JP2019130732A - Image processing system, image processing method and ink jet recording device - Google Patents

Abstract

To provide an image processing method by which granular feeling and streak unevenness which are specific to ink jet recording are so made as to be not conspicuous.SOLUTION: Whether an image of a processing object is a concerned image such that granular feeling is concerned during viewing or not is determined. In addition, color decomposition treatment, such that a gradation region, in which an ink having a low brightness is used when it is determined that the image is a concerned image, is a gradation region having a brightness lower than that of a gradation region in which the ink is used when it is determined that the image is not a concerned image.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an image processing apparatus and an image processing method for inkjet recording.

  Patent Document 1 discloses a method in which the color recognized when a person views an image varies depending on the viewing environment, and the image processing performed at the time of image output varies depending on the viewing environment. .

  FIG. 1 shows the luminance value of image data and an image output based on the luminance value when viewed under a general illuminance of about 100 to 300 lux and under a high illuminance illumination of 1000 lux or more. It is a figure which shows the difference in the coloring in the case of doing. Even if the output image is based on the same brightness value, the image viewed under high-light illumination has higher color development and can express a wider range of gradations than the image viewed under general illumination. I know that there is.

  In Patent Document 1, in consideration of the above situation, image processing such as color conversion processing is made different depending on the viewing environment, so that stable color reproduction independent of the viewing environment can be realized.

Japanese Patent Laid-Open No. 2006-54356

  By the way, in an ink jet recording apparatus, there are reduction factors of image quality peculiar to ink jet recording, such as dot granularity and unevenness, and the conspicuousness of such factors may depend on the viewing environment. For example, under high illumination illumination, the contrast between the area where dots are recorded and the area where no dots are recorded becomes strong, and uneven stripes depending on the graininess of the dots and the ejection characteristics of the nozzles tend to stand out. In particular, since black ink has a high density, it can be said that the above-mentioned reduction factor is easily noticeable.

  However, Patent Document 1 does not pay attention to harmful effects peculiar to ink jet recording such as graininess and stripe unevenness. Therefore, even if the method of Patent Document 1 is employed and the same color development is obtained under high illumination illumination and normal illumination, it is not possible to alleviate the graininess and unevenness of dots under high illumination illumination.

  The present invention has been made to solve the above problems. Therefore, an object of the present invention is to provide an image processing apparatus and an image processing method for preventing the graininess and unevenness of dots peculiar to inkjet recording from being noticeable even under high illumination illumination.

  Therefore, the present invention is an image processing apparatus for recording an image on a recording medium by causing a recording head to eject a plurality of colors of ink according to a multi-value density signal, and an image to be processed is recorded on the recording medium. A judging means for judging whether or not there is a concern that the graininess may be recognized when the recorded image is viewed, and a multi-value RGB signal of the image to be processed according to the judgment of the judging means Color separation means for converting the color separation means into the multi-value density signal corresponding to each of the inks of the plurality of colors, and the color separation means, when the judgment means judges that the image is a concern image, A gradation area that uses an ink with relatively low lightness among color inks and has a lightness that is lower than a gradation area that uses the ink when the determination means determines that it is not the concerned image As in frequency, and converting the multi-value RGB signal of the image data of the processing target in the multi-value density signals.

  According to the present invention, it is possible to prevent graininess and stripes from becoming noticeable even in a high-illumination viewing image.

It is a figure for demonstrating the difference in the coloring by the illumination intensity at the time of appreciation. It is a block diagram which shows the control structure of the printing system which can be used by this invention. It is a schematic block diagram of the recording device in a printing system. FIG. 3 is a block diagram illustrating a configuration of a series of image processing executed in the printing system. It is a flowchart for demonstrating the process of the recording process of 1st Embodiment. FIG. 5 is a diagram comparing LUT1 and LUT2 used in color separation processing. It is a flowchart for demonstrating the process of the recording process of 2nd Embodiment. It is a figure which shows the relationship between illumination intensity and the coloring of a to-be-photographed object. It is a flowchart for demonstrating the process of the recording process of 4th Embodiment. It is a figure which shows the production | generation method of a color conversion LUT.

(First embodiment)
FIG. 2 is a block diagram showing a control configuration of a printing system that can be used in the present invention. The printing system of this embodiment includes a host device 100 and an ink jet recording device 200.

  The host device 100 is a personal computer or the like, and includes a CPU 10, a memory 11, a storage unit 13, an input unit 12 such as a keyboard and a mouse, and an interface 14 for communication with the recording device 200. The CPU 10 performs various processes according to various programs and parameters stored in the storage unit 13 while using the memory 11 as a work area. For example, the user can generate a recording command after creating a desired image on the application of the host device 100 and setting various recording conditions via the input unit 12. “Whether or not the image is supposed to be viewed under high illumination illumination”, which will be described later, is also information set by the user via the input unit 12.

  The recording apparatus 200 is an inkjet recording apparatus, and includes a CPU 20, a memory 41, a storage unit 42, an interface (I / F) 43 for communication with the host apparatus 100, and a recording unit 44 that executes a recording operation. In accordance with various programs and parameters stored in the storage unit 42, the CPU 20 performs various processes while using the memory 41 as a work area to control the entire apparatus. For example, an image processing flowchart described later with reference to FIGS. 5 and 7 is also executed by the CPU 20 according to various programs and table parameters stored in the storage unit 42.

  FIG. 3 is a schematic configuration diagram of the recording apparatus 200 in the printing system. The configuration described here corresponds to the recording unit 44 in FIG. The recording apparatus 200 of the present embodiment includes recording heads 21K, 21C, 21M, and 21Y (hereinafter simply referred to as recording head 21) that eject black (K), cyan (C), magenta (M), and yellow (Y) inks, respectively. Also called). These four recording heads 21 are mounted on a carriage 28 in the arrangement shown in the figure, and the carriage 28 can reciprocate along a guide shaft 23 extending in the x direction in the figure. A driving force for moving the carriage 28 is transmitted from the carriage motor 24 via the motor pulley 25, the driven pulley 26 and the timing belt 27.

  The recording medium S in the area that can be recorded by the reciprocating movement of the recording head 21 is sandwiched between the upstream side and the downstream side in the y direction by the two pairs of transport rollers 29, 30, and 31, and maintains a smooth surface. . While the ink is ejected from each of the recording heads 21K, 21C, 21M, and 21Y according to the recording data, the carriage 28 moves in the x direction, thereby performing one recording scan. An image is formed stepwise on the recording medium S by alternately repeating such a recording scan and a predetermined amount of conveying operation by the conveying roller pairs 29, 30 and 31, 32.

  FIG. 4 is a block diagram for explaining a configuration of a series of image processing executed in the printing system of the present embodiment. In this embodiment, the CPU 10 of the host apparatus 100 executes the color space conversion pre-processing 401, and the CPU 20 of the recording apparatus 200 executes the color separation process 402, the output γ process 403, and the quantization process 404. Hereinafter, each process will be described in detail.

  When the host device 100 prints an image created by an application or the like, the image data is provided to the printer driver. In this embodiment, the image data at this time is assumed to be 8-bit RGB data for each color in accordance with the sRGB standard. Then, the printer driver generates the same 8-bit R′G′B ′ data by performing color space conversion pre-processing 401 on the 8-bit RGB data. The color space conversion pre-process is a conversion process for associating a color space that can be expressed by the sRGB standard with a color space that can be expressed by the recording apparatus 200. Specifically, referring to a three-dimensional lookup table (LUT) stored in the memory 11 in advance, each color 8-bit RGB signal is similarly converted to an 8-bit R′G′B ′ signal for each color. Here, for the sake of explanation, the conversion process from 8 bits to 8 bits is used. However, the conversion process may be a form in which the number of gradations is expanded, such as 8 bits to 10 bits. In the present embodiment, the image data is provided to the recording apparatus 200 via the interface 14 in the state of R′G′B ′.

  The CPU 20 of the recording apparatus 200 that has received the R′G′B ′ image data performs a color separation process 402 on the acquired R′G′B ′ signal. In the color separation process, color coordinate data including three elements R, G, and B is converted into K (black), C (cyan), M (magenta), and yellow (Y) corresponding to the ink colors used by the recording apparatus 200. ) To separate the color coordinate data consisting of four elements. Specifically, referring to a three-dimensional LUT stored in the memory 41 in advance, each color 8-bit R′G′B ′ signal is converted into a 10-bit KCMY signal for each color.

  Subsequently, the CPU 20 performs output γ processing 403 for each of (K, C, M, Y). The output γ process is a correction process for adjusting the input signals of K, C, M, and Y and the image density expressed by the recording medium to have a linear relationship. Specifically, referring to the one-dimensional LUT stored in the memory 41 in advance, each of the 10-bit (K), (C), (M), and (Y) signals of each color is converted into the same 10-bit (K ′) of each color. (C ') (M') (Y ') signal is converted.

  Further, the CPU 20 performs a quantization process 404. The quantization process 404 is a process for converting a 10-bit multi-value density signal for each of K, C, M, and Y into a 1-bit binary signal indicating dot recording “1” or non-recording “0”. is there. As the quantization processing method, a known dither method, error diffusion method (ED), or the like can be employed. Through the quantization process, dot recording “1” or non-recording “0” for each pixel is determined for each ink color.

  FIG. 5 is a flowchart for explaining a recording process performed by the CPU 20 of the recording apparatus 200 when a recording command is input from the host apparatus 100. When the recording command is received, the CPU 20 first analyzes the received image data in step S500. In addition to the RGB data of the image to be recorded, the image data includes various information related to the recording process such as the image size and the recording mode designated by the user. In the present embodiment, information on whether or not an image is assumed to be viewed under high illumination illumination (hereinafter referred to as a high illumination viewing image) is also included in the image data together with these information. To do.

  In step S <b> 501, the CPU 20 determines whether the processing target image is a high illuminance viewing image. In No, it progresses to step S502 and sets standard color separation table LUT1 for a process target image. On the other hand, in the case of Yes, the process proceeds to step S503, and the color separation table LUT2 prepared for the high-illumination ornamental image is set for the processing target image.

  In step S504, the CPU 20 executes the color separation process 402 described with reference to FIG. 4 using the color separation table set in step S502 or step S503. Following this, output γ processing 403 and quantization processing 404 are executed, and the obtained 1-bit data is stored in the print buffer of the memory 41.

  Thereafter, in step S505, the CPU 20 sequentially reads the 1-bit data stored in the print buffer, and executes the recording scan on the recording medium S according to the recording mode analyzed in step S500. This process is complete | finished above.

  6A and 6B are diagrams for comparing LUT1 and LUT2 used in the color separation process 402. FIG. FIG. 6A shows an LUT 1 used for a standard image, and FIG. 6B shows an LUT 2 used for a high-illumination viewing image. Both LUT1 and LUT2 are three-dimensional LUTs. Here, the surface of the achromatic color gradation where the input signal goes from white (R = G = B = 255) to black (R = G = B = 0), The relationship between the input signal RGB and the output signal CMYK is shown.

  In the case of LUT1, as the input signal gradually decreases from R = G = B = 255, the output signals of C, M, and Y gradually increase. However, the black (K) output signal remains zero until the input signal reaches R = G = B = 127. In this way, in the low gradation region where the graininess of the dots is conspicuous, only yellow, cyan, and magenta inks with high lightness are mixed even when an achromatic color (R = G = B) is expressed. The black ink with low brightness is used as much as possible.

  From the intermediate gradation in which the image area is almost filled with dots, that is, when the input signal exceeds R = G = B = 127, the output signals of C, M, and Y gradually decrease, and the black (K) signal gradually increases. To increase. When R = G = B = 0, the output signals of C, M, and Y are 0, and the output signal of K is the maximum value.

  In LUT2, the outline of the graph is the same as that of LUT1. However, in the case of LUT2, even if the input signal exceeds R = G = B = 127, the output signals of C, M, and Y continue to rise for a while and the output signal of black (K) remains 0. When the input signal exceeds R = G = B = 85, the output signals of C, M, and Y decrease with a steeper slope than LUT1, and the black (K) signal increases with a steeper slope than LUT1. When R = G = B = 0, the output signals of C, M, and Y are 0 and the output signal of K is the maximum value, as in LUT1.

  When these two LUTs are compared, the starting point at which the output signal of K becomes larger than 0 is shifted to the higher density side in LUT2 (85) than in LUT1 (127). This means that the first black dot is recorded in the state where more color dots are recorded in LUT2 than in LUT1. That is, the LUT 2 has an effect of making the contrast of isolated black dots weaker than that of the LUT 1 and suppressing graininess and unevenness.

  However, when LUT2 is used, since the amount of cyan, magenta, and yellow, and thus the overall ink consumption, is greater than when LUT1 is used, the running cost may be reduced. Therefore, in the present embodiment, for a standard image that is not a high-illumination viewing image, the LUT 1 is used in which the running cost is given priority and the ink consumption is suppressed.

  As described above, in the present embodiment, for a high-illumination ornamental image in which the granularity of dots and uneven stripes are conspicuous, priority is given to reducing the granularity and unevenness of black ink, and the gradation region using black dots LUT2 in which is reduced to the high concentration side is used. On the other hand, for a standard image that is not a high illumination viewing image, a standard LUT 1 giving priority to running cost is used. Thereby, it is possible to perform color conversion processing suitable for each of the high-illumination ornamental image and the standard image so that the graininess and the unevenness are not conspicuous.

  Here, as an example, the case where the input signal is fixed to an achromatic color gradation (R = G = B) has been described. However, the LUT 2 of this embodiment can obtain the same effect as described above in any hue. The input signal and the output signal are associated with each other. That is, in the LUT 2 of this embodiment, the starting point of black (K) is in a gradation region having a lightness lower than that of the LUT 1 in any color, so that graininess is not noticeable. .

(Second Embodiment)
Also in this embodiment, the printing system and the image processing method described with reference to FIGS. The present embodiment is characterized in that the recording operation method is switched in addition to the LUT used in the color separation process 402 based on whether or not the image is a high-illumination ornamental image.

  FIG. 7 is a flowchart for explaining the recording processing steps when the number of multi-passes during the recording operation is switched together with the LUT. The only difference from the flowchart described in FIG. 5 is steps S802 and S803.

  If it is determined in step S801 that the processing target image is not a high-illumination viewing image, the CPU 20 proceeds to step S802, and sets the color separation table LUT1 and “also a multi-pass recording mode”. On the other hand, if it is determined in step S801 that the processing target image is a high illumination viewing image, the CPU 20 proceeds to step S803 and sets the color separation table LUT2 and “16-pass multi-pass recording mode”.

  Thereafter, in step S805, the CPU 20 sequentially reads the 1-bit data stored in the print buffer, and executes the recording scan on the recording medium S according to the recording mode set in step S802 or step S803. That is, when the processing target image is not a high-illumination ornamental image, the image is recorded by 8-pass multi-pass recording. When the processing target image is a high-illumination viewing image, the image is recorded by 16-pass multi-pass recording.

  Here, multipass recording is a recording method in which an image in a unit area of a recording medium is completed by a plurality of recording scans by the recording head while interposing a transport operation for a distance shorter than the recording width of the recording head. . If such multi-pass printing is performed, since one pixel line extending in the scanning direction can be printed in place of a plurality of nozzles, unevenness due to ejection characteristics of individual nozzles and density unevenness are reduced and uniform. Can be obtained. The effect can be enhanced as the number of multipaths is increased. On the other hand, however, if the number of multipaths is increased too much, the throughput when outputting an image decreases. Therefore, the number of multipasses in multipass printing is preferably adjusted appropriately according to the type of recording medium, the image quality desired by the user, and the like.

  In this embodiment, for high-illumination ornamental images in which dot granularity and streak are easily noticeable during viewing, priority is given to reducing the black ink granularity and streak, and LUT2 is used and 16-pass multipass printing is performed. Do. On the other hand, for a standard image that is not a high-illumination viewing image, priority is given to reducing the running cost and improving the throughput, and LUT1 is used and 8-pass multipass printing is performed. As a result, it is possible to perform color conversion processing and multi-pass recording suitable for each of the high-illumination ornamental images and the standard images, and output an image in which graininess and unevenness are not noticeable in a preferable state.

  In the above, the 8-pass multi-pass recording and the 16-pass multi-pass recording are exemplified, but of course the number of multi-passes is not limited to this. As long as the number of multi-passes when recording a high-illumination ornamental image is smaller than the number of multi-passes when recording a standard image, various multi-pass numbers can be adopted.

  In the above, the recording process of the high-illumination ornamental image and the standard image is made different for the two elements of the LUT and the multi-pass recording method used in the color separation process 402, but more elements may be made different. . For example, for high-illumination viewing images, quantization processing 404 performs error diffusion processing in which the graininess of highlight portions is not noticeable, and for standard images, quantization processing 404 performs fast dither processing. You may make it do.

  In addition, in the recording process of a high-illumination ornamental image, for the purpose of improving the glossiness of the image surface, a predetermined clear ink may be recorded separately from the color ink, or the applied amount may be adjusted. May be.

(Third embodiment)
Also in this embodiment, the printing system and the image processing method described with reference to FIGS. In the present embodiment, it is assumed that the LUT used in the color separation process 402 is switched based on whether or not it is an “image shot by underexposure”.

  FIG. 8 is a diagram showing the relationship between the illumination intensity and the color of the subject. Even for a subject having the same gradation range, the color expression range is wider under high illumination illumination than under standard illumination illumination. However, when shooting this subject with a digital camera, there is an upper limit of detectable illuminance in the digital camera itself, so output values above a specific illuminance are unified (saturated) to the upper limit, and the desired gradation expression can be achieved. There may not be. Therefore, when shooting under high-illuminance illumination, there is a known technique that harmonizes the gradation range of the subject with the illuminance area that can be detected by the digital camera by setting the exposure of the digital camera to be underexposed. It has been.

  However, in an image taken with underexposure, the frequency with which black dots are isolated and recorded particularly in the dark part of the image is high, so that the graininess tends to be noticeable even if not viewed under high illumination illumination. is there.

  Therefore, in the present embodiment, the LUT used in the color separation process 402 is switched based on whether or not the processing target image is an image captured by underexposure. Specifically, processing according to the flowchart shown in FIG. 5 is possible, and in step S501, the CPU 20 determines whether or not the processing target image is an image captured by underexposure. At this time, the information indicating whether or not the image is captured by underexposure may be input from the input unit 12 when the user designates the recording mode, but a flag indicating that the image itself is underexposure. May be attached. For example, the digital camera may provide information indicating underexposure as tag information such as EXIF to the host device together with the image data, or the host device sets a flag based on the image data received from the digital camera. A standing form may be used. In any case, any information provided in association with RGB image data when a recording command is input to the recording apparatus 200 may be used.

(Fourth embodiment)
Also in this embodiment, the printing system and the image processing method described with reference to FIGS. In the present embodiment, an LUT used in the color separation process 402 is newly generated based on the illuminance at the time of viewing input by the user. That is, when the user generates a recording command, the user also inputs a value of viewing illuminance when viewing the recorded material along with various other parameters.

  FIG. 9 is a flowchart for explaining a recording process in the present embodiment. When the recording command is received, the CPU 20 first analyzes the received image data in step S900. In addition to the RGB data of the image to be recorded, the image data includes ornamental illumination information set by the user. The viewing illuminance information may be attached as tag information to the image data at the time of shooting.

  In step S901, the CPU 20 determines whether or not the viewing intensity acquired in step S900 is greater than or equal to a preset threshold value. If it is less than the threshold value, the process advances to step S902 to set the color separation table LUT1 for the processing target image. On the other hand, if it is equal to or greater than the threshold, the process advances to step S903 to generate a color conversion LUT for the processing target image based on the acquired viewing intensity.

  FIG. 10 is a diagram illustrating a method for generating a color conversion LUT in step S903. In the figure, both LUT1 shown in FIG. 6A and LUT2 shown in FIG. 6B are shown only for black (K). Here, the color conversion table LUT1 for standard images stored in the memory 41 is a three-dimensional table created under P lux which is standard illuminance. Similarly, the LUT 2 for high-illumination ornamental images stored in the memory 41 is a three-dimensional table created under Q Lux, which is the reference high-illuminance. LUT3 is a three-dimensional table created for the case where the viewing intensity is X lux (P <X <Q).

  Here, paying attention to the starting point at which the output signal of K becomes larger than 0, the starting point of LUT1 is p = 127, and the starting point of LUT2 is q = 85. In this case, the starting point x of the LUT 3 is calculated using the following equation according to the internal division relationship between P, X, and Q.

x = p + (X−P) × (q−p) / (Q−P)
Then, for any input signal greater than or equal to x, the black (K) output value of LUT3 is calculated by substituting the output signals of LUT1 and LUT2 for p and q in the above equation.

  The same applies to color inks (CMY). That is, when the input signal is from 0 to x, the output signal is the same as the LUT1 shown in FIG. 6A, and for any input signal equal to or greater than x, the same as the LUT1 shown in FIG. An output value is calculated according to the above equation with the LUT2 shown.

  Returning to the flowchart of FIG. In step S904, the CPU 20 executes the color separation process 402 described with reference to FIG. 4 using the color separation table set or generated in step S902 or step S903. Following this, output γ processing 403 and quantization processing 404 are executed, and the obtained 1-bit data is stored in the print buffer of the memory 41.

  Thereafter, in step S905, the CPU 20 sequentially reads the 1-bit data stored in the print buffer, and executes the recording scan on the recording medium S according to the recording mode analyzed in step S500. This process is complete | finished above.

  According to the present embodiment described above, appropriate color conversion processing can be performed according to the illuminance at the time of viewing. As a result, the balance between the reduction in graininess and the running cost can be adjusted more finely than in the first embodiment.

  In the above, assuming that (P <X <Q), the output signal value of the LUT 3 is calculated from the internal values of P and Q. However, when the value of X is X <P or X> Q In addition, the output signal value can be calculated from the external division value of P and Q.

  In the above description, the description has been made with respect to the content of completing the three-dimensional LUT 3 for an arbitrary viewing illuminance X in step S903, but the present embodiment is not limited to this. If an appropriate output signal can be acquired in association with each input signal based on the internal division relationship and the external division relationship, it is not necessary to completely generate output signals for all lattice points.

(Other embodiments)
Although the four embodiments have been described above, they can be combined with each other. For example, the method of generating a new lookup table as described in the fourth embodiment can be applied to the configuration of the third embodiment, that is, the configuration in which the LUT is varied according to the exposure amount at the time of shooting. . At this time, data indicating the degree of underexposure (for example, the aperture price number) may be input by the user, or may be attached to the image data as tag information at the time of shooting.

  Further, a plurality of LUTs based on both the illuminance at the time of viewing and the exposure amount at the time of photographing may be prepared by combining the first embodiment and the third embodiment. In this case, for example, a new parameter may be obtained by appropriately weighting the illuminance at the time of viewing and the exposure amount at the time of shooting, and an LUT associated with this parameter may be prepared. Further, the fourth embodiment may be further combined with the first and third embodiments, and a new LUT may be generated from both the illuminance at the time of viewing and the exposure amount at the time of photographing.

  In the above description, the ink jet recording apparatus using four colors of ink of cyan, magenta, yellow and black has been described as an example. However, the present invention is not limited to this. In addition to the inks described above, the present invention functions effectively even with a configuration using light-colored inks such as light cyan ink and light magenta ink, and special color inks such as red, blue, and green. For example, when light-based ink is used, in order to more actively suppress the graininess in high-light viewing, the starting point in the high-light viewing image of cyan or magenta output signals with relatively low brightness is used as the starting point in the normal image. What is necessary is just to move to the low brightness side. Whatever the combination of multiple color inks, the starting point of the LUT for the high-illumination viewing image of the ink with lower lightness is positioned on the lower lightness side than the starting point of the LUT for the standard viewing image. Thus, it is within the scope of the present invention.

  Furthermore, in the above, the description has been made with the content of performing the characteristic image processing of the present invention when the image to be processed is an image on the premise of high illumination viewing and when the image is captured by underexposure. Further, the image that is particularly concerned about the appearance of graininess or streak is not limited to the above. For example, when recording on a special recording medium or when used for a special purpose, there are various situations in which there is a concern that a graininess or unevenness peculiar to inkjet recording may be recognized. In any case, if the image to be processed can be determined to be a concern image and the characteristic image processing as described above can be performed on the image, the present invention functions effectively.

  Although the serial type ink jet recording apparatus has been described as an example with reference to FIG. 3, the present invention is not limited to this. Even a full-line type ink jet recording apparatus has problems such as graininess and unevenness as long as it is an ink jet recording apparatus, and the present invention can be effectively functioned.

  Furthermore, the configuration of the present invention is not in an exclusive relationship with the color conversion process disclosed in Patent Document 1. The function of stabilizing color development even when the viewing environment is different as in Patent Document 1 and the function of suppressing graininess and streak that are noticeable when the illuminance at the time of viewing is high as in the present invention are simultaneously performed with the same LUT. It can also be realized.

  Furthermore, in the above embodiment, the host device 100 performs only the color space conversion pre-processing 401 among the image processing steps shown in FIG. 4, and the configuration after the color separation processing 402 is performed by the recording device 200. However, the present invention is not limited to this. For example, the host device may perform part or all of the processing after the color space conversion pre-processing 401. In this case, the host apparatus 100 is the image processing apparatus of the present invention.

  The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

20 CPU
21 Recording Head 200 Inkjet Recording Device 402 Color Separation Processing S Recording Medium

Claims (21)

An image processing apparatus for recording an image on a recording medium by causing a recording head to discharge a plurality of colors of ink according to a multi-value density signal,
A judging means for judging whether or not the image to be processed is a concern image for which it is feared that graininess is recognized when the image recorded on the recording medium is viewed;
Color separation means for converting a multi-value RGB signal of the image to be processed into the multi-value density signal corresponding to each of the plurality of color inks according to the judgment of the judgment means;
In the color separation unit, when the determination unit determines that it is the concerned image, a gradation region that uses ink having relatively low lightness among the plurality of colors of ink is included in the determination unit. If it is determined that there is not, the multi-value RGB signal of the image data to be processed is converted into the multi-value density signal so that it is in a gradation area having a lower brightness than the gradation area using the ink. An image processing apparatus.   The image processing apparatus according to claim 1, wherein the determination unit determines that the image to be processed is the concern image when it is assumed that the image is viewed under high illuminance.   2. The determination unit according to claim 1, wherein the determination unit determines that the image to be processed is the concerned image when the image to be processed is an image captured in an under-exposure state than standard. Image processing apparatus. The color separation means uses the look-up table in which multi-value RGB signals and multi-value density signals corresponding to each of the plurality of colors of ink are associated in advance, thereby converting the multi-value RGB signals into the multi-value RGB signals. Convert to multi-value density signal,
A first look-up table is used when the determining means determines that the image is not a concern image, and a different one from the first look-up table is used when the determining means determines that the image is a concern image. The image processing apparatus according to claim 1, wherein two look-up tables are used. The color separation means uses the look-up table in which multi-value RGB signals and multi-value density signals corresponding to each of the plurality of colors of ink are associated in advance, thereby converting the multi-value RGB signals into the multi-value RGB signals. Convert to multi-value density signal,
When the determination means determines that the image is not the concern image, the first lookup table is used,
If the determination means determines that the image is a concern image, based on the first look-up table and the illuminance when the recorded matter to be recorded based on the image to be processed is viewed The image processing apparatus according to claim 1, wherein a multi-value RGB signal is converted into the multi-value density signal.   6. The ink according to claim 1, wherein the plurality of colors of ink include cyan, magenta, yellow, and black inks, and the relatively light ink is the black ink. The image processing apparatus described. It further comprises setting means for setting the number of multi-passes for multi-pass recording,
When the determination unit determines that the image is a concern image, the setting unit sets the processing target image to be recorded with a predetermined number of multipaths, and the determination unit determines that the image is not the concern image. 7. The image processing apparatus according to claim 1, wherein the image processing apparatus is configured to record the processing target image with a multipass number smaller than the predetermined multipass number. . A quantization means for quantizing the multi-value density signal generated by the color separation means into a binary density signal;
When the determination unit determines that the image is a concern image, the quantization unit quantizes the image to be processed using an error diffusion method, and when the determination unit determines that the image is not the concern image. The image processing apparatus according to claim 1, wherein the image to be processed is quantized using a dither method. A determination unit that determines an amount of the clear ink different from the plurality of colors applied to the recording medium;
The determination unit is configured such that the amount of clear ink applied when the determination unit determines that the image is a concern image is greater than the amount of clear ink applied when the determination unit determines that the image is not the concern image. The image processing apparatus according to claim 1, further comprising: determining a clear ink application amount.   The determination means determines whether or not the image to be processed is the concerned image based on information set by a user or information attached to data of the image to be processed. The image processing apparatus according to any one of 1 to 9. An image processing method for recording an image on a recording medium by causing a recording head to eject a plurality of colors of ink according to a multi-value density signal,
A determination step of determining whether or not the image to be processed is a concern image in which it is feared that graininess is recognized when the image recorded on the recording medium is viewed;
A color separation step of converting a multi-value RGB signal of the image to be processed into the multi-value density signal corresponding to each of the plurality of color inks according to the judgment of the judgment step;
In the color separation step, when the determination step determines that the image is a concern image, a gradation region that uses an ink having relatively low lightness among the plurality of colors of ink is used. If it is determined that there is not, the multi-value RGB signal of the image data to be processed is converted into the multi-value density signal so that it is in a gradation area having a lower brightness than the gradation area using the ink. An image processing method.   The image processing method according to claim 11, wherein the determination step determines that the image to be processed is the concern image when it is assumed that the image is viewed under high illuminance.   12. The determination step according to claim 11, wherein the processing target image is determined as the concerned image when the processing target image is an image captured in an under-exposure state than standard. Image processing method. In the color separation step, the multi-value RGB signal is converted into the multi-value RGB signal by using a lookup table in which a multi-value RGB signal and a multi-value density signal corresponding to each of the plurality of colors of ink are associated in advance. Convert to multi-value density signal,
A first look-up table is used when the determination step determines that the image is not a concern image, and a difference from the first look-up table is used when the determination step determines that the image is a concern image. The image processing method according to claim 11, wherein two look-up tables are used. In the color separation step, the multi-value RGB signal is converted into the multi-value RGB signal by using a lookup table in which a multi-value RGB signal and a multi-value density signal corresponding to each of the plurality of colors of ink are associated in advance. Convert to multi-value density signal,
When the determination step determines that the image is not the concern image, the first lookup table is used.
If the determination step determines that the image is a concern image, the first look-up table and the illuminance when the recorded matter to be recorded based on the image to be processed is viewed based on the illuminance. The image processing method according to claim 11, wherein a multi-value RGB signal is converted into the multi-value density signal.   16. The ink according to claim 11, wherein the plurality of colors of ink include cyan, magenta, yellow, and black inks, and the relatively light ink is the black ink. The image processing method as described. A setting step for setting the number of multi-passes for multi-pass recording;
If the determination step determines that the image is a concern image, the setting step sets the processing target image to be recorded with a predetermined number of multipaths, and determines that the determination step is not the concern image. 17. The image processing method according to claim 11, wherein the image to be processed is set to be recorded with a multipass number smaller than the predetermined multipass number. . A quantization step of quantizing the multi-value density signal generated by the color separation step into a binary density signal;
The quantization step quantizes the image to be processed using an error diffusion method when the determination step is determined to be the concern image, and the determination step determines that the determination image is not the concern image. The image processing method according to claim 11, wherein the image to be processed is quantized using a dither method. A determination step of determining the amount of clear ink different from the plurality of colors of ink applied to the recording medium;
In the determination step, the amount of clear ink applied when the determination step determines that the image is a concern image is larger than the amount of clear ink applied when the determination step determines that the image is not a concern image. The image processing method according to claim 11, further comprising: determining a clear ink application amount.   The determination step determines whether or not the image to be processed is the concerned image based on information set by a user or information attached to data of the image to be processed. The image processing method according to any one of 11 to 19. An inkjet recording apparatus,
A judging means for judging whether or not the image to be processed is a concern image for which it is feared that graininess is recognized when the image recorded on the recording medium is viewed;
Color separation means for converting a multi-value RGB signal of the image to be processed into the multi-value density signal corresponding to each of a plurality of colors according to the judgment of the judgment means;
A recording unit that records an image on a recording medium using a recording head that discharges the plurality of colors of ink according to the multi-value density signal;
With
In the color separation unit, when the determination unit determines that it is the concerned image, a gradation region that uses ink having relatively low lightness among the plurality of colors of ink is included in the determination unit. If it is determined that there is not, the multi-value RGB signal of the image data to be processed is converted into the multi-value density signal so that it is in a gradation area having a lower brightness than the gradation area using the ink. An ink jet recording apparatus.

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