JP2016025405A - Image data generation apparatus, image recording device, image data generation method and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily perform correction with respect to a change of a recording state.SOLUTION: In an image data generation section 423, on the basis of pixel values of a source image at a plurality of pixel positions and a plurality of first thresholds which are set correspondingly to the plurality of pixel positions, respectively, an intermediate pixel value acquisition part 425 calculates a relation indicating a relative magnitude of the pixel value to a reference value while defining the first threshold at each of the pixel positions as the reference value. By applying the relation to a common reference value that is common at the plurality of pixel positions, intermediate pixel values at the pixels positions are calculated and intermediate image data are generated. Regarding the plurality of pixel positions, a halftone image data generation part 426 compares the intermediate pixel value at each of the pixel positions with a second threshold that is set to each of the pixel positions on the basis of the common reference value, thereby meshing processing is performed on the intermediate image data, and halftone image data are generated. Thus, the correction with respect to the change of the recording state can be easily performed.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a technique for generating halftone image data by performing shading processing on multi-tone original image data.

  Conventionally, a multi-tone original image, that is, a continuous tone original image is halftone and recorded on a recording target. For example, FM (Frequency Modulated) screening is used for halftone dot conversion of the original image. In FM screening, gradation is expressed by changing the distribution density of micro dots, which are the minimum pixel units arranged irregularly. FM screening is used, for example, for forming halftone dots in an original image in an inkjet image recording apparatus.

  When halftone images are converted into halftone dots by FM screening, generally, a threshold matrix in which a plurality of elements are arranged in a row direction and a column direction and a threshold value is assigned to each element is prepared in advance. The pixel values of the original image are compared with the threshold values of the elements of the threshold matrix. Thereby, whether or not to form dots at each pixel position on the recording medium is determined.

  In the image recording apparatus, the temperature rise of the recording head due to continuous image recording, the temperature rise of the ink and the temperature of the recording medium accompanying the temperature rise of the recording head, the density change of the ink mist around the recording head, etc. In some cases, the dots on the recording medium spread larger than the intended size due to the change in the recording state accompanying the above, and the density of the image is higher than the desired density. Alternatively, the dots on the recording medium may not expand to the intended size, and the image density may be less than the desired density.

  In Patent Document 1, when the original image is halftoned, calibration corresponding to a change with time or the like is performed on the original image data to create new image data, and then the new image data is compared with the threshold matrix. Technology is disclosed. Also disclosed is a technique for comparing original image data and a new threshold matrix after creating a new threshold matrix by performing calibration corresponding to a change over time on the threshold matrix.

JP 7-336536 A

  By the way, since recent image recording apparatuses are required to record high-definition images at high speed, the amount of image data increases, and the amount of calculation related to the above-described shading processing also increases. Further, in an image recording apparatus, in order to record an image at high speed, image shading processing and image recording are usually performed in parallel.

  On the other hand, in the image data processing apparatus of Patent Document 1, it is necessary to recreate image data or recreate a threshold matrix every time a recording state changes in the image recording apparatus. And re-comparison for each pixel (re-shading process) is required. As described above, when the data amount of the image data and the calculation amount related to the shading process are large, the image data processing apparatus performs the time required for re-creating the image data or the threshold matrix and the re-shading process. The time required increases. For this reason, there is a possibility that data processing cannot be performed in parallel with image recording. In other words, there is a possibility that correction for changes in the recording state cannot be performed in real time.

  The present invention has been made in view of the above problems, and an object thereof is to easily perform correction for a change in recording state.

  The invention according to claim 1 is an image data generation device that generates halftone image data by performing a shading process on multi-tone original image data, and the original data at a plurality of pixel positions arranged in a matrix form Based on the pixel value of the image and a plurality of first threshold values set corresponding to the plurality of pixel positions, the pixel value relative to the reference value is set with the first threshold value at each pixel position as a reference value. An intermediate pixel value for obtaining intermediate image data by obtaining an intermediate pixel value at each pixel position by obtaining a relationship indicating magnitude and applying the relationship to a common reference value common to the plurality of pixel positions For the plurality of pixel positions, the acquisition unit compares the intermediate pixel value at each pixel position with a second threshold set for each pixel position based on the common reference value, And a halftone image data generator for generating halftone image data between the image data by performing shading process.

  A second aspect of the present invention is the image data generating device according to the first aspect, wherein all the second threshold values set for the plurality of pixel positions are equal.

  A third aspect of the present invention is the image data generation device according to the first or second aspect, wherein the generation of the intermediate image data in the intermediate pixel value acquisition unit is performed by a graphics processing unit.

  The invention according to claim 4 is the image data generation device according to any one of claims 1 to 3, wherein the number of bits indicating the number of gradations of the original image data and the number of gradations of the intermediate image data are provided. Is equal to the number of bits indicating

  A fifth aspect of the present invention is the image data generation device according to any one of the first to fourth aspects, wherein the common reference value is a minimum gradation value and a maximum gradation value of the intermediate image data. The median between.

  A sixth aspect of the present invention is the image data generating device according to any one of the first to fifth aspects, wherein dots of a plurality of sizes can be arranged at the plurality of pixel positions in the halftone image data. And the first threshold includes a plurality of first threshold elements corresponding to the plurality of sizes, and the shared reference value includes a plurality of shared reference value elements respectively corresponding to the plurality of first threshold elements. The reference value at each pixel position is a maximum first threshold element that is not more than the pixel value or a minimum first threshold element that is not less than the pixel value among the plurality of first threshold elements, and the relationship is the This is applied to a common reference value element corresponding to the reference value among a plurality of common reference value elements.

  A seventh aspect of the present invention is an image recording apparatus for recording an image on a recording medium, the image data generating apparatus according to any one of the first to sixth aspects, and a dot recording position on the recording medium. A dot output unit for recording, a moving mechanism for moving the dot recording position on the recording medium relative to the recording medium, and a parallel movement of the dot recording position on the recording medium relative to the recording medium And an output control unit that performs output control of the dot output unit based on the halftone image data generated by the image data generation device.

  According to an eighth aspect of the present invention, in the image recording apparatus according to the seventh aspect, the dot output section records dots by ejecting fine ink droplets at the dot recording positions on the recording medium. The discharge part to be provided is provided.

  A ninth aspect of the present invention is the image recording apparatus according to the eighth aspect, wherein the ejection section is arranged along a direction intersecting a relative movement direction of the recording medium by the moving mechanism. An ejection unit element is provided, and the moving mechanism records an image when the recording medium passes through the position facing the plurality of ejection unit elements only once, and each of the plurality of pixel positions is recorded on each ejection unit element. The second threshold values set for the corresponding pixel position group are equal.

  The invention according to claim 10 is an image data generation method for generating halftone image data by performing shading processing on multi-tone original image data, and a) a plurality of pixel positions arranged in a matrix The relative value of the pixel value relative to the reference value using the first threshold value at each pixel position as a reference value based on the pixel value of the original image in FIG. Obtaining intermediate image data by obtaining an intermediate pixel value at each pixel position by obtaining a relationship indicating a specific size and applying the relationship to a common reference value common to the plurality of pixel positions. And b) for the plurality of pixel positions, by comparing the intermediate pixel value at each pixel position with a second threshold set for each pixel position based on the common reference value, During ~ Performing shading processing on the image data and a step of generating a halftone image data.

  The invention according to claim 11 is a program for generating halftone image data by performing a shading process on multi-tone original image data, and the computer executes the program in a) matrix Based on the pixel value of the original image at a plurality of pixel positions arranged in a shape and a plurality of first threshold values set corresponding to each of the plurality of pixel positions, the first threshold value at each pixel position is set as a reference value By calculating the relationship indicating the relative magnitude of the pixel value with respect to the reference value and applying the relationship to a common reference value common to the plurality of pixel positions, the intermediate pixel value at each pixel position is determined. Obtaining intermediate image data, and b) for each of the plurality of pixel positions, the intermediate pixel value at each pixel position and the pixel position based on the common reference value. And by comparing the second threshold value set, to execute a process of generating a halftone image data by performing shading processing on the intermediate image data.

  In the present invention, it is possible to easily perform correction for a change in recording state.

1 is a diagram illustrating a configuration of an image recording apparatus according to an embodiment. It is a bottom view which shows a discharge unit. It is a figure which shows the structure of a control unit. It is a block diagram which shows the function of a control unit. It is a figure which shows the flow of the image recording by an image recording device. It is a figure which shows a color component image and a threshold value matrix. It is a figure which shows a threshold value matrix. It is a figure which shows a repetition area | region. It is a figure which shows the relationship between a 1st threshold value and a pixel value. It is a figure which shows the relationship between a common reference value and a conversion value. It is a figure which shows the relationship between a 1st threshold value and a pixel value. It is a figure which shows the relationship between a common reference value and a conversion value. It is a figure which shows the relationship between a 1st threshold value and a pixel value. It is a figure which shows the relationship between a common reference value and a conversion value. It is a figure which shows a repetition area | region. It is a figure which shows dot arrangement | positioning. It is a figure which shows dot arrangement | positioning. It is a figure which shows dot arrangement | positioning. It is a bottom view which shows another discharge unit. It is a block diagram which shows the function of another control unit. It is a figure which shows the relationship between a 1st threshold value element and a pixel value. It is a figure which shows the relationship between a common reference value element and a conversion value.

  FIG. 1 is a diagram showing a configuration of an image recording apparatus 1 according to an embodiment of the present invention. The image recording apparatus 1 is a sheet-fed printing apparatus (so-called inkjet printer) that sequentially records color images on a plurality of recording media 9 by ejecting micro droplets of ink onto the recording medium 9. The recording medium 9 is, for example, printing paper.

  In FIG. 1, two horizontal directions perpendicular to each other are shown as an X direction and a Y direction, and an up and down direction perpendicular to the X direction and the Y direction is shown as a Z direction. The X direction and the Y direction in FIG. 1 are not necessarily horizontal, and similarly, the Z direction is not necessarily vertical. That is, the upper side and the lower side in FIG. 1 do not necessarily need to coincide with the upper side and the lower side in the direction of gravity.

  As shown in FIG. 1, the image recording apparatus 1 includes a moving mechanism 2, a discharge unit 3, a supply unit 51, a discharge unit 52, and a control unit 4. The moving mechanism 2 moves the plurality of recording media 9 in the moving direction which is the (+ Y) direction in FIG. The discharge unit 3 is arranged above the moving mechanism 2 (on the (+ Z) side) and is fixed to a frame (not shown). The discharge unit 3 discharges fine droplets of ink toward the recording medium 9 being transported by the moving mechanism 2. The supply unit 51 supplies the recording medium 9 to the moving mechanism 2. The discharge unit 52 receives the recording medium 9 after printing from the moving mechanism 2. The control unit 4 controls mechanisms such as the moving mechanism 2, the discharge unit 3, the supply unit 51 and the discharge unit 52.

  The moving mechanism 2 includes a plurality of stages 21, an annular guide 22, and a belt driving mechanism 23. Each of the plurality of stages 21 sucks and holds one sheet-like recording medium 9. The guide 22 internally includes a belt to which a plurality of stages 21 are connected, and guides the plurality of stages 21. The belt drive mechanism 23 moves the belt in the guide 22 counterclockwise in FIG. 1 to move the stage 21 holding the recording medium 9 below the discharge unit 3 (that is, on the (−Z) side) ( Move in the + Y) direction.

  FIG. 2 is a bottom view showing the discharge unit 3. The ejection unit 3 includes a plurality of heads 31 (four in the present embodiment) that eject different colors of ink toward the recording medium 9, and these heads 31 have the same structure. Have The plurality of heads 31 are arranged in the Y direction (that is, the moving direction of the recording medium 9) and attached to the attachment portion 30 of the ejection unit 3. Each head 31 has a plurality of ejection ports 33 arranged in the X direction perpendicular to the Y direction. In FIG. 2, the number of the discharge ports 33 is drawn less than the actual number. The plurality of discharge ports 33 are not necessarily arranged in the X direction, but may be arranged along a direction intersecting the Y direction.

  The most (−Y) side head 31 in FIG. 2 ejects black (K) color ink. The head 31 on the (+ Y) side of the black head 31 ejects cyan (C) color ink. The head 31 on the (+ Y) side of the cyan head 31 ejects magenta (M) color ink. The most (+ Y) side head 31 ejects yellow (Y) color ink.

  In the image recording apparatus 1, each head 31 is provided over the entire recording area on the recording medium 9 (for example, over the entire X direction of the recording medium 9) in the X direction. Then, the output unit 41 (see FIG. 4) of the control unit 4 controls the discharge unit 3 and the moving mechanism 2, and the positions where the recording medium 9 faces the plurality of heads 31 of the discharge unit 3 are in the (+ Y) direction. In this case, black, cyan, magenta, and yellow inks are sequentially ejected onto the recording medium 9 to complete the image recording on the recording medium 9.

  In other words, in the image recording apparatus 1, each head 31 in the ejection unit 3, which is a dot output unit, is disposed at a plurality of dot recording positions arranged on the recording medium 9 over the entire width in the width direction perpendicular to the moving direction. Ink droplets are ejected from the plurality of ejection ports 33 (see FIG. 2) to record dots. Then, the plurality of dot recording positions on the recording medium 9 are moved only once relative to the recording medium 9 in the moving direction by the moving mechanism 2 to perform single pass printing on the recording medium 9. .

  FIG. 3 is a diagram illustrating a configuration of the control unit 4. The control unit 4 has a general computer system configuration including a CPU 401 that performs various arithmetic processes, a ROM 402 that stores basic programs, and a RAM 403 that stores various information. The control unit 4 includes a fixed disk 404 for storing information, a display 405 for displaying various information such as images, a keyboard 406a and a mouse 406b for receiving input from an operator, an optical disk, a magnetic disk, a magneto-optical disk, and the like. A read / write device 407 that reads and writes information from the computer-readable storage medium 8 and a communication unit 408 that transmits and receives signals to and from other components of the image recording device 1.

  In the control unit 4, the program 80 is read from the storage medium 8 via the reading / writing device 407 in advance and stored in the fixed disk 404. The CPU 401 executes arithmetic processing using the RAM 403 and the fixed disk 404 according to the program 80. The function of the control unit 4 may be realized by a dedicated electrical circuit, or a partially dedicated electrical circuit may be used.

  FIG. 4 is a block diagram illustrating functions of the control unit 4. FIG. 4 also shows a part of the configuration of the image recording apparatus 1 connected to the control unit 4. The control unit 4 includes the above-described output control unit 41 and a calculation unit 42 that performs various calculations.

  The calculation unit 42 includes an image memory 421, a plurality of matrix storage units 422 (also referred to as SPM (Screen Pattern Memory)), an image data generation unit 423 (halftoning circuit), and a color component image generation unit 424. Prepare.

  The color component image generation unit 424 performs color separation processing while performing gray replacement (GCR (Gray Component Replacement)) on a multi-tone color image input from the outside. Gray replacement is a gray portion expressed by overlapping cyan, magenta, and yellow dots in each pixel by expressing the shade of black ink, thereby providing cyan, magenta, and yellow colors added to the gray portion. This is a process for reducing the amount of ink.

  By color separation processing by the color component image generation unit 424, a color component image that is a gradation image of a plurality of color components (that is, black, cyan, magenta, and yellow) included in the color image is generated. Data of the gradation image of each color component of black, cyan, magenta and yellow (hereinafter referred to as “color component image data”) is stored in the image memory 421. The plurality of matrix storage units 422 are memories that store threshold matrixes corresponding to black, cyan, magenta, and yellow color components, respectively.

  As shown in FIG. 4, a threshold value matrix 81 is stored in each matrix storage unit 422. The threshold value matrix 81 is used for FM (Frequency Modulated) screening that expresses gradation by changing the number of irregularly arranged dots. In FIG. 4, the threshold value matrix 81 stored in one matrix storage unit 422 is illustrated, but the threshold value matrix 81 is also stored in each of the other color component matrix storage units 422. In the following description, each of the plurality of threshold values included in the threshold value matrix 81 is referred to as a “first threshold value”.

  The image data generation unit 423 generates halftone image data by performing a shading process on the multi-tone original image data. The image data generation unit 423 includes an intermediate pixel value acquisition unit 425 and a halftone image data generation unit 426. The intermediate pixel value acquisition unit 425 is an intermediate image data generation unit that generates intermediate image data for each color component based on the color component image data and the threshold value matrix 81. The intermediate pixel value acquisition unit 425 includes a common reference value storage unit 427 that stores in advance a common reference value used to generate intermediate image data.

  The halftone image data generation unit 426 performs a halftone process on the above-described intermediate image data for each color component, and generates halftone image data used for image recording in the image recording apparatus 1. The halftone image data generation unit 426 includes a second threshold storage unit 428 that stores a second threshold used to generate halftone image data. Note that the intermediate pixel value acquisition unit 425 and the halftone image data generation unit 426 may each be realized by software.

  The output control unit 41 includes a discharge control unit 411 and a movement control unit 412. The movement control unit 412 controls the relative movement of the recording medium 9 with respect to the ejection unit 3 by the movement mechanism 2 based on the output from the image data generation unit 423. The ejection control unit 411 controls the ejection of ink from the plurality of ejection ports 33 (see FIG. 2) of each head 31 in synchronization with the relative movement of the recording medium 9 based on the output from the image data generation unit 423. . In other words, the output control unit 41 performs ejection based on the halftone image data generated by the image data generation unit 423 in parallel with the relative movement of the plurality of dot recording positions on the recording medium 9 with respect to the recording medium 9. The output control of unit 3 is performed.

  Next, the operation of the image recording apparatus 1 for recording an image will be described with reference to FIG. FIG. 5 shows a flow of image recording focusing on one recording medium 9. In the image recording apparatus 1, four threshold value matrices 81 used for the shading process of four color component images are respectively stored in the four matrix storage units 422 of the calculation unit 42 shown in FIG. In addition, multi-tone color image data is input to the color component image generation unit 424 from an external computer. The gradation value of each color component of the color image (that is, the pixel value that each pixel of each color component image can take) is 0 to 255. A gradation value of 0 corresponds to an image density of 0% and is expressed by no ink dots being formed. The gradation value 255 corresponds to an image density of 100% (solid).

  Subsequently, the color component image generation unit 424 performs color separation processing while performing gray replacement on the multi-tone color image. Thereby, black color component image data, cyan color component image data, magenta color component image data, and yellow color component image data are generated (step S11). The color component image data of each color component generated by the color component image generation unit 424 is stored in the image memory 421. The color component image data indicating the gradation image of each color component is original image data indicating the original image of each color component. In the color separation process in step S11, gray replacement need not be performed.

  When the color component image data is generated, the intermediate pixel value acquisition unit 425 generates intermediate image data that is gradation image data based on the color component image data and the threshold value matrix 81 for each color component (step S12). ).

  FIG. 6 is a diagram abstractly showing a color component image that is a gradation image and a threshold matrix in order to explain the generation of intermediate image data. In the threshold matrix 81, a row direction corresponding to the width direction of the recording medium 9 (shown as x direction in FIG. 6) and a column direction corresponding to the moving direction (shown as y direction in FIG. 6). In the color component image 70, a plurality of pixels are arranged in the row direction and the column direction.

  When the intermediate image data is generated, the color component image 70 is divided into a number of regions having the same size as shown in FIG. The matrix storage unit 422 shown in FIG. 4 has a storage area corresponding to one repetitive area 71, and stores a threshold value matrix 81 by setting a first threshold value for each address (coordinate) of this storage area. .

  Conceptually, each repetition area 71 of the color component image 70 and the threshold matrix 81 are overlapped, and each pixel is determined based on the pixel value of each pixel in the repetition area 71 and the first threshold value corresponding to the threshold matrix 81. A relationship indicating the relative magnitude of the pixel value with respect to the first threshold value is obtained. Subsequently, a common reference value common to all the pixels is read from the common reference value storage unit 427, and the above relationship in each pixel is applied to the common reference value, thereby obtaining an intermediate pixel value of each pixel. It is done. Intermediate image data is generated by obtaining an intermediate pixel value for each pixel in all the repeating regions 71. The pixel value of each pixel in the repetitive area 71 described above is the pixel value of the color component image 70 at a plurality of pixel positions (that is, a plurality of drawing positions) arranged in a matrix in the halftone image area that is an output image area. It is.

  A specific calculation method of the intermediate pixel value will be described using a threshold matrix 81 illustrated in FIG. In FIG. 7, the number of first threshold values included in the threshold value matrix 81 is drawn smaller than the actual number. In the description according to FIG. 7, the minimum value Pmin1 and the maximum value Pmax1 of the pixel values that can be taken in the color component image 70 are “0” and “16”, respectively, and the common reference stored in the common reference value storage unit 427 in advance. The value Tb is “8”, and the minimum value Pmin2 and the maximum value Pmax2 of the pixel values that can be taken in the intermediate image are “0” and “16”, respectively. That is, in the example according to FIG. 7, the number of bits indicating the number of gradations of the original image data (in this case, 4 bits) is equal to the number of bits indicating the number of gradations of the intermediate image data. In the example according to FIG. 7, the common reference value Tb is a median value between the minimum gradation value Pmin2 and the maximum gradation value Pmax2 of the intermediate image data.

  Assuming that the pixel value Ps of all the pixels in the repetitive area 71 of the color component image 70 is “5” as shown in FIG. 8, the uppermost pixel is “4” that is the first threshold Ta. As shown in FIG. 9, a relationship indicating the relative magnitude of “5” that is the pixel value Ps with respect to the reference value is obtained. In FIG. 9, the pixel value Ps is indicated by a hollow triangle (the same applies to FIGS. 11 and 13). In FIG. 9, the relative position of the pixel value Ps with respect to the first threshold Ta indicates the relationship. Then, by applying the relationship to “8” that is the common reference value Tb, the conversion value Pc is obtained as shown in FIG. In FIG. 10, the conversion value Pc is indicated by a solid triangle (the same applies to FIGS. 12 and 14). The relative position of the conversion value Pc with respect to the common reference value Tb in FIG. 10 is approximately equal to the relative position of the pixel value Ps with respect to the first threshold value Ta in FIG.

  As illustrated in FIG. 9, when the pixel value Ps is equal to or greater than the first threshold value Ta, the conversion value Pc is obtained as “8.67” by Equation 1, for example. Further, the intermediate pixel value Pm is obtained, for example, as “8” which is an integer part of the conversion value Pc.

(Equation 1)
Pc = (Ps−Ta) × (Pmax2−Tb) / (Pmax1−Ta) + Tb

  In the second pixel from the left in the uppermost row shown in FIGS. 7 and 8, the first threshold value “9” is used as a reference value, and the relative value of “5” that is the pixel value Ps with respect to the reference value is set. The relationship indicating the magnitude is obtained as shown in FIG. In FIG. 11, the relative position of the pixel value Ps with respect to the first threshold Ta indicates the relationship. Then, by applying the relationship to “8” that is the common reference value Tb, the conversion value Pc is obtained as shown in FIG. The relative position of the conversion value Pc with respect to the common reference value Tb in FIG. 12 is approximately equal to the relative position of the pixel value Ps with respect to the first threshold value Ta in FIG.

  As illustrated in FIG. 11, when the pixel value Ps is smaller than the first threshold Ta, the conversion value Pc is obtained as “4.44” by Equation 2, for example. Further, the intermediate pixel value Pm is obtained as, for example, “4” which is an integer part of the conversion value Pc.

(Equation 2)
Pc = Ps × Tb / Ta

  In the third pixel from the left in the uppermost row shown in FIG. 7 and FIG. 8, the relative value of “5” that is the pixel value Ps with respect to the reference value is set with “2” that is the first threshold Ta as the reference value. The relationship indicating the magnitude is obtained as shown in FIG. In FIG. 13, the relative position of the pixel value Ps with respect to the first threshold value Ta indicates the relationship. Then, by applying the relationship to “8” that is the common reference value Tb, the conversion value Pc is obtained as shown in FIG. The relative position of the conversion value Pc with respect to the common reference value Tb in FIG. 14 is approximately equal to the relative position of the pixel value Ps with respect to the first threshold value Ta in FIG.

  As illustrated in FIG. 13, when the pixel value Ps is equal to or greater than the first threshold value Ta, the conversion value Pc is obtained as “9.71” by the above equation 1, for example. Further, the intermediate pixel value Pm is obtained as, for example, “9” that is an integer part of the conversion value Pc. In the intermediate pixel value acquisition unit 425, the intermediate pixel value Pm is obtained for all the pixels in the repetitive region 71 based on the pixel value Ps and the first threshold value Ta as shown in FIG. Then, intermediate image data is generated by obtaining the intermediate pixel value Pm for each pixel in all the repetitive regions 71.

  As described above, the generation of the intermediate image data by the intermediate pixel value acquisition unit 425 (step S12) corresponds to the pixel value Ps of the original image at the plurality of pixel positions in the halftone image region and the plurality of pixel positions, respectively. Based on the plurality of first threshold values Ta of the threshold value matrix 81 set as above, the first threshold value Ta of each pixel position is used as a reference value, and the relative magnitude of the pixel value Ps of the original image with respect to the reference value is indicated. A relationship is required. Then, by applying the relationship to the common reference value Tb common to a plurality of pixel positions in the halftone image region, the intermediate pixel value Pm at each pixel position is obtained, and intermediate image data is generated. In the control unit 4, generation of intermediate image data in the intermediate pixel value acquisition unit 425 is preferably performed by a graphics processing unit (GPU (Graphics Processing Unit)).

  When the intermediate image data is generated, the halftone image data generation unit 426 stores in advance the intermediate pixel value Pm at each pixel position in the intermediate image data and the second threshold storage unit 428 for the plurality of pixel positions. The second threshold value Tc is compared. Details of the second threshold Tc will be described later. Then, a halftone pixel value “1” is given to a pixel position where the intermediate pixel value Pm is equal to or greater than the second threshold value Tc. Also, a halftone pixel value “0” is assigned to a pixel position where the intermediate pixel value Pm is smaller than the second threshold value Tc. As described above, the halftone image data generation unit 426 generates halftone image data by performing the shading process on the intermediate image data using the second threshold value Tc (step S13).

  In the image recording apparatus 1, a plurality of halftone image data respectively corresponding to a plurality of color component images included in a multi-tone color image is generated. Actually, when the halftone image data of each color component of the first printed portion of the color image is generated and prepared, the movement mechanism 2 is moved by the movement control unit 412 of the output control unit 41 shown in FIG. Under the control, the movement of the recording medium 9 shown in FIG. 1 in the moving direction is started (step S14).

  The plurality of heads 31 of the discharge unit 3 are controlled by the discharge control unit 411 of the output control unit 41 based on the halftone image data of the corresponding color component while synchronizing with the movement of the recording medium 9. A halftone image by dots of each color component is recorded on the recording medium 9 (step S15). Specifically, a fine droplet of ink is ejected to form a dot at a pixel position in the halftone image area where the halftone pixel value is “1” (that is, a recording pixel on the recording medium 9). The Also, no dot is formed at the pixel position where the halftone pixel value is “0”. The recording of the halftone image of each color component is performed in parallel with the generation of the halftone image data described above.

  In the image recording apparatus 1, as described above, the recording medium 9 is sequentially supplied by the supply unit 51 and is collected by the discharge unit 52 after image recording. When the entire halftone image is recorded on the desired number of recording media 9, the supply of the recording media 9 is stopped and the image recording operation is terminated (step S16).

  Next, the second threshold value Tc stored in the second threshold value storage unit 428 will be described. The second threshold value Tc is based on the common reference value Tb before the image recording by the image recording apparatus 1 is started or when the image recording on the plurality of recording media 9 is temporarily interrupted. Is set. The second threshold value Tc can be set for each pixel position in the halftone image area.

  The second threshold value Tc is a temperature rise of the head 31 (see FIG. 2) due to continuous image recording, a temperature rise of ink and a temperature rise of the recording medium 9 due to the temperature rise of the head 31, and the ink mist around the head 31. It is set so as to suppress a change in image recording result (that is, a printing result) due to a change in recording state such as a density change. For example, when an image recorded on a test medium on the recording medium 9 or a test medium is darker than a desired density as a whole, the common reference value Tb is used for all pixel positions in the halftone image area. The second threshold value Tc that is greater than and equal to each other is set in a lump. In the examples according to FIGS. 9 to 14, the common reference value Tb is “8”, and “9” obtained by adding “1” to the common reference value Tb is set as the second threshold value Tc for all pixel positions. Is done. The second threshold value Tc is input by the operator via the keyboard 406a, for example.

  On the other hand, when the image is entirely lighter than the desired density, for example, the second threshold value Tc that is smaller than the common reference value Tb and equal to each other for all pixel positions in the halftone image region. Set all at once. In the examples according to FIGS. 9 to 14, the common reference value Tb is “8”, and “6” obtained by subtracting “2” from the common reference value Tb is set as the second threshold value Tc for all pixel positions. Is done.

  When the image has a desired density, for example, second threshold values Tc that are equal to the common reference value Tb and equal to each other are collectively set for all pixel positions in the halftone image region. In the examples according to FIGS. 9 to 14, the common reference value Tb is “8”, and “8” equal to the common reference value Tb is set as the second threshold value Tc for all pixel positions.

  16 to 18 show a case where the same second threshold value Tc is set at a time for all pixel positions in the halftone image region (that is, all the pixel values set for a plurality of pixel positions in the halftone image region). FIG. 6 is a diagram illustrating a change in the halftone image due to a change in the second threshold value Tc.

  FIG. 16 is a diagram illustrating a halftone image when the second threshold value Tc set for all pixel positions is “8” equal to the common reference value Tb. In FIG. 16, dots 92 are formed at the five upper left pixel positions. In FIG. 16, parallel diagonal lines are added to the pixel positions where the dots 92 are formed (the same applies to FIGS. 17 and 18). The arrangement of the dots 92 shown in FIG. 16 compares the threshold value matrix 81 shown in FIG. 7 with the repetition area 71 of the original image shown in FIG. 8 without generating intermediate image data, and the pixel value of the repetition area 71 is This is the same as when dots are formed at pixel positions that are equal to or higher than the first threshold value in the threshold matrix 81. That is, the arrangement of the dots 92 shown in FIG. 16 is the same as that in the case where the original image data is converted into halftone dots using the threshold value matrix 81.

  In FIG. 17, “9”, which is larger by “1” than the common reference value Tb with respect to all the pixel positions as the second threshold value Tc, corresponding to the fact that the image is darker than the desired density as a whole. It is a figure which shows the halftone image at the time of setting. In FIG. 17, two dots 92 are not formed among the five dots 92 shown in FIG. 16, and three dots 92 are formed. As a result, the overall density of the image recorded on the recording medium 9 can be corrected to be close to a desired density.

  In FIG. 18, “6”, which is smaller by “2” than the common reference value Tb with respect to all the pixel positions as the second threshold value Tc, corresponding to the fact that the image is entirely lighter than the desired density. It is a figure which shows the halftone image at the time of setting. In FIG. 17, in addition to the five dots 92 shown in FIG. 16, one dot 92 at the lower right is also formed. As a result, the density of the image recorded on the recording medium 9 can be corrected to be high overall, and can be brought close to the desired density.

  As described above, in the image data generation unit 423, the intermediate pixel value acquisition unit 425 has a plurality of pixel values Ps of the original image at a plurality of pixel positions and a plurality of pixel values respectively set corresponding to the plurality of pixel positions. Based on the first threshold value Ta, the relationship indicating the relative magnitude of the pixel value Ps with respect to the reference value is obtained using the first threshold value Ta at each pixel position as a reference value. Then, by applying the relationship to the common reference value Tb common to the plurality of pixel positions, the intermediate pixel value Pm at each pixel position is obtained and intermediate image data is generated. In addition, for the plurality of pixel positions, the halftone image data generation unit 426 generates an intermediate pixel value Pm at each pixel position and a second threshold value Tc set for each pixel position based on the common reference value Tb. By the comparison, halftone image data is generated by performing a shading process on the intermediate image data.

  Thereby, when the recording state of the image recording apparatus 1 is changed, the image recorded on the recording medium 9 is compared with the case where the original image data (that is, a plurality of color component image data) and the threshold matrix are corrected. The density can be easily corrected. In other words, the image data generation unit 423 can easily correct the density of the image recorded on the recording medium 9 with respect to the change in the recording state. Further, in the image data generation unit 423, the density of the image recorded on the recording medium 9 is corrected by changing the second threshold value Tc set based on the common reference value Tb. By comparing the common reference value Tb and the second threshold value Tc, it is possible to easily grasp the correction content indicating how the image has been corrected. Further, when there are pixel position groups having the same second threshold value Tc, only one second threshold value Tc needs to be stored in the second threshold value storage unit 428 for the pixel position group. Compared to storing image data or a corrected threshold matrix, the amount of data stored in the second threshold storage unit 428 can be reduced.

  In the examples shown in FIGS. 16 to 18, all the second threshold values Tc set for the plurality of pixel positions are equal. Therefore, the amount of data stored in the second threshold storage unit 428 can be further suppressed. Further, it is possible to make it easier to grasp the correction contents.

  As described above, in the image data generation unit 423, the intermediate image data generation in the intermediate pixel value acquisition unit 425 is performed by the graphics processing unit (GPU). Thereby, the generation of the intermediate image data can be speeded up.

  In the examples shown in FIGS. 7 to 15, the number of bits indicating the number of gradations of the original image data is equal to the number of bits indicating the number of gradations of the intermediate image data. As a result, the intermediate image data can be shaded with high resolution. As a result, the density correction of the image recorded on the recording medium 9 can be performed with high accuracy.

  In the example shown in FIGS. 7 to 15, the common reference value Tb is a median value between the minimum gradation value Pmin2 and the maximum gradation value Pmax2 of the intermediate image data. Thereby, the correction for decreasing the density of the image on the recording medium 9 and the correction for increasing the image density can be performed in the same manner.

  In the example shown in FIGS. 7 to 15, the conversion value Pc is obtained using Equation 1 and Equation 2 based on the pixel value Ps and the first threshold Ta, and the intermediate pixel value Pm is obtained based on the conversion value Pc. . Thereby, the relationship between the pixel value Ps and the first threshold value Ta can be accurately reflected in the relationship between the intermediate pixel value Pm and the common reference value Tb.

  FIG. 19 is a bottom view showing another preferred discharge unit 3a. In the ejection unit 3a, each head 31 includes a plurality of head elements 34 that are a plurality of ejection unit elements. In each head 31, a plurality of head elements 34 are arranged along the X direction perpendicular to the Y direction (that is, the moving direction of the recording medium 9). Each head element 34 has a plurality of discharge ports 33. The plurality of head elements 34 are not necessarily arranged in the X direction, and may be arranged along a direction intersecting the Y direction.

  When the discharge unit 3 a shown in FIG. 19 is provided in the image recording apparatus 1 instead of the discharge unit 3 shown in FIG. 1, the image data generation unit 423 may set the second threshold Tc for each head element 34. In other words, for each head element 34, the same second threshold value Tc may be set for the pixel position group corresponding to the plurality of ejection ports 33 provided in the head element 34. In the image recording apparatus 1, the above-described change in recording state is likely to occur in units of head elements 34. For this reason, as described above, the second threshold value Tc set for the pixel position group corresponding to each head element 34 among the plurality of pixel positions in the halftone image area is equalized, so that the actual recording state It is possible to easily perform the above-described correction in accordance with the change in the amount of data stored in the second threshold value storage unit 428 while suppressing the amount of data.

  In the image recording apparatus 1 shown in FIGS. 1 and 2, the size of the micro droplets of ink ejected from each head 31 may be switchable. For example, the size of the small droplets of ink ejected from each head 31 is among three types: “large size”, “medium size” smaller than the large size, and “small size” smaller than the medium size. Can be switched. Thereby, the dot size of the ink formed on the recording medium 9 is switched between “large size”, “medium size”, and “small size”. In the following description, large size, medium size, and small size dots are also referred to as “large dots”, “medium dots”, and “small dots”, respectively. In the halftone image data generated by the image data generation unit 423, a plurality of (three in the above example) size dots can be arranged at the plurality of pixel positions.

  FIG. 20 is a block diagram illustrating functions of the control unit 4 when the dot size can be switched. As shown in FIG. 20, each matrix storage unit 422 includes a large dot matrix 811 that is a threshold matrix for large dots, a medium dot matrix 812 that is a threshold matrix for medium dots, and a threshold for small dots. A small dot matrix 813 which is a matrix is stored. The large dot matrix 811, the medium dot matrix 812, and the small dot matrix 813 are threshold matrices used for FM screening.

  FIG. 20 shows a large dot matrix 811, a medium dot matrix 812, and a small dot matrix 813 stored in one matrix storage unit 422, but each of the other color component matrix storage units 422 is also illustrated. A large dot matrix 811, a medium dot matrix 812, and a small dot matrix 813 are stored. In the following description, the three threshold matrixes of the large dot matrix 811, the medium dot matrix 812, and the small dot matrix 813 are collectively referred to as a “matrix set”. At the same position of the three threshold matrixes, the threshold of the large dot matrix 811 is the largest and the threshold of the small dot matrix 813 is the smallest. The threshold value of the medium dot matrix 812 is a value between the threshold values of the large dot matrix 811 and the small dot matrix 813.

  In the following description, the threshold values of the large dot matrix 811, the medium dot matrix 812, and the small dot matrix 813 in each matrix element are referred to as “first threshold element Ta1,” “first threshold element Ta2,” and “first threshold element,” respectively. This is called “threshold element Ta3”, and the three first threshold elements Ta1, Ta2, and Ta3 in each matrix element are collectively called a first threshold. In other words, the first threshold value Ta includes a plurality of first threshold value elements Ta1, Ta2, and Ta3 respectively corresponding to the plurality of dot sizes described above. In addition, the common reference value Tb stored in the common reference value storage unit 427 includes a plurality of common reference value elements Tb1, Tb2, and Tb3 respectively corresponding to the plurality of first threshold elements Ta1, Ta2, and Ta3.

  21 and 22 are diagrams illustrating specific examples of acquisition of the intermediate pixel value Pm by the intermediate pixel value acquisition unit 425 illustrated in FIG. As shown in FIG. 21, the first threshold elements Ta1, Ta2, Ta3 corresponding to one pixel position are, for example, “11”, “6”, “3”, and the pixel value Ps at the pixel position is “ 10 ". As shown in FIG. 22, the common reference value elements Tb1, Tb2, and Tb3 are, for example, values “12” and “8” that equally divide between the maximum gradation value Pmax2 and the minimum gradation value Pmin2. , “4”. In this case, the first threshold element Ta2 (= 6) which is the maximum first threshold element of the plurality of first threshold elements Ta1, Ta2 and Ta3 that is equal to or smaller than the pixel value Ps (= 10) is the reference value at the pixel position. It becomes. Then, a relationship indicating the relative magnitude of the pixel value Ps with respect to the first threshold value element Ta2 that is the reference value is obtained, and the common reference value corresponding to the reference value among the plurality of common reference value elements Tb1, Tb2, and Tb3. This relationship is applied to the element Tb2. Thereby, the conversion value Pc of the pixel position is obtained as “11.2” by Equation 3, for example. Further, the intermediate pixel value Pm is obtained as, for example, “11” that is an integer part of the conversion value Pc.

(Equation 3)
Pc = (Ps−Ta2) × (Tb1−Tb2) / (Ta1−Ta2) + Tb2

  Alternatively, as the reference value at the pixel position, the first threshold element Ta1 (= 11), which is the smallest first threshold element of the plurality of first threshold elements Ta1, Ta2, and Ta3 that is equal to or greater than the pixel value Ps (= 10). It may be selected. In this case, a relationship indicating the relative magnitude of the pixel value Ps with respect to the first threshold value element Ta1 that is the reference value is obtained, and the common reference corresponding to the reference value among the plurality of common reference value elements Tb1, Tb2, and Tb3. The relationship is applied to the value element Tb1. Thereby, the conversion value Pc of the pixel position is obtained as “11.2” by Equation 4, for example. Further, the intermediate pixel value Pm is obtained as, for example, “11” that is an integer part of the conversion value Pc.

(Equation 4)
Pc = Tb1- (Ta1-Ps) × (Tb1-Tb2) / (Ta1-Ta2)

  In the intermediate pixel value acquisition unit 425 shown in FIG. 20, the intermediate pixel value Pm is similarly obtained for other pixel positions, and intermediate image data is generated. In the halftone image data generation unit 426, the second threshold value elements Tc1, Tc2, Tc3 set based on the common reference value elements Tb1, Tb2, Tb3 are stored in the second threshold value storage unit 428 in advance as the second threshold value. Has been. Then, the halftone image data generation unit 426 compares the intermediate pixel value Pm at each pixel position with the second threshold elements Tc1, Tc2, and Tc3 for the plurality of pixel positions, thereby shading the intermediate image data. Processing is performed to generate halftone image data.

  For example, a halftone pixel value “3” is assigned to a pixel position where the intermediate pixel value Pm is equal to or greater than the second threshold element Tc1, and the intermediate pixel value Pm is equal to or greater than the second threshold element Tc2 and less than the second threshold element Tc1. A halftone pixel value “2” is given to a certain pixel position. A pixel position at which the intermediate pixel value Pm is greater than or equal to the second threshold element Tc3 and less than the second threshold element Tc2 is given a halftone pixel value “1”, and the intermediate pixel value Pm is less than the second threshold element Tc3. The halftone pixel value “0” is given to the position. Large dots are formed at pixel positions where the halftone pixel value is “3” (that is, recording pixels on the recording medium 9), and medium dots are formed at pixel positions where the halftone pixel value is “2”. The Further, a small dot is formed at a pixel position where the halftone pixel value is “1”, and no dot is formed at a pixel position where the halftone pixel value is “0”.

  For example, in a test-recorded image, when the density of the pixel corresponding to the pixel position according to FIGS. 21 and 22 is a desired density, the second threshold value element Tc1 is equal to the common reference value element Tb1 “12”. Is set. In this case, the intermediate pixel value Pm (= 11) is greater than or equal to the second threshold element Tc2 (= 8) and less than the second threshold element Tc1 (= 12). For this reason, the halftone pixel value “2” is given to the pixel positions according to FIGS. 21 and 22, and medium dots are formed in the corresponding recording pixels on the recording medium 9. On the other hand, in the image recorded on a trial basis, when the density of the pixel corresponding to the pixel position according to FIGS. 21 and 22 is lower than the desired density, for example, “1” is set from the common reference value Tb1. The subtracted “11” is set as the second threshold element Tc1. In this case, the intermediate pixel value Pm (= 11) is equal to or greater than the second threshold element Tc1 (= 11). For this reason, the halftone pixel value “3” is given to the pixel positions according to FIGS. 21 and 22, and a large dot is formed in the corresponding recording pixel on the recording medium 9.

  As described above, in the image data generation unit 423, the recording state of the density of the image recorded on the recording medium 9 can be changed even when the size of the micro droplets of the ink ejected from each head 31 can be switched. Can be easily corrected.

  Various changes can be made in the image recording apparatus 1.

  For example, the intermediate pixel value Pm is not necessarily an integer part of the conversion value Pc, and may be an integer obtained by rounding off the first decimal place of the conversion value Pc, and is obtained by rounding up the decimal part of the conversion value Pc. It may be an integer.

  In the above example, the conversion value Pc is a ratio indicated by the difference between the reference value and the pixel value Ps with respect to the difference between the reference value and the minimum gradation value Pmin1, the maximum gradation value Pmax1, or another first threshold value element. However, the conversion value Pc may be obtained by various other methods. For example, the conversion value Pc may be obtained by adding a value obtained by subtracting the reference value from the pixel value Ps to the common reference value. In this case, when the converted value Pc and the intermediate pixel value Pm are smaller than the minimum gradation value Pmin2, the value is equal to the minimum gradation value Pmin2, and when it is larger than the maximum gradation value Pmax2, the maximum gradation value is set. The value is equal to Pmax2.

  The common reference value Tb stored in the common reference value storage unit 427 shown in FIG. 4 does not necessarily need to be a median value between the minimum gradation value Pmin2 and the maximum gradation value Pmax2 of the intermediate image data. It may be appropriately determined between the tone value Pmin2 and the maximum gradation value Pmax2. Further, the common reference value elements Tb1, Tb2, Tb3 stored in the common reference value storage unit 427 shown in FIG. 20 do not necessarily divide between the minimum gradation value Pmin2 and the maximum gradation value Pmax2 of the intermediate image data. It does not have to be a value and may be changed as appropriate. For example, when density correction relating to large dots is performed with higher accuracy than medium dots and small dots, the difference between the maximum gradation value Pmax2 and the common reference value element Tb1, and the common reference value element Tb1 and the common reference value element The common reference value elements Tb1, Tb1, Tb2, and the common reference value element Tb1, so that the difference between the common reference value element Tb2 and the common reference value element Tb3 is larger than the difference between the common reference value element Tb3 and the minimum gradation value Pmin2. Tb2 and Tb3 are set.

  The number of bits indicating the number of gradations of the original image data and the number of bits indicating the number of gradations of the intermediate image data are not necessarily equal. The number of bits indicating the number of gradations of the intermediate image data is not the same as the number of bits of the original image data. It may be smaller than the number of bits indicating the logarithm. Thereby, the time required for generating the intermediate image data can be shortened. The generation of the intermediate image data in the intermediate pixel value acquisition unit 425 may be performed by various devices other than the graphics processing unit.

  When the dot size can be switched, the dot size of each color ink does not necessarily need to be three types of large size, medium size, and small size, and may be two types or four or more types. In the image recording apparatus 1, ink of color components other than black, cyan, magenta, and yellow may be used for dot recording. Further, the above-described image data generation unit 423 may be applied to an image recording apparatus that records an image with only one color of ink.

  The threshold value matrix stored in the matrix storage unit 422 may be used for AM (Amplitude Modulated) screening that expresses gradation by changing the size of a cluster that is a set of regularly arranged dots. Good.

  In the image recording apparatus 1, the generation and printing operations of halftone image data are not necessarily performed in parallel. If a sufficiently large memory can be provided in the output control unit 41, the halftone of the entire image can be provided. The image recording operation may be started after the generation of the image data is completed.

  In the image recording apparatus 1, if the recording medium 9 moves relative to the ejection units 3 and 3a in the Y direction, for example, the ejection units 3 and 3a are located above the stopped recording medium 9. The moving mechanism 2 may move in the Y direction. The structure of the image recording apparatus 1 may be applied to, for example, an image recording apparatus that performs interlaced printing, or may be applied to an image recording apparatus that records an image on a long roll paper. The recording medium 9 may be a film or a thin metal plate other than printing paper.

  The image data generation unit 423 may be used in an image recording apparatus having another structure. For example, the image data generation unit 423 may be used in an electrophotographic image recording apparatus. In this case, the light emitting unit that irradiates light to the photosensitive drum to form a latent image and the rotation mechanism that rotates the photosensitive drum are the dot output unit and the moving mechanism that relatively moves the dot recording position, respectively.

  The image data generation unit 423 is, for example, an image recording apparatus that records an image on a printing plate by scanning a light beam emitted from a light source unit on a printing plate that is a recording medium via a polygon mirror or the like. May be used. In this case, the light source that emits the light beam serves as a dot output unit, and the polygon mirror or the like serves as a moving mechanism that moves the dot recording position on the printing plate relative to the printing plate.

  The image data generation unit 423 may be used as an image data generation device that generates halftone image data by performing a shading process on multi-tone original image data independently of the image recording device.

  The configurations in the above-described embodiments and modifications may be combined as appropriate as long as they do not contradict each other.

DESCRIPTION OF SYMBOLS 1 Image recording apparatus 2 Moving mechanism 3, 3a Discharge unit 9 Recording medium 31 Head 34 Head element 41 Output control part 70 Color component image 80 Program 81 Threshold matrix 92 Dot 423 Image data generation part 425 Intermediate pixel value acquisition part 426 Halftone image Data Generation Unit 811 Large Dot Matrix 812 Medium Dot Matrix 813 Small Dot Matrix S11 to S16 Steps

Claims (11)

An image data generation device that generates halftone image data by performing a shading process on multi-tone original image data,
Based on the pixel values of the original image at a plurality of pixel positions arranged in a matrix and the plurality of first threshold values set corresponding to each of the plurality of pixel positions, the first threshold value at each pixel position is used as a reference By calculating a relationship indicating a relative magnitude of the pixel value with respect to the reference value as a value, and applying the relationship to a common reference value common to the plurality of pixel positions, an intermediate pixel value at each pixel position An intermediate pixel value acquisition unit for generating intermediate image data by obtaining
For the plurality of pixel positions, by comparing the intermediate pixel value at each pixel position with a second threshold value set for each pixel position based on the common reference value, the intermediate image data A halftone image data generation unit for generating halftone image data by performing a shading process;
An image data generation apparatus comprising: The image data generation device according to claim 1,
All the said 2nd threshold values set with respect to the said several pixel position are equal, The image data generation apparatus characterized by the above-mentioned. The image data generation device according to claim 1 or 2,
The image data generation device, wherein the intermediate image data is generated by the graphics processing unit in the intermediate pixel value acquisition unit. The image data generation device according to any one of claims 1 to 3,
An image data generating apparatus, wherein the number of bits indicating the number of gradations of the original image data is equal to the number of bits indicating the number of gradations of the intermediate image data. The image data generation device according to any one of claims 1 to 4,
The image data generating apparatus, wherein the common reference value is a median value between a minimum gradation value and a maximum gradation value of the intermediate image data. The image data generation device according to any one of claims 1 to 5,
In the halftone image data, dots of a plurality of sizes can be arranged at the plurality of pixel positions,
The first threshold includes a plurality of first threshold elements respectively corresponding to the plurality of sizes;
The shared reference value includes a plurality of shared reference value elements respectively corresponding to the plurality of first threshold elements;
The reference value at each pixel position is a maximum first threshold element equal to or lower than the pixel value or a minimum first threshold element equal to or higher than the pixel value among the plurality of first threshold elements.
The image data generating apparatus, wherein the relationship is applied to a common reference value element corresponding to the reference value among the plurality of common reference value elements. An image recording apparatus for recording an image on a recording medium,
The image data generation device according to any one of claims 1 to 6,
A dot output section for recording dots at dot recording positions on a recording medium;
A moving mechanism for moving the dot recording position on the recording medium relative to the recording medium;
An output control unit that performs output control of the dot output unit based on halftone image data generated by the image data generation device in parallel with relative movement of the dot recording position on the recording medium with respect to the recording medium; ,
An image recording apparatus comprising: The image recording apparatus according to claim 7,
The image recording apparatus, wherein the dot output unit includes an ejection unit that ejects a minute droplet of ink to the dot recording position on the recording medium to record a dot. The image recording apparatus according to claim 8, wherein
The discharge unit includes a plurality of discharge unit elements arranged along a direction intersecting a relative movement direction of the recording medium by the moving mechanism;
The moving mechanism records an image by passing the recording medium only once at a position facing the plurality of ejection unit elements,
2. The image recording apparatus according to claim 1, wherein the second threshold value set for a pixel position group corresponding to each ejection unit element among the plurality of pixel positions is equal. An image data generation method for generating halftone image data by performing shading processing on multi-tone original image data,
a) a first threshold value at each pixel position based on the pixel values of the original image at a plurality of pixel positions arranged in a matrix and a plurality of first threshold values set corresponding to the pixel positions, respectively. Is used as a reference value to obtain a relationship indicating a relative magnitude of the pixel value with respect to the reference value, and the relationship is applied to a common reference value common to the plurality of pixel positions, thereby obtaining an intermediate value between the pixel positions. Obtaining pixel values and generating intermediate image data;
b) For the plurality of pixel positions, by comparing the intermediate pixel value at each pixel position with a second threshold value set for each pixel position based on the common reference value, the intermediate image Halftone image data is generated by shading the data;
An image data generation method comprising: A program for generating halftone image data by performing a shading process on multi-tone original image data, and the execution of the program by a computer is performed on the computer,
a) a first threshold value at each pixel position based on the pixel values of the original image at a plurality of pixel positions arranged in a matrix and a plurality of first threshold values set corresponding to the pixel positions, respectively. Is used as a reference value to obtain a relationship indicating a relative magnitude of the pixel value with respect to the reference value, and the relationship is applied to a common reference value common to the plurality of pixel positions, thereby obtaining an intermediate value between the pixel positions. Obtaining pixel values and generating intermediate image data;
b) For the plurality of pixel positions, by comparing the intermediate pixel value at each pixel position with a second threshold value set for each pixel position based on the common reference value, the intermediate image Halftone image data is generated by shading the data;
A program characterized by having executed.

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