JP4752689B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus and an image forming method for forming a scan area image on a recording medium by scanning a recording head N (N ≧ 2) times on the recording medium.

  2. Description of the Related Art Conventionally, an image forming apparatus called an ink jet printer has been widely used for the reason that a sound during image recording is quiet and image recording can be performed easily and inexpensively. The image forming apparatus includes a recording head having a large number of nozzles that eject ink as fine droplets, and forms an image by scanning the recording head on a recording medium.

  Since the recording head has minute nozzles, defects such as so-called bent nozzles and missing nozzles are likely to occur. However, in the above image forming apparatus, the recording head is placed on the recording medium even if any of the many nozzles is defective. Thus, it is possible to form a high-quality image by reducing the printing rate of one scan and scanning a plurality of times (see, for example, Patent Documents 1 and 2).

For example, when the recording head forms the target image in two scans (with one reciprocal scan) to form the target image on the left side in FIG. 12, the upper right side in FIG. 12 at the first scan. In the next second scan, the lower right dot distribution in FIG. 12 is formed, and the dot distribution is superimposed to form a target image.
Japanese Patent Laid-Open No. 5-31922 JP-A-7-52391

  By the way, in the image formation stage, the gradation value of each pixel of the image to be recorded is processed by a known quantization process (for example, a dither method, an error diffusion method, etc.). According to the rule (in FIG. 12, the odd-numbered columns are assigned to the first scan and the even-numbered rows are assigned to the second scan), as shown in the upper and lower rows on the right side of FIG. Thus, a cluster of dots is formed, and a large gap (see a circle) is formed in the dot distribution. That is, the dot distribution is non-uniform in each of the first and second scans of the recording head.

In this way, when dots are present non-uniformly in each scan of the recording head, dots formed at close positions are mixed with each other, which may cause deterioration in image quality. Also, in this case, if each dot spreads differently depending on the type of recording medium, installation environment, etc., the size of the dots may also become uneven, and the unevenness may reach the entire image as a lump. There is sex. Furthermore, when a color image is formed with inks such as C (cyan), M (magenta), Y (yellow), and K (black), dot clusters are scattered sparsely in each scan of the recording head. Therefore, the color ink overlay order varies with each scan, and an image with many color irregularities is formed.
An object of the present invention is to suppress degradation in image quality that is induced by non-uniform dot distribution.

In order to solve the above problem, the invention according to claim 1
In an image forming apparatus that scans a recording head N (N ≧ 2) times on a recording medium and forms an image of the scanning area on the recording medium.
Quantization means for quantizing the gradation value of the target pixel of the image using a dot dispersion type dither mask;
Dividing means for dividing the gradation value of the target pixel into N regions;
Determining means for determining in which region of the gradation value of the pixel of interest the threshold in the dot dispersion type dither mask corresponding to the pixel of interest exists;
The dot data, which is the quantization result by the quantization unit of the pixel of interest corresponding to the gradation value of the region where the threshold exists, is determined from the first scan to the Nth scan of the recording head according to the determination result by the determination unit. Among them, the disassembly means corresponding to the number of scans of the recording head, which corresponds to ejecting ink from the recording head in any scan to form dots,
It is characterized by having.

The invention described in claim 2
The image forming apparatus according to claim 1 .
The dividing means divides the gradation value of the target pixel equally.

The invention according to claim 3
The image forming apparatus according to claim 1 .
The dividing unit divides the gradation value of the target pixel in an uneven manner.

The invention according to claim 4
The image forming apparatus according to claim 1 ,
The dot dispersion type dither mask is a blue noise type dither mask.

The invention described in claim 5
In an image forming method of scanning a recording head on a recording medium N (N ≧ 2) times to form an image of the scanning area on the recording medium,
A quantization step of quantizing a gradation value of a pixel of interest of the image using a dot dispersion type dither mask;
A dividing step of dividing the gradation value of the target pixel into N regions;
A determination step of determining in which region of the gradation value of the pixel of interest the threshold in the dot dispersion type dither mask corresponding to the pixel of interest exists;
The dot data, which is the quantization result of the quantization process of the pixel of interest corresponding to the gradation value of the region where the threshold exists, is determined from the first scan to the Nth scan of the recording head according to the determination result of the determination process. Among them, a disassembly step corresponding to the number of scans of the recording head, which corresponds to form dots by ejecting ink from the recording head in any scan,
It is characterized by having.

The invention described in claim 6
The image forming method according to claim 5 .
In the dividing step, the gradation value of the target pixel is divided equally.

The invention described in claim 7
The image forming method according to claim 5 .
In the dividing step, the gradation value of the pixel of interest is divided unevenly.

The invention according to claim 8 provides:
In the image forming method according to any one of claims 5 to 7 ,
The dot dispersion type dither mask is a blue noise type dither mask.

According to the invention of claim 1, 5, becomes a dot distribution uniform in each scanning of the recording head, it is possible to suppress the quality degradation of an image attracted from the uneven dot distribution.

Further , according to the first and fifth aspects of the present invention, the dot pattern can be matched in each scan of the recording head with a simple configuration in which the gradation value of the target pixel is divided into N regions.

According to the invention of claim 2, 6, also the dot distribution becomes uniform at each scanning in uniform and the same scanning occupancy of the dot recording head, for example, the defects such as bends so-called nozzles of the recording head When trying to compensate by scanning, it is possible to effectively suppress a decrease in image quality.

According to the third and seventh aspects of the invention, the dot occupancy rate is unequal in each scan of the recording head, and the dot distribution is also unequal during the same scan, for example, C, M, Y, K color. In the case of forming an image, the dot distribution can be changed for each color in each scan of the recording head, and the deterioration of the image quality due to the color overlapping order can be effectively suppressed.

  The best mode for carrying out the present invention will be described below with reference to the drawings. However, although various technically preferable limitations for carrying out the present invention are given to the embodiments described below, the scope of the invention is not limited to the following embodiments and illustrated examples.

  As shown in FIG. 1, an image forming apparatus 1 according to the present invention has a recording head 3 that reciprocally scans on a recording medium 2 in the left-right direction in FIG. The recording head 3 has a plurality of nozzles 4 along the length direction of the recording medium 2 (FIG. 1 shows a small number of nozzles 4 in order to simplify the following description and the description of the drawing. .., While ejecting K ink from each nozzle 4, scans from left to right in FIG. 1 at odd scans 1, 3, 5,..., And even scans 2, 4, 6,. Thus, scanning is performed from right to left in FIG.

  The image forming apparatus 1 includes a transport mechanism 5 (see FIG. 3) that transports the recording medium 2 from the lower side to the upper side in FIG. The transport mechanism 5 transports the recording medium 2 by ½ of the nozzle length of the recording head 3 every time the recording head 3 scans. At the time of image formation, the recording head 3 and the conveyance mechanism 5 are interlocked with each other, and scanning of the recording head 3 and conveyance of the conveyance mechanism 5 are alternately repeated so that an image is formed on the recording medium 2. It has become.

  The recording head 3 may eject a single K ink as described above, or may eject C, M, Y, and K inks. The configuration of the recording head 3 can be appropriately changed according to the image forming mode (see the first to fifth modes below).

  Further, as shown in FIG. 2, the transport mechanism 5 may transport the recording medium 2 by the nozzle length of the recording head 3 each time the recording head 3 scans. Alternatively, the scanning path of the even-numbered recording head 3 may coincide with the scanning path.

  As shown in FIG. 3, the image forming apparatus 1 includes a control device 10 that controls each operation of the recording head 3 and the transport mechanism 5. The control device 10 includes a general-purpose CPU 11 (Central Processing Unit), RAM 12 (Random Access Memory), ROM 13 (Read Only Memory), and the like. The ROM 13 stores a processing program for executing processing by an image forming method to be described later, and the CPU 11 executes the processing program in the ROM 13 while using the RAM 12 as a work area.

  Next, the “image forming method” according to the present invention will be described.

  In this image forming method, it is assumed that an image having the number of pixels of “m rows × n columns (m and n are positive integers)” is formed while performing a quantization process by a known blue noise dither method. In the quantization process, a blue noise dither mask (size: 256 × 256 pixels) is applied as a dot dispersion type dither mask. The image forming method is divided into five first to fifth modes depending on the image forming mode. Hereinafter, one mode will be described as processing executed by the CPU 11 of the control device 10.

[First embodiment]
The first mode is a case where the recording head 3 forms an image of the scanning area by two scans and forms a monochrome image with only K (black) dots.

  As shown in FIG. 4, first, the CPU 11 recognizes the coordinates (x, y) of the image to be subjected to image processing as quantization means (0, 0) (step SA1), and thereafter the coordinates in order. The quantization process is repeatedly performed on all the pixels until (x, y) changes from (0, 0) to (n, m) (steps SA2 to SA6, quantization process).

  Here, when the quantization process is executed for each pixel, the process of step SA4 is executed for each pixel. In the process of step SA4, the CPU 11 serves as a decomposing unit, and the quantization result is decomposed according to the number of scans of the recording head 3 using the same dot dispersion type dither mask as the dot dispersion type dither mask used in the quantization process. (Decomposition process).

  That is, as shown in FIG. 5, the gradation value data is set from the input value (pixel value) using the pixel corresponding to the coordinates (x, y) as the target pixel (step SB1). When the processing of step SB1 is completed, the CPU 11 becomes a dividing means and equally divides the gradation value data into two areas of 0 to data / 2 and data / 2 to data (division process). Thereafter, the CPU 11 serves as a determination unit, and whether or not the half value of the gradation value data is larger than the threshold value in the mask corresponding to the target pixel, the threshold value is 0 to data / 2 of the gradation value data. It is determined whether or not the region exists (step SB2, part of the determination step).

  If it is determined in step SB2 that the half value of the gradation value data is larger than the threshold value and the threshold value exists in the 0 to data / 2 region of the gradation value data, the CPU 11 as the disassembling means pays attention to it. In the pixel, the ink is ejected from the recording head 3 in the second scan so as to form a dot (step SB3, part of the decomposition process).

  On the other hand, if it is determined in step SB2 that the half value of the gradation value data is equal to or smaller than the threshold value and the threshold value does not exist in the 0 to data / 2 region of the gradation value data, the process proceeds to step SB4. Transition. In the process of step SB4, the CPU 11 serves as a determination means to determine whether or not the threshold value exists in the data / 2 to data area of the gradation value data based on whether or not the gradation value data is greater than the threshold value. (Part of the decision process).

  If it is determined in step SB4 that the gradation value data is larger than the threshold value and the threshold value is in the data / 2 to data area of the gradation value data, the CPU 11 as the decomposing means performs the first scan for the target pixel. Corresponding to form dots by ejecting ink from the recording head 3 (step SB5, part of the disassembling process).

  On the other hand, if it is determined in step SB4 that the gradation value data is equal to or less than the threshold value and the threshold value does not exist in the data / 2 to data area of the gradation value data, the CPU 11 determines that the target pixel is 1 even in the second scan. Corresponding not to form dots even at the scanning time (step SB6).

  4 and 5, an image is actually formed on the recording medium 2. That is, the CPU 11 of the control device 10 controls the recording head 3, and the recording head 3 performs the first scanning or the second scanning for each pixel of the image according to the contents of the processing of the above steps SB3, SB6. Ink is ejected to form dots, or the ink simply passes over the recording medium 2 without ejecting ink to form a monochrome image on the recording medium 2.

  In the first aspect described above, in the processing of steps SB2 to SB6, the gradation value of the target pixel is divided into two, and it is determined in which region of the gradation value of the target pixel the threshold value in the mask exists. Based on the determination result, the quantization result of the target pixel (the result of forming a dot) is made to correspond to one of the first and second scans of the recording head 3.

  Therefore, as shown in FIG. 6, when forming the left target image in FIG. 6, the first and second scans of the recording head 3 have a uniform dot distribution in each scan, and the dots are mixed together. The unevenness of the generated image can be suppressed. Furthermore, since the gradation value of the pixel of interest is equally divided into two, the dot occupancy is also equal in each scan of the recording head 3. At this time, since the line of one pixel arranged in the scanning direction of the recording head 3 is equally divided into two scans, for example, a dot missing line that occurs when a so-called nozzle bending or nozzle missing occurs evenly for each scan. It becomes diffused, and dot omission can be made inconspicuous.

[Second embodiment]
The second mode is a case where the recording head 3 forms an image of the scanning region by scanning N times (in the second mode, N is a positive integer of 3 or more), and only K is used. It is assumed that a monochrome image is formed with dots.

The second mode is a modification of the first mode, and is different from the first mode in that the process of FIG. 5 is replaced with the process of FIG. 7, and otherwise the same as the first mode. .
In this processing, as shown in FIG. 7, the gradation value data is set from the input value (pixel value) using the pixel corresponding to the coordinates (x, y) as the target pixel (step SC1). When the process of step SC1 is completed, the CPU 11 becomes a dividing means, and the gradation value data is set to 0 to data / N, data / N to data × 2 / N,..., Data × (N−1) / N to data ×. Divide into N / N areas equally (dividing step). After that, the CPU 11 serves as a determination unit, and whether or not the threshold value exists in the 0 to data / N region depending on whether or not the 1 / N value of the gradation value data is larger than the threshold value in the mask corresponding to the target pixel. (Step SC2, part of the determination process).

  If it is determined in step SC2 that the 1 / N value of the gradation value data is larger than the threshold value and the threshold value is in an area of 0 to data / N, the CPU 11 as the disassembling means performs the Nth scan for the target pixel. In step SC3, ink is ejected from the recording head 3 to form dots.

  On the other hand, if it is determined in step SC2 that the 1 / N value of the gradation value data is equal to or smaller than the threshold value and the threshold value does not exist in the region of 0 to data / N, the process proceeds to step SC4. In the process of step SC4, whether or not the threshold value exists in the region of data / N to data × 2 / N depending on whether or not the value of 2 / N of the gradation value data is larger than the threshold value by the CPU 11 as a determination means. Determine whether or not (part of the determination process).

  If it is determined in step SC4 that the 2 / N value of the gradation value data is larger than the threshold value and the threshold value is in the region of data / N to data × 2 / N, the CPU 11 as the disassembling means recognizes the target pixel. Then, at (N-1) scan, ink is ejected from the recording head 3 so as to form dots (step SC5, part of the disassembling process).

  On the other hand, if it is determined in step SC4 that the value of 2 / N of the gradation value data is equal to or less than the threshold value and the threshold value does not exist in the area of data / N to data × 2 / N, the CPU 11 thereafter It becomes a judging means and judges whether or not the comparison value is larger than the threshold value while using each value of 3 / N to N / N of the gradation value data as a comparison value (part of the judgment step), and the judgment result Accordingly, the CPU 11 serves as a disassembling unit to eject dots from the recording head 3 at any one of the (N-2) to first scans to form dots or not to form dots at any scan. Correspond (steps SC6 to SC8, part of the decomposition process).

  In the second aspect described above, even when an image is formed by a plurality of scans of the recording head 3 of three or more scans, the dot distribution of each scan can be made uniform, and the dots are mixed together. The unevenness of the generated image can be suppressed.

[Third Aspect]
The third mode is a case where the recording head 3 forms an image of the scanning area by two scans and forms a color image with C, M, Y, and K dots.

  As shown in FIG. 8, first, the CPU 11 serves as a quantization means, and recognizes the coordinates (x, y) of the image to be subjected to image processing as (0, 0) (step SD1), and thereafter C Is the first, M is the second, Y is the third, K is the fourth color order col, all the coordinates (x, y) from (0, 0) to (n, m) The quantization process is repeatedly performed for each color of C, M, Y, and K on the pixel (steps SD2 to SD8, quantization process).

  In the process of step SD4, the color order col does not have to follow the arrangement of C, M, Y, and K, and can be arbitrarily set. For example, the color order col may be fourth for C, third for M, second for Y, and first for K.

  Here, when the quantization process is executed for each pixel, the process of step SD5 is executed for each pixel. In the process of step SD5, the CPU 11 serves as a decomposing means, and the quantization result is decomposed according to the number of scans of the recording head 3 using the same dot dispersed dither mask as the dot dispersed dither mask used in the quantization process. (Decomposition process).

  That is, as shown in FIG. 9, the gradation value data is set from the input value (pixel value) using the pixel corresponding to the coordinates (x, y) as the target pixel (step SE1), and C, M, Y, K An offset value Offset is calculated according to the color type (step SE2). The offset value Offset is a value that can be arbitrarily set according to the color types of C, M, Y, and K. For example, Offset = Color [col] = Color [C, M, Y, K] = Color [0 , 64, 128, 192], the offset value Offset of C is 0, the offset value Offset of M is 64, the offset value Offset of Y is 128, and the offset value Offset of K can be calculated as 192.

  When the process of step SE2 is completed, the coordinate obtained by adding the offset value Offset to the coordinate (x, y) is recognized as the coordinate (X, Y) (step SE3). When the processing of step SE3 is completed, the CPU 11 serves as a dividing means and equally divides the gradation value data into two areas of 0 to data / 2 and data / 2 to data (division process). Thereafter, the CPU 11 serves as a determination unit, and whether or not the half value of the gradation value data is larger than the threshold value in the mask corresponding to the coordinate (X, Y), the threshold value is 0 of the gradation value data. It is determined whether or not it exists in the area of ~ data / 2 (step SE4, part of the determination process).

  If it is determined in step SE4 that the half value of the gradation value data is larger than the threshold value and the threshold value is in the 0 to data / 2 region of the gradation value data, the CPU 11 as the disassembling means coordinates In the pixels corresponding to (X, Y), the ink is ejected from the recording head 3 in the second scan so as to form dots (step SE5, part of the decomposition process).

  On the other hand, if it is determined in step SE4 that the value of 1/2 of the gradation value data is equal to or smaller than the threshold value and the threshold value does not exist in the 0 to data / 2 region of the gradation value data, the process of step SE6 is performed. Transition. In the process of step SE6, the CPU 11 determines whether the threshold value exists in the data / 2 to data area of the gradation value data by determining whether the gradation value data is larger than the threshold value. (Part of the decision process).

  If it is determined in step SE6 that the gradation value data is larger than the threshold value and the threshold value exists in the data / 2 to data area of the gradation value data, the CPU 11 as the disassembling means takes the coordinates (X, Y). In the corresponding pixel, the ink is ejected from the recording head 3 in the first scan so as to form a dot (step SE7, part of the decomposition process).

  On the other hand, if it is determined in step SE6 that the gradation value data is equal to or smaller than the threshold value and the threshold value does not exist in the data / 2 to data area of the gradation value data, the CPU 11 corresponds to the coordinates (X, Y). In the pixel to be matched, no dot is formed in the second scan or the first scan (step SE8).

  8 and 9, an image is actually formed on the recording medium 2. That is, the CPU 11 of the control device 10 controls the recording head 3, and the recording head 3 performs the first scanning or the second scanning with respect to each pixel of the image according to the contents of the processing of the above steps SE5, 7 and 8. Dots are formed by ejecting C, M, Y, and K inks, or simply passing over the recording medium 2 without ejecting ink, and forming a color image on the recording medium 2.

  In the above third aspect, even when a color image of a plurality of colors is formed by scanning of the recording head 3 of two scans, the dot distribution of each scan can be made uniform, and the dots are mixed with each other. By doing so, it is possible to suppress image unevenness.

[Fourth aspect]
The fourth mode is a case where the image of the scanning area is formed by the recording head 3 scanning N times (in the fourth mode, N is a positive integer of 3 or more), and C, M Suppose that a color image is formed with, Y, and K dots.

The fourth aspect is a modification of the third aspect, and is different from the third aspect in that the process of FIG. 9 is replaced with the process of FIG. 10, and the other aspects are the same as the third aspect. .
In this process, as shown in FIG. 10, the processes of steps SE1 to SE3 are executed (steps SF1 to SF3). When the process of step SF3 is completed, the CPU 11 becomes a dividing means, and the gradation value data is set to 0 to data / N, data / N to data × 2 / N,..., Data × (N−1) / N to data ×. Divide into N / N areas equally (dividing step). Thereafter, the CPU 11 serves as a determination unit, and whether or not the threshold value is 0 to data / N depending on whether or not the 1 / N value of the gradation value data is larger than the threshold value in the mask corresponding to the coordinates (X, Y). (Step SF4, a part of the determination process).

  If it is determined in step SF4 that the 1 / N value of the gradation value data is larger than the threshold value and the threshold value is in an area of 0 to data / N, the CPU 11 as the disassembling means has the coordinates (X, Y). In the pixel corresponding to, the ink is ejected from the recording head 3 to form dots at the Nth scan (step SF5, part of the decomposition process).

  On the other hand, if it is determined in step SF4 that the 1 / N value of the gradation value data is equal to or less than the threshold value and the threshold value does not exist in the region of 0 to data / N, the process proceeds to step SF6. In the process of step SF6, whether the threshold value exists in the region of data / N to data × 2 / N depends on whether or not the value of 2 / N of the gradation value data is larger than the threshold value by the CPU 11 as a determination means. Determine whether or not (part of the determination process).

  If it is determined in step SF6 that the 2 / N value of the gradation value data is larger than the threshold value and the threshold value is in the region of data / N to data × 2 / N, the CPU 11 as the disassembling means uses the coordinates ( In the pixel corresponding to (X, Y), the ink is ejected from the recording head 3 at the (N-1) th scan to form a dot (step SF7, part of the decomposition process).

  On the other hand, if it is determined in step SF6 that the value of 2 / N of the gradation value data is equal to or less than the threshold value and the threshold value does not exist in the region of data / N to data × 2 / N, the CPU 11 thereafter It becomes a judging means and judges whether or not the comparison value is larger than the threshold value while using each value of 3 / N to N / N of the gradation value data as a comparison value (part of the judgment step), and the judgment result Accordingly, the CPU 11 serves as a disassembling unit to eject dots from the recording head 3 at any one of the (N-2) to first scans to form dots or not to form dots at any scan. Correspond (steps SF8 to SF10, part of the disassembly process).

  In the above fourth aspect, even when a color image of a plurality of colors is formed by a plurality of scans of the recording head 3 of three or more scans, the dot distribution of each scan can be made uniform, It is possible to suppress unevenness in the image that occurs due to the mixture of the two.

[Fifth aspect]
The fifth mode is a case where the recording head 3 forms an image of the scanning region by two scans and forms a color image with C, M, Y, and K dots.

The fifth aspect is a modification of the third aspect, and is different from the third aspect in that the process of FIG. 9 is replaced with the process of FIG. 11, and is otherwise the same as the third aspect. .
In this process, as shown in FIG. 11, the processes of steps SE1 to SE3 are executed (steps SG1 to SG3), and then the coefficient Coef (0 ≦ Coef ≦ 1) is calculated (step SG4). The coefficient Coef can be arbitrarily set according to the types of C, M, Y, and K colors. For example, Coef = Color2 [col] = Color2 [C, M, Y, K] = Color2 [1/3, 2 / 3,1 / 2,1 / 2], the C coefficient Coef is 1/3, the M coefficient Coef is 2/3, the Y coefficient Coef is 1/2, and the K coefficient Coef can be calculated as 1/2.

  When the process of step SG4 is completed, the CPU 11 serves as a dividing means and divides the gradation value data into two areas of 0 to data.times.Coef and data.times.Coef to data unevenly (dividing step). Thereafter, the CPU 11 becomes a judging means, and whether or not the value obtained by multiplying the gradation value data by the coefficient Coef is larger than the threshold value in the mask corresponding to the coordinates (X, Y), the threshold value is 0 of the gradation value data. It is determined whether or not it exists in the area of ~ data × Coef (step SG5, part of the determination process).

  If it is determined in step SG5 that the value obtained by multiplying the gradation value data by the coefficient Coef is larger than the threshold value and the threshold value is in the 0 to data × Coef region of the gradation value data, the CPU 11 as the disassembling means The pixels corresponding to the coordinates (X, Y) are made to correspond by ejecting ink from the recording head 3 in the second scan to form dots (step SG6, part of the decomposition process).

  On the other hand, if it is determined in step SG5 that the value obtained by multiplying the gradation value data by the coefficient Coef is equal to or less than the threshold and the threshold does not exist in the 0 to data × Coef region of the gradation value data, the process in step SG7 Migrate to In the process of step SG7, the CPU 11 serves as a determination means to determine whether or not the threshold value exists in the area of data × Coef to data of the gradation value data based on whether or not the gradation value data is larger than the threshold value. (Part of the decision process).

  If it is determined in step SG7 that the gradation value data is larger than the threshold value and the threshold value exists in the area of data × Coef to data of the gradation value data, the CPU 11 as the disassembling means takes the coordinates (X, Y). In the corresponding pixel, the ink is ejected from the recording head 3 in the first scan so as to form a dot (step SG8, part of the decomposition process).

  On the other hand, if it is determined in step SG7 that the gradation value data is equal to or less than the threshold value and the threshold value does not exist in the data × Coef to data area of the gradation value data, the CPU 11 corresponds to the coordinates (X, Y). In the pixel to be matched, no dot is formed at any scanning time (step SG9).

  In the fifth aspect described above, the gradation value of the target pixel is divided unevenly, and it is determined in which region of the gradation value of the target pixel the threshold value in the mask exists. Dot occupancy can be made uneven in each scan. Thus, for example, when a color image is formed with each color of C, M, Y, and K, the M printing rate is increased in the first scan, and the C printing rate is increased in the second scan. It is possible to change the printing rate of each scan every time, and it is possible to make the color overlapping order more uniform and to effectively suppress the deterioration in image quality due to the difference in the color overlapping order.

1 is a diagram (schematic diagram) illustrating a schematic configuration of an image forming apparatus 1. It is drawing which shows the modification of FIG. 2 is a block diagram illustrating a schematic circuit configuration of the image forming apparatus 1. FIG. 3 is a flowchart showing each process of the image forming method according to the first aspect over time. It is a flowchart which shows the process of step SA4 which concerns on a 1st aspect in time. It is a dot distribution diagram showing a monochrome image formed in the first mode. It is a flowchart which shows the process of step SA4 which concerns on a 2nd aspect in time. 14 is a flowchart showing each process of the image forming method according to the third aspect over time. It is a flowchart which shows the process of step SD5 which concerns on a 3rd aspect in time. It is a flowchart which shows the process of step SD5 which concerns on a 4th aspect in time. It is a flowchart which shows the process of step SD5 which concerns on a 5th aspect in time. It is a dot distribution diagram showing a monochrome image formed in a conventional manner.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Recording medium 3 Recording head 4 Nozzle 5 Conveyance mechanism 10 Control apparatus 11 CPU (quantization means, decomposition | disassembly means, division | segmentation means, judgment means)
12 RAM
13 ROM

Claims (8)

In an image forming apparatus that scans a recording head N (N ≧ 2) times on a recording medium and forms an image of the scanning area on the recording medium.
Quantization means for quantizing the gradation value of the target pixel of the image using a dot dispersion type dither mask;
Dividing means for dividing the gradation value of the target pixel into N regions;
Determining means for determining in which region of the gradation value of the pixel of interest the threshold in the dot dispersion type dither mask corresponding to the pixel of interest exists;
The dot data, which is the quantization result by the quantization unit of the pixel of interest corresponding to the gradation value of the region where the threshold exists, is determined from the first scan to the Nth scan of the recording head according to the determination result by the determination unit. Among them, the disassembly means corresponding to the number of scans of the recording head, which corresponds to ejecting ink from the recording head in any scan to form dots,
An image forming apparatus comprising: The image forming apparatus according to claim 1 .
The image forming apparatus, wherein the dividing unit divides the gradation value of the target pixel equally. The image forming apparatus according to claim 1 .
The image forming apparatus, wherein the dividing unit divides the gradation value of the target pixel in an uneven manner. The image forming apparatus according to claim 1 ,
An image forming apparatus, wherein the dot dispersion type dither mask is a blue noise type dither mask. In an image forming method of scanning a recording head on a recording medium N (N ≧ 2) times to form an image of the scanning area on the recording medium,
A quantization step of quantizing a gradation value of a pixel of interest of the image using a dot dispersion type dither mask;
A dividing step of dividing the gradation value of the target pixel into N regions;
A determination step of determining in which region of the gradation value of the pixel of interest the threshold in the dot dispersion type dither mask corresponding to the pixel of interest exists;
The dot data, which is the quantization result of the quantization process of the pixel of interest corresponding to the gradation value of the region where the threshold exists, is determined from the first scan to the Nth scan of the recording head according to the determination result of the determination process. Among them, a disassembly step corresponding to the number of scans of the recording head, which corresponds to form dots by ejecting ink from the recording head in any scan,
An image forming method comprising: The image forming method according to claim 5 .
In the dividing step, the gradation value of the target pixel is equally divided. The image forming method according to claim 5 .
An image forming method, wherein in the dividing step, the gradation value of the target pixel is divided unevenly. In the image forming method according to any one of claims 5 to 7 ,
The dot forming dither mask is a blue noise type dither mask.

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