JP6625168B2 - Image processing apparatus, recording apparatus, image processing method, and program - Google Patents

Description

  The present invention relates to an image processing apparatus, an image processing method, a program, and a storage medium for forming an image on a recording medium by performing a quantization process.

  When an image is recorded using the pseudo gradation method, it is necessary to quantize multi-valued image data, and an error diffusion method and a dither method are known as quantization methods used at this time. In particular, the dither method of determining dot recording or non-recording by comparing a previously stored threshold value with the gradation value of multi-valued data has a smaller processing load than the error diffusion method, and many image processing apparatuses Has been useful in. In such a dither method, the dispersibility of dots particularly in a low gradation region is a problem. For example, in Patent Document 1, a threshold matrix having blue noise characteristics is used as a threshold matrix for obtaining preferable dot dispersibility. A method of using it has been proposed.

  FIGS. 18A to 18C are diagrams for explaining dither processing using a threshold matrix having blue noise characteristics. FIG. 18A shows an example of image data input to a 10 pixel × 10 pixel area. Here, a state where the gradation value “36” is input to all the pixels is shown. FIG. 18B shows a threshold matrix prepared corresponding to the above-described 10 pixel × 10 pixel area. Each of the pixels is associated with one of the threshold values 0 to 254. In the case of the dither method, when the gradation value indicated by the multi-valued image data is larger than the threshold value, the pixel is designated as dot recording “1”. On the other hand, when the gradation value indicated by the multi-valued image data is equal to or less than the threshold value, the pixel is designated as dot non-printing “0”. FIG. 18C shows the result of quantization by the dither method. Pixels indicating recording “1” are shown in gray, and pixels not recording “0” are shown in white. The distribution of recorded “1” pixels as shown in FIG. 18C depends on the arrangement of thresholds in the threshold matrix. By using a threshold matrix having blue noise characteristics as shown in FIG. 18B, even when multivalued data equal to a predetermined area is input as shown in FIG. 18A, as shown in FIG. The recording “1” pixel is arranged in a highly dispersive state.

  FIGS. 19A and 19B are diagrams illustrating blue noise characteristics and human visual characteristics (VTF) at a clear visual distance of 300 mm. In both figures, the horizontal axis indicates frequency (cycles / mm), and the left side of the graph indicates a low frequency, and the right side indicates a high frequency. On the other hand, the vertical axis indicates the intensity (power) corresponding to each frequency.

Referring to FIG. 19A, the blue noise characteristic has characteristics such as a low frequency component being suppressed, a sharp rise, and a high frequency component being flat. The frequency fg corresponding to the peak with a sharp rise is called a principal frequency. On the other hand, for the human visual characteristics (VTF) shown in FIG. 19B, the following approximate formula of Dooley is used as an example. Here, 1 indicates the observation distance, and f indicates the frequency.
VTF = 5.05 × exp (−0.138 × πlf / 180)
× (1-exp (0.1 × πlf / 180)) (1)

  As can be seen from FIG. 19B, the human visual characteristic has high sensitivity in a low frequency region and low sensitivity in a high frequency region. That is, the low-frequency component is noticeable, but the high-frequency component is not. The blue noise characteristic is based on such a visual characteristic. In the visual characteristic, a high-sensitivity (visible) low-frequency region has almost no power and a low-sensitivity (invisible) high-frequency It has power in the area. For this reason, when a person visually observes an image that has been subjected to quantization processing using a threshold matrix having blue noise characteristics, dot bias and periodicity are hardly perceived, and the image is recognized as a comfortable image.

  On the other hand, Patent Document 2 discloses that even when a preferable dispersibility is obtained with each color material (that is, a single color), the dispersibility is impaired when an image is recorded with a plurality of color materials (that is, mixed colors), and a granular feeling is noticeable. A dither method for resolving the situation is disclosed. Specifically, a method is disclosed in which one common dither matrix having suitable dispersibility as shown in FIG. 18B is prepared, and a quantization process is performed while shifting the thresholds between a plurality of colors. I have. Hereinafter, such a quantization method disclosed in Patent Document 2 is referred to as inter-color processing in this specification. According to the inter-color processing, dots of different colors are recorded in a mutually exclusive and highly dispersive state in the low gradation part, so that a suitable image quality can be realized even in a mixed color image.

U.S. Pat. No. 5,111,310 U.S. Pat. No. 6,867,884

  However, in the inter-color processing, the granularity of a dot pattern in which ink dots of a plurality of colors are mixed can be made inconspicuous, but the dispersibility of a specific ink dot may be rather conspicuous. According to Patent Document 2, priority is given to enhancing the dispersibility of black ink having the highest dot power among a plurality of color inks, and a threshold is set without applying an offset among a plurality of channels for a common threshold matrix. Black is set for the channel. However, for example, when a full-color image is expressed using cyan, magenta, and yellow without using black, setting the channel of the lowest threshold area to one of cyan and magenta having the same dot power results in the other granularity. Was noticeable in some cases. Hereinafter, a specific description will be given.

  FIG. 20 is a diagram illustrating a dot recording state in a case where the inter-color processing is performed by assigning each of the three color inks to the first to third channels. Using an equal threshold matrix having blue noise characteristics, a threshold is set without offsetting the first color data addressed to the first channel, and the second color data is based on the first color data. To set the offset threshold. Further, a threshold value offset based on the data of the first color and the data of the second color is set for the data of the third color. For this reason, in the sum 1940 of the dot pattern 1910 of the first color and the dot patterns of the first to third colors, the dots are appropriately dispersed and the graininess is suppressed. However, on the other hand, both the second color dot pattern 1920 and the third color dot pattern 1930 are inferior in dispersibility and granularity.

  FIGS. 21A to 21C are diagrams showing numerically the granularity of the dot pattern shown in FIG. In FIG. 21A, the horizontal axis represents the spatial frequency, and the vertical axis represents the average intensity (power) corresponding to the spatial frequency. Regarding the dot patterns of the first color and the mixed color, it can be seen that the power in the low frequency region is sufficiently suppressed and the peak is located near the principal frequency fg. That is, it has the characteristic of blue noise. On the other hand, for the second color and the third color, a certain amount of power exists in the low frequency region, there is no sharp peak, and the power has already decreased near the principal frequency fg. That is, it does not have the characteristic of blue noise.

  FIG. 21B is a diagram showing, as a response value, a result obtained by multiplying the frequency characteristic shown in FIG. 21A by the human visual characteristic (VTF) shown in FIG. 18B. FIG. 21C shows the integrated value of FIG. The larger the response value or its integral value, the more visually the graininess of the dot pattern is perceived. In the case of this example, the response values and the integral values of the second and third colors are larger than the response values and the integral values of the first color and the mixed dot pattern, and the granularity is easily perceived. That is, even if the graininess in the mixed color image is suppressed by adopting Patent Document 2, the graininess of a dot pattern of a specific ink color is conspicuous in the same mixed color image, and the image quality may be impaired.

  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 capable of suppressing graininess of an entire image as compared with the related art when recording a color image by a pseudo gradation method using a plurality of color materials. To provide.

For this purpose, the present invention provides first multivalued data corresponding to a first color, second multivalued data corresponding to the first color and another second color, and the first color and the first color. Acquiring means for acquiring third multi-valued data corresponding to a third color having a higher lightness than the second color; and a first threshold matrix and a second threshold matrix different from the first threshold matrix. Storage means for storing a threshold matrix, and among a plurality of thresholds arranged in the first threshold matrix and the second threshold matrix stored in the storage means, a threshold corresponding to the position of a pixel to be processed The first quantization data corresponding to the first color, the second quantization data corresponding to the second color, and the third quantization data corresponding to the third color comprising a generating means for generating quantized data, a serial While the recording means and the recording medium are relatively moved in order to impart wood, the first quantized data, based on the second quantized data and the third quantized data, before type recording Means for applying data processing for recording an image on a recording medium by applying the recording material of the first color, the recording material of the second color, and the recording material of the third color to the recording medium by means A processing device, wherein the generation unit generates the first quantized data by comparing the first multi-valued data with a threshold value arranged in the first threshold value matrix; The second quantized data is generated by comparing the multi-level data with a threshold value arranged in the second threshold value matrix, and the second multi-level data, the third multi-level data, and the second The second multi-valued data arranged in a threshold matrix of 2 Based on the compared is a threshold value and generates said third quantized data.

  According to the present invention, in a color image recorded using a plurality of color materials, it is possible to suppress graininess in the entire image.

FIG. 3 is a block diagram illustrating a configuration of control of the inkjet recording system. FIG. 1 is a schematic perspective view of a recording apparatus that can be used in the present invention. FIG. 3 is a block diagram illustrating a configuration of control of the recording apparatus. FIG. 3 is a block diagram illustrating a configuration of an ASIC 3001. 5 is a flowchart illustrating processing of image data. It is a block diagram for explaining the detail of a quantization process. (A) and (b) are a block diagram and a flowchart for explaining processing in the inter-color processing unit. FIG. 7 is a diagram illustrating a threshold range determined as recording (1) in a general inter-color process. (A) and (b) are figures which showed the granularity of each dot pattern numerically. FIG. 6 is a diagram illustrating a threshold range determined as recording (1) in the first embodiment. (A) and (b) are figures which showed the granularity of each dot pattern numerically. (A) And (b) is a figure which compares the granularity of this embodiment with the conventional method. FIG. 14 is a diagram illustrating a threshold range determined as recording (1) in the second embodiment. It is a figure showing the conversion state of the gray line in the color conversion processing of a 3rd embodiment. FIG. 14 is a diagram illustrating a threshold range determined as recording (1) in the third embodiment. It is a figure showing the conversion state of the gray line in the color conversion processing of a 4th embodiment. FIG. 14 is a diagram illustrating a threshold range determined as recording (1) in a fourth embodiment. (A)-(c) is a figure for demonstrating a dither process. (A) And (b) is a figure which shows a blue noise characteristic and a visual characteristic. FIG. 9 is a diagram illustrating a dot recording state when inter-color processing is performed for three colors. (A)-(c) is a figure which shows the granularity of a dot pattern numerically. FIG. 9 is a diagram illustrating an example of a first threshold matrix and a second threshold matrix.

(1st Embodiment)
FIG. 1 is a block diagram showing a configuration of control of an inkjet recording system applicable to the present invention. The ink jet recording system according to the present embodiment includes an image supply device 3, an image processing device 2, and an ink jet recording device 1 (hereinafter, also simply referred to as a recording device). The image data supplied from the image supply device 3 is subjected to predetermined image processing in the image processing device 2 and then sent to the recording device 1 where it is recorded using ink as a color material.

  In the printing apparatus 1, a printing apparatus main control unit 101 controls the entire printing apparatus 1, and is configured by a CPU, a ROM, a RAM, and the like. The print buffer 102 can store image data before being transferred to the print head 103 as raster data. The recording head 103 is an inkjet recording head having a plurality of recording elements capable of discharging ink as droplets, and discharges ink from each recording element in accordance with image data stored in the recording buffer 102. In the present embodiment, it is assumed that print element arrays for three colors of cyan, magenta, and yellow are arranged on the print head 103.

  The paper supply / discharge motor control unit 104 controls conveyance of a recording medium and supply / discharge of paper. The recording device interface (I / F) 105 exchanges data signals with the image processing device 2. An I / F signal line 114 connects the two. As the type of the I / F signal line 114, for example, one having a specification of Centronics can be applied. The data buffer 106 temporarily stores the image data received from the image processing device 2. The system bus 107 connects each function of the recording device 1.

  On the other hand, in the image processing apparatus 2, the image processing apparatus main control unit 108 performs various processes on the image supplied from the image supply device 3 to generate image data recordable by the recording apparatus 1. Yes, with a CPU, ROM, RAM, etc. The characteristic configuration of the present invention shown in FIGS. 6 and 7A described later is also provided in the image processing apparatus main control unit 108. The flowchart described in FIGS. This is executed by the CPU of the main control unit 108. An image processing device interface (I / F) 109 exchanges data signals with the recording device 1. The external connection interface (I / F) 113 exchanges image data with the image supply device 3 connected to the outside. The display unit 110 displays various information to the user, and for example, an LCD or the like can be applied. The operation unit 111 is a mechanism for a user to perform a command operation, and for example, a keyboard or a mouse can be applied. The system bus 112 connects the image processing apparatus main control unit 108 to each function.

  The recording device 1 can directly receive and record image data stored in a storage medium such as a memory card or image data from a digital camera in addition to the image data supplied from the image processing device 2. I can do it.

  FIG. 2 is a schematic perspective view of the recording apparatus 1 used in the present embodiment. The recording device 1 functions as a normal PC printer that receives and prints data from the image processing device 2, and prints image data recorded on a storage medium such as a memory card or image data received from a digital camera. Has functions.

  The main body forming the outer shell of the recording apparatus 1 has outer members of a lower case 1001, an upper case 1002, an access cover 1003, a paper feed tray 1007, and a discharge tray 1004. The lower case 1001 forms a substantially lower half of the device 1 and the upper case 1002 forms a substantially upper half of the main body. A storage space for storing each mechanism is formed inside the combination of the two cases.

  The paper feed tray 1007 is capable of stacking and holding a plurality of print media, and when a feed print command is input, the uppermost one is automatically fed into the apparatus. . On the other hand, one end of the discharge tray 1004 is rotatably held by the lower case 1001 so that the opening formed in the front surface of the lower case 1001 can be opened and closed by the rotation. When the recording operation is performed, the recording sheet can be discharged from here by rotating the discharge tray 1004 to the front side to open the opening, and the discharged recording sheets can be sequentially stacked. It has become. The paper discharge tray 1004 accommodates two auxiliary trays 1004a and 1004b. By pulling out each tray as needed, the supporting area of the recording medium can be expanded or reduced in three stages. Has become.

  A recording head 103 for recording an image on a recording medium, a carriage on which the recording head 103 and the ink tank are mounted and movable in the X direction in the drawing, and a predetermined amount of the recording medium And a transport mechanism for transporting the information to the user.

  When a print command is input, the print medium carried into the apparatus from the paper feed tray 1007 is transported to a printable area by the print head 103. Then, when one print scan is performed by the print head 103, the transport mechanism transports the print medium in the Y direction by a distance corresponding to the print width D. By repeating the above-described print scanning by the print head 103 and the operation of transporting the print medium, an image is formed stepwise on the print medium. The recording medium on which recording has been completed is discharged to a discharge tray 1004.

  One end of the access cover 1003 is rotatably held by the upper case 1002 so that an opening formed on the upper surface can be opened and closed. By opening the access cover 1003, the recording head 103, the ink tank, and the like housed inside the main body can be replaced. Although not shown here, a projection is provided on the back surface of the access cover 1003 so that when the access cover 1003 is closed, a detection is performed by a microswitch installed on the main body. That is, the open / closed state of the access cover 1003 can be detected based on the detection result of the protrusion by the microswitch.

  A power key 1005 is provided on the upper surface of the upper case 1002 so as to be able to be pressed. On the upper surface of the upper case 1002, an operation panel 1010 including a liquid crystal display unit 110, various key switches, and the like is provided.

  The paper interval selection lever 1008 is a lever for adjusting the distance between the ink ejection surface of the recording head 103 and the surface of the recording medium. The card slot 1009 is an opening for receiving an adapter to which a memory card can be attached. The image data stored in the memory card is sent to the control unit 3000 of the recording device via the adapter inserted into the card slot 1009, and after being subjected to predetermined processing, is recorded on the recording medium. Examples of the memory card (PC) include a compact flash (registered trademark) memory, a smart media, a memory stick, and the like. The viewer (liquid crystal display unit) 1011 displays an image for each frame, an index image, and the like when searching for an image to be printed from images stored in the memory card. In the present embodiment, the viewer 1011 is detachable from the recording apparatus 1 main body. A terminal 1012 is a terminal for connecting a digital camera, and a terminal 1013 is a USB bus connector for connecting a personal computer (PC).

  FIG. 3 is a block diagram for explaining a control configuration of the recording apparatus 1. In the control unit 3000 (control board), the DSP 3002 (digital signal processor) has a CPU therein and performs various image processing and control of the entire recording apparatus. The memory 3003 has a program memory 3003a for storing a program to be executed by the CPU of the DSP 3002, a RAM area for storing a program at the time of execution, and a memory area functioning as a work memory for storing image data and the like. The printer engine 3004 is provided with a printer engine for recording a color image using a plurality of color inks.

  A USB bus connector 3005 is a port for connecting a digital camera 3012. The connector 3006 connects the viewer 1011. A USB bus hub 3008 (USB HUB) is a concentrator for USB transfer to the printer engine 3004. When image data on which predetermined image processing has been performed is received from an externally connected image processing apparatus 2 (PC), the USB bus hub 3008 transmits the image data as it is to the printer engine. Thus, the connected PC 2 can directly exchange data and signals with the printer engine 3004 (that is, function as a general PC printer).

  The power connector 3009 inputs a DC voltage converted from commercial AC by the power supply 3013 into the device. The exchange of signals between the control unit 3000 and the printer engine 3004 is performed via the USB bus 3021 or the IEEE1284 bus 3022.

  FIG. 4 is a block diagram illustrating a configuration of the ASIC 3001. The PC card interface unit 4001 reads image data stored in the attached PC card 3011 and writes data to the PC card 3011. The IEEE1284 interface unit 4002 exchanges data with the printer engine 3004. The IEEE1284 interface unit is a bus used when recording image data stored in the digital camera 3012 or the PC card 3011. The USB interface unit 4003 exchanges data with the PC 2. A USB host interface unit 4004 exchanges data with the digital camera 3012. The operation panel interface unit 4005 inputs various operation signals from the operation panel 1010 and outputs display data to the display unit 1006. A viewer interface unit 4006 controls display of image data on the viewer 1011. An interface 4007 is an interface unit that controls various switches, LEDs 4009, and the like. The CPU interface unit 4008 controls data exchange with the DSP 3002. These units are connected by an internal bus (ASIC bus) 4010. These control programs are configured in a multitask format in which each function module is tasked.

  FIG. 5 is a flowchart for explaining image data processing performed by the image processing apparatus main control unit 108 of the present embodiment. This processing is executed by a CPU provided in the image processing apparatus main control unit 108 according to a program stored in the ROM. In FIG. 5, when image data of a target pixel is input from the image supply device 3 (step S200), the image processing apparatus main control unit 108 first performs color correction in step S201. The image data received by the image processing device 2 from the image supply device 3 is 8-bit luminance data of R (red), G (green), and B (blue) for expressing a standardized color space such as sRGB. is there. In step S201, the luminance data is converted into RGB 12-bit luminance data corresponding to a color space unique to the printing apparatus. As a method of converting the signal value, a known method such as referencing a look-up table (LUT) stored in a ROM or the like in advance can be adopted.

  In step S202, the image processing apparatus main control unit 108 converts the converted RGB data into 16-bit gradation data (density) for each of C (cyan), M (magenta), and Y (yellow), which are the ink colors of the printing apparatus. Data). At this stage, a 16-bit gray image is generated for three channels (for three colors). In the ink color separation process, as in the color correction process, a look-up table (LUT) stored in advance in a ROM or the like can be referred to.

  In step S203, the image processing apparatus main control unit 108 performs a predetermined quantization process on the 16-bit gradation data corresponding to each of the ink colors, and converts the data into quantized data of several bits. For example, when quantizing to three values, 16-bit grayscale data is converted into 2-bit data of level 0 to level 2. The quantization process will be described later in detail.

  In the following step S204, the image processing apparatus main controller 108 performs an index expansion process. Specifically, one dot arrangement pattern is selected from a plurality of dot arrangement patterns that define the number and positions of dots to be recorded in each pixel, in association with the level obtained in step S203. At this time, the dot arrangement table may have a form in which the number of dots to be recorded in an area corresponding to each pixel is made different depending on the level value, or a form in which the dot size is made different in accordance with the level value. May be.

  When such index development processing is completed, the dot data is output as binary data (step S205). This ends the process.

  The respective processes shown in the respective steps in FIG. 5 are processed in the ink jet recording system of the present embodiment, but up to which processes are performed by the image processing apparatus 2 and which processes are performed by the printing apparatus 1. The clear division of whether to do so is not particularly defined. For example, when the image processing apparatus 2 performs up to quantization, the quantized data is transferred to the recording apparatus 1 and the recording apparatus main control unit 101 uses the index pattern stored in the data buffer 106 to execute the processing in step S204. The index operation may be performed to control the recording operation. Further, depending on the performance of the recording apparatus 1, it is also possible to directly receive multi-valued RGB image data and perform all the steps of S201 to S204.

  FIG. 6 is a block diagram for explaining details of the quantization processing executed in step S203 of FIG. In the quantization processing of the present embodiment, first, processing relating to an input value is performed, then processing relating to a threshold is performed, and finally, quantization processing according to a dither method is performed. These series of processes are performed in parallel for each color (for each channel). Hereinafter, individual processes will be described in detail with reference to FIG.

  The image data acquisition unit 301 acquires 16-bit gradation data indicating the density of each pixel. It is assumed that the image data acquisition unit 301 of the present embodiment can receive a signal of a maximum of 16 bits for eight colors. The figure shows a state in which 16-bit data of each of the first to third colors is input.

  The noise addition processing unit 302 adds a predetermined noise to 16-bit gradation data. By adding noise, even when gradation data of the same level are continuously input, it is possible to avoid a state in which the same pattern is continuously arranged, and to reduce streaks and textures. The noise addition processing unit 302 generates noise for each pixel and adds the noise to the input value by multiplying a predetermined random table, the fixed intensity, and the fluctuation intensity according to the input value. Here, the random table is a table for setting the sign of the noise, and sets positive, zero, or negative for each pixel position. The random table of this embodiment can have a maximum of eight surfaces, and the size of each table can be set arbitrarily. The fixed intensity indicates the intensity of the noise amount, and the magnitude of the noise determines the magnitude of the noise. In the present embodiment, it is possible to appropriately adjust the noise amount by setting an optimal random table and a fixed intensity for each print mode according to the granularity of the image, the degree of the streak and the texture, and the like. .

  The normalization processing unit 303 normalizes the range of each level to 12 bits after associating the tone value of each pixel represented by 16 bits with a level value that can be indexed in step S204. Hereinafter, a specific description will be given. If the index expansion process in step S204 is a process corresponding to the n value of level 0 to level (n-1), the normalization processing unit 303 equally divides the 65535 gradation represented by 16 bits into (n-1). . Further, the range corresponding to each level is normalized to 12 bits (4096 gradations). As a result, for each pixel, 12-bit data in a state associated with one of level 0 to level (n-1) is obtained.

  For example, when the index expansion processing corresponds to three values of level 0, level 1, and level 2, the normalization processing unit 303 divides 65535 gradations represented by 16 bits into two equal parts. Then, the gradation values 0 to 32767 and the gradation values 32768 to 65535, which are the respective ranges, are normalized to 12 bits (0 to 4095 gradations). Pixels having input gradation values of 0 to 32767, which are the first range, output level 0 or level 1 by the subsequent quantization processing, and pixels having the input gradation values 32768 to 65535, which are the second range, have the quantization of the subsequent stage. Level 1 or level 2 is output by the conversion process. With the above control, the subsequent quantization processing can be performed by the same processing regardless of the number of quantizations (n).

  The processing of the image data acquisition unit 301 to the normalization unit 303 described above is performed in parallel for the gradation data of each color. That is, in the case of the present embodiment, 12-bit data for cyan, magenta, and yellow is generated and input to the dither processing unit 311.

  In the dither processing unit 311, the 12-bit data to be quantized (data to be processed) is transmitted to the quantization processing unit 306 as it is. On the other hand, 12-bit data of a color other than the data to be processed is input to the inter-color processing unit 304 as reference data. The inter-color processing unit 304 performs a predetermined process on the threshold acquired by the threshold acquiring unit 305 based on the reference data, determines a final threshold, and transmits the final threshold to the quantization processing unit 306. The quantization processing unit 306 determines recording (1) or non-recording (0) by comparing the processing target data with the threshold value input from the inter-color processing unit 304.

  The threshold obtaining unit 305 selects one corresponding threshold matrix from a plurality of dither patterns 310 stored in a memory such as a ROM, and obtains a threshold corresponding to the pixel position of the processing target data. In the present embodiment, the dither pattern 310 is a threshold matrix formed by arranging thresholds of 0 to 4095 so as to have blue noise characteristics, and includes various types such as 512 × 512 pixels, 256 × 256 pixels, and 512 × 256 pixels. It can present various sizes and shapes. That is, a plurality of threshold matrices having different sizes and shapes are stored in the memory in advance, and the threshold storage unit 305 selects a threshold matrix corresponding to the print mode and the ink color from among them. Then, the threshold value corresponding to the pixel position (x, y) of the processing target data is provided to the inter-color processing unit from among the plurality of threshold values arranged in the selected threshold value matrix.

  The present invention is characterized by a color processing method in the color processing section 304. Before describing the characteristic inter-color processing method, here, a general inter-color processing as disclosed in Patent Document 2 will be described.

  FIGS. 7A and 7B are a block diagram and a flowchart for describing the configuration and steps of processing in the inter-color processing unit 304. The inter-color processing unit 304 uses 12-bit data corresponding to colors other than the processing target data as reference data, performs predetermined processing on the threshold value obtained by the threshold obtaining unit 305 using these reference data, and quantizes the processing target data. Calculate a threshold value for performing For example, when the processing target data is cyan 12-bit data, the reference data is magenta and yellow 12-bit data. In FIG. 7A, the data to be processed is shown as In1 (x, y), and the reference data is shown as In2 (x, y) and In3 (x, y). Here, (x, y) indicates a pixel position, which is a coordinate parameter for the threshold acquisition unit 305 to select a threshold corresponding to the pixel position of the processing target data from the threshold matrix.

Referring to FIG. 7A, the reference data In2 (x, y) and In3 (x, y) input to the inter-color processing unit 304 are first input to the threshold offset amount calculation unit 308 (step S1). S401). Then, the threshold offset amount calculation unit 308 calculates a threshold offset Ofs_1 (x, y) for the processing target data In1 (x, y) using these reference data (step S402). In the present embodiment, the threshold offset value Ofs_1 (x, y) is calculated by (Equation 2).
Ofs_1 (x, y) = Σi [Ini (x, y)] (Equation 2)

  Here, i is a reference data (hereinafter referred to as actual reference data) used to calculate a threshold value for the processing target data In1 among the reference data In2 (x, y) and In3 (x, y). This is a parameter for indicating. The number and type of such actual reference data are specified in advance for each processing target data.

In this example, when the processing target data is In1 (x, y), there is no actual reference data (null), and when the processing target data is In2 (x, y), the actual reference data is In1 (x, y). y). The actual reference data when the processing target data is In3 (x, y) is In1 (x, y) and In2 (x, y). Therefore, the offsets Ofs_1 (x, y) to Ofs_3 (x, y) for the individual pieces of processing target data In1 (x, y) to In3 (x, y) can be expressed as follows from (Equation 2). .
Ofs_1 (x, y) = Σi [In (x, y)]
= 0 (Equation 2-1)
Ofs_2 (x, y) = Σi [In (x, y)]
= In1 (x, y) (Equation 2-2)
Ofs — 3 (x, y) = Σi [In (x, y)]
= In1 (x, y) + In2 (x, y) (Equation 2-3)

  When the threshold offset values Ofs_1 (x, y) to Ofs_3 (x, y) are calculated in this way, they are input to the threshold offset amount adding unit 309. The threshold offset amount adding unit 309 obtains the threshold Dth corresponding to the coordinates (x, y) of the processing target data In (x, y) from the threshold obtaining unit 305 (Step S403).

In step S404, the threshold offset amount adding unit 309 subtracts the threshold offset value Ofs_1 (x, y) input from the threshold offset amount calculation unit 308 from the threshold value Dth (x, y) input from the threshold acquisition unit 305. Then, a quantization threshold value Dth '(x, y) is obtained.
Dth ′ (x, y) = Dth (x, y) −Ofs_1 (x, y) (formula 3)

At this time, when Dth '(x, y) becomes a negative value, Dth_max (the maximum value of the threshold value of the dither pattern) is added to obtain a quantization threshold value Dth' (x, y). As a result, the quantization threshold Dth 'always becomes Dth' = 0 to Dth_max.
That is,
When Dth '(x, y) <0, Dth' (x, y) = Dth '(x, y) + Dth_max (Equation 4)
And

  When the quantization threshold Dth ′ (x, y) is obtained by (Equation 3) or (Equation 4), the quantization processing unit 306 generates the processing target data In1 (x, y) and the quantization threshold Dth ′ (x, y). y) are compared, and dot recording (1) or non-recording (0) is determined for the pixel position (x, y). This ends the process.

  Thereafter, as described with reference to the flowchart of FIG. 5, an index expansion process is performed on the quantized data Out1 (x, y) represented by several bits, and a dot pattern to be recorded at the pixel position (x, y) is obtained. It is determined. At this time, the number (size) of dots recorded at the pixel position (x, y) is, for example, 1 dot (or small dot) when the level value is 1, and 2 dots (or small dot) when the level value is 2. The number is set to a number (size) corresponding to the level value, such as (large dot).

  FIG. 8 shows that, when the first to third multi-value data (In1 to In3) are input for each of the first to third colors, among the plurality of thresholds 0 to Dth_max arranged in the threshold matrix, FIG. 9 is a diagram illustrating a range of a threshold value determined as recording (1). The horizontal axis indicates threshold values Dth0 to 4094, and reference numeral 1710 indicates Dth_max (the maximum threshold value of the dither pattern). Each line indicates the range of the threshold at which the dots are arranged. In the case of this example, Ofs_1 = 0 for the first color from (Equation 2-1). Therefore, a pixel position corresponding to a threshold value of 0 to In1 (1702 to 1703) among 0 to Dth_max is set to recording (1).

  For the second color, Ofs_2 = In1 from (Equation 2-2). Therefore, when quantization is performed using the threshold value Dth ′ obtained according to (Equation 3) and (Equation 4), the threshold value of In1 to In1 + In2 (1705 to 1706) among the threshold values 0 to Dth_max arranged in the dither pattern 310 is recorded (1). Is set.

  For the third color, Ofs_3 = In1 + In2 from (Equation 2-3). Therefore, when quantization is performed using the threshold value Dth ′ calculated according to (Equation 3) and (Equation 4), In1 + In2 to In1 + In2 + In3 (1708 to 1709) are set as recording (1) among the threshold values 0 to Dth_max arranged in the threshold matrix. Will be done. However, in this example, it is assumed that In1 + In2 + In3 exceeds Dth_max. In this case, for a region exceeding Dth_max, a region corresponding to the remainder obtained by dividing (In1 + In2 + In3) by Dth_max, that is, a threshold of 0 to In1 + In2 + In3-Dth_max is set to recording (1). That is, the range of the threshold value determined as recording (1) is In1 + In2 to Dth_max (1708 to 1710) and 0 to In1 + In2 + In3-Dth_max (1707 to 1711).

  As described above, in a general inter-color process, a unique quantization threshold value Dth ′ is obtained for each color by using a mutual input value as an offset value while using a common threshold value matrix. Then, by using the newly obtained quantization threshold value Dth 'in the quantization process, dots can be arranged so that a dot recording pattern in which a plurality of colors are mixed has a blue noise characteristic.

  However, as described above, when a color having a high dot power exists in a mixed dot pattern of a plurality of colors, the graininess of the dot pattern of the color is conspicuous, and the image quality may be impaired. Here, the dot power is equivalent to the conspicuousness of one dot, and depends, for example, on the brightness of the dot when one dot is recorded on a recording medium. The lower the brightness (the higher the density), the higher the dot power. Even if a dot pattern having the blue noise characteristic is formed together with the dots of other colors, the dot pattern of that color has the blue noise characteristic. Otherwise, the graininess will be noticeable.

9A and 9B show the granularity of each dot pattern when the first color is cyan, the second color is magenta, and the third color is yellow in the above-described general inter-color processing. FIG. FIG. 9A shows the response values of the dot pattern and the mixed dot pattern of each ink color, and FIG. 9B shows the integrated value. The response value is a result of multiplying the frequency characteristic of each dot pattern by a human visual characteristic (VTF) and a dot power coefficient. For the visual characteristics (VTF), the approximate expression of Dooley already shown as (Equation 1) is used. The dot power coefficient is a value equivalent to the intensity of the dot power, and increases as the brightness decreases. Here, as an example, CIEL ^* a ^* b ^* of the cyan in the color space lightness L ^* = 55, the lightness L ^* = 55 magenta, and a dot power coefficient of each color lightness L ^* = 85 for yellow.

  Since the mixed dot pattern and the cyan dot pattern of the first color have blue noise characteristics, both the response value and the integral value are relatively low. The dot pattern of the third color, yellow, does not have the blue noise characteristic, but has a smaller dot power than cyan and magenta, so that both the response value and its integral value are sufficiently low. On the other hand, the dot pattern of magenta, which is the second color, does not have the blue noise characteristic and has a strong dot power, so that both the response value and its integral value are relatively high.

  The present inventors have conducted intensive studies and, in view of the above, in view of the above, if the response value of a specific color dot pattern exceeds the response value of a mixed dot pattern, there is a tendency that granularity tends to be visually perceived. It was judged. Then, setting the threshold matrix and the reference color setting in the inter-color processing so that the response value of the dot pattern of each ink color is smaller than the response value of the mixed dot pattern suppresses the graininess of the entire image. And found that it was effective. Hereinafter, the characteristic color processing of the present embodiment will be described.

Referring to FIGS. 7A and 7B again, in the present embodiment, when the processing target data is the cyan data In1 (x, y), the threshold obtaining unit 305 sets the first threshold having the blue noise characteristic. Select a matrix. Then, the threshold offset amount calculation unit 308 sets the threshold offset value, that is, the reference data to null.
Ofs_1 (x, y) = 0

When the processing target data is the magenta data In2 (x, y), the threshold acquisition unit 305 selects a second threshold matrix having a blue noise characteristic but different from the first threshold matrix. The threshold offset amount calculation unit 308 sets the threshold offset value, that is, the reference data, to null.
Ofs_2 (x, y) = 0

When the data to be processed is the yellow data In3 (x, y), the threshold acquisition unit 305 selects the second threshold matrix as in the case of In2 (x, y). The threshold offset amount calculation unit 308 sets the threshold offset value, that is, the reference data, to In2 (x, y).
Ofs_3 (x, y) = In2 (x, y)

  The threshold offset amount adding unit 309 subtracts the threshold offset value Ofs_1 (x, y) input from the threshold offset amount calculating unit 308 from the threshold Dth (x, y) in the threshold matrix selected by the threshold obtaining unit 305. , The quantization threshold value Dth ′ (x, y). Thereafter, processing similar to the normal inter-color processing described above is performed.

  FIG. 22 is an example of a first threshold matrix and a second threshold matrix that can be employed in the present embodiment. Each of the threshold matrices has a blue noise characteristic, but the threshold distributions are different from each other. These two matrices are not particularly limited as long as they have blue noise characteristics, and may or may not have a correlation. However, a blue dot formed by overlapping a cyan dot and a magenta dot has a stronger dot power than cyan and magenta. Therefore, the respective thresholds are set so that such a blue dot is not generated as much as possible. Is preferred. Note that the first threshold matrix and the second threshold matrix may be, for example, two matrices having the same threshold matrix shifted from each other in the vertical and horizontal directions.

  FIG. 10 is a diagram illustrating, for each color, a range of a threshold value determined as recording (1) in the threshold value matrix in the present embodiment. In the case of the present embodiment, the threshold offset value of the first color cyan is Ofs_1 = 0. Therefore, the pixel position corresponding to 0 to In1 (902 to 903) among the threshold values 0 to Dth_max of the first threshold value matrix is set to recording (1).

  Also for magenta, which is the second color, the threshold offset value is Ofs_2 = 0. Therefore, a pixel position corresponding to a threshold value of 0 to In2 (905 to 906) among 0 to Dth_max of the second threshold value matrix is set to recording (1).

  For yellow as the third color, the threshold offset value is Ofs_3 = In2. Therefore, of the thresholds 0 to Dth_max of the second threshold matrix, In2 to In2 + In3 (908 to 909) are set to recording (1).

  According to the present embodiment, a blue noise characteristic can be obtained with a cyan dot pattern and a magenta dot pattern and a mixed dot pattern of magenta and yellow with relatively strong dot power.

  FIGS. 11A and 11B are diagrams showing the granularity of each dot pattern in the present embodiment numerically in the same manner as the conventional general inter-color processing shown in FIG. FIG. 11A shows the response values of the dot pattern and the mixed dot pattern of each ink color, and FIG. 11B shows the integrated value. The cyan dot pattern of the first color and the magenta dot pattern of the second color have blue noise characteristics, and both the response value and the integrated value thereof are relatively low. Further, the yellow dot pattern, which is the third color, does not have the blue noise characteristic, but has a very small dot power as compared with cyan and magenta, so that both the response value and its integral value are sufficiently low. . On the other hand, the mixed dot pattern of cyan, magenta, and yellow is composed of two dot patterns each having the blue noise characteristic, so that the responsiveness and the integrated value are slightly different from those of the conventional inter-color processing. Get higher. However, the responsiveness and the integrated value, that is, the graininess can be suppressed to a sufficiently low level as compared with a state where no inter-color processing is employed.

  FIGS. 12A and 12B show a case where a threshold matrix having no correlation in each of cyan, magenta and yellow without using inter-color processing and a case where the present embodiment is used. It is a figure which compares the granularity in a mixed dot pattern. It can be seen that the response value and the integral value of the mixed dot pattern in the present embodiment are suppressed lower than those of the mixed dot pattern according to the conventional method.

  That is, according to the present embodiment, while sufficiently suppressing the granularity of the mixed dot pattern of cyan, magenta, and yellow, the response value of the dot pattern for each color is made lower than the response value of the mixed dot pattern. Can be suppressed. As a result, it is possible to suppress the granularity of the entire image as compared with the related art and output a smooth image.

In addition, as long as the overlapping of dots between different colors is suppressed, the granularity can be suppressed to some extent regardless of the frequency characteristics of the mixed dot pattern. For this reason, the graininess of the entire image can be suppressed to a lower level than in the related art even if the second threshold matrix shared by the two colors does not necessarily have the blue noise characteristic. Further, in order to avoid dot duplication, it is not always necessary to perform inter-color processing between two colors, and a method of setting a threshold is devised so that mutually exclusive threshold areas are set as much as possible. Good. For example, when the two colors are magenta and yellow, if the threshold value of yellow is obtained using the following equation, dot overlap of magenta and yellow can be suppressed as small as possible.
Y threshold = maximum threshold in threshold matrix−M threshold

In the above description, the response value for quantitatively comparing the granularity of the mixed dot pattern and the dot pattern of each color is determined from the frequency characteristics of the dot pattern, the human visual characteristics (VTF), and the dot power coefficient. However, the response value is not limited to this. For the visual characteristics, an expression other than the approximate expression of Dooley can be adopted. For the dot power coefficient, not the lightness L ^* but the optical density when recorded on a recording medium can be adopted. Alternatively, the response value may be set by employing a known evaluation value such as RMS granularity or Wiener spectrum.

  In the following, a case where various combinations of ink colors used to express a color image are variously described will be described as another embodiment.

(Second embodiment)
In this embodiment, as in the first embodiment, cyan, magenta, and yellow ink systems are used. However, in the present embodiment, the inter-color processing is performed while using the first threshold matrix for cyan and yellow, and the second threshold matrix is used for magenta.

Also in this embodiment, the block diagrams and flowcharts shown in FIGS. 7A and 7B can be used. In the present embodiment, when the processing target data is the cyan data In1 (x, y), the threshold obtaining unit 305 selects the first threshold matrix having the blue noise characteristic. The threshold offset amount calculation unit 308 sets the threshold offset value to null.
Ofs_1 (x, y) = 0

When the processing target data is the magenta data In2 (x, y), the threshold acquisition unit 305 selects a second threshold matrix having a blue noise characteristic but different from the first threshold matrix. The threshold offset amount calculation unit 308 sets the threshold offset value to null.
Ofs_2 (x, y) = 0

When the data to be processed is the yellow data In3 (x, y), the threshold acquisition unit 305 selects the first threshold matrix as in the case of In1 (x, y). The threshold offset amount calculation unit 308 sets the threshold offset value to In1 (x, y).
Ofs_3 (x, y) = In1 (x, y)

  As the first threshold matrix and the second threshold matrix, for example, those shown in FIG. 22 can be used as in the first embodiment.

  FIG. 13 is a diagram illustrating, for each color, a range of thresholds determined as recording (1) in the set threshold matrix in the present embodiment. In the case of the present embodiment, the threshold offset value of cyan as the first color is Ofs_1 = 0. Accordingly, among the threshold values 0 to Dth_max of the first threshold value matrix, the pixel positions corresponding to 0 to In1 (1202 to 1203) are set to recording (1).

  Also for magenta, which is the second color, the threshold offset value is Ofs_2 = 0. Therefore, the pixel position corresponding to 0 to In2 (1208 to 1209) among the thresholds 0 to Dth_max of the second threshold matrix is set to recording (1).

  The threshold matrix of the third color, yellow, is Ofs_3 = In1. Therefore, among the threshold values 0 to Dth_max of the first threshold value matrix, the pixel positions corresponding to In1 to In1 + In3 (1205 to 1206) are set to recording (1).

  According to the present embodiment, it is possible to obtain blue noise characteristics with a cyan dot pattern and a magenta dot pattern having relatively strong dot powers, and a mixed dot pattern of cyan and yellow. Then, similarly to the first embodiment, while sufficiently suppressing the granularity of the mixed dot pattern of cyan, magenta, and yellow, the response value of the dot pattern for each color is set lower than the response value of the mixed dot pattern. Can be suppressed. As a result, it is possible to suppress the graininess of the entire image lower than before.

(Third embodiment)
In this embodiment, an ink system in which black is added to cyan, magenta, and yellow is used. The brightness of the black ink is lower than that of the other inks. Here, the brightness is set to L ^* = 10. Therefore, the black dot power is the largest among the four inks. In such an ink system, in the present embodiment, inter-color processing is performed using the first threshold matrix for black and cyan, and inter-color processing is performed using the second threshold matrix for magenta and yellow.

  In the case of the present embodiment, in step S202 of FIG. 5, the image processing apparatus main control unit 108 converts the RGB data into 16-bit gradation data of C (cyan), M (magenta), Y (yellow), and K (black). (Concentration data). In step S203, quantization processing is performed on each of these four colors.

  FIG. 14 shows a conversion state of a gray line of a lookup table referred to by the image processing apparatus main control unit 108 in the color conversion step of step S202. The abscissa indicates each grid point of the gray level transitioning from white to black, and the ordinate indicates the output signal value corresponding to each color in 256 gray levels here. The output signal value of each color corresponds to the input data In0 to In3 for the quantization processing unit.

  As can be seen from the figure, in the highlight to medium density region from white to gray, a black image is not used, and a gray image is expressed using only cyan, magenta, and yellow. Black is used in a medium to high density region. In a high-density area where black ink is used, many dots of other colors have already been recorded, so that the recording density of the ink dots is sufficiently high, and the granularity of the black dots is hardly regarded as a problem. In the present embodiment, in consideration of such a situation, a combination of a threshold matrix and a reference color used for each ink is set as follows.

First, when the processing target data is the black data In0 (x, y), the threshold obtaining unit 305 selects a first threshold matrix having a blue noise characteristic. The threshold offset amount calculation unit 308 sets the threshold offset value to null.
Ofs_0 (x, y) = 0

When the processing target data is cyan data In1 (x, y), the threshold acquisition unit 305 selects the first threshold matrix in the same manner as In0 (x, y). The threshold offset amount calculation unit 308 sets the threshold offset value to In0 (x, y).
Ofs_1 (x, y) = In0 (x, y)

When the processing target data is the magenta data In2 (x, y), the threshold acquisition unit 305 selects a second threshold matrix having a blue noise characteristic but different from the first threshold matrix. The threshold offset amount calculation unit 308 sets the threshold offset value to null.
Ofs_2 (x, y) = 0

When the data to be processed is the yellow data In3 (x, y), the threshold acquisition unit 305 selects the second threshold matrix as in the case of In2 (x, y). The threshold offset amount calculation unit 308 sets the threshold offset value to In2 (x, y).
Ofs_3 (x, y) = In2 (x, y)

  In the present embodiment, the first threshold matrix and the second threshold matrix shown in FIG. 22 can be used.

  FIG. 15 is a diagram illustrating a range of thresholds determined as recording (1) in a set threshold matrix in the present embodiment. Here, a case where a signal having a gray intermediate density of about (128) is input is shown. In the case of such a density, the signal value In0 (x, y) of the black ink is 0 as described with reference to FIG. Therefore, there is no threshold area determined to be recording (1).

  For cyan, the threshold offset value is Ofs_1 = In0 (x, y). However, In0 (x, y) = 0 as described above. Therefore, the pixel positions corresponding to 0 to In1 (1404 to 1405) among the thresholds 0 to Dth_max of the first threshold matrix are set to recording (1).

  For magenta, the threshold offset value is Ofs_2 = 0. Therefore, among the threshold values 0 to Dth_max of the second threshold value matrix, the pixel positions corresponding to 0 to In2 (1407 to 1408) are set to recording (1).

  For yellow, the threshold offset value is Ofs_3 = In2. Therefore, of the threshold values 0 to Dth_max of the second threshold value matrix, In2 to In2 + In3 (1410 to 1411) are set to recording (1).

  According to the present embodiment, black dots are not recorded in the highlight to medium density region where graininess is a problem, so that cyan is subjected to inter-color processing as in the first and second embodiments. And the same dot pattern as in the case of treating as the first color can be obtained. That is, blue noise characteristics can be obtained with a cyan dot pattern, a magenta dot pattern, and a mixed dot pattern of magenta and yellow. As a result, similarly to the above embodiment, while sufficiently suppressing the graininess of the mixed dot pattern, the response value of the dot pattern for each color is suppressed lower than the response value of the mixed dot pattern, thereby suppressing the graininess of the entire image. can do.

  In the third embodiment, the same threshold matrix is used for cyan and black, and the same threshold matrix is used for magenta and yellow. However, as in the relationship between the first embodiment and the second embodiment, cyan and magenta are used. Can be replaced. That is, the combination of the threshold matrix and the reference color used for each ink can be set as follows.

When the processing target data is the black data In0 (x, y), the threshold obtaining unit 305 selects a first threshold matrix having a blue noise characteristic. The threshold offset amount calculation unit 308 sets the threshold offset value to null.
Ofs_0 (x, y) = 0

When the processing target data is the cyan data In1 (x, y), the threshold obtaining unit 305 selects a second threshold matrix having a blue noise characteristic but different from the first threshold matrix. The threshold offset amount calculation unit 308 sets the threshold offset value to null.
Ofs_1 (x, y) = 0

When the processing target data is the magenta data In2 (x, y), the threshold acquisition unit 305 selects the first threshold matrix as in In0 (x, y). The threshold offset amount calculation unit 308 sets the threshold offset value to In0 (x, y).
Ofs_2 (x, y) = In0 (x, y)

When the data to be processed is the yellow data In3 (x, y), the threshold acquisition unit 305 selects the second threshold matrix as in the case of In1 (x, y). The threshold offset amount calculation unit 308 sets the threshold offset value to In1 (x, y).
Ofs_3 (x, y) = In1 (x, y)

  Even in such a case, the same dot pattern as in the case where magenta is treated as the first color of the inter-color processing can be obtained in the highlight to medium density area without recording black dots. . That is, a blue noise characteristic can be obtained with a cyan dot pattern, a magenta dot pattern, and a mixed dot pattern of cyan and yellow, and the graininess of the entire image can be reduced as compared with the related art.

(Fourth embodiment)
In the present embodiment, an ink system in which gray is added to cyan, magenta, yellow, and black is used. The gray ink has higher lightness than cyan, magenta, and black, and here the lightness is set to L ^* = 70. For this reason, the gray dot power is the second smallest after yellow. In such an ink system, in the present embodiment, inter-color processing is performed using black, cyan, and gray using a first threshold matrix, and inter-color processing is performed using magenta and yellow using a second threshold matrix.

  In the case of the present embodiment, in step S202 of FIG. 5, the image processing apparatus main control unit 108 converts the RGB data into C (cyan), M (magenta), Y (yellow), K (black), and Gray (gray). Is decomposed into 16-bit gradation data (density data). In step S203, quantization processing is performed on each of these five colors.

  FIG. 16 shows a conversion state of a gray line of a lookup table referred to by the image processing apparatus main control unit 108 in the color conversion step of step S202. The horizontal axis indicates each grid point of gradation from white to black, and the vertical axis indicates the output signal value corresponding to each ink color in 256 gradations. As can be seen from the figure, the gray image is expressed using cyan, magenta, yellow, and a relatively large number of grays without using black ink in the highlight to gray medium density areas. It can be seen that the signal values of cyan and magenta are lower than in FIG. 14 in which the gray ink is not used as described in the third embodiment. That is, according to the present embodiment, the number of cyan and magenta dots having a larger dot power than gray is suppressed by introducing gray ink.

  On the other hand, black is not used in the highlight-medium density region, but is used in the medium-high density region, as in the third embodiment. In a high-density region where black ink is used, the recording density of the ink dots is sufficiently high, and the granularity of the black dots hardly causes a problem. In the present embodiment, in consideration of such a situation, a combination of a threshold matrix and a reference color used for each ink is set as follows.

First, when the processing target data is the black data In0 (x, y), the threshold obtaining unit 305 selects a first threshold matrix having a blue noise characteristic. The threshold offset amount calculation unit 308 sets the threshold offset value to null.
Ofs_0 (x, y) = 0

When the processing target data is cyan data In1 (x, y), the threshold acquisition unit 305 selects the first threshold matrix in the same manner as In0 (x, y). The threshold offset amount calculation unit 308 sets the threshold offset value to In0 (x, y).
Ofs_1 (x, y) = In0 (x, y)

When the processing target data is the magenta data In2 (x, y), the threshold acquisition unit 305 selects a second threshold matrix having a blue noise characteristic but different from the first threshold matrix. The threshold offset amount calculation unit 308 sets the threshold offset value to null.
Ofs_2 (x, y) = 0

When the data to be processed is the yellow data In3 (x, y), the threshold acquisition unit 305 selects the second threshold matrix as in the case of In2 (x, y). The threshold offset amount calculation unit 308 sets the threshold offset value to In2 (x, y).
Ofs_3 (x, y) = In2 (x, y)

When the data to be processed is gray data In4 (x, y), the threshold obtaining unit 305 selects the first threshold matrix as in In0 (x, y) and In1 (x, y). The threshold offset amount calculation unit 308 sets the threshold offset value to In0 (x, y) + In1 (x, y).
Ofs_4 (x, y) = In0 (x, y) + In1 (x, y)

  As the first threshold matrix and the second threshold matrix, those shown in FIG. 22 can be used as in the above embodiment.

  FIG. 17 is a diagram illustrating, for each color, a range of a threshold value determined as recording (1) in the threshold value matrix in the present embodiment. Here, a case where a signal (128) having a gray intermediate density is input is shown. In the case of such a density, the signal value In0 (x, y) of the black ink is 0 as described with reference to FIG. Therefore, there is no threshold area determined to be recording (1).

  For cyan, the threshold offset amount is Ofs_1 = In0 (x, y). However, In0 (x, y) = 0 as described above. Therefore, among the threshold values 0 to Dth_max of the first threshold value matrix, the pixel positions corresponding to 0 to In1 (1604 to 1605) are set to recording (1).

  For gray, the threshold offset amount is Ofs_4 = In0 + In1. Therefore, of the thresholds 0 to Dth_max of the first threshold matrix, In0 + In1 to In0 + In1 + In4, that is, substantially In1 to In1 + In4 (1607 to 1608) are set to recording (1).

  For magenta, the threshold offset value is Ofs_2 = 0. Accordingly, among the threshold values 0 to Dth_max of the second threshold value matrix, the pixel positions corresponding to 0 to In2 (1610 to 1611) are set to recording (1).

  For yellow, the threshold offset value is Ofs_3 = In2. Therefore, of the threshold values 0 to Dth_max of the second threshold value matrix, In2 to In2 + In3 (1613 to 1614) are set to recording (1).

  According to the present embodiment, black dots are not recorded in the highlight to medium density region where graininess is a problem, so that cyan is subjected to inter-color processing as in the first and second embodiments. And the same dot pattern as in the case of treating as the first color can be obtained. That is, blue noise characteristics can be obtained with a cyan dot pattern, a magenta dot pattern, a mixed dot pattern of cyan and gray, and a mixed dot pattern of magenta and yellow. On the other hand, a blue noise characteristic cannot be obtained with a yellow dot pattern and a gray dot pattern. However, since gray and yellow have very small dot power compared to cyan and magenta, the response value and the integral thereof as described in the first embodiment are sufficiently low.

  As described above, according to the present embodiment, cyan and magenta having relatively large dot powers are set as the effective first colors of the inter-color processing, and yellow and gray having relatively small dot powers are set to the inter-color processing. Are set for the second and subsequent colors. Thus, similarly to the above-described embodiment, while sufficiently suppressing the graininess of the mixed dot pattern, the response value of the dot pattern for each color is suppressed lower than the response value of the mixed dot pattern, and the graininess of the entire image is reduced. It can be suppressed more than before.

  Note that the effect of the present embodiment of using the gray ink can be obtained without using the black ink. In the case where the black ink is not used, in the graph shown in FIG. 16, the signal values of cyan, magenta, and yellow increase in place of black in the medium to high density region. Also in such a mode, in the highlight to intermediate density region, the gray signal value is higher than the cyan and magenta signal values, and the effect of suppressing the graininess can be obtained.

  Also in the fourth embodiment, the relationship between cyan and magenta can be switched, and the combination of the threshold matrix and the reference color used for each ink can be set as follows.

When the processing target data is the black data In0 (x, y), the threshold obtaining unit 305 selects a first threshold matrix having a blue noise characteristic. The threshold offset amount calculation unit 308 sets the threshold offset value to null.
Ofs_0 (x, y) = 0

When the processing target data is the cyan data In1 (x, y), the threshold obtaining unit 305 selects a second threshold matrix having a blue noise characteristic but different from the first threshold matrix. The threshold offset amount calculation unit 308 sets the threshold offset value to null.
Ofs_1 (x, y) = 0

When the processing target data is the magenta data In2 (x, y), the threshold acquisition unit 305 selects the first threshold matrix as in In0 (x, y). The threshold offset amount calculation unit 308 sets the threshold offset value to In0 (x, y).
Ofs_2 (x, y) = In0 (x, y)

When the data to be processed is the yellow data In3 (x, y), the threshold acquisition unit 305 selects the second threshold matrix as in the case of In1 (x, y). The threshold offset amount calculation unit 308 sets the threshold offset value to In1 (x, y).
Ofs_3 (x, y) = In1 (x, y)

When the data to be processed is gray data In4 (x, y), the threshold acquisition unit 305 selects the first threshold matrix as in In0 (x, y) and In2 (x, y). The threshold offset amount calculation unit 308 sets the threshold offset value to In0 (x, y) + In2 (x, y).
Ofs_4 (x, y) = In0 (x, y) + In2 (x, y)

  Even in this case, in the highlight-medium density area, cyan and magenta are treated as the first colors of the inter-color processing without recording black dots, and yellow and gray are treated as the second and subsequent colors. The same dot pattern as in the case of handling can be obtained. That is, a blue noise characteristic can be obtained with a cyan dot pattern, a magenta dot pattern, a mixed dot pattern of cyan and yellow, and a mixed dot pattern of magenta and gray, and the graininess of the entire image can be made lower than before. it can.

  As described above, according to the present invention, the combination of the threshold matrix and the reference color in the inter-color processing is set so that the color having relatively large dot power becomes the virtual first color of the inter-color processing. . As a result, while sufficiently suppressing the graininess of the mixed dot pattern, the response value of the dot pattern for each color can be suppressed to be lower than the response value of the mixed dot pattern. Can also be kept low.

  In the above, the case where cyan, magenta, yellow, black, and gray inks are used in the four embodiments has been described as an example. However, the present invention can be applied to systems using various types of inks. For example, instead of gray, light cyan ink or light magenta ink can be used as the light-colored light ink, and special color inks such as red, green, and blue can be used together. In any case, while a plurality of threshold matrices are prepared, the threshold matrix and the reference data in the inter-color processing are set so that a color having a relatively large dot power becomes a virtual first color in the inter-color processing. If the combination is set, the effects of the present invention described above can be obtained.

  In the above description, 16-bit data is quantized to several levels by the quantization process and then binarized by the index expansion process. However, the quantization process executed in step S203 is a multi-value quantization process. It is not necessary. That is, the quantization processing in step S203 may directly convert 16-bit gradation data into 1-bit binary data by dither processing. In this case, the index expansion processing shown in step S204 is omitted, and the binary data obtained in step S203 is output to the recording device 1 as it is. Of course, the number of input / output data bits in other steps in FIG. 2 is not limited to the above-described embodiment. In order to maintain accuracy, the number of output bits may be larger than the number of input bits, and the number of bits may be variously adjusted according to the application or situation.

  Further, in the above embodiment, the description has been made using the serial type recording apparatus shown in FIG. 2, but the present invention can also be applied to a full line type recording apparatus.

  Furthermore, a program for realizing one or more functions of the above-described embodiment is supplied to a system or an apparatus via a network or a storage medium, and one or more processors in a computer of the system or the apparatus read and execute the program. The present invention is feasible. Further, it can be realized by a circuit (for example, an ASIC) that realizes one or more functions.

1 Recording device
2 Image processing device
108 Image processing device main controller
301 Image Data Acquisition Unit
305 Threshold acquisition unit
306 Quantization processing unit
308 Threshold offset calculation unit
309 Threshold offset adder
310 dither pattern

Claims (29)

First multi-valued data corresponding to a first color, second multi-valued data corresponding to the first color and another second color, and more than the first color and the second color. Acquiring means for acquiring third multi-value data corresponding to a third color having a high lightness;
Storage means for storing a first threshold matrix and a second threshold matrix having a different threshold array from the first threshold matrix;
By performing a quantization process using a threshold value according to the position of a pixel to be processed among a plurality of threshold values arranged in the first threshold value matrix and the second threshold value matrix stored in the storage unit. Generating means for generating first quantized data corresponding to the first color, second quantized data corresponding to the second color, and third quantized data corresponding to the third color When,
With
While the recording means and the recording medium for applying a recording material are relatively moved, the first quantized data, based on the second quantized data and the third quantized data, before Symbol Data processing for recording an image on a recording medium is performed by applying the recording material of the first color, the recording material of the second color, and the recording material of the third color to a recording medium by a recording unit. An image processing device,
The generation unit generates the first quantized data by comparing the first multi-valued data with a threshold value arranged in the first threshold value matrix, and generates the first multi-valued data and the second multi-valued data. The second quantized data is generated by comparing a threshold value arranged in a second threshold value matrix with the second threshold value matrix, and the second quantized data is assigned to the second threshold value matrix. And generating the third quantized data based on the second multi-valued data and a threshold value to be compared with the second multi-valued data.   The generating means offsets a threshold used for comparison with the second multi-level data based on the second multi-level data, and compares the offset threshold with the third multi-level data. The image processing apparatus according to claim 1, wherein the third quantized data is generated using the third quantized data. The image processing apparatus according to claim 1, wherein the second color and the third color have different hues. 4. The image processing apparatus according to claim 3 , wherein the third color is yellow, one of the first color and the second color is cyan, and the other is magenta. The generation unit generates the first quantized data by comparing the first multi-valued data with a threshold value arranged in the first threshold value matrix, and generates the first color data and the second color data. A fourth multi-value data corresponding to a fourth color different from any of the color and the third color, a threshold value arranged in the first threshold value matrix, and the first multi-value data; The image processing apparatus according to claim 3, wherein fourth quantized data corresponding to the fourth color is generated based on the fourth color data. The image processing apparatus according to claim 5 , wherein the first color is black, the second color is magenta, the third color is yellow, and the fourth color is cyan. The image processing apparatus according to claim 5 , wherein recording using the first color is not performed in a region from highlight to intermediate density. A conversion unit that converts the RGB data into multi-value data corresponding to a recording material used for recording, wherein the acquisition unit acquires the multi-value data obtained by the conversion by the conversion unit. The image processing apparatus according to any one of claims 1 to 7 , wherein In the frequency analysis result of the dot patterns obtained for an input value of multi-value data showing the concentration of lower than intermediate concentrations low gray scale region, wherein, wherein the strength of the low-frequency region is smaller than the intensity of the high frequency region Item 9. The image processing device according to any one of Items 1 to 8 . 10. The image processing apparatus according to claim 1, wherein each of the first threshold matrix and the second threshold matrix has a blue noise characteristic. Each of the first threshold matrix and the second threshold matrix has a maximum intensity in a frequency analysis result of a dot pattern obtained for an input value of multi-value data indicating a density of a low gradation area lower than the intermediate density. it strength of a frequency lower than the principal frequency is a frequency corresponding to the peak with a rising claims 1, characterized in that it is suppressed than the power of a frequency higher than the principal frequency to according to any one of the 10 Image processing device. The image processing apparatus according to claim 1, wherein the quantized data is data having three or more values. The image processing apparatus according to claim 1, wherein the quantized data is binary data. 14. The image processing apparatus according to claim 1 , further comprising a moving unit that relatively moves the recording unit and the recording medium. 15. The image processing apparatus according to claim 1 , wherein the recording material is ink. First multi-valued data corresponding to a first color, second multi-valued data corresponding to the first color and another second color, and more than the first color and the second color. Acquiring means for acquiring third multi-value data corresponding to a third color having a high lightness;
Storage means for storing at least a plurality of threshold matrices including a first threshold matrix and a second threshold matrix having a different threshold array from the first threshold matrix;
Selecting means for selecting a threshold matrix corresponding to a color corresponding to data to be processed from the plurality of threshold matrices stored in the storage means,
By performing a quantization process using a threshold value corresponding to the position of a pixel to be processed among a plurality of threshold values arranged in a threshold value matrix selected by the selection unit, a first color value corresponding to the first color is obtained. Generating means for generating quantized data of the second color, second quantized data corresponding to the second color, and third quantized data corresponding to the third color;
With
While the recording means and the recording medium for applying a recording material are relatively moved, the first quantized data, based on the second quantized data and the third quantized data, before Symbol the first color recording material by the recording means, data for recording an image on the second color of the recording material and the third color Liqui recording medium by the applying to a recording medium recording material An image processing apparatus for performing processing,
It said generating means compares the first multi-level data and disposed in the first threshold matrix threshold to generate said first quantized data, the said second multi-level data first The second quantized data is generated by comparing a threshold value arranged in a second threshold value matrix with the second threshold value matrix, and the second quantized data is assigned to the second threshold value matrix. An image processing apparatus for generating the third quantized data based on a threshold value to be compared with the second multi-valued data. 17. The image processing apparatus according to claim 16, wherein the second color and the third color have different hues. First multi-valued data corresponding to a first color, second multi-valued data corresponding to the first color and another second color, and more than the first color and the second color. Acquiring means for acquiring third multi-value data corresponding to a third color having a high lightness;
Among the plurality of thresholds arranged in the first threshold matrix and the second threshold matrix in which the arrangement of the thresholds is different from that of the first threshold matrix, the quantization process is performed using a threshold corresponding to the position of the pixel to be processed. By doing so, first quantized data corresponding to the first color, second quantized data corresponding to the second color, and third quantized data corresponding to the third color are generated. Means for generating
With
While the recording means and the recording medium for applying a recording material are relatively moved, the first quantized data, based on the second quantized data and the third quantized data, before Symbol Data processing for recording an image on a recording medium is performed by applying the recording material of the first color, the recording material of the second color, and the recording material of the third color to a recording medium by a recording unit. An image processing device,
The generation unit generates the first quantized data by comparing the first multi-valued data with a threshold value arranged in the first threshold value matrix without using the second threshold value matrix. Generating the second quantized data by comparing the second multi-valued data with a threshold value arranged in the second threshold value matrix without using the first threshold value matrix; Generating the third quantized data based on the multi-valued data and the third multi-valued data and a threshold value arranged in the second threshold value matrix and compared with the second multi-valued data. An image processing apparatus comprising: First multi-valued data corresponding to a first color, second multi-valued data corresponding to the first color and another second color, and more than the first color and the second color. Acquiring means for acquiring third multi-value data corresponding to a third color having a high lightness and a different hue from the second color;
Storage means for storing a first threshold matrix and a second threshold matrix having a different threshold array from the first threshold matrix;
By performing a quantization process using a threshold value according to the position of a pixel to be processed among a plurality of threshold values arranged in the first threshold value matrix and the second threshold value matrix stored in the storage unit. Generating means for generating first quantized data corresponding to the first color, second quantized data corresponding to the second color, and third quantized data corresponding to the third color When,
With
While relatively moving a recording means for applying a recording material and a recording medium, the recording is performed based on the first quantized data, the second quantized data, and the third quantized data. Means for applying data processing for recording an image on a recording medium by applying the recording material of the first color, the recording material of the second color, and the recording material of the third color to the recording medium by means A processing device,
The generation unit generates the first quantized data by comparing the first multi-valued data with a threshold value arranged in the first threshold value matrix, and generates the first multi-valued data and the second multi-valued data. The second quantized data is generated by comparing a threshold value arranged in a second threshold value matrix with the second threshold value matrix, and the second quantized data is assigned to the second threshold value matrix. An image processing apparatus for generating the third quantized data based on a threshold value to be compared with the second multi-valued data. 20. The image processing apparatus according to claim 17, wherein the second color is magenta or cyan, and the third color is yellow. 21. The image processing apparatus according to claim 20, wherein one of the first color and the second color is cyan and the other is magenta. First multi-valued data corresponding to a first color, second multi-valued data corresponding to the first color and another second color, and more than the first color and the second color. Acquiring means for acquiring third multi-value data corresponding to a third color having a high lightness;
Storage means for storing a first threshold matrix and a second threshold matrix having a different threshold array from the first threshold matrix;
By performing a quantization process using a threshold value according to the position of a pixel to be processed among a plurality of threshold values arranged in the first threshold value matrix and the second threshold value matrix stored in the storage unit. Generating means for generating first quantized data corresponding to the first color, second quantized data corresponding to the second color, and third quantized data corresponding to the third color When,
The recording material of the first color, the recording material of the second color, and the recording material of the third color based on the first quantized data, the second quantized data, and the third quantized data. Recording means for applying a recording material to a recording medium,
Moving means for relatively moving the recording means and the recording medium;
A recording device comprising:
The generation unit generates the first quantized data by comparing the first multi-valued data with a threshold value arranged in the first threshold value matrix, and generates the first multi-valued data and the second multi-valued data. The second quantized data is generated by comparing a threshold value arranged in a second threshold value matrix with the second threshold value matrix, and the second quantized data is assigned to the second threshold value matrix. And generating the third quantized data based on a threshold value to be compared with the second multi-valued data. First multi-valued data corresponding to a first color, second multi-valued data corresponding to the first color and another second color, and more than the first color and the second color. An obtaining step of obtaining third multi-value data corresponding to a third color having a high lightness;
A threshold corresponding to the position of a pixel to be processed is read from a storage unit that stores a first threshold matrix and a second threshold matrix in which the arrangement of the thresholds is different from that of the first threshold matrix, and quantization is performed using the threshold. By performing the processing, the first quantized data corresponding to the first color, the second quantized data corresponding to the second color, and the third quantized data corresponding to the third color A generating step of generating
Has,
While the recording means and the recording medium for applying a recording material are relatively moved, the first quantized data, based on the second quantized data and the third quantized data, before Symbol Data processing for recording an image on a recording medium is performed by applying the recording material of the first color, the recording material of the second color, and the recording material of the third color to a recording medium by a recording unit. An image processing method,
The generation step generates the first quantized data by comparing the first multi-level data with a threshold value arranged in the first threshold value matrix, and generates the second multi-level data and the second The second quantized data is generated by comparing a threshold value arranged in a second threshold value matrix with the second threshold value matrix, and the second quantized data is assigned to the second threshold value matrix. And generating the third quantized data based on the second multi-valued data and a threshold value to be compared. First multi-valued data corresponding to a first color, second multi-valued data corresponding to the first color and another second color, and more than the first color and the second color. An obtaining step of obtaining third multi-value data corresponding to a third color having a high lightness; and a plurality of at least a first threshold matrix and a second threshold matrix having a different arrangement of the threshold from the first threshold matrix. Selecting a threshold matrix corresponding to the color corresponding to the data to be processed from the threshold matrix of
By performing a quantization process using a threshold value corresponding to the position of a pixel to be processed among a plurality of threshold values arranged in the threshold value matrix selected in the selection step, a first color value corresponding to the first color is obtained. Generating quantized data, second quantized data corresponding to the second color, and third quantized data corresponding to the third color;
Has,
While the recording means and the recording medium for applying a recording material are relatively moved, the first quantized data, based on the second quantized data and the third quantized data, before Symbol Data processing for recording an image on a recording medium is performed by applying the recording material of the first color, the recording material of the second color, and the recording material of the third color to a recording medium by a recording unit. An image processing method,
The generating step, by comparing the first multi-level data and disposed in the first threshold matrix threshold to generate said first quantized data, the said second multi-level data first The second quantized data is generated by comparing a threshold value arranged in a second threshold value matrix with the second threshold value matrix, and the second quantized data is assigned to the second threshold value matrix. And generating the third quantized data based on the second multi-valued data and a threshold value to be compared. First multi-valued data corresponding to a first color, second multi-valued data corresponding to the first color and another second color, and more than the first color and the second color. An obtaining step of obtaining third multi-value data corresponding to a third color having a high lightness;
Among the plurality of thresholds arranged in the first threshold matrix and the second threshold matrix in which the arrangement of the thresholds is different from that of the first threshold matrix, the quantization process is performed using a threshold corresponding to the position of the pixel to be processed. By doing so, first quantized data corresponding to the first color, second quantized data corresponding to the second color, and third quantized data corresponding to the third color are generated. Generating process,
Has,
While the recording means and the recording medium for applying a recording material are relatively moved, the first quantized data, based on the second quantized data and the third quantized data, before Symbol Data processing for recording an image on a recording medium is performed by applying the recording material of the first color, the recording material of the second color, and the recording material of the third color to a recording medium by a recording unit. An image processing method,
The generating step generates the first quantized data by comparing the first multi-valued data with a threshold value arranged in the first threshold value matrix without using the second threshold value matrix. Generating the second quantized data by comparing the second multi-valued data with a threshold value arranged in the second threshold value matrix without using the first threshold value matrix; Generating the third quantized data based on the multi-valued data and the third multi-valued data and a threshold value arranged in the second threshold value matrix and compared with the second multi-valued data. An image processing method comprising: First multi-valued data corresponding to a first color, second multi-valued data corresponding to the first color and another second color, and more than the first color and the second color. An obtaining step of obtaining third multi-value data corresponding to a third color having a high lightness and a different hue from the second color;
A threshold corresponding to the position of a pixel to be processed is read from a storage unit that stores a first threshold matrix and a second threshold matrix in which the arrangement of the threshold is different from the first threshold matrix, and quantization is performed using the threshold. By performing the processing, the first quantized data corresponding to the first color, the second quantized data corresponding to the second color, and the third quantized data corresponding to the third color A generating step of generating
Has,
While relatively moving a recording means for applying a recording material and a recording medium, the recording is performed based on the first quantized data, the second quantized data, and the third quantized data. Means for applying data processing for recording an image on a recording medium by applying the recording material of the first color, the recording material of the second color, and the recording material of the third color to the recording medium by means Processing method,
The generation step generates the first quantized data by comparing the first multi-level data with a threshold value arranged in the first threshold value matrix, and generates the second multi-level data and the second The second quantized data is generated by comparing a threshold value arranged in a second threshold value matrix with the second threshold value matrix, and the second quantized data is assigned to the second threshold value matrix. And generating the third quantized data based on the second multi-valued data and a threshold value to be compared. 27. The image processing method according to claim 23, wherein the second color is magenta or cyan, and the third color is yellow. 28. The image processing method according to claim 27, wherein one of the first color and the second color is cyan and the other is magenta. A program for causing a computer to function as each unit of the image processing apparatus according to claim 1 .