JP2012162070A - Recording apparatus and recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a recording apparatus capable of making inconspicuous a wide-ranging image quality failure represented by color banding.SOLUTION: A color swath plotted by one scan is divided in a sub-scanning direction by a positive integer of 3 or more so that respective regions are in a complementary relationship, and an uneven print mask function is applied to carry out a plotting operation so that the width of each region of the divided color swath substantially coincides with the width of positive integer times of a conveyance pitch when conveying a recording medium. The apparatus can thereby suppress printing failures such as boundary banding, beading and a solid blur in addition to bidirectional banding due to a difference in color overlapping order between a forward path and a return path. Consequently, stable achievement of high printing image quality can be expected.

Description

  The present invention relates to a recording apparatus and a recording method for printing by controlling the operation of a print head. In particular, the present invention relates to an ink jet recording apparatus and a recording method.

  In a recording apparatus typified by an ink jet printer, high image quality is a major point that affects its performance as well as high printing speed. In order to achieve high image quality, it is necessary to land droplets ejected from the print head accurately and uniformly on a predetermined position on the paper. In particular, in the case of a color printer, it is important to improve the landing accuracy in order to prevent a so-called color misregistration problem that the hue is changed by shifting the landing position of each color.

  However, when bi-directional printing is performed, the order in which dots are ejected and landed from each color print head in the forward pass and the return pass is switched depending on the print head arrangement order. There is a problem that so-called bidirectional color banding occurs.

  For example, Japanese Patent Laid-Open No. 2003-226004 discloses drawing based on a color swath to which a non-uniform print mask function is applied, which lowers the probability of using nozzles corresponding to the peripheral region of the edge compared to other nozzles. A technique for making bidirectional color banding inconspicuous by performing an operation is disclosed.

JP 2003-226004 A

  As described above, the cause of the bi-directional color banding is that the color stacking order differs between the forward pass and the return pass. Among them, the first scan (first scan) first drawn on the recording medium is the first scan. The contribution rate of the last scan (final scan) is high. The former is explained by the fact that the ink ejected on the paper for the first time spreads in a short time and forms large dots, and the ink ejected later forms a slightly smaller dot on the spread ink. it can. In other words, the influence of the first ejected color in the first scan and the print head color positioned in the front of the carriage traveling direction become strong. For the latter, the influence of this color is strong because the print head color located at the end of the final scan, that is, the rear of the carriage traveling direction is at the top of the print surface. An example of typical bidirectional color banding is shown in FIG. FIG. 3A shows a proper image. FIG. 3B is a diagram illustrating an example of bidirectional banding. Striped patterns appear in images with bidirectional banding, and the quality is poor compared to proper images.

  Bidirectional color banding may also occur between the left and right edges of the print area. Even within an area where the order of color overlap is the same, the time difference between the forward path and the backward path is large near the origin in the main scanning direction (direction in which the carriage scans). In other words, it takes time to draw at the beginning of the outbound trip and at the end of the return trip. On the other hand, at the end opposite to the origin, the time difference drawn from the forward path to the return path is small. This time difference causes a difference in the dry state of the dots on the paper in the immediately preceding scan, so that the nature of the ink ejected thereon naturally changes. In other words, color banding occurs due to the time difference.

  When printing a large poster or advertising material, there is a technique called tiling that arranges a plurality of small printed materials horizontally to make a large printed material. When there is color banding at the left and right ends, when tiling, the color difference between the joints of the printed matter becomes conspicuous, and the image quality may be significantly reduced.

  In Japanese Patent Laid-Open No. 2003-226004, a non-uniform print mask function is applied to color swaths for dark ink colors (for example, cyan, magenta, and black), and a uniform print mask function is applied to light ink colors (for example, yellow). This makes bidirectional color banding less noticeable.

  However, by applying a non-uniform print mask function, if attention is paid to a certain scan, the difference in nozzle use probability increases near the non-uniform end of the color swath. This is nothing but a difference between the drawing process for forming dots in a certain area and the drawing process for forming dots in another area. This is the same as the cause of the color banding due to the time difference between the left and right ends. This is more conspicuous when the print mask function uses a polygonal line or S-shaped gradation curve and has a steep slope such as 0% to 100% or 100% to 0%. Color banding corresponding to the gradation curve constituting the non-uniform print mask function will occur.

  Further, in the color swath, a difference between the non-uniform portion of the print mask function and the uniform portion may appear as color banding. This is because the non-uniform upper and lower areas of the print mask function complement each other and form a conventional dot for one scan. The number will increase. That is, a difference occurs in the time until the image is completed. This difference is exactly the cause of the color banding because it is different between the drawing process for forming dots in one area and the drawing process for forming dots in another area.

  For bidirectional color banding, instead of bidirectional printing, unidirectional printing is performed, so that the overlapping order of ink colors and the time difference can be unified over the entire drawing area. This reduces color banding, but is not practical because the printing speed is reduced by a factor of 1/2 compared to bidirectional printing. In addition, in unidirectional printing, image quality defects due to specific vibrations on the carriage travel path are accumulated every scan, which may lead to image quality defects such as vertical stripes and color unevenness.

  In addition, by mounting two or more print heads for each color so that the colors are arranged symmetrically on the carriage, it is possible to unify the color stacking order regardless of the forward or backward path. Since a double or more head is required, the cost increases such as an increase in the size and weight of the carriage and an increase in the size of an actuator for driving the carriage.

  In addition, when the positioning accuracy at the time of paper conveyance is poor or the paper conveyance amount itself is not appropriate, streaks that darken or lighten may appear at the upper and lower ends of the color swath. These are border bandings called black stripes, white stripes, and so on. An example of this is shown in FIGS. 4 (a) and 4 (b). FIG. 4A shows an example of boundary banding. FIG. 4B is another example of boundary banding. These appear as streaks with a difference in color density between the upper and lower ends of the color swath and the other portions. In order to prevent these problems, it is necessary to adjust the sheet conveyance amount as appropriate. However, it is difficult to keep the conveyance amount constant for a long period of time.

  Boundary banding can also occur due to slow drying after ink landing on a specific paper. Inside the color swath, since ink is present with high probability around the ink, the ink becomes a wall and the movement of the ink is prevented. However, at the end of the color swath, that is, the edge, there is a space where nothing exists on one side, so that the ink easily moves. A so-called phenomenon called “mottling” occurs, and as a result, only this edge portion causes a change in hue from other regions. This phenomenon is sometimes called beading.

  Furthermore, the dot diameter after landing may be small for a specific sheet. In this case, density unevenness easily occurs due to slight deviation in landing. In general, the density strength often appears as horizontal stripes in the paper feed direction. This is a phenomenon called “hot weather”. An example of this is shown in FIG. FIG. 5 is a diagram showing an example of blurring. This is an example in which density unevenness occurs in a portion where landing deviation occurs, and this appears as white streaks.

  The conventional printing method called high image quality mode is designed to reduce the number of passes by simply applying print masks that are regularly arranged in a very narrow range to the color swath, and to increase the number of passes. It was out. As shown in FIG. 6, a standard print mode called 4 passes in which drawing of an area of 4 scans is completed, as shown in FIG. It is common. An example of the print mask function applied to the color swath in this case is shown in FIG. Although the upper and lower blocks of the color swath divided into two are complementary, the contents are regular and uniform, and due to the fine periodicity of the print mask, intensive and selective image quality failure could not be wiped out. .

  Furthermore, there is a method of applying a print mask function as shown in FIG. This is a technique in which a non-uniform print mask having a larger size and generated using an FM screen mask or the like is applied to the upper and lower blocks of the two color swaths so as to have a complementary relationship for drawing. This can alleviate image quality defects. This becomes more effective by making the gradation curve constituting the probability distribution of nozzles used in the print mask function non-linear such as an S-shape. While this method is effective against a wide range of image quality anomalies such as bi-directional color banding and boundary banding, it is more prominent image quality failure, errors and vibration factors that are fixedly present in the mechanical parts that make up the printer in the first place. In many cases, the image quality anomalies that occur in the system cannot be prevented.

  The present invention has been made in view of such circumstances, and can make a wide range of image quality defects inconspicuous, such as color banding at the time of bidirectional printing in a recording apparatus, boundary banding, beading, and blurring. An object is to provide a recording apparatus and a recording method.

  The recording apparatus of the present invention ejects ink onto a recording medium while scanning the print head, and in the recording apparatus for forming an image on the recording medium, the color swath produced by one scan at the time of bidirectional printing is 3 or more. Drawing is performed by applying a print mask function in which each of the blocks of the print head corresponding to each region divided by the first positive integer is different and the images drawn by each of the blocks are complementary. The width of each area of the color swath divided by the first positive integer substantially matches the width of the second positive integer multiple of the transport pitch when transporting the recording medium, and the block is Dots divided by nozzles divided by the second positive integer and drawn by adjacent nozzles in one of the nozzle groups drawn by the one scan In, characterized in that contains dots to be drawing by other nozzle groups of the nozzle of said nozzle group when other scan.

  The recording method of the present invention is a recording method of a recording apparatus that ejects ink onto a recording medium while scanning a print head and forms an image on the recording medium. Is obtained for each block of the print head corresponding to each area divided by a first positive integer of 3 or more, and a print mask function is obtained in which the images drawn by each block are in a complementary relationship. A step of performing a drawing operation by applying the print mask function, a width of each area of the color swath divided by the first positive integer, and a second of the conveyance pitch when conveying the recording medium The width of the positive integer multiple substantially matches, and the block is divided into nozzle groups divided by the second positive integer, and one of the nozzle groups of the nozzle group drawn in the one scan is used. A step of conveying the dots drawn by the nozzles of the other nozzle groups in the nozzle group during the other scans between the dots drawn by the adjacent nozzles in the nozzle group. It is characterized by having.

  According to the present invention, in addition to bi-directional banding resulting from the difference in color stacking order between the forward path and the return path, boundary banding, beading, shading, and errors and vibrations that are fixedly present in the mechanical components constituting the printer A wide range of printing defects caused by factors can be suppressed.

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention. FIG. 2 is a schematic view of the carriage mechanism. FIG. 3A shows a proper image. FIG. 3B is a diagram illustrating an example of bidirectional color banding. FIG. 4A and FIG. 4B are diagrams illustrating an example of boundary banding. FIG. 5 is a diagram illustrating an example of smoothness. FIG. 6 is a diagram showing the principle of drawing in a printing mode called 4-pass. FIG. 7 is a diagram showing the principle of drawing in a printing mode having a multi-pass effect by dividing the color swath into two and making each region complementary by using the printing mode shown in FIG. 6 as a base. FIG. 8 is a diagram showing an example of a regular and uniform print mask function applied to the print mode shown in FIG. FIG. 9 is a diagram illustrating an example of a non-uniform print mask function that is applied to the print mode illustrated in FIG. 7 and has an effect of suppressing printing defects. FIG. 10 is a diagram showing the principle of printing in a printing mode having a multi-pass effect by dividing the color swath into three and making each region complementary by using the printing mode shown in FIG. 6 as a base. FIG. 11 is a diagram illustrating an example of a non-uniform print mask function that is applied to the print mode illustrated in FIG. 10 and has an effect of suppressing printing defects. FIG. 12 is a flowchart showing an example of the operation of the embodiment. FIG. 13 is a diagram showing the principle of printing in a printing mode having a multi-pass effect by dividing the color swath into four and making each region complementary by using the printing mode shown in FIG. 6 as a base. FIG. 14 is a diagram illustrating an example of a non-uniform print mask function that is applied to the print mode illustrated in FIG. 13 and has an effect of suppressing printing defects. FIG. 15 is a diagram showing the relationship between the nozzles and the printing position. FIG. 16 is a diagram illustrating an example when a plurality of print heads are arranged in the sub-scanning direction. FIG. 17 is a diagram illustrating an example of a print mode when a plurality of print heads are arranged in the sub-scanning direction. FIG. 18 is a diagram for explaining an example of an improved printing mode when a plurality of print heads are arranged in the sub-scanning direction.

  Hereinafter, a recording apparatus and a recording method according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In this figure, the recording apparatus 1 is an ink jet printer. The recording apparatus 1 includes a control unit 20 that controls the operation of the entire apparatus. The control unit 20 includes a CPU 21 of a control unit that performs overall control of processing operations in the control unit 20, a ROM 22 of a storage unit in which programs for performing various controls and printing operations of the recording apparatus 1, and the execution of the printing operation are performed. The RAM 23 of the storage means used as a working storage area by each control unit, the EEPROM 24 of the storage means configured by a non-volatile memory for storing setting values and data immediately before the power is turned off, and the state operated in the operation panel 44 are read. At the same time, the operation panel control unit 25 that displays information on the display unit included in the operation panel 44, the print control unit 26 that is a control unit that controls the print operation by the print head 41 with respect to the recording medium, and the operation of the carriage mechanism 42 From a carriage control unit 27 as a control means for controlling, a grid roller or the like for conveying a sheet as a recording medium A sheet conveyance control unit 28 which is a control means for controlling the operation of the formed sheet conveyance mechanism 43, an image memory 30 for storing an image to be printed, and an image memory writing / reading control unit for performing writing / reading control on the image memory 30 31, a host I / F unit 29 which is an interface for inputting / outputting image data and control commands to / from a host computer.

  The print control unit 26 and the carriage control unit 27 control the printing operation while coordinating the print positions based on the carriage position read by the linear encoder 45.

  FIG. 2 is a schematic view of an example constituting the carriage mechanism. The carriage mechanism 42 is provided with means for detecting the position of the print head 41. When ejecting droplets from the print head 41 in the recording apparatus 1, a linear encoder 45 incorporating a scale sensor attached to the carriage 420 and a linear scale 421 fixed along the traveling path of the carriage 420 are used. The current position during the reciprocation of the carriage 420 is detected, and information is input to the control unit 20. The control unit 20 recognizes the position of the print head 41 and generates ink ejection timing, thereby improving the positional accuracy of the droplets that have landed on the paper 422. In this example, four color print heads 41 are mounted in the order of K (black), C (cyan), M (magenta), and Y (yellow) from the left side when viewed from the paper 422 feeding direction, that is, from the head in the forward direction. Yes. In the forward direction, ink colors are formed on the paper 422 in this order, and the reverse is the reverse direction.

  Ink jet printers using these configurations require multiple scans and bi-directional carriage scans in order to suppress the deflection and omission of the nozzles of the print head 41 and periodic unevenness due to vibration of the drive system. Usually, a certain area is drawn. This is generally called a multipath method. In the multi-pass method in which an image of a certain region is completed by n scans, the number of dots ejected in one scan is 1 / n with respect to the total dots constituting a certain region. For example, in a printing mode called 4-pass that completes an image in 4 scans, a quarter of dots constituting a certain area are ejected for each scan, and the image is completed by conveying the paper 422 each time. I will let you. In this case, the conveyance pitch of the paper 422 is approximately ¼ of the color swath constituted by the total number of nozzles of the print head 41. FIG. 6 shows this state focusing on only a certain print color. The conveyance pitch of the paper 422 is ¼ of the used nozzle range of the print head 41, and ¼ constituent dots of the image are ejected by the color swath created in one scan. It can be seen that the image is completed by taking 4 scans for each area.

  FIG. 15 is a diagram showing the relationship between the nozzles and the printing position. An example of completing an image with four scans will be described with reference to FIG. A plurality of nozzles 46 are arranged in the print head 41 at intervals of 180 dpi. Here, only a part of the nozzle is shown. Ink is ejected from the nozzle 46 onto the paper 422. The ejected ink is landed on the paper 422, and the landed dots are marked on the line as a print line 47. The print lines 47 are spaced at 720 dpi. In this case, the print head 41 is divided into ¼ blocks, the conveyance amount of the paper 422 is set to the block width +720 dpi, and printing is performed at ¼ intervals of the nozzles 46 by scanning four times. Further, the print head 41 can be divided into 1/8 blocks, the conveyance amount of the paper 422 is set to the block width +720 dpi, and the top block and the fifth block from the top can be ejected on the same line. In this case, printing on the same line can record an image with ink ejected from two different nozzles.

  FIG. 7 shows an example of a print mode that requires twice the number of scans and aims at the effect of a larger multi-pass method. In this regard, the print mask function shown in FIGS. 8 and 9 is applied to suppress printing defects. In FIG. 7, the used nozzles of the print head are divided into eight blocks which are equally divided, and further divided into eight upper divided blocks and four lower blocks. The upper 4 blocks and the lower 4 blocks are printed complementarily to each other. That is, printing is performed with the lower block at a position where printing is not performed with the upper block, thereby completing the image.

  An example of a print mode to which an embodiment of the present invention is applied will be described with reference to FIG. At the time of 4-pass printing in FIG. 6, the used nozzle range of the head, that is, 1/4 of the color swath was used as the paper conveyance amount, but here, it is further divided into three to fill 1/12 of the color swath. In addition, the color swath print mask function equally divides the entire used nozzle range of the head into three, so that the upper, middle, and lower blocks are complementary to the other two blocks. That is, the image is completed using the upper, middle, and lower three blocks. In addition, since the width of each block in a complementary relationship with four times the paper conveyance amount matches, the number of scans required to complete an image in the entire drawing range is not equal to 12 scans. Therefore, there is a problem that the difference between the non-uniform portion of the print mask function, that is, the portion where the nozzle use probability changes, and the uniform portion, ie, the portion where the nozzle use probability changes, appears as color banding. Does not happen. Further, the dots constituting the entire drawing range are drawn by selecting one scan that is determined probabilistically by the print mask function among the three scans, and a powerful multi-pass effect can be obtained. By using a print mask function as shown in FIG. 11 as an example, the print ratio of the first scan and the final scan, which is dominant with respect to color banding, is inevitably lowered, so that bidirectional color banding is suppressed. effective. Furthermore, since the printing rate at the end of the color swath is also reduced, there is an effect of suppressing boundary banding and beading. The distribution of the printing rate is constant in the second block at the center. The printing rate of the first block at the end is the same as the printing rate of the central second block on the central second block side, but the printing rate gradually decreases toward the outside. The printing rate of the third block at the end is the same as the printing rate of the central second block on the central second block side, but the printing rate gradually decreases toward the outside.

  The operation will be described using a flowchart. FIG. 12 is a flowchart showing an example of the operation of the embodiment. The operation of the process for applying the print mask function to the print head 50 will be described. The drawing is controlled by the CPU 21 based on a program stored in the ROM 22. A print mask function based on a gradation curve or the like is stored in advance in the ROM 22 and is read out from the ROM 22 when applied. The print head 50 is divided into a first area 51, a second area 52, and a third area 53 so that the widths of the areas are equally divided. A print mask function stored in the ROM 22 is applied to each area. As an example, a non-uniform print mask function as shown in FIG. 11 is applied to the entire color swath composed of the first area 51, the second area 52, and the third area 53, and the print applied to each area. The mask function is complemented with others and the printing rate is 100%. That is, the image to be drawn is an image in which the image printed in the first area 51, the image printed in the second area 52, and the image printed in the third area 53 are complemented.

  First, when the process is started, the process proceeds to step S2 when the non-uniform print mask function is used, and to step S3 when not used (step S1). In step S1, it is determined what print mask function is applied to the print head 50, and the process branches. This is a kind of selection means. Here, the RAM 23 stores a flag for determining whether or not to use the RAM 23 in advance. The flag is varied based on a user setting or a print mode setting. It is also possible to input a print mode from the operation panel 44 as input means and perform branch processing based on the input. You may branch according to the conditions decided beforehand by the program.

  Next, step S2 will be described. Here, a description will be given using an example in which a color swath is divided into three regions. The color swath is divided into three areas as an example, and the present invention is not limited to this. When a non-uniform print mask function is used, the color swath is divided into three regions and the print mask function to be used is applied to each region. Whether the nozzle is used or not is determined based on the print mask function. Data for determining use and non-use is stored corresponding to each nozzle. For example, “1” data is stored in the RAM 23 corresponding to each nozzle when used, and “0” data is not used. The print mask function is stored as a table or calculation formula in which data is stored. A mask is created for each nozzle by calculating based on this print mask function. As another example, a mask to which a print mask function is applied in advance may be stored and selected and used.

  Next, step S3 will be described. If a uniform print mask function is used, the uniform print mask function is applied to each region of the segmented nozzle. Whether the nozzle is used or not is determined based on the uniform print mask function. Data for determining use or non-use is stored for each nozzle. For example, “1” data is stored in the RAM 23 corresponding to each nozzle when used, and “0” data is not used. The print mask function is stored as a table or calculation formula in which data is stored. A mask is created for each nozzle by calculating based on this print mask function. As another example, a mask to which a print mask function is applied in advance may be stored and selected and used.

After a mask is set for the print head 50, printing is performed based on the mask and image data stored in the image memory 30.
When a line having a 720 dpi interval is printed by a head having a nozzle interval of 180 dpi, the nozzles in each of the three blocks are further divided into four nozzle groups. The four nozzle groups in each block print a corresponding line. Each line also has a different nozzle use probability, and has the effect of suppressing various bandings.

  Similarly, as shown in FIG. 13, the paper conveyance amount is set to 1/16 of the color swath, and the print swath function of the color swath equally divides the entire used nozzle range of the head into four and prints each block in a complementary relationship. Modes are also possible. In this case, the dots constituting the entire drawing range are drawn by selecting one scan that is determined probabilistically by the print mask function from among the four scans, and an extremely powerful multipass effect can be brought about. By applying the print mask function shown in FIG. 14 as an example, the effect of suppressing various banding becomes larger. Masks are set so that the use probability of the nozzles is different for each part of the head divided into blocks. The closer to the end of the head, the lower the probability of use of the nozzle, and the closer to the end of the head, the lower the probability of using the nozzle. Each block has a complementary relationship. This makes it possible to perform good drawing. When a line having a 720 dpi interval is printed by a head having a nozzle interval of 180 dpi, the nozzles in each of the four blocks are further divided into four nozzle groups. The four nozzle groups in each block print a corresponding line. Each line also has a different nozzle use probability, and has the effect of suppressing various bandings.

  Next, a non-uniform print mask function will be described. An example of the gradation curve constituting the probability distribution of the nozzles applied to the print mask function will be described. Making the gradient curve steep makes color banding within the area covered by this curve, so it is desirable that the gradient be as gentle as possible. On the other hand, since the high printing rate at the end of the color swath causes boundary banding and beading, an appropriate gradation curve that balances these must be set. For this reason, a steep curve in which the printing rate changes from 0% to 100% is unsuitable, and by selecting a curve connecting 30% to 70% as shown in FIG. The occurrence of color banding can be suppressed.

  However, the selection of the shape of these gradation curves and the setting of the printing rate for the start and end points differ depending on the width of the non-uniform area, and the effect varies depending on the image to be printed. It is preferable to change depending on the application.

  The larger the number of color swath divisions, that is, the greater the number of passes required for drawing, the slower the printing speed, but the higher image quality can be obtained. That is, based on a basic four-pass printing mode (referred to as standard printing mode), the number of color swath divisions is tabulated, and an arbitrary value is selected by the user from the operation panel 44. A combination of print speed and print image quality according to the user's application can be realized. A print mode can be selected based on an input from the operation panel 44. For example, this table is called “image quality improvement mode”, and weights from 1 to 3 are assigned. If you want to output printed matter that does not place much importance on image quality, it is more productive to select “Image quality improvement mode 1” with the number of divisions set to 2 and increase the printing speed as much as possible, but you want to output printed matter that emphasizes image quality. In some cases, it is possible to select “image quality improvement mode 3” in which the number of divisions is 4, and to obtain high image quality even when productivity is lowered. In order to balance these, “image quality improvement mode 2” with the number of divisions set to 3 may be selected.

  Further, the application of the present invention has been described so far for the standard print mode. Of course, this application is also possible for other print modes. In the draft printing mode where the number of scans has been reduced with emphasis on productivity, deterioration of image quality has been regarded as a problem in the past, but by applying the “image quality improvement mode” to this as well, the printing speed is faster than the standard printing mode. Therefore, the image quality can be improved compared to the conventional draft printing mode. In the high image quality printing mode in which the number of scans is increased with emphasis on image quality, a higher image quality can be expected by applying the “image quality improvement mode”. In other words, by adding an additional “image quality improvement mode” function to the existing print mode, the user can select the print mode from the operation panel 44 in a matrix manner. Fine-tuned operation is possible.

  Further, depending on the printer, in order to improve the printing speed, a plurality of print heads may be arranged in the sub-scanning direction and used as a print head having an apparently large number of nozzles. An example of this is shown in FIG. The print head 411 and the print head 412 are arranged in the sub-scanning direction so that the specific nozzles overlap. By applying such a positional relationship for each color, it is possible to realize a printing speed that is approximately twice as high. However, extremely high positioning accuracy is required with respect to the print head 411 and the print head 412, and even a slight error may cause deterioration in image quality.

  Consider a case in which a line with a 540 dpi interval is printed by a head with a 180 dpi nozzle interval when such a print head is arranged. Unlike the lines of 720 dpi intervals described so far, 1/3 of the dots of the image are ejected by the color swath that is drawn in one scan. Therefore, basically, an image is completed by requiring 3 scans. On the other hand, when the color swath shown in FIG. 10 is divided into three parts and the areas are made complementary to each other, application as a printing mode having a more multi-pass effect can be expressed as shown in FIG. Two print heads 411 and 412 are arranged in the sub-scanning direction, and their joints are 413. The color swath is divided into nine parts, considering two print heads as one print head. Here, there is a problem that the joint 413 is not aligned with the division position of the color swath.

  As described above, when a plurality of print heads are arranged in the sub-scanning direction and regarded as a print head having an apparently large number of nozzles, extremely high positioning accuracy is required for these. This applies not only to positioning in the sub-scanning direction and main scanning direction, but also to each tilting and positioning in the vertical direction. A slight error in these attachments is nothing but deterioration of the landing position accuracy, and as a result, the image quality is deteriorated.

  The joint 413 that is a problem here can be said to be a point where the positioning error between the print head 411 and the print head 412 appears most prominently. If the print head is attached away in the sub-scanning direction, white stripes may be visible at the joint 413, and if the print head is attached too close, the black stripes may be visible at the joint 413. Further, when printing by the other print head overlaps with this portion, for example, when printing by the print head 411 and the print head 412 overlaps, a landing position error in the sub-scanning direction remarkably occurs. As a result, density unevenness occurs in the upper and lower portions with the joint 413 as a boundary. This density unevenness may be visually recognized in the entire printing range at a period in which the color swath is divided, and is a serious cause of image quality deterioration.

  In order to deal with this problem, a print mode as shown in FIG. 18 can be considered. In this case, the color swath is first divided into 10, that is, the nozzles of the print head are divided into 10 continuous nozzle groups, and the paper feed pitch for each scan is also combined therewith. However, the upper one nozzle group is completely non-discharged, and only the remaining nine lower nozzle groups are used for printing. Furthermore, the color swath is divided into three, and a print mask function having a complementary relationship is applied to the mask used in each block. Therefore, the joint 413 matches the position where the color swath is divided into each nozzle group. Since the joint 413 does not appear in the middle of each nozzle group into which the color swaths are divided, there is no possibility of landing position errors in the upper and lower parts. As a result, density unevenness due to positioning errors of a plurality of heads can be reduced. By limiting the number of nozzles that can be used, a decrease in printing speed is inevitable, but it is extremely effective as a technique for preventing deterioration in image quality.

  As described above, the non-uniform print mask function is applied to reduce the probability that the nozzle corresponding to the peripheral area of the color swath edge is used as compared with the other nozzles. In addition to bidirectional banding, which is caused by the color stacking order differing between the forward path and the return path, printing defects such as border banding, beading, and blurring are suppressed by making the width of the correct area approximately match the paper transport amount. be able to. As a result, it can be expected to stably achieve high print image quality.

DESCRIPTION OF SYMBOLS 1 ... Recording device, 20 ... Control part, 21 ... CPU, 22 ... ROM, 23 ... RAM, 24 ... EEPROM, 25 ... Operation panel control part, 26 ... Print control unit, 27 ... carriage control unit, 28 ... paper conveyance control unit, 29 ... host I / F unit, 30 ... image memory, 31 ... image memory write / read control unit , 41 ... print head, 42 ... carriage mechanism, 43 ... paper transport mechanism, 44 ... operation panel, 45 ... linear encoder

Claims (7)

In a recording apparatus that ejects ink onto a recording medium while scanning the print head and forms an image on the recording medium,
Each of the blocks of the print head corresponding to each area obtained by dividing the color swath produced by one scan during bi-directional printing by a first positive integer of 3 or more is different. The drawing operation is performed by applying a print mask function in which the images to be complemented are complementary.
The width of each area of the color swath divided by the first positive integer substantially coincides with a width of a second positive integer multiple of the conveyance pitch when conveying the recording medium, and the block is The nozzle group is divided into positive integers and is divided between the dots created by the adjacent nozzles in one of the nozzle groups drawn in the one scan. A recording apparatus comprising dots created by nozzles of another nozzle group in the nozzle group.   The print mask function to be applied to the block is probabilistically drawn only for at least two of the dots drawn by the number of scans corresponding to the product of the first positive integer and the second positive integer. The recording apparatus according to claim 1.   The shape of a gradation curve constituting the probability distribution of use of the nozzle corresponding to the print mask function is such that the probability of use of the nozzle in the block does not change from 0% to 100%. The recording apparatus according to claim 1 or 2.   A set of the first positive integer that divides the color swath and the gradation curve that constitutes a probability distribution of nozzles corresponding to the print mask function is provided for each print mode. The first positive integer that divides the color swath according to the selected printing mode and the gradation curve are acquired in association with the print mode, and the acquired color swath is acquired from the first color swath. 4. The recording according to claim 3, wherein the print mask function based on the gradation curve is applied to the nozzles of the block corresponding to each area of the color swath divided by a positive integer divided by. apparatus.   The first positive integer that divides the color swath, and has a plurality of the first positive integer that divides the color swath and the gradation curve that forms a probability distribution of the nozzles corresponding to the print mask function. The positive integer and the gradation curve are respectively stored in a table prepared in the storage means, and the first positive integer and the gradation for dividing the color swath from the table based on the input of the input means The print mask function based on the gradation curve is applied to the nozzle of the block corresponding to each area of the color swath divided by the first positive integer that obtains a curve and divides the obtained color swath The recording apparatus according to claim 3. A plurality of the print heads are used in combination in the sub-scanning direction;
The nozzles at the joint of the print head and the nozzles at the end of the block do not coincide with each other, and the nozzles at the joint and the nozzles at the end of the nozzle group coincide with each other. The recording apparatus according to any one of claims 1 to 5. In a recording method of a recording apparatus for ejecting ink to a recording medium while scanning a print head and forming an image on the recording medium,
Each of the blocks of the print head corresponding to each area obtained by dividing the color swath produced by one scan during bi-directional printing by a first positive integer of 3 or more is different. Obtaining a print mask function in which the images to be complemented have a complementary relationship, and performing the drawing operation by applying the print mask function;
The width of each area of the color swath divided by the first positive integer substantially matches the width of the second positive integer multiple of the transport pitch when transporting the recording medium, and the block is the second In the case of another scan, the dots are divided by nozzles divided by a positive integer and are drawn by adjacent nozzles in one of the nozzle groups drawn in one scan. And a step of transporting so that dots drawn by the nozzles of the other nozzle groups in the nozzle group are included.