JP5603185B2 - Recording apparatus and recording method - Google Patents

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 stacking order of dots ejected and landed from each color print head in the forward and return passes is changed depending on the print head arrangement order. There is a problem that so-called bidirectional color banding occurs.

  For example, Japanese Patent No. 3896329 discloses a drawing operation based on a color swath to which a non-uniform print mask function is applied, which lowers the probability of use of nozzles corresponding to the peripheral region of the end compared to other nozzles. A technique for making bidirectional color banding less noticeable is disclosed.

Japanese Patent No. 3896329

  As described above, the cause of bidirectional color banding is that the color stacking order differs between the forward and backward passes. Among them, the first scan (first scan) and the last scan (first scan) that are drawn on the paper first. The contribution rate of the 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. That is, the influence of the color that is ejected first in the first scan and the color of the print head that is located in the front in the carriage traveling direction is 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.

  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 large posters or advertisements, there is a technique called tiling that arranges a plurality of small prints horizontally to make a large print. 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 degraded.

  In Japanese Patent No. 3896329, a non-uniform print mask function is applied to the color swath 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). Two-way color banding is less noticeable. However, this is only reduced, and bidirectional color banding may still be noticeable depending on the hue and density of the image to be drawn.

  In addition, by applying a non-uniform print mask function, when 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. This suggests the possibility of deteriorating the image quality.

  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 dot for one conventional scan, so the uniform print mask function scans more than the area drawn by all scans. 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 become darker or lighter 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). 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.

  In addition, measures against bidirectional color banding can be taken by a print mode as shown in FIG. This is sometimes referred to as a 5-pass mode or the like in comparison with the standard print mode shown in FIG. 5 being referred to as 4-pass. In this print mode, the range of nozzles used by the print head is divided into five, and the amount of paper transport is adjusted to the width. If one block on the paper feed direction side is not used in the forward path and one block on the opposite side is not used in the backward path, the same area on the paper is drawn with color swaths in the forward path and the backward path. This means that the order in which the ink colors are superimposed is fixed, and thus bi-directional color banding does not occur in principle.

  However, in the 5-pass mode, there is a drawback that not all the nozzles of the print head can be used for each scan. For example, if only 4 blocks are used for each scan in a state where the head is divided into 5, the printing speed is reduced to 4/5 times.

  In the 5-pass mode, since the same area is drawn on the forward path and the return path, the upper and lower edges of the color swath have a state in which twice the normal amount of ink has been ejected. This easily causes ink mottling and promotes the generation of boundary banding and beading.

  The present invention has been made in view of such circumstances, and provides a recording apparatus and a recording method capable of making color banding during bidirectional printing in a recording apparatus inconspicuous without reducing productivity from the conventional print mode. The purpose is to provide.

In the recording apparatus of the present invention, a print head that is divided into a plurality of blocks having the same width of the used nozzle range and in which ink ejection is controlled is arranged for each of the plurality of ink colors, and the nozzles of the blocks are used. Control for controlling the ejection of the print head and the conveyance of the recording medium in a recording apparatus that forms a color image on the recording medium while scanning the print head with a predetermined probability determined for each block. And the control means does not convey the recording medium between the forward path and the return path of the print head when printing is performed by reciprocating scanning of the print head, and is not performed between the return path and the subsequent path. The recording medium is transported by the width, the areas drawn on the forward path and the return path between transporting the recording medium are matched, and the ink color overlaps for all the printing areas. The printing head is fixed to the forward has the block at least 3 or more, the printing once the sum of the probabilities that are used in the nozzle of the blocks of each located at both ends of the print head in the scanning Apply a uniform print mask function that is the same as the probability that the nozzles of each block located in the central part of the head will be used, so that the blocks located at both ends of the print head mutually The probability that the nozzles of the block on the downstream side in the transport direction of the recording medium among the blocks located at the both ends of the print head are used by complementing the ejection position is: the to Rukoto characterized large relative probability of use of the nozzles of the blocks upstream.

In the recording method of the present invention, a print head that is divided into a plurality of blocks having the same width of the used nozzle range and in which ink ejection is controlled is arranged for each of the plurality of ink colors, and the nozzles of the blocks are used. In a recording method of a recording apparatus for forming a color image on a recording medium while scanning the print head as a constant value predetermined for each block , in the case of printing by reciprocating the print head The recording medium is not transported between the forward path and the return path of the print head, and the recording medium is transported by the block width between the return path and the subsequent outbound path, and the forward path and the return path between transport of the recording medium. to match the area to be drawing in and for all drawing area and a step of drawing by fixing the stacking order of the ink color, it was closed, the print head, Each block located in the central portion of the print head, which has at least three blocks, and the sum of the probabilities of use of the nozzles of the respective blocks located at both ends of the print head in one scan. Applying a uniform print mask function that is the same as the probability of use of the nozzles of the block, the blocks located at both ends of the print head complement each other with the ink ejection positions to perform the drawing operation. The probability that the nozzles of the blocks on the downstream side in the transport direction of the recording medium among the blocks located at the both ends of the print head are used is that of the nozzles of the blocks on the upstream side. It is characterized by a large probability of being used .

  According to the present invention, it is possible to suppress printing defects such as bi-directional banding caused by the color stacking order being different between the forward pass and the return pass without reducing productivity from the conventional print mode.

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 is a diagram illustrating an example of an appropriate image. FIG. 3B is a diagram illustrating an example of bidirectional color banding. FIG. 4 is a diagram illustrating an example of boundary banding. FIG. 5 is a diagram showing the principle of drawing in the standard print mode called 4-pass. FIG. 6 is a diagram showing the principle of drawing in a print mode that can suppress bidirectional color banding, which is called 5-pass. FIG. 7 is a diagram illustrating the principle of drawing in a printing mode in which bidirectional color banding can be suppressed at the same printing speed as four passes. FIG. 8 is a diagram illustrating the principle of drawing in a print mode that can suppress the occurrence of boundary banding and beading while suppressing bidirectional color banding. FIG. 9 is a diagram illustrating the principle of drawing in the print mode that can suppress the generation of boundary banding and beading while more effectively suppressing bidirectional color banding. FIG. 10 is a diagram showing the principle of drawing in the print mode in which the printing rate on the side where the number of scans is early can be reduced and the occurrence of boundary banding and beading can be suppressed while the bidirectional color banding is more effectively suppressed. . FIG. 11 is a flowchart for explaining the operation of the embodiment.

  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 the embodiment. 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 are performed. 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 that is a control unit that controls the operation of the formed sheet conveyance mechanism 43, an image memory 30 that stores an image to be printed, and a control unit 31 that is a control unit that controls writing / reading on the image memory 30. And a host I / F unit 29 which is an interface for inputting and outputting image data and control commands with the 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 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. . In the forward direction, the ink color is formed on the recording medium 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 caused by 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 standard print mode called 4-pass that completes an image in 4 scans, each quarter of the dots are ejected by ¼ dot, and the image is transferred by transporting the paper 422 each time. I will complete it. 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. 5 shows this state focusing only on 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.

  The operation of a printing mode called a 5-pass mode that has an effect of suppressing bidirectional color banding will be described with reference to FIG. In this printing mode, the used nozzle range of the print head is divided into five, and the paper conveyance amount is one block. No nozzle for one block on the paper feed direction side is used on the return path, and no nozzle for one block on the opposite side is used on the forward path. As a result, the same area on the paper is drawn by the color swath in the forward path and the backward path. The first scan that is drawn on the paper is always forward, and the ink colors overlap in the order of K, C, M, and Y. The return path has already been drawn by the forward path, and the ink colors overlap in the order of Y, M, C, and K. Since the remaining two scans are repeated, as a result, in all drawing regions, K, C, M, Y, Y, M, C, K, K, C, M, Y, Y, M, C, The ink colors overlap in the order of K, and the image is completed. Therefore, bi-directional color banding caused by the different ink color superposition order in principle does not occur.

  However, in the 5-pass mode, there is a drawback that not all the nozzles of the print head can be used for each scan. For example, if only 4 blocks are used for each scan in a state where the head is divided into 5, the printing speed is reduced to 4/5.

  In the 5-pass mode, since the same area is drawn on the forward path and the return path, the upper and lower edges of the color swath have a state in which twice the normal amount of ink has been ejected. This easily causes ink mottling and promotes the generation of boundary banding and beading.

  Next, a printing mode according to an embodiment of the present invention will be described with reference to FIG. The color swath does not limit the range of nozzles used by the print head as in the 5-pass mode for both the forward path and the return path. No paper is conveyed between the forward path and the backward path, and the sheet conveyance amount between the backward path and the forward path is ½ of the used nozzle range. As a result, in all drawing areas, the ink color overlaps in the order of K, C, M, Y, Y, M, C, K, K, C, M, Y, Y, M, C, and K to complete the image. Will do. Therefore, bi-directional color banding caused by the different ink color superposition order in principle does not occur. Further, since the use nozzle range of the print head is not limited, the print speed does not decrease with respect to the standard print mode called 4-pass.

  The operation of drawing one color swath in the print mode shown in FIG. 7 will be described in more detail using a flowchart. FIG. 11 is a flowchart for explaining the operation of the embodiment. The operation until the image is completed in the drawing area corresponding to twice the conveyance pitch of the recording medium is described. In accordance with the program stored in the ROM 22, the CPU 21 performs various calculations and controls, and the recording apparatus 1 performs a drawing operation.

  First, a mask for the recording head 41 is selected and applied according to the print mode (step S1). This is because printing is performed using different masks depending on the printing mode. The mask selects whether or not the nozzles of the recording head are used. Based on this mask and image data stored in the image memory 30, ink is ejected from the nozzles. The mask is generated based on a print mask function configured by a probability distribution in which the nozzles of the recording head are used. For example, for a non-uniform print mask function, a probability distribution of nozzles is used such that the printing rate decreases as the end of the swath is approached, and the probability distribution of nozzles used so that the printing rate increases as the distance increases. What is comprised is typical. In another example of the print mask function, the probability distribution in which the nozzles are used is randomly configured. By printing using a mask to which such a print mask function is applied, an output image having a dot distribution based on the print mask function can be obtained. When using such a mask, for example, the print head is divided into a plurality of blocks, and the mask is configured so that the images drawn for each of the upper and lower blocks are complemented, so that each upper and lower block has a dot. You can draw so that there are no defects.

  Next, it is determined whether or not it is the first scan. If it is the first scan, the process proceeds to step S3, and if not, the process proceeds to step S4 (step S2).

  In step S3, forward printing is performed by the first area 50 of the print head (step S3). When the forward printing is finished, the process is finished and waits for the next scan.

  In step S4, it is determined whether or not it is the third scan. If it is the third scan, the process proceeds to step S5, and if not, the process proceeds to step S6 (step S4).

  In step S5, forward printing is performed by the first area 50 and the second area 51 of the print head (step S5). When the forward printing is finished, the process is finished and waits for the next scan.

  In step S6, it is determined whether or not it is the fifth scan. If it is the fifth scan, the process proceeds to step S7, and if not, the process proceeds to step S8 (step S6).

  In step S7, forward printing is performed by the second area 51 of the print head (step S7). When the forward printing is finished, the process is finished and waits for the next scan.

  In step S8, it is determined whether or not it is the second scan. If it is the second scan, the process proceeds to step S9, and if not, the process proceeds to step S10 (step S8).

  In step S9, the backward printing is performed by the first area 50 of the print head (step S9). When the backward printing is completed, the process proceeds to step S13.

  In step S10, it is determined whether or not it is the fourth scan. If it is the fourth scan, the process proceeds to step S11, and if not, the process proceeds to step S12 (step S10).

  In step S11, the backward printing is performed by the first area 50 and the second area 51 of the print head (step S11). When the backward printing is completed, the process proceeds to step S13.

  In step S12, since it is the sixth scan, the backward printing is performed by the second area 51 of the print head (step S12).

  Step S13 is a process after the return pass printing is completed, and the sheet is conveyed (step S13). The sheet conveyance is a conveyance pitch having a width equal to or substantially equal to the width of the first area 50 of the print head. Here, the width of the first region 50 and the width of the second region 50 are set equal. When the paper conveyance is finished, the process is finished and the next scan is awaited.

  In this way, on the recording medium, the forward printing is performed by the first area 50 of the print head at the first scan, and the backward printing is performed by the first area 50 of the print head at the second scan. That is, bi-directional printing is performed with a half width of the print head. At this time, the first area 50 performs printing corresponding to a printing rate of 1/4 of the image completed in the forward path, and printing corresponding to 1/4 printing rate of the image completed in the backward path. Thereafter, conveyance is performed with a width equal to or approximately equal to the width of the first region 50. Then, the second area 51 performs printing corresponding to a printing rate of 1/4 of the image completed in the forward path, and printing corresponding to 1/4 printing rate of the image completed in the backward path. The first area 50 and the second area 51 reciprocate and print, thereby completing the image.

  Although the description has been made focusing on the printing of the portion corresponding to the width twice as large as the transport pitch, the printing is usually performed by continuously performing this operation. In the first scan described above, in addition to the forward print using the first area 50 of the print head, the forward print is performed on the area drawn up to the previous scan using the second area 51 of the print head. In the second scan described above, in addition to the return pass printing using the first area 50 of the print head, the return pass printing is performed on the area drawn up to the previous scan using the second area 51 of the print head. In the above-mentioned fifth scan, in addition to the forward printing using the second area 51 of the print head, the first forward printing is performed in the drawing area using the first area 50 of the print head. Thus, printing corresponding to a printing rate of 1/4 of the completed image is performed. In the above-mentioned sixth scan, in addition to the return pass printing using the second area 51 of the print head, the return pass printing is performed on the area drawn up to the previous scan using the first area 50 of the print head. With this printing, printing corresponding to a printing rate of 1/4 of the completed image is performed. Thus, by making it continuous, an image can be formed on a recording medium and a desired image can be obtained.

  Similarly, the print mode according to the embodiment of the present invention will be described with reference to the print mode of FIG. The color swath does not restrict the use nozzle range of the print head in the forward pass and the return pass as in the 5-pass mode, but the upper and lower one block obtained by dividing the use nozzle range into three uses the nozzle for one central block. The probability is 1/2. The sheet is not conveyed between the forward path and the backward path, and the sheet conveyance amount between the backward path and the forward path is 1/3 of the used nozzle range. Thereby, in every drawing area, K, C, M, Y, Y, M, C, K, K, C, M, Y, Y, M, C, K, K, C, M, Y, Y, The ink color overlaps in the order of M, C, and K to complete the image. Therefore, bi-directional color banding caused by the different ink color superposition order in principle does not occur. Further, since the printing rate for each of the upper and lower blocks is low, mottling at the edge of the color swath is suppressed, and boundary banding and beading are less likely to occur. Furthermore, since the printing rates of the first scan and the final scan that are dominant with respect to color banding are low, there is an advantage that color banding at the left and right ends is less likely to occur. However, in this printing mode, the printing speed is reduced to 2/3 times that of a standard printing mode called 4-pass, but the effect of improving the image quality is greater than that in the printing mode shown in FIG.

  In the printing mode of FIG. 8, it is also conceivable that the printing rate of each block above and below the color swath is not fixed to ½ of the central portion. For example, if the upper block is set to 1/4 and the lower block is set to 3/4, the influence of the first scan can be further suppressed, the upper block is set to 3/4, and the lower block is set to In the case of 1/4, the influence of the final scan can be further suppressed. Color banding can be more effectively suppressed by selectively using media having a large influence on the first scan and media having a large influence on the final scan. Furthermore, it is conceivable to change the weighting of the printing rate of each block in the forward pass and the return pass. In this print mode, the upper and lower block masks are arranged to complement each other. That is, the lower block discharges to a position where the upper block does not discharge, and the lower block discharges to a position where the upper block discharges. By applying such a print mask function to the print head, ejection is controlled by the mask obtained from the print mask function.

  Next, the print mode in FIG. 9 will be described. Each block obtained by dividing the range of nozzles used into four has a print rate of 1/2, that is, a print rate of 1/8 of the completed image, with respect to one block in the standard print mode called 4-pass. The sheet is not conveyed between the forward path and the backward path, and the sheet conveyance amount between the backward path and the forward path is 1/4 of the used nozzle range. As a result, in any drawing area, K, C, M, Y, Y, M, C, K, K, C, M, Y, Y, M, C, K, K, C, M, Y, Y, The ink color overlaps in the order of M, C, K, K, C, M, Y, Y, M, C, and K to complete the image. Therefore, bi-directional color banding caused by the different ink color superposition order in principle does not occur. Since the printing rate for one scan is reduced, banding due to other factors can be reduced. However, in this printing mode, the printing speed is reduced by a factor of 1/2 compared to the standard printing mode called 4-pass, but the effect of improving the image quality is greater than the printing mode shown in FIGS.

  In the printing mode of FIG. 9, it is conceivable to arbitrarily change the printing rate of each block of the color swath. Color banding can be more effectively suppressed by properly using the weighting of the printing rate for media having a large influence on the first scan and media having a large influence on the final scan. Since the effect on the completed image is different for each scan, a greater effect can be obtained by taking measures to suppress color banding for each scan. For example, an example is shown in FIG. In the first scan and the second and third scans immediately after that, there is a high probability that ink is ejected to the media surface for the first time. When ink is ejected onto the medium and when it is ejected onto the ink, the subsequent behavior changes. For this reason, it is possible to effectively suppress color banding by reducing the color swath printing rate that is used when printing is performed on the side where the number of scans is high, which has a high probability of ink being ejected to the media surface for the first time. It will be a measure. In this example, the drawing of the same area is completed by eight scans. In each scan from the first scan to the fourth scan, printing corresponding to a printing rate of 1/16 of the completed image is performed. In each scan from the fifth scan to the eighth scan, printing corresponding to a printing rate of 3/16 of the completed image is performed. Here, an example is shown in which the printing rate is changed separately for the first half scan and the second half scan. In FIG. 10 of the scan effected by the number of scans depending on the drawing conditions, the printing rate is changed above and below the color swath, but this may be finely variable for each block. Furthermore, it is conceivable to change the weighting of the printing rate of each block in the forward pass and the return pass. The printing rate of each block used for the media to be used in advance is stored in the EEPROM 24, and when the media is used, the printing rate is read and set for each block. Specifically, after the recording medium is set, the recording medium set from the operation panel 44 is selected, the printing rate of each block corresponding to the selected recording medium is acquired from the EEPROM 24, and a mask to be used for each block is set. The Depending on the media, the printing rate may be a constant printing rate, but the printing mask function that constitutes the probability distribution of the nozzles used may be non-uniform.

  As described above, a non-uniform region is appropriately provided in the color swath print mask function in the printing method in which a sheet is not conveyed between the forward path and the backward path and a large amount of paper is conveyed between the backward path and the forward path. Although the printing speed is reduced by using together, improvement in image quality can be expected. That is, based on a basic four-pass printing mode (referred to as a standard printing mode), the user can select a plurality of printing modes in which the effect of suppressing color banding is selected according to the printing speed described so far. Therefore, it is possible to realize a combination of printing speed and printing image quality according to the user's application. For example, the lower print mode described with reference to FIGS. 7 to 9 is called “color banding improvement mode”, and weights 1 to 3 are assigned. If you want to output printed matter that does not place much importance on image quality, it is better to select “Color Banding Improvement Mode 1”, which has a higher printing rate per scan and increases the printing speed as much as possible. If you want to output the printed matter, you can consider the use of a low printing rate per scan, select “Color Banding Improvement Mode 3”, and obtain high image quality even if productivity is reduced. In order to balance these, “color banding improvement mode 2” may be selected. For example, a flag corresponding to the print mode is stored in the RAM 23, a mask and a transport pitch are selected according to the flag, and printing is performed. The flag can be changed by an input on the operation panel 44, or can be changed in accordance with a predetermined condition.

  As described above, the print area of the forward path and the return path in bidirectional printing are matched, the ink color overlap order is fixed for all the print areas, paper is not conveyed between the forward path and the return path, and the return path and the forward path are By increasing the conveyance amount in the meantime, bidirectional color banding can be suppressed without lowering the printing speed. In addition, boundary banding and beading can be simultaneously suppressed by using a non-uniform region in the color swath print mask function. 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 (5)

A print head that is divided into a plurality of blocks having the same width of the used nozzle range and in which ink ejection is controlled for each block is arranged for each of a plurality of ink colors, and the probability that the nozzle of the block is used is set for each block. In a recording apparatus for forming a color image on a recording medium while scanning the print head as a predetermined value ,
Control means for controlling ejection of the print head and conveyance of the recording medium;
The control means does not convey the recording medium between the forward path and the return path of the print head when printing is performed by reciprocating the print head, and the width of the recording medium is not between the return path and the subsequent path. And the areas drawn in the forward path and the return path between the conveyance of the recording medium are matched, and the overlapping order of the ink colors is fixed for all the drawing areas ,
The print head has at least three or more blocks, and the sum of the probabilities of use of the nozzles of the blocks located at both ends of the print head in one scan is calculated as a central portion of the print head. Applying a uniform print mask function that is the same as the used probability of the nozzle of each block located at
The blocks located at both ends of the print head mutually perform the drawing operation by complementing the ink ejection positions,
The probability that the nozzles of the block on the downstream side in the transport direction of the recording medium among the blocks located at the both ends of the print head are used is the use of the nozzles of the block on the upstream side. recording apparatus characterized largely be Rukoto relative probability that. The probability that the nozzle of the block on the upstream side is used is 1/4 of the probability that the nozzle of the block located in the central portion is used, and the nozzle of the block on the downstream side is used. 2. The recording apparatus according to claim 1, wherein the probability that the nozzle is used is 3/4 of the probability that the nozzle of the block located in the central portion is used .   3. The image according to claim 1, wherein each block is drawn by applying a predetermined print mask function when drawing is performed by reciprocating scanning of the number of times equal to the number of divisions of the block. The recording device described.   The recording apparatus according to claim 3, wherein the print mask function is predetermined according to the type of the recording medium.   A print head that is divided into a plurality of blocks having the same width of the used nozzle range and in which ink ejection is controlled for each block is arranged for each of a plurality of ink colors, and the probability that the nozzle of the block is used is set for each block. In a recording method of a recording apparatus for forming a color image on a recording medium while scanning the print head as a predetermined constant value,
  In the case where printing is performed by reciprocating scanning of the print head, the recording medium is not transported between the forward path and the backward path of the print head, and the recording medium is transported by the block width between the backward path and the subsequent forward path. And a step of matching the areas drawn in the forward path and the return path between the conveyance of the recording medium, and fixing the ink color overlapping order for all the drawing areas,
  The print head has at least three or more blocks, and the sum of the probabilities of use of the nozzles of the blocks located at both ends of the print head in one scan is calculated as a central portion of the print head. Applying a uniform print mask function that is the same as the use probability of the nozzles of the blocks located in each of the blocks, the blocks located at both ends of the print head complement each other with the ink ejection position. The printing operation is performed, and the probability that the nozzles of the blocks on the downstream side in the transport direction of the recording medium among the blocks located at both ends of the print head are used is the upstream side. A recording method, characterized by being large relative to the probability of use of the nozzles of a block.