JP2009262453A - Recorder and control method of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recorder for reducing the correlativity between scans, without reducing dot dispersibility and to provide a control method of the recorder. <P>SOLUTION: In the recorder, inputted image data and a first coefficient are multiplied together to perform first low gradation processing. On the other hand, the inputted image data and a second coefficient having a previously set difference from the first coefficient are multiplied together, to perform second low gradation processing. At this time, in the recorder, the second low gradation processing is performed in pixel units, according to the processing result of the first low gradation processing or a previously set value is set as the processing result, without performing the second low gradation processing. In the recorder, the processing result of the first low gradation processing and the processing result of the second low gradation processing are reduced to produce the drive signal of a recording head corresponding to one scan of a plurality of scans. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a recording apparatus that includes a plurality of recording heads and executes multi-pass printing, and a control method thereof.

  As an example of an apparatus using a recording head provided with a plurality of recording elements, an ink jet recording apparatus using a recording head (inkjet head) provided with a plurality of ink ejection ports is known. In such a recording apparatus, the size and position of the dots formed by the ink may vary due to variations in the ejection port diameters and ejection directions of the ejection ports, and density unevenness may occur in the printed image. In particular, in a serial type recording apparatus that performs recording by scanning the recording head in a direction different from the arrangement direction of the plurality of recording elements, e.g., a direction orthogonal to the recording head, the density unevenness due to the above-described variation in the discharge port diameter is Printed as stripes.

  In order to correct such density unevenness, when image formation is performed using a recording head according to an ink jet recording method, image data subjected to gradation reduction processing (binarization processing, etc.) is transferred to a plurality of different ejection openings. There has been proposed a method of forming an image with ink ejected from the printer. Specifically, one pixel or a pixel consisting of a line corresponding to one scan of the recording head is complemented by forming an image by, for example, a plurality of scans (scans, passes). As a result, it is possible to disperse density unevenness due to variations in the ejection ports of the recording head.

  There has also been proposed a recording apparatus in which two recording heads are provided for each ink color, and an image is formed for each half band unit of the recording head in one scan, and one pixel or one line image formation is realized with different recording heads. Yes. In this case, since the image of the predetermined area is formed by different nozzles of the two heads, it is possible to disperse and reduce density unevenness caused by characteristic variations of the plurality of nozzles. In addition, since the seam of the image is a half band unit, the banding period is halved, and the banding is less noticeable. Here, the band indicates a unit of width in the nozzle row direction in which the recording head prints in one scan.

  In this manner, a method of relatively reducing density unevenness by dispersing density unevenness caused by variations in ejection ports of the recording head on a recording medium is called a multi-pass (also called multi-scan) method. . Further, in this multi-pass method, a so-called sequential multi-scan (SMS) method is also proposed in which the ink discharge ports are used in a certain order mainly for the purpose of making the frequency of use of the ink discharge ports uniform. ing.

Further, Japanese Patent Laid-Open No. 2004-228688 proposes a method of dividing image data into a plurality of scans, performing gradation reduction processing with different coefficients for each divided data, and recording the result without mask processing. . In the method of Patent Document 1, print data for all passes is generated by the gradation reduction process for the number of times of division. The relationship is reduced and the dot dispersibility in the pass is improved.
JP 2000-103088 A

  However, the conventional techniques have the following problems. Originally, if recording is performed by the multi-pass method using an ideal apparatus, the unit recording pixels should be formed uniformly. However, in an actual printing apparatus, a registration change occurs between main scans due to mechanical attachment errors between a plurality of printing heads. For this reason, a difference occurs in the unit recording pixel interval overlapped in the multi-pass, and as a result, a moire effect and a non-uniformity in the half-scan interval occur. In particular, in the reciprocating main scanning recording, there is a difference in the mounting head accuracy of the recording head and the shape of the ejection port between the forward path and the backward path, thereby causing reciprocal unevenness.

  Such a problem is caused by the fact that the “complementary relationship” between print images formed by a plurality of scans is complete. In other words, in the above-described method, half-band images completed by two scans are in a completely complementary relationship (hereinafter, the relationship in which dots printed in each pass are spatially complemented is referred to as “complementary”. Called "Relationship"). For this reason, if an error occurs in registration for each band, for example, if the horizontal registration for a half dot shifts, complementation is performed with the horizontal registration shifted.

  FIG. 10 is a diagram illustrating ideal formation positions of the formed dots. Reference numeral 21 (black dot) indicates a dot formed by the first scan, and reference numeral 22 (white dot) indicates a dot printed by the second scan. Originally, if recording is performed by the above method using an ideal apparatus, the solid (uniform) image shown in FIG. 10 is evenly distributed without overlapping dots even if the images recorded by the respective scans are overlapped. Should be in line.

  FIG. 11 is a diagram illustrating a formation position when the formed dots are displaced. As shown in FIG. 11, in an actual apparatus, registration slightly changes in each scan due to an error in physical accuracy. Therefore, when images recorded in each scan are overlapped, dots are formed with each other. It will be close, away, or overlap. FIG. 11 shows the formation position when a horizontal registration shift of half a dot occurs in the first scan. In this way, density is generated between dots or dot overlap occurs. As a result, a dark band or a thin band is formed, and half-band unevenness occurs. In other words, in the conventional multi-pass method, when an image is formed by a plurality of scans, the image completed by the plurality of scans is in a completely complementary relationship, so that a change in registration appears as an uneven image. It has been known.

  Further, in the conventional multi-pass method, control is performed to distribute the result of the gradation reduction processing to other scans using a predetermined distribution pattern. This is because the binarization process and the distribution process are independent and perform a process having no correlation, and there are the following problems. For example, if the binarization results are all “1”, the data to be sent to the first print head and the data to be sent to the second print head are alternately distributed, and the data has regularity. Will be born and the dispersibility of the dots will be significantly reduced. Further, if the binarization result coincides with the distribution pattern, the data is concentrated on one recording head, and the density of the print data for each scan is biased.

  Therefore, in the method described in Patent Document 1, image data is divided at a predetermined ratio, and binarization processing is performed with a different coefficient for each divided data, thereby correlating the binarization processing and the distribution processing. Thus, the above-described problems are solved and the dispersibility of density unevenness is improved. However, in the method described in Patent Document 1, in order to reduce the correlation between paths, noise is added to the optimum parameter that should be originally set in the input image in the gradation reduction processing, and as a result, the path is reduced. There was a possibility that the dot dispersibility in the inside deteriorated.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a recording apparatus and a control method therefor that can reduce the correlation between scans without reducing dot dispersibility.

  The present invention can be realized, for example, as a recording apparatus that records an image by executing a plurality of scans by a recording head in the same area on a recording medium. The recording apparatus multiplies input image data by a first coefficient, reduces the gradation of the multiplication result, and first gradation reduction means, and input image data is predetermined from the first coefficient. A second gradation reducing means for multiplying a second coefficient having a difference, and using the processing result of the first gradation reducing means as a restriction condition to reduce the gradation, and a first gradation reducing means; And a generating means for generating a print head drive signal corresponding to one of the plurality of scans by subtracting the processing result of the above and the processing result of the second gradation reducing means. In generating each drive signal corresponding to one scan, the difference between the first coefficient and the second coefficient is kept constant, and different first and second coefficients are set for each scan. To do.

  Further, the present invention can be realized as a control method of a recording apparatus that records an image by executing a plurality of scans by the recording head in the same area on the recording medium. This control method multiplies input image data by a first coefficient, reduces the gradation of the multiplication result, a first gradation reduction step, and input image data is predetermined from the first coefficient. The second coefficient having a difference is multiplied, and the processing result of the first low gradation step is used as a constraint, and the second gradation reduction step for reducing the gradation of the multiplication result and the first gradation reduction step Including a generation step of generating a print head drive signal corresponding to one of the plurality of scans by subtracting the processing result and the processing result of the second gradation reduction step, a plurality of times In the generation of each drive signal corresponding to the scanning, the difference between the first coefficient and the second coefficient is kept constant, and different first and second coefficients are set for each scanning. .

  The present invention can provide, for example, a recording apparatus that reduces the correlation between scans without reducing dot dispersibility and a control method therefor.

  An embodiment of the present invention is shown below. The individual embodiments described below will help to understand various concepts, such as superordinate concepts, intermediate concepts and subordinate concepts of the present invention. Further, the technical scope of the present invention is determined by the scope of the claims, and is not limited by the following individual embodiments.

  Hereinafter, the present embodiment will be described with reference to FIGS. 1 to 9. In the present embodiment, unlike the conventional multi-pass method, instead of generating image data for each pass as a product of the mask data in order to divide the image data on which the gradation reduction processing has been performed, the two-pass method is used. Two tone reduction processes are executed to generate print data for each pass. Specifically, the second tone reduction process is executed using the result of the first tone reduction process as a constraint, and the result of the first tone reduction process and the second tone reduction process are executed. The difference from the result is used as print data. Here, the difference result is set as print data in one recording head, and the result of the second subordinate processing is set as print data in the other recording head.

<Recording head>
First, an example of a recording head provided in the recording apparatus according to the present embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a diagram illustrating a configuration example of a recording head according to the present embodiment. Examples of the recording apparatus applicable to the present invention include a printer, a FAX, and a copier that form an image on a recording medium using an inkjet method.

  This recording apparatus forms an image with four basic colors of CMYK inks. The recording apparatus records an image in the same area on the recording medium by performing a plurality of scans by the recording head. The recording head unit 601 includes two recording heads of each ink color. Specifically, a head 603 aligned in the upper part of FIG. 1 (hereinafter referred to as a rear head) and a head 602 aligned in the lower part (hereinafter referred to as a front head) are 2. It is arranged at a distance of 5 bands. Here, the band indicates a unit of width in the nozzle row direction in which the recording head prints in one scan.

  Here, a configuration in which a plurality of recording heads including a front head and a rear head are provided has been described. However, since the present invention is characterized by generation of print data generated for each pass, the recording apparatus having one recording head is provided. Is also applicable. For example, when forming one pixel or one line of an image with four scans (passes), with the configuration described above, distribution is performed so that two passes are executed by the front head and the remaining two passes are executed by the rear head. To do. On the other hand, when one recording head is provided, all the passes are executed by the recording head. Thus, the present invention does not limit the configuration of the recording head.

  FIG. 2 is a diagram illustrating the operation of the recording head according to the present embodiment. Here, the printing operation of the front head 602 and the rear head 603 will be described. The recording apparatus performs sub-scanning once for each main scanning. The paper feed amount in the sub-scanning direction is one band, and an image is formed in a state where the front head 602 and the rear head 603 are shifted by a half band, that is, a half band overlap. Here, the half band 703 is formed by the upper half of the front head 602 and the lower half of the rear head 603, respectively. On the other hand, the half band 704 is formed by the lower half of the front head 602 and the upper half of the rear head 603, respectively.

<Operation of Recording Device as Comparative Example>
Here, with reference to FIG. 3 to FIG. 5, the operation of the recording apparatus as a comparative example of the present embodiment will be described. FIG. 3 is a diagram illustrating a control configuration of a recording apparatus as a comparative example. FIG. 3 shows binarization of multi-valued image data input to a recording apparatus having two recording heads for each ink color, conversion into head drive data, and printing by ejecting ink from nozzles. The processing content of is shown. Moreover, the alphabet attached | subjected to the end of the reference number shown in FIG. 3 shows the color of an ink. For example, K indicates black and Y indicates yellow.

  (1) Multi-value image data transferred from a host computer or the like is stored in an image data storage device 801. After that, data is read from each band from here and sent to the palette conversion circuit 802.

  (2) In the palette conversion circuit 802, the image data is decomposed into multi-value data for each ink color. Hereinafter, the black ink Bk will be described as a representative.

  (3) In the γ conversion circuit 803-K, γ conversion is performed on the multivalued data separated into the respective ink colors.

  (4) The unevenness correction circuit 804 -K corrects unevenness due to the variation in nozzle characteristics using the unevenness correction table (multi-value → multi-value lookup table).

  (5) The binarization circuit 805-K converts multi-value data into binary data by the error diffusion method (ED).

  (6) An SMS (sequential multi-scan) circuit 806-K determines whether binary data of each color is printed by the front head 602-K or the rear head 603-K. This SMS circuit-K is assigned alternately with front, rear, front, rear,... From the first dot appearing from the left end of the image when attention is paid to a certain raster, and each TMC (Timing Memory Controller) circuit 807- It is output to K1,807-K2. As a result, adjacent dots are not printed by the same head, and printing can be performed at a double speed of the head drive frequency. Furthermore, the dots that appear first in each raster are printed by the rear head 603-K for odd rasters and the front head 602-K for even rasters.

  (7) The TMC circuits 807-K1 and 807-K2 output one band of data to the heads 602-K and 603-K one by one in the nozzle row direction. The horizontal registration adjustment value adjusts the positional deviation in the head main scanning direction between the heads 807-K1 and 807-K2, but the output timing of data for one column differs depending on the horizontal registration adjustment value.

  (8) PHC (Printer Head Connector) boards 808-K1 and 808-K2 output binary data in the nozzle row direction in correspondence with the nozzles that actually perform printing. The vertical registration adjustment value adjusts the positional deviation in the nozzle row direction between the heads 807-K1 and 807-K2. In the head in this example, in addition to 1344 nozzles, the upper and lower 8 nozzles are print effective nozzles, so the vertical registration tone value is in the range of -8 to +8. When the vertical registration tone value is ± 0, the central 1344 nozzles are used. When the vertical registration tone value is ± 1 to 8, the actual 1344 nozzles are shifted from the center by 1 to 8 nozzles. With this vertical registration adjustment value, data for 1344 nozzles is output in correspondence with the nozzles that actually perform printing.

  (9) Finally, binary data of each nozzle is converted into head drive data by a print controller (Head CPU) 809, and printing is performed by ejecting ink.

  Here, the processes (5) and (6) described above will be specifically described with reference to FIG. FIG. 4 is a diagram illustrating a state in which image data input to a recording apparatus as a comparative example is converted into print data.

  Reference numeral 401 denotes multi-value data after being separated into ink colors and subjected to γ conversion and unevenness correction processing. The multi-value data 401 is binarized by performing error diffusion processing 402 which is the gradation reduction processing of (5). Here, the matrix A shown in FIG. 4 will be described with reference to FIG. FIG. 5 is a diagram showing a matrix used for error diffusion processing. Matrix A and B shown in FIG. 5 indicate the pixel of interest “*” and the pixels adjacent to the pixel of interest. The error diffusion process binarizes each pixel that is a multi-valued image.

  For example, each pixel of a multi-valued image having a density value of 8 bits (0 to 255) is converted into 0 or 255 and binarized. Further, in the error diffusion processing, conversion is performed so that the sum of density values in each pixel of the multi-valued image is substantially the same as the sum of density values in each pixel of the binary image. For example, when the pixel indicated by * in the matrix A is converted to 255, if the original density value is 180, an error of 180−255 = −75 occurs. As shown in the matrix A, this error is distributed to the adjacent pixels at the ratio shown in the matrix A. The distributed error and the density value of the pixel are added, and error diffusion processing is sequentially performed for each pixel.

  Returning to the description of FIG. Reference numeral 403 denotes binary data after error diffusion processing. When the error diffusion process is executed, the SMS circuit 806 determines whether to print with the front head or the rear head (6). Reference numeral 404 denotes data for distributing print data to two recording heads. Here, F indicates that the signal is distributed to the front head, and R indicates that the signal is distributed to the rear head. Then, print data indicated by 405 is sent to the front head, and data indicated by 406 is sent to the rear head.

  As described above, since the image of the predetermined area is formed by the different nozzles of the two heads, it is possible to reduce density unevenness caused by the characteristic variation of the plurality of nozzles. In addition, since the seam of the image is a half band unit, the banding period is halved, and the banding is less noticeable.

However, in the recording apparatus of the comparative example, as indicated by 404, the binarization result is distributed to another scan (pass) using a distribution pattern prepared in advance. This is because the binarization process and the distribution process are independent, and a process having no correlation is performed, which has the following problems.
1. When all of the binarization results are “1”, the data to be sent to the front head and the data to be sent to the rear head are alternately distributed, resulting in regularity in the data and dot dispersibility. Is significantly reduced.
2. If the binarization result coincides with the distribution pattern, the data concentrates on one head, and the density of print data for each scan is biased.

<Operation of Recording Apparatus According to this Embodiment>
Next, the operation of the recording apparatus according to the present embodiment will be described with reference to FIGS. FIG. 6 is a diagram illustrating a control configuration of the recording apparatus according to the present embodiment. FIG. 6 shows the processing contents from binarizing the multi-valued image data input to the recording apparatus according to the present embodiment, converting it into head drive data, and discharging ink from the nozzles for printing. . As described above, the recording head according to the present embodiment may be configured with a single recording head for each ink color, or may be configured with two or more recording heads.

  As shown in FIG. 6, the difference from the comparative example described in FIG. 3 is that the binarization circuit 805-K and the SMS circuit 806-K are changed to an image processing circuit 810-K. Therefore, the processing content of the image processing circuit 810-K will be mainly described below with reference to FIGS.

  FIG. 7 is a diagram illustrating a configuration of the image processing circuit according to the present embodiment. The image processing circuit 810 includes binarization units 100 and 101 and a subtracter 2000. The binarization units 100 and 101 include printing duty setting devices 1500 and 1501, multipliers 1100 and 1101, adders 1200 and 1201, threshold setting devices 1800 and 1801, and comparators 1300 and 1301, respectively. Further, the binarization units 100 and 101 include subtracters 1900 and 1901, error buffers 1600 and 1601, and error calculators 1700 and 1701, respectively.

  Reference numeral 1000 denotes a multi-value input image signal (data) input to the image input circuit. Reference numerals 1400 and 1401 denote already generated print data. The print data 1400 and 1401 are stored in a memory (not shown) and are given to the comparator 1301 as a constraint condition for the binarization process. Reference numerals 1950 and 1951 denote error data after binarization processing. Reference numerals 1960 and 1961 denote error data read from the error buffers 1600 and 1601. Reference numeral 2001 denotes a drive signal for driving the recording head.

  Print duty setting devices 1500 and 1501 set the print duty for the input image data. Multipliers 1100 and 1101 multiply the input image data 1000 by a print duty (first coefficient or second coefficient). Adders 1200 and 1201 add errors to the multiplication results of multipliers 1100 and 1101. The threshold setting devices 1800 and 1801 input threshold values for binarizing the multi-value data to the comparators 1300 and 1301. The comparators 1300 and 1301 compare the image signal added with the error with the threshold set by the threshold setting units 1800 and 1801, and output 0 or 255 (or “1”). The 1 subtracters 1900 and 1901 calculate errors from the image data input to the comparators 1300 and 1301 and the results of the comparators 1300 and 1301, and input the errors to the error buffers 1600 and 1601. The error calculators 1700 and 1701 calculate a plurality of error data read from the error buffers 1600 and 1601 by multiplying them by a predetermined coefficient.

  The binarization unit 100 functions as first gradation reduction means, and binarizes the multilevel data multiplied by the first coefficient. On the other hand, the binarization unit 101 functions as a second gradation reduction unit, and binarizes the multilevel data multiplied by the second coefficient. First, the processing of the binarization unit 100 that is the first gradation reduction means will be described below.

  The input image data 1000 input to the binarization unit 100 is multiplied by the setting value (first coefficient) set in the print duty setting device 1500 by the multiplier 1100, and the error calculated by the error calculator 1700. Data is added by the adder 1200 and input to the comparator 1300.

  The comparator 1300 compares the data input from the adder 1200 with the threshold set in the threshold setter 1800. The input data to the comparator 1300 and the output result from the comparator are input to the subtractor 1900, and the subtraction result is stored in the error buffer 1600 as error data 1950.

  The error data on the error buffer 1600 is input to an error calculator 1700, calculated by multiplying a predetermined coefficient, and an error is added to the input image data by an adder 1200.

  Here, the input image data 1000 is multi-value data of 0 to 255 which is 8-bit data. It goes without saying that the same applies to data normalized to 0-1. The comparator 1300 binarizes the multi-value data using a threshold value, but it is desirable that the output be the same as the input data range. That is, by setting “0” (no dot generation) and “255” (dot generation), a correct error can be calculated by the subtracter 1900 for error calculation. This error is, for example, 180−255 = −75 when 180 is converted to 255.

  Further, 100% may be set in the print duty setting device 1500. As a result, the operation of the binarization unit 100 is exactly the same as the normal error diffusion for the input image data 1000.

  Next, the operation of the binarization unit 101 that is the second gradation reduction means will be described. Since the basic operation principle of the binarization unit 101 is the same as that of the binarization unit 100, a duplicate description is omitted.

  The difference between the binarization unit 100 and the binarization unit 101 is the operation of the comparator 1301. In the binarization unit 101, the comparator 1301 compares the input data with the threshold set by the threshold setter 1801. At this time, print data 1400 that is a calculation result of the binarization unit 100 is further input to the comparator 1301 as a constraint condition. Specifically, the comparator 1301 performs the same comparison as the comparator 1300 when the print data 1400 of the binarization unit 100 is “255 (1)”, and does not perform the comparison when the print data 1400 is “0”. "0" is output to. Thereby, the output result of the binarization unit 101 is limited by the output result of the binarization unit 100.

  The subtracter 2000 functions as a generation unit and subtracts the output result of the binarization unit 100 and the output result of the binarization unit 101 to cope with one scan among a plurality of scans. A drive signal for the recording head to be generated is generated.

  Next, data generated in each process when the above-described gradation reduction process is executed will be described with reference to FIG. FIG. 8 is a diagram illustrating a data flow of the gradation reduction processing according to the present embodiment. Here, in order to generate print data of 25% duty necessary for 4-pass printing, a state of generating from 75% density data and 50% density data of input image data is shown.

  Reference numeral 200 denotes input data which is multi-value data. First, the multipliers 1100 and 1101 multiply the input data 200 by 0.75 and 0.5 set in the print duty setters 1500 and 1501, respectively. Thereby, input data 201 and 202 to be binarized are generated.

  Next, the binarization unit 100 binarizes the input data multiplied by 0.75, and generates output data 204. Subsequently, the binarization unit 101 performs binarization processing on the input data 202 multiplied by 0.5 using the output data 204 as a constraint condition, and generates output data 206. Finally, the subtracter 2000 calculates a difference between the output data 204 of the binarization unit 100 and the output data 206 of the binarization unit 101, and generates output data 207 as a drive signal for the print head.

  The output data 207 is a difference between the binarization processing data of 75% density data of the input data and the binarization processing data of 50% density of the input data. In addition, because the binarization processing result of 75% density has given restrictions, the print position (“1”) of the output data 206 after the binarization processing of 50% density is the binarization processing of 75% density. It is completely included in the printing position of the subsequent output data 204. Therefore, the difference between the binarization processing data output by the two binarization units 100 and 101 is the density difference set by the input data, which is the density of the output density.

  As described above, the output data shown in the present embodiment is output at the duty difference density set in the print duty setting devices 1500 and 1501. Therefore, if the set density difference is constant, the output density is also kept constant.

  When performing 4-pass printing, four types of 25% density data are required, but data is generated from different densities under the condition that the duty difference set in the print duty setting devices 1500 and 1501 is 25%. By doing so, it is possible to generate data with reduced correlation between paths.

  FIG. 9 is a diagram illustrating a setting example of the print duty setting device when performing multi-pass printing. Reference numeral 901 is an example of the set density for each pass when four-pass printing is performed. As shown in 901, 75% (first coefficient) is set in the print duty setting device 1500 of the binarization unit 100 shown in the second pass, and 50% (first) is set in the print duty setting device 1501 of the binarization unit 101. The procedure for setting 25 coefficients and generating a printing dot of 25% density has been described with reference to FIG. However, in other passes, as indicated by reference numeral 901, a dot pattern with reduced correlation between the passes can be generated by setting a print duty different from that in the second pass. However, as indicated by 901, it is desirable to keep the difference between the first coefficient and the second coefficient constant (25% here). Thereby, the dot pattern can be evenly distributed for each of a plurality of passes. Further, it is desirable that the sum of the differences between the first coefficient and the second coefficient is 100%. As a result, the target density corresponding to the input image data can be maintained in the present recording apparatus that records an image in the same area on the recording medium by performing a plurality of scans by the recording head.

  Reference numeral 902 denotes another setting at the time of 4-pass printing. Thus, since the difference between the value set in the print duty setting device 1500 and the value set in the print duty setting device 1501 is the density of the generated dots, if the difference is set to be constant, An arbitrary density may be set to generate a dot pattern. Also in this case, it is possible to generate a dot pattern with reduced correlation between passes.

  Also, as shown in 903, when performing 3-pass printing, the difference between the value set in the print duty setter 1500 and the value set in the print duty setter 1501 is set to 33%. A dot pattern may be generated. Further, for example, the third pass may be set to 34% so that the sum of the differences of the respective paths becomes 100%.

  When binarization processing (gradation reduction processing) is executed, there are optimum settings for the error distribution method shown in the error buffer 1600 and the threshold value set in the threshold value setting unit 1800 depending on input data and algorithms. As described above, according to the recording apparatus according to the present embodiment, since the binarization process can be executed while keeping these settings optimal, it is possible to obtain a high-quality print result with suppressed density unevenness. Is possible.

  As described above, the recording apparatus according to the present embodiment performs the first gradation reduction process by multiplying the input image data by the first coefficient, while the first coefficient is applied to the input image data. The second gradation reduction process is executed by multiplying the second coefficient having a predetermined difference from. Here, the recording apparatus executes the second gradation reduction process in units of pixels or executes the second gradation reduction process according to the processing result of the first gradation reduction process. Without processing, a predetermined value (for example, “0”) is used as the processing result. Further, the printing apparatus subtracts the processing result of the first gradation reduction process and the processing result of the second gradation reduction process, thereby recording corresponding to one of the multiple scans. A head drive signal is generated. In addition, the printing apparatus maintains a constant difference between the first coefficient and the second coefficient for each scan, and sets different first and second coefficients for each scan. As described above, the printing apparatus can reduce the correlation for each scan without reducing the dispersibility of the dots by generating the drive signal of the print head from different coefficients, that is, different densities. Also, by making the difference between the first coefficient and the second coefficient constant, the output density can be kept constant.

FIG. 3 is a diagram illustrating a configuration example of a recording head according to the present embodiment. FIG. 6 is a diagram illustrating an operation of a recording head according to the present embodiment. It is a figure which shows the control structure of the recording device used as a comparative example. It is a figure which shows a mode that the image data input into the recording device used as a comparative example is converted into print data. It is a figure which shows the matrix used for an error diffusion process. It is a figure which shows the control structure of the recording device which concerns on this embodiment. It is a figure which shows the structure of the image processing circuit which concerns on this embodiment. It is a figure which shows the data flow of the gradation reduction process which concerns on this embodiment. It is a figure which shows the example of a setting of the printing duty setting device in the case of performing multipass printing. It is a figure which shows the ideal formation position of the formed dot. It is a figure which shows the formation position when the formed dot has shifted | deviated.

Explanation of symbols

100: first binarization unit 101: second binarization unit 810: image processing circuit 1000: input image data 1100, 1101: multiplier 1200, 1201: adder 1300, 1301: comparators 1400, 1401: Print data 1500, 1501: Print duty setter 1600, 1601: Error buffer 1700, 1701: Error calculator 1800, 1801: Threshold setter 1900, 1901: Subtractor 1960, 1961: Error data 2000: Subtractor 2001: Drive signal

Claims (5)

A recording apparatus for recording an image by executing a plurality of scans by a recording head on the same area on a recording medium,
First gradation reduction means for multiplying input image data by a first coefficient and reducing the gradation of the multiplication result;
The input image data is multiplied by a second coefficient having a predetermined difference from the first coefficient, and the multiplication result is reduced by using the processing result of the first gradation reduction means as a constraint. Second gradation reduction means for
By subtracting the processing result of the first gradation reduction means and the processing result of the second gradation reduction means, the drive of the recording head corresponding to one of the plurality of scans is performed. Generating means for generating a signal,
In generating each drive signal corresponding to the plurality of scans, the difference between the first coefficient and the second coefficient is kept constant, and the first coefficient and the second coefficient that are different for each scan are set. A recording apparatus characterized by setting. The first and second gradation reducing units execute a binarization process for binarizing density values corresponding to each pixel of input image data,
The constraint condition is that the binarization process is executed when the processing result of the first gradation reduction means is one of two values, and the binarization process when the result is the other value. The recording apparatus according to claim 1, wherein a predetermined value is used as a processing result of the second gradation reduction means without executing the step. The first coefficient and the second coefficient are ratios to input image data,
The recording apparatus according to claim 1 or 2, wherein a sum of differences between the first coefficient and the second coefficient used for generating each drive signal is 100%.   4. The distribution device according to claim 1, further comprising distribution means for distributing the generated drive signals to the plurality of recording heads when the recording apparatus includes a plurality of recording heads. 5. The recording device described in 1. A control method of a recording apparatus for recording an image by executing a plurality of scans by a recording head on the same area on a recording medium,
A first gradation reduction step of multiplying input image data by a first coefficient and reducing the gradation of the multiplication result;
The input image data is multiplied by a second coefficient having a predetermined difference from the first coefficient, and the multiplication result is reduced in gradation using the processing result of the first low gradation step as a constraint. A second gradation reduction step;
By subtracting the processing result of the first gradation reduction step and the processing result of the second gradation reduction step, driving the recording head corresponding to one of the multiple scans Generating a signal, and
In generating each drive signal corresponding to the plurality of scans, the difference between the first coefficient and the second coefficient is kept constant, and the first coefficient and the second coefficient that are different for each scan are set. A control method for a recording apparatus, comprising: setting.

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