referred to as “paper feeding direction” or “sub-scanning direction”. When the conveyance of the predetermined amount of the recording medium 1408 is completed, the carriage 1402 moves again along the guide shaft 1403. In this way, an image is recorded on the entire recording medium 1408 by repeating scanning with the carriage 1402 of the recording head and paper feeding.

(Configuration of image forming system)
Next, the hardware configuration of the image forming system of this embodiment will be described with reference to the block diagram of FIG. A host 1500 as an image processing apparatus is realized by a personal computer, for example. The host 1500 includes a CPU 1503, a memory 1504, an input unit 1505 such as a keyboard, an external storage device 1506, an interface (hereinafter referred to as I / F) 1508 between the image forming apparatus 1501, and a monitor 1502. Video I / F 1507. The CPU 1503 executes various processes as image generation means in accordance with the program stored in the memory 1504, and executes the image processing of this embodiment. For example, these programs are stored in the external storage device 1506 as a printer driver, or supplied from an external connection device and appropriately read out and executed by the CPU 1503 using a memory 1504 used as a work area. The host 1500 outputs various information to the monitor 1502 via the video I / F 1507 and inputs various information via the input unit 1505. Further, the host 1500 transmits print data including image data subjected to image processing to the image forming apparatus 1501 via the I / F 1508.

  The image forming apparatus 1501 includes a control unit 1509 including a CPU 1510 that executes various processes, a ROM 1511 that stores control programs and various data, and a RAM 1512 that is used as a work area of the CPU 1510. The image forming apparatus 1501 further includes an interface 1515 with the host 1500, a motor driver 1516 for driving various motors, and a head driver 1514 for driving the recording head 1513. The various motors are a main scanning motor 1404, a paper feed motor 1411, and an LF motor 1413. The control unit 1509 receives print data from the host 1500 and executes image processing of this embodiment, and controls various motors and the recording head 1513 via a driver to record an image as image forming means.

<Image processing configuration>
Next, the configuration of image processing executed in the image forming system of this embodiment will be described with reference to the block diagram of FIG. A printer driver 1602 operating on the host 1500 converts input image data received from the application program 1601 into print data and outputs the print data to the image forming apparatus 1501. Conversion from input image data to print data is executed by a resolution conversion unit 1603, a color matching unit 1604, a color separation unit 1605, and a halftone processing unit 1606. The image forming apparatus 1501 converts the print data received from the printer driver 1602 into an ink ejection signal by the path decomposition unit 1609 and the ejection signal generation unit 1611, and records it on the recording medium 1408 by the recording head 1513. Details of processing performed by each unit will be described later. Note that part of the image processing executed by the host 1500 may be performed by the image forming apparatus 1501.

(Resolution converter)
A resolution conversion unit 1603 converts the resolution of the input image data into the resolution of the image forming apparatus 1501 and outputs the converted image. In this embodiment, the resolution of the image forming apparatus 1501 is 2400 dpi in the main scanning direction and 1200 dpi in the sub-scanning direction. The input image data is, for example, 600 dpi 8-bit RGB data. In this case, the input image data is represented by a set of pixels having a width of 1/600 inch, and each pixel has three types of red (R), green (G), and blue (B), each having a value from 0 to 255. Consists of signals. A resolution conversion unit 1603 converts the input image data into image data in the main scanning direction 2400 dpi and the sub-scanning direction 1200 dpi by a bicubic method that is a known resolution conversion method.

(Color matching part)
The color matching unit 1604 refers to the color table stored in the color table storage unit 1607, and determines the color signals (R, G, B) constituting the output image data of the resolution conversion unit 1603 depending on the image forming apparatus 1501. It converts into a signal (R ', G', B '), and outputs it. R ′, G ′, B ′ of the color signals (R ′, G ′, B ′) are 8-bit signals and take values from 0 to 255. The color table stored in the color table storage unit 1607 describes color signals (R ′, G ′, B ′) corresponding to discrete color signals (R, G, B). The color signals (R ′, G ′, B ′) are calculated by a known three-dimensional lookup table method (hereinafter referred to as 3DLUT method) using the color table. Preferably, a plurality of color tables corresponding to the type of recording medium and the purpose of image formation are prepared, and an appropriate color table can be selected.

(Color separation part)
The color separation unit 1605 refers to the color separation table stored in the color separation table storage unit 1608 and uses the color signal (R ′, G ′, B ′) as a color material amount signal (C) for the number of recording dots of each color material. , M, Y, K) for output (hereinafter, the color material amount signal is also referred to as color material amount data). Hereinafter, the color material amount signals (C, M, Y, K) are, for example, 8-bit signals, and C, M, Y, K each take a value in the range of 0 to 255.

  If the color material amount signal (C, M, Y, K) is (0, 20, 100, 255), the C dot, M dot, Y dot, and K dot are 0/255, 20/255, 100, respectively. / 255, 255/255. That is, in an image having a total number of pixels of n, 0/255 × n C dots, 20/255 × n M dots, 100/255 × n Y dots, and 255/255 × n K dots are formed. For example, in an image in which the color material amount signals (C, M, Y, K) of all 256 pixels in total 16 pixels in length and width are (0, 20, 100, 255), 0 C dots and 20 M Dots, 100 Y dots, and 256 K dots are formed.

FIG. 17 is a schematic diagram illustrating an example of a color separation table stored in the color separation table storage unit 1608. As shown in the figure, the color separation table is a three-dimensional lookup in which color material amount signals (C, M, Y, K) corresponding to discrete color signals (R ′, G ′, B ′) are stored. Table (hereinafter also referred to as 3DLUT). In this example, 729 (= 9 ³ ) lattice points in which R ′, G ′, and B ′ are any one of nine values of 0, 32, 64, 96, 128, 160, 192, 224, and 255, respectively. A color material amount signal is stored for each of the color signals. If the color signal R′G′B′in output from the color matching unit 1604 is a color signal described in the 3DLUT, the color separation unit 1605 searches the 3DLUT for the corresponding color material amount signal CMYKout and outputs it. If the color signal R′G′B′in is a color signal not described in the 3DLUT, the corresponding color material amount signal CMYKout is calculated and output using a known 3DLUT method (interpolation process).

  FIG. 18 is a schematic diagram showing color spaces (R ′, G ′, B ′). In the figure, Wp, Cp, Mp, Yp, Rp, Gp, Bp, and Kp are defined by the following signal values.

Wp = (R ′, G ′, B ′) = (255, 255, 255) (3)
Cp = (R ′, G ′, B ′) = (0, 255, 255) (4)
Mp = (R ′, G ′, B ′) = (255, 0, 255) (5)
Yp = (R ′, G ′, B ′) = (255, 255, 0) (6)
Rp = (R ′, G ′, B ′) = (255, 0, 0) (7)
Gp = (R ′, G ′, B ′) = (0, 255, 0) (8)
Bp = (R ′, G ′, B ′) = (0, 0, 255) (9)
Kp = (R ′, G ′, B ′) = (0, 0, 0) (10)
The color represented by the color material signal corresponding to the color signal on the surface of the cube in the R′G′B ′ color space constitutes the outermost contour of the color gamut. The color gamut of the dark portion particularly relates to a color signal of a black-color line that connects vertices represented by Kp and Cp, Mp, Yp, Rp, Gp, and Bp.

  FIG. 19 is a schematic diagram showing a black-color line color separation table of this embodiment, and the amount of color material in each of the Kp-Yp line (a) and the Kp-Gp line (b) constituting the outermost contour of the color gamut. Represents a signal. The horizontal axis of FIG. 19A is the value of R ′ or G ′ of the color signal (R ′, G ′, B ′), and (R ′, G ′, B ′) = (0, 0, 0). To (255, 255, 0) of Kp-Yp line color signals. The horizontal axis in FIG. 19B is the value of G ′ of the color signal (R ′, G ′, B ′), and (R ′, G ′, B ′) = (0, 0, 0) to (0 , 255, 0) shows the color signal of the Kp-Gp line. The vertical axis is a color material amount signal. Although not shown in the drawing, the color material amount signals C and M are both 0 regardless of the color signal in FIG. 19A, and the color material amount signal M is not related to the color signal in FIG. 19B. 0.

  As shown in the figure, in the black-color line of this embodiment, the sum of the color material amount signal K for black ink and the maximum signal value Colmax among the color material amount signals C, M, and Y for chromatic ink is 255 ( That is, it is set to be the maximum value that the input image data can take. In addition, at least one of the color material amount signals C, M, and Y of the chromatic ink is set to 0. The reason why the black-color line color material amount signal is set under such conditions will be described below.

  First, the reason why the sum of the color material amount signal K and the largest signal value Colmax among the color material amount signals C, M, and Y is set to 255 will be described.

  The first reason is that the black dots and the chromatic color dots are formed exclusively so that they do not overlap. As described above, when the black dots and the chromatic color dots are formed exclusively, it is possible to reproduce a darker or lighter color in the dark portion than when they are formed in an overlapping manner. Therefore, it is preferable to exclusively form black dots and chromatic color dots in the image corresponding to the color signals (R ′, G ′, B ′) at the outermost color gamut. However, when the sum of the color material amount signal K and Colmax exceeds 255, black dots and chromatic color dots overlap. For example, a case will be described in which the color material amount signals (C, M, Y, K) of all 256 pixels of 16 pixels vertically and horizontally are (0, 0, 32, 255). In the image in this case, since black dots are formed on all the pixels and yellow dots are further formed, 32 pixels where the black dots and the yellow dots overlap are generated. That is, since black dots and chromatic color dots are formed in an overlapping manner, the saturation cannot be increased in the dark part.

  The second reason is to prevent generation of pixels with exposed paper white. If the image that reproduces the color of the dark part includes pixels with paper white exposed, the density or saturation is reduced by the amount of paper white. Therefore, in the image corresponding to the color signals (R ′, G ′, B ′) at the outermost color gamut, any ink dot is preferably formed on all the pixels. However, if the sum of the color material amount signal K and Colmax is less than 255, pixels in which paper white is exposed are generated. A description will be given by taking an example of an image in which the color material amount signals (C, M, Y, K) of all 256 pixels of 16 pixels in length and width are (0, 0, 120, 127). In this case, there are 120 pixels where yellow dots are formed, 127 pixels where black dots are formed, and 9 pixels where none of the ink dots are formed, resulting in pixels where paper white is exposed. . That is, since the paper white is exposed, the saturation cannot be increased in the dark part.

  The third reason is to make the exclusive color one color or less. As described above, an image in which the exclusive color is one color or less can reproduce a color with higher saturation than an image including a plurality of exclusive colors. Therefore, it is preferable that the image corresponding to the color signal (R ′, G ′, B ′) at the outermost color gamut has an exclusive color of one color or less. However, if the sum of the color material amount signal K and Colmax is less than 255, a plurality of exclusive colors may be generated. Black and chromatic color dots are not overlapped for images with color material amount signals (C, M, Y, K) of (64, 0, 96, 127) for a total of 256 pixels of 16 pixels in length and width, and paper. A case where the pixel is formed so as not to generate white pixels will be described as an example. In this case, 32 pixels are formed by only cyan dots, 64 pixels are formed by only yellow dots, 32 pixels are formed by overlapping cyan dots and yellow dots, and black dots are formed. There are 127 pixels. That is, two colors of cyan dots and yellow dots become exclusive colors.

  Returning to FIG. 16, the details of the processing of the halftone processing unit 1606 will be described. In the following description, in image processing for processing multi-value data represented by a plurality of bits, the minimum target structural unit is referred to as a pixel, and data corresponding to the pixel is referred to as pixel data. . A pixel is a minimum unit that can express a gradation, and has a gradation value of 1 bit or more.

  In the halftone processing unit 1606, 8 bits (0 to 255) of the color signal values C, M, Y, and K determined by the color separation unit 1605 are recorded as 1 bit (for example, the image forming apparatus 1501 can record). 0 or 1), that is, binary data. FIG. 20 is a block diagram for explaining the configuration of the halftone processing unit 1606. An input terminal 2001 inputs pixel data. An accumulated error adding unit 2002 adds accumulated errors. A threshold setting terminal 2003 sets a quantization threshold. The quantization unit 2004 performs quantization processing. A quantization error calculation unit 2005 calculates an error in the quantization process. The error diffusion unit 2006 diffuses the quantization error. The accumulated error memory 2007 stores accumulated errors. The output terminal 2008 outputs pixel data formed after a series of processing. The quantization threshold set at the threshold setting terminal 2003 is used when the input pixel data is converted into two or more gradation numbers (two gradations in this embodiment).

  The halftone processing unit 1606 sequentially processes the input individual pixel data, and outputs the pixel data from the output terminal 2008 one pixel at a time. FIG. 21 is a diagram showing a state of processing scanning. The input terminal 2001 selects pixels to be processed one by one from image data configured by arranging a plurality of pixels, and inputs the pixel data. Each square in the figure indicates an individual pixel, a pixel 2101 indicates a pixel located at the upper left end of the image, and a pixel 2102 indicates a pixel located at the lower right end of the image. First, the pixel 2101 at the upper left corner of the image area is started as a selected pixel (hereinafter also referred to as a target pixel), and then the process proceeds while switching the target pixel one pixel at a time in the right direction in the direction of the arrow in the figure. When the processing is completed up to the right end of the uppermost row, the target pixel is moved to the left end pixel of the pixel row one stage below. In this order, the process scan is advanced along the arrows in the figure. When the process reaches the lower right pixel 2102 as the final pixel, the process scan of the image is completed.

  The operation performed by the halftone processing unit 1606 will be described with reference to the flowchart of FIG.

  When the processing is started, 8-bit pixel data to be processed is input from the input terminal 2001 for each color of C, M, Y, and K (step S2201).

  Next, the accumulated error adding unit 2002 adds the accumulated error for the target pixel position stored in the accumulated error memory 2007 to the input pixel data (step S2202). Here, the data stored in the cumulative error memory 2007 and the storage form of the data will be described with reference to FIG. The accumulated error memory 2007 includes one storage area E0_i {i = C, M, Y, K} and W recording areas E_i (x) {x = 1 to W for each color. i = C, M, Y, K} is secured. Here, W represents the number of pixels in the horizontal direction of the image data to be processed. In each region, an accumulated error E_i (x) applied to the target pixel is stored. The accumulated error value is obtained by a method described later, but is initially initialized with an initial value of 0 in all areas. In the accumulated error addition unit 2002, the value of the accumulated error E_i (x) corresponding to the horizontal position x (0 <x ≦ W) of the pixel is added to the input pixel data. That is, the pixel data input to the input terminal 2001 is I_i {i = C, M, Y, K}, and the data after the cumulative error addition in step S2202 is (I_i) ′ {i = C, M, Y, K}. Then, the following equation is obtained.

(I_i) ′ = I_i + E_i (x) (11)
In the subsequent step S2203, the order of the ink when the data (I_i) ′ {i = C, M, Y, K} after adding the cumulative error is sorted in descending order is Order_i {i = C, M, Y, K}. Record. For example, when the data (C, M, Y, K) of each color after adding the cumulative error is (255, 48, 224, 128), Order_i has the following data.

Order_C = 1 (12)
Order_M = 4 (13)
Order_Y = 2 (14)
Order_K = 3 (15)
In step S2204, the integrated value T_Ink is calculated from the image data after adding the cumulative error of each ink as shown in equation (16).

T_Ink = I_C ′ + I_M ′ + I_Y ′ + I_K ′ (16)
In step S2205, the integrated value T_Ink is compared with a preset threshold value and quantized in four steps. Examples of quantization results when the output value is N are shown in equations (17) to (21).

N = 0 (T_ink <128) (17)
N = 1 (128 ≦ T_ink <383) (18)
N = 2 (383 ≦ T_ink <638) (19)
N = 3 (638 ≦ T_ink <893) (20)
N = 4 (T_ink ≧ 893) (21)
N indicates the number of colors in which dots are formed in the target pixel. N may be changed according to the number of inks mounted in the image forming apparatus. For example, when the number of inks is 5, N may be 6. Needless to say, the threshold value is not limited to the above.

  In step S2206, it is determined whether or not the value of N calculated in step S2205 is zero. If N is 0, in step S2207, the output tone values O_i {i = C, M, Y, K} of all colors in the target pixel are set to 0.

  If the value of N is not 0, in step S2208, the ink recorded with Order_i = 1, that is, the ink with the largest amount of data after adding the cumulative error (the ink with the maximum recording amount) is the chromatic ink (C , M, Y).

  If the ink recorded at Order_i = 1 is not a chromatic color, the output gradation value O_K of the black ink of the pixel of interest is set to 1 in step S2209. After the determination of the K output gradation value, in step S2211, the C, M, and Y output gradation values O_i {i = C, M, Y} are set to zero.

  If the ink recorded in Order_i = 1 is a chromatic color, the N color component is set to 1 in step S2211 according to Order_i. For example, as in the above-described example, when the data (C, M, Y, K) after adding the accumulated error for each color is (255, 48, 224, 128), N = 3, so the accumulated error is added at the target pixel. The dots for the three colors are set to ON in the order of later data. According to the formulas (12) to (15), since the three colors are C, Y, and K in descending order, the output gradation value O_i {i = C, M, K} is set to 1. At the same time, O_M is set to 0.

  In step S2212, the black dot output tone value O_K is set to zero. That is, although N = 3 in the above-described example, K included in the three colors in order of the data after the cumulative error addition is forcibly overwritten to 0, so that only the dots for two colors are actually present. Not recorded.

  With the above processing, the quantization processing for all colors of C, M, Y, and K is completed. Next, error calculation and error diffusion processing will be described.

  In step S2213, the quantization error calculation unit 2005 calculates a quantization error E_i from the pixel data (I_i) ′ after the accumulated error addition and the output pixel value O_i by the following equation.

E_i = (I_i) ′ − O_i × 255 (28)
In step S2214, the error diffusion unit 2006 performs an error diffusion process as follows according to the horizontal position x of the target pixel. That is, the quantization error to be stored in the storage areas E0_i and E_i (x) is calculated according to the following process and stored in the accumulated error memory. In addition, the arrow in a formula represents substitution calculation.

E_i (x + 1) ← E_i (x + 1) + E_i × 7/16 (x <W)
(29)
E_i (x-1) ← E_i (x-1) + E_i × 3/16 (x> 1)
(30)
E_i (x) ← E0_i + E_i × 5/16 (1 <x <W)
(31)
E_i (x) ← E0_i + E_i × 8/16 (x = 1)
(32)
E_i (x) ← E0_i + E_i × 13/16 (x = W)
(33)
E0_i ← E_i × 1/16 (x <W)
(34)
E0_i ← 0 (x = W)
(35)
Thus, the error diffusion process for one pixel input to the input terminal 2001 is completed.

  In step S2215, it is determined whether each process of step S2201 to step S2208 has been performed on all pixels of the image. That is, it is determined whether or not the input pixel has reached the pixel 2102 in FIG. 21. If not, the target pixel is advanced by one in the direction of the arrow, and the process returns to step S2201. If it is determined that the processing has been performed for all pixels, the halftone processing of this embodiment is completed, and the 256-value color material amount signal (C, M, Y, K) output from the color separation unit 1605 is completed. ) Is converted into binary signals (C ′, M ′, Y ′, K ′) representing ON / OFF of the dots.

  Regarding the image after the halftone processing of this embodiment is performed on the image data whose color material amount signals (C, M, Y, K) after color separation are all (127, 0, 64, 128). This will be described with reference to the schematic diagram of FIG. For simplicity, an area composed of predetermined 8 × 4 pixels is extracted from the above-described image. K in the figure indicates that only the black dot is ON. Similarly, C indicates that only cyan dots are ON, and C / Y indicates that both cyan and yellow dots are ON. It can be seen that black dots and chromatic dots are arranged exclusively. As shown in FIG. 24, it can be seen that one of the inks is ON, and the paper white is not exposed. It can also be seen that there is no pixel in which only the yellow dot is ON, and two chromatic colors are not formed exclusively. In the above description, the method of executing the binarization processing by the error diffusion method has been described. However, the binarization processing may be executed by using, for example, the dither method, and the chromatic color dots are turned OFF with the black dots being ON pixels. If the binarization is performed, the halftone processing method is not limited.

(Path decomposition part)
The 1-bit data of each color C, M, Y, and K processed by the halftone processing unit 1606 is sent to the image forming apparatus 1501. Since the presence or absence of dots for each area on the recording medium has been determined, a desired image can be formed by inputting this information as it is into the drive circuit of the recording head. That is, image formation for the recording head width may be completed in one main scan.

  However, since an inkjet recording apparatus usually employs a recording method called multipass recording, the multipass recording method will be briefly described below. In the ink jet recording method, a line type for forming an image by moving only the recording medium in the sub-scanning direction using a recording head corresponding to the print area width, and a main recording and sub-scanning using a recording head having a shorter width than the line type. There is a serial type in which scanning is alternately repeated to form images sequentially. The recording main scan is to move and scan a carriage on which the recording head is mounted with respect to the recording medium, and the sub-scan is to convey a predetermined amount in a direction orthogonal to the recording main scan. In this case, the width of the area printed in one printing main scan is determined by the arrangement density and the number of the plurality of ink discharge ports formed in the printing head. When recording is performed in one recording scan, variations in the ink recording position occur due to manufacturing errors of the nozzles that eject ink, airflow due to the recording main scanning of the recording head, and so on, resulting in density stripes called “banding”. The image quality is deteriorated. Therefore, in practice, in order to further improve the image quality, a multi-pass recording method is often employed.

  In the multi-pass method, an image is completed for the first time by a plurality of recording main scans using different blocks. Therefore, not all recordable image data is recorded in one recording main scan. Here, a so-called mask is used for distributing the image data to each block (thinning out the image data into each block). This mask is often determined independently of the image signal. For example, by installing an AND circuit of the mask and the image signal in each recording element, the image signal given in each recording scan is recorded. A configuration for determining whether or not to do so can be formed.

  FIG. 25 schematically shows a recording head and a recording pattern in order to explain the multipass recording method. Reference numeral 2501 denotes a recording head, which generally has about 768 nozzles, but here it is assumed to have 16 nozzles for simplicity. As shown in the drawing, the nozzles are divided into first to fourth nozzle groups, and each nozzle group includes four nozzles. Reference numeral 2502 denotes a mask pattern, and the area where each nozzle performs recording is shown in black. The patterns recorded by each nozzle group are complementary to each other. When these patterns are overlapped, recording of a region corresponding to a 4 × 4 area is completed. Each pattern indicated by pattern 2503 to pattern 2506 shows a state in which an image is completed by overlapping recording scans. When each recording scan is completed, the recording medium is conveyed by the width of the nozzle group in the direction of the arrow in the figure. Therefore, the same area of the recording medium (area corresponding to the width of each nozzle group) is configured such that an image is completed only after four recording scans. As described above, the formation of each same area of the recording medium by a plurality of nozzle groups by a plurality of scans has an effect of reducing variations peculiar to the nozzles and variations in the conveyance accuracy of the recording medium.

  Here, for the sake of simplicity, a 4 × 4 area has been described as an example. For example, in the case of a print head having 768 nozzles, the vertical direction is the number obtained by dividing the 768 area by the number of print passes, and the horizontal direction is 256 areas. A mask pattern (mask data) having a degree is generally used.

  In this embodiment, the mask data is stored in a memory in the main body of the forming apparatus, and the path decomposition unit 1609 performs AND processing between the mask data and the output signal of the halftone process described above. The formation pixels that are actually ejected are determined in each recording scan. The ejection data C′i, M′i, Y′i, and K′i (i is a scan number) for each scan generated by the pass decomposing unit 1609 are printed by the ejection signal generating unit 1610 at an appropriate timing. 1513 is sent to the drive circuit. Accordingly, the recording head 1513 is driven and each ink is ejected according to the ejection data.

  Note that the processing of the path decomposing unit 1609 in the image forming apparatus 1501 is executed under the control of the CPU 1510 that constitutes the control unit of the forming apparatus using a dedicated hardware circuit for them.

  The control method of the dot arrangement data of the black color material (black color material data) and the dot arrangement data of each chromatic color material (chromatic color material data) at the outermost shell of the color gamut in the dark part has been described above. As described above, in the color located in the outermost shell of the dark part in the color gamut that can be formed using the black color material and the plurality of chromatic color materials, the black color material data and the chromatic color material data are By making it exclusive, the color gamut of the dark part can be expanded. By making the black color material data and the chromatic color material data exclusive in at least the color gamut in which the value of the black color material amount data is larger than any chromatic color material amount data value The effect of expanding the color gamut can be obtained.

In addition, when controlling dot exclusion and overlap using error diffusion processing, a so-called dot generation delay may occur in the conventional method. For example, this is a case where dots of color material data that are desired to be prevented from overlapping are determined based on the result of halftone processing of certain color material data preferentially. This method also allows dot exclusion and superimposition control, but due to the influence of preferentially determined color material data, other non-prioritized color material data will be added to pixels that are behind the original dot-on position. Will turn on. This dot generation delay may cause image degradation.
However, as shown in the above-described embodiment, since the dots of the color material having the maximum recording amount are preferentially turned on for each pixel, image deterioration due to dot generation delay can be reduced.

  Note that the color separation table setting method in the color separation unit 1605 is not limited to the above-described method. For example, in a color separation table for a recording medium in which an upper limit value of the total color material amount is set, ink overflow can be avoided by setting the color material amount data so as to satisfy the upper limit value. Further, by setting the color material amount data to be equal to or less than the above upper limit value, the ink consumption can be suppressed. In this case, there may occur a pixel in which paper white where no dots are formed is exposed, or there may be two or more exclusive colors. However, even in such a case, by arranging black dots and chromatic color dots exclusively, the color gamut can be expanded within the setting range of the color separation table.

[Other Examples]
(Image processing)
The resolution conversion method is not limited to the bicubic method. Further, it is preferable to convert the resolution to match the dot arrangement on the recording medium.

(Configuration of image forming apparatus)
Although the four-pass printing configuration has been described in the above embodiment, the number of main scans is not limited to four. A configuration in which recording is performed by two or eight main scans may be used.

  The present embodiment can also be effectively applied to a full-line type ink jet printer that does not perform main scanning.

  Furthermore, the present invention can be applied to an image forming apparatus of another recording method such as an electrophotographic printer or a sublimation printer. In this case, toner or an ink ribbon is used as a recording material instead of ink. In the above embodiment, an example of an image forming system combined with a host computer has been described. However, an image forming apparatus used as an image output terminal of an information processing device such as a computer may be used. Further, it may be a copying apparatus combined with a reader or the like, or a facsimile apparatus having a transmission / reception function.

(Type of recording agent)
In the image forming apparatus, black ink (black color material) described in Embodiment 1 and ink (recording agent or color material) other than chromatic inks of C, M, and Y may be mounted. Specifically, a gray ink (gray color material) having a relatively higher lightness than the black ink and a light color ink (light color material) having a relatively higher lightness than the chromatic color ink may be further mounted. Also in this case, the black ink and the non-black ink are exclusive, and the non-black ink recorded exclusively is one color or less. Further, the above embodiment may be applied to a gray ink capable of reproducing a high density black color instead of the black ink. Further, gray light ink may be handled as chromatic ink. Further, in a printer equipped with two types of black ink, the above embodiment may be applied only to one black ink.

(Program, print media)
The present invention can also be realized by supplying a storage medium storing a program code of software for realizing the functions of the above-described embodiments (for example, the steps shown in the above flowchart) to a system or apparatus. In this case, the functions of the above-described embodiments are realized by the computer (or CPU or MPU) of the system or apparatus reading and executing the program code stored in the storage medium so that the computer can read the program code.

Claims (10)

Quantization means for quantizing image data having black color material data corresponding to a black color material and a plurality of chromatic color material data corresponding to each of the plurality of chromatic color materials for each pixel;
Among the black color material and the chromatic color material, an acquisition means for acquiring a maximum recording color material having a maximum pixel value in a target pixel;
Deciding means for deciding whether or not to exclusively form dots in the target pixel of each of the black color material and the chromatic color material according to the maximum recording color material and the quantization result by the quantization means And an image processing apparatus. When the maximum recording color material in the target pixel is a black color material, the determination unit determines that the black color material dot is formed and the chromatic color material dot is not formed, and the maximum recording color material is formed. The image processing apparatus according to claim 1 , wherein when the color material is the chromatic color material, it is determined that the dots of the chromatic color material are formed without forming the dots of the black color material . The determination unit, the case where the quantization result of the pixel of interest is 0, the image processing according to claim 1 or 2, characterized in that it is formed to be the black colorant and either said chromatic colorant dots apparatus. The determining means determines the number of color material colors that can be recorded based on the maximum recording color material ,
When the maximum recording color material is a chromatic color material, the dots of the color material having the number of recordable color materials are formed, and the dots of the black color material are not formed. The image processing apparatus according to claim 1.   The image processing apparatus according to claim 1, wherein the quantization by the quantization unit is quantization according to the number of color materials representing the image data. The image processing apparatus according to claim 1, wherein the quantization unit uses an error diffusion method. The image processing apparatus according to claim 1, wherein the quantization unit uses a dither method. It claims 1 to based on image data obtained by the image processing apparatus according to any one of 7, an image forming apparatus for forming an image on a recording medium by an inkjet method. A program that causes a computer to function as each unit of the image processing apparatus according to any one of claims 1 to 7 . A method for controlling an image processing apparatus having quantization means, acquisition means, and determination means,
The quantization means quantizes image data having black color material data corresponding to a black color material and a plurality of chromatic color material data corresponding to each of the plurality of chromatic color materials for each pixel,
The acquisition unit acquires a maximum recording color material having a maximum pixel value in a target pixel among the black color material and the chromatic color material,
Whether the determination unit exclusively forms dots in the target pixel of each of the black color material and the chromatic color material according to the maximum recording color material and the quantization result by the quantization unit. Determining a control method.

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