JP5657432B2 - Image generating apparatus and method, and image forming apparatus - Google Patents

Description

  The present invention relates to an image generation apparatus and method, and an image forming apparatus, and more particularly to an image processing technique for suppressing the amount of ink at the same density.

  In order to realize high-speed printing by inkjet, it is necessary to dry the ink at high speed in order to suppress set-off after paper discharge. However, providing a mechanism that realizes this leads to an increase in apparatus cost. Further, the ink jet printing is generally performed on an ink jet dedicated paper having enhanced ink absorption. These papers are usually sufficiently stiff base paper to suppress cockling phenomenon.

  In order to perform printing without selecting a paper type at high speed, it is indispensable to solve the above problems. The above problem can be solved to some extent by suppressing the amount of ink. For example, GCR processing for reducing the total ink amount by replacing CMY color with K color is performed. However, these processes are not sufficient for printing on various types of paper at a higher speed, and it is desired to further reduce the amount of ink.

  In recent years, in inkjet printing, multi-dot printing is performed in which gradation representation is performed by changing the ratio of a plurality of dots of different sizes. These ratios are set so as to suppress banding and grain deterioration while realizing smooth gradation.

  In multi-dot printing, by replacing one large dot with a plurality of small dots, the graininess is improved while keeping the same gradation value. However, when the recording rate (ratio of hitting dots on the pixels) is increased in this way, the visibility is different between the recording rate of 100% and immediately before (eg 97%), and a tone jump occurs. is there.

  In response to this problem, Japanese Patent Application Laid-Open No. H10-228688 discloses that the dots other than the largest dot can be formed on all pixels with respect to the correspondence between the gradation value of the image and the dot recording rate of various dots that can be formed. Even under the conditions, printing is performed such that a small number of pixels where dots are not formed are associated with each other, and whether or not various dots are formed is determined based on the dot recording rate thus associated, and dots are formed according to the determination result. An apparatus is disclosed. According to this, the dot formation density does not correspond to 100% in the intermediate gradation region, and it is possible to avoid the deterioration of the image quality due to the generation of the pseudo contour and to perform the high quality printing.

  Patent Document 2 discloses a technique for improving graininess by gradually increasing the upper limit value of specific dots other than the largest droplet. According to this, it is possible to improve the graininess of the printed image while suppressing the occurrence of banding due to the formation of specific dots.

Japanese Patent No. 4521909 JP 2008-68549 A

  However, the techniques of Patent Documents 1 and 2 do not fully consider the suppression of the ink amount. As a result, there is a problem in that the amount of ink increases, causing a cockling phenomenon and a reverse phenomenon.

  In order to perform high-speed printing, a single pass method has been studied. In this method, there is a problem that streaks are likely to occur because drawing is performed in one scan. In order to solve this problem, it is common to suppress the generation of streaks by mixing large-sized dots by multi-dot printing.

  However, when large sized dots are used, white background is more likely to occur than when small sized dots are used, and the amount of ink required to produce the same density increases.

  As described above, in order to realize high-speed printing, it is a problem to suppress both an increase in ink amount and unevenness (banding).

  The present invention has been made in view of such circumstances, and an object thereof is to provide an image generation apparatus and method, and an image forming apparatus that suppress the amount of ink at the same density while suppressing occurrence of banding and gradation shift. And

を満たして記録対象の全体を被覆できる記録率を下回らないように設定することを特徴とする。
前記目的を達成するために本発明に係る画像生成装置は、Ｍ階調（Ｍ≧４）の画像データをそれぞれサイズの異なる（Ｎ−１）種類のドット及びドット無しに対応するＮ値（Ｍ＞Ｎ＞２）の画像データに量子化し、階調ごとに各ドットの比率を変化させることで階調表現を行う画像生成装置において、第１の階調域においては、第１のドットの比率を０以外の値とするとともに、前記第１のドットよりもサイズが大きい第２のドットの比率を上昇させることで出力階調を上昇させ、前記第１の階調域よりも高い第２の階調域においては、前記第２のドットの比率を所定の値に固定又は減少させるとともに、前記第１のドットの比率を上昇させることで出力階調を上昇させることを特徴とする。 In order to achieve the above object, the image generating apparatus according to the present invention uses N values (M−1) corresponding to (N−1) types of dots having different sizes and no dots for image data of M gradations (M ≧ 4). >N> 2) In an image generation apparatus that performs gradation expression by quantizing image data and changing the recording rate of each dot for each gradation, in the first gradation area, the first dot The recording rate is set to a value other than 0, and the output gradation is increased by increasing the recording rate of the second dot having a size larger than that of the first dot, which is higher than the first gradation range. In the second gradation region, the quantization that increases the output gradation by increasing the recording ratio of the first dot while the recording ratio of the second dot is fixed or decreased to a value other than 0. Means for quantizing, wherein the quantizing means includes the second floor. In the third gradation region higher than the region, the recording rate of the first dot is fixed or increased, and the dots to be used other than the first dot are sequentially changed to the output gradation by changing the dots to be larger in size. Furthermore, the recording rate of each dot other than the first dot used in the second gradation area and the third gradation area is set to r _l (l = 1 to N−2). When the ideal dot radius of each dot other than the first dot is R _l and the horizontal and vertical recording unit pixel sizes are Lx and Ly, respectively, the recording rate r _l is

Is set so as not to fall below the recording rate that satisfies the above and covers the entire recording target.
In order to achieve the above object, the image generating apparatus according to the present invention uses N values (M−1) corresponding to (N−1) types of dots having different sizes and no dots for image data of M gradations (M ≧ 4). >N> 2) In the image generation apparatus that performs gradation expression by quantizing the image data and changing the ratio of each dot for each gradation, the ratio of the first dot in the first gradation area Is set to a value other than 0, and the output gradation is increased by increasing the ratio of the second dot having a size larger than that of the first dot, and the second gradation higher than the first gradation range is set. In the gradation range, the ratio of the second dots is fixed or decreased to a predetermined value, and the output gradation is increased by increasing the ratio of the first dots.

  According to the present invention, it is possible to suppress the amount of ink at the same density while suppressing the occurrence of uneven stripes.

Flow chart showing image conversion processing Flow chart showing quantization processing for each pixel The figure which shows the threshold value table classified by gradation Flow chart showing quantization processing for each pixel Graph showing the relationship between the gradation value and the recording rate of each size Graph showing the relationship between the gradation value and the recording rate of each size Graph showing the relationship between the gradation value and the recording rate of each size Graph showing the relationship between optical density and ink amount FIG. 2 is a block diagram showing the main configuration of an image forming apparatus according to the present embodiment. 1 is an overall configuration diagram of an ink jet recording apparatus according to an embodiment of the present invention. Plane perspective view showing a configuration example of an inkjet head Plane perspective view showing another structural example of the head Sectional drawing which follows the AA line in FIG. Main block diagram showing the system configuration of the inkjet recording apparatus

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Image conversion process flow]
In the present embodiment, description will be given by taking CMYK four-color printing as an example. FIG. 1 is a flowchart showing image conversion processing according to the present embodiment.

  When image data to be printed is input, color conversion processing and color separation processing are first performed (step S1).

  If the input image values (C, M, Y, K) of the 4th plate are output after being subjected to only gamma conversion processing, the total amount of ink of each color of C, M, Y, K will exceed the specified value. , There is a possibility that settling or bleeding may occur after printing. The expression of colors in printing is basically possible with the three colors C, M, and Y, but the total amount of ink can be suppressed by replacing some of C, M, and Y with K.

  Therefore, in the color conversion process of the present embodiment, CMYK → C′M′Y′K ′ conversion is performed while the total ink amount is less than or equal to the specified value.

  The color-converted CMYK values are subjected to color separation processing. For example, C, M, Y, and K color data having 8 bit gradations each having a resolution of 1200 dpi are generated.

  Each color data is gamma-converted for each color (step S2) and multi-valued (step S3).

  When inks of similar colors and different densities (for example, cyan C and light cyan LC) are used, these processes may be performed for each similar color.

[About multi-value processing]
In the halftone processing (multi-value processing) in the present embodiment, the gradation for each input color has n values (n−1 types of dot sizes) corresponding to n−1 types (n> 3) of different dot sizes. Quantize to + no drop). Here, the recording rate of each of the n−1 different size dots is uniquely determined for each gradation.

  Here, the recording rate refers to the ratio of the number of pixels in which dots are actually recorded to the number of recordable pixels included in a certain area. For example, a droplet recording rate of 0% means a state where no droplet droplets are formed at all, and a medium droplet recording rate of 50% means that half of the pixels that can be recorded are medium. The state where the dot of a drop is formed is said. A large droplet recording rate of 100% means a state in which large dots are formed in all pixels.

  In this specification, “recording rate” may be expressed as “ratio”.

(Halftone processing by dither matrix)
First, an example of quantization processing using a dither matrix will be described. FIG. 2 is a flowchart showing the quantization processing of each pixel according to this embodiment. Here, a four-value quantization process having three types of dot sizes of small droplets, medium droplets, and large droplets will be described as an example.

  First, the threshold value of the droplet in the target pixel is set from the gradation value of the target pixel and the threshold value table for each gradation (FIG. 3) (step S11). In the threshold table for each gradation, threshold values for the dither matrix for each gradation are stored in advance.

  By comparing the set threshold value with the dither matrix for small droplets, the on / off state of the droplets at the target pixel (presence / absence of small droplet ejection) is determined (step S12). That is, when the threshold value set is larger than the value of the droplet dither matrix, the pixel is turned on (there is a droplet).

  Simultaneously with the small droplet processing described above, for medium droplets and large droplets, the threshold values for medium droplets and large droplets in the target pixel are set from the gradation value of the target pixel and the threshold value table for each gradation (step). S13, S15) and comparing the set threshold values with the medium drop dither matrix and the large drop dither matrix, respectively, to determine on / off of the medium drop and the large drop in the target pixel (steps S14, S16).

  Finally, on / off of small droplets, medium droplets, and large droplets in the target pixel is compared, and the largest size among the on dot sizes is selected (step S17).

  As described above, the recording rate of each of the small droplet, the medium droplet, and the large droplet is determined by the threshold value table for each gradation. For example, in an 8-bit dither matrix, when 1 is set as the threshold value, the recording rate is 1/2 ^ 8. In this way, it is possible to specify and quantize the recording rate of four-valued dots (no drops, small drops, medium drops, large drops).

(Halftone processing by combining dither matrix and error diffusion)
Next, an example of quantization processing using both a dither matrix and an error diffusion method will be described. FIG. 4 is a flowchart showing the quantization processing of each pixel according to this embodiment. In FIG. 4, dither [x] [y] represents a two-dimensional dither matrix component. th_dth [i] [level] indicates a threshold value to be compared with the dither matrix (i = 0, 1, 2). th_edf [level] indicates an error diffusion threshold. dot [j] [level] is associated with a dot size of {no drop, small drop, medium drop, large drop} for each gradation value (level) (j = 0, 1, 2, 3 ).

  When each pixel quantization process starts, first, the gradation value including the peripheral error is obtained by taking the sum of the original gradation value of the target pixel and the peripheral error diffused to the target pixel by error diffusion. Calculate (step S101).

  Next, the image area is divided by comparing the dither matrix value (dither [x] [y]) with the threshold th_dth [i] [level]. The threshold th_dth [i] [level] is set for each gradation value (level) of the target pixel and is stored in advance in a predetermined memory. Here, the first threshold th_dth [0] [level], the second threshold th_dth [1] [level], and the third threshold th_dth [2] [level] are used to divide into four regions.

  First, the value of the dither matrix is compared with the first threshold th_dth [0] [level] (step S102). If the value of the dither matrix is smaller as a result of the comparison, the dot size specified by dot [0] [level] is selected (step S103).

  If the value of the dither matrix is equal to or greater than the first threshold value in step S102, the dither matrix value is subsequently compared with the second threshold value th_dth [1] [level] (step S104). If the value of the dither matrix is smaller as a result of the comparison, the dot size specified by dot [1] [level] is selected (step S105).

  If the value of the dither matrix is equal to or greater than the second threshold value in step S104, the dither matrix value is further compared with the third threshold value th_dth [2] [level] (step S106). If the value of the dither matrix is equal to or smaller than the third threshold th_dth [2] [level], the process proceeds to step S107, and the gradation value including the peripheral error is compared with the error diffusion threshold th_edf [level] (step S107). ). The error diffusion threshold th_edf [level] is also set for each gradation value of the target pixel and is stored in advance in a predetermined memory. If the gradation value including the peripheral error is smaller than the error diffusion threshold as a result of the comparison in step S107, the dot size specified by dot [2] [level] is selected (step S108).

  On the other hand, if the gradation value including the peripheral error is equal to or greater than the error diffusion threshold in step S107, the dot size specified by dot [3] [level] is selected (step S109). As described above, in the region where the dither threshold is equal to or smaller than the third threshold (and equal to or greater than the second threshold), binarization processing by the error diffusion method is performed.

  If the dither matrix value is larger than the third threshold value in step S106, the dot size specified by dot [4] [level] is selected (step S110).

  The dot size of each dot [j] [level] can be determined as appropriate for each gradation value. For example, for a certain gradation value, dot [0] [level] is a small drop, dot [1] [level] is a medium drop, dot [2] [level] is no drop, dot [3] [level] Is a large drop, and dot [4] [level] is a large drop.

  Thus, quantization according to the divided areas is performed. As described above, after selecting the dot size of the target pixel, the quantization error is calculated (step S111). The quantization error is an error generated by quantizing the gradation value including the peripheral error, and is a difference between the gradation value including the peripheral pixel and the quantization threshold. A quantization threshold is associated with each dot [0] [level], dot [1] [level], dot [2] [level], dot [3] [level], and dot [4] [level]. Tone value.

  The calculated quantization error is diffused to surrounding pixels according to a predetermined error diffusion matrix (step S112). Subsequently, the quantization target pixel is shifted to an adjacent pixel, and the same processing is performed to quantize all the pixels.

  According to the above quantization processing, the recording rate of dot [0] [level], dot [1] [level], dot [4] [level] in each area corresponding to steps S103, S105, and S110 is dither. The remaining area is determined by binarization using an error diffusion method (steps S108 and S109). By performing quantization in this way, a four-value recording rate can be uniquely determined for each gradation.

  In this example, each threshold th_dth [i] [level] for area division uses the threshold value in the original gradation value of the target pixel. However, the threshold value in the gradation value including the peripheral error may be used. .

[About dot recording rate]
Next, the recording rate of each dot size quantized as described above will be described.

(First embodiment)
Here, a case of three values of large droplets, small droplets, and no droplets will be described as an example. FIG. 5 is a graph showing the relationship between the gradation value and the recording rate of each dot size according to the first embodiment.

  As shown in FIG. 5, in the gradation range a having the lowest gradation value, the recording rate of large droplets is kept constant (= 0), and the recording rate of small droplets is increased (recording rate of small droplets = 0 to threshold value). TH2) to increase the output gradation.

  In the gradation area b (corresponding to the “first gradation area”) having the second largest gradation value after the gradation area a, the recording rate of small droplets is constant (= TH2), and the recording rate of large droplets is increased. The output gradation is increased by causing (large droplet recording rate = 0 to threshold value TH1). The recording rate of the droplets is not constant and may be increased or decreased.

  In the gradation area c (corresponding to the “second gradation area”) having the next largest gradation value after the gradation area b, the recording rate of large droplets is constant (= TH1), and the recording rate of small droplets is increased. The output gradation is raised by performing (Recording rate of droplets = threshold value TH2 to threshold value TH3). The recording rate of large droplets may be decreased so as not to fall below a predetermined value.

  In the gradation area d having the highest gradation value next to the gradation area c and having the highest gradation value, the recording rate of the droplets is decreased (the recording rate of the droplets = threshold value TH3 to TH3). 0) The output gradation is increased by increasing the recording rate of large droplets (recording rate of large droplets = threshold values TH1 to 100).

  As described above, the present embodiment is characterized in that after the recording rate of the large droplets reaches a certain value (TH1) in the halftone to shadow region, the recording rate of the small droplets once fixed at the recording rate is increased again. There is. In the past, it was common to reduce droplets without increasing them.

  The density per same ink amount is generally higher when the number of dots is increased with smaller droplets. Therefore, the amount of ink can be suppressed by performing quantization at such a recording rate. When the ink amount restriction is the same, the color reproduction range can be expanded by increasing the density per halftone or shadow ink amount as in this embodiment.

  The large drop recording rate TH1 in the gradation value (gradation range c) at which the recording rate of the small droplets starts to increase again is such that the large drops cover substantially the entire recording medium when recording is performed on the recording medium. It is desirable that the ratio be The recording rate covering substantially the whole is a value obtained from the following equation.

Here, L _x, L _y transverse respectively longitudinal recording unit pixel size, the R _L is an ideal radius of dots formed when the large droplet is landed on the recording medium.

  As described above, since the recording rate of the large droplets reaches the recording rate TH1 that covers the entire recording medium with the large droplets, the recording rate of the small droplets is increased again, which is sufficient to suppress the occurrence of uneven stripes. A large amount of large droplets is secured, and no streaking occurs even if the recording rate of small droplets where streaks are conspicuous increases as the gradation value increases.

  By setting the recording rate as described above, it is possible to avoid the occurrence of unevenness and to suppress the ink amount. Further, since the ink amount is suppressed, the color reproduction range can be expanded when compared with the same amount of ink limit.

(Second Embodiment)
Next, the case of four values of large droplet, medium droplet, small droplet, and no droplet will be described as an example. FIG. 6 is a graph showing the relationship between the gradation value and the recording rate of each dot size according to the second embodiment.

  As shown in FIG. 6, in the gradation range a having the lowest gradation value, the recording rate of medium droplets and large droplets is constant (= 0), and the recording rate of small droplets is increased (recording rate of small droplets = 0 to threshold value TH2) to increase the output gradation.

  In gradation area b, which has the next largest gradation value after gradation area a, the recording rate of small droplets and large droplets is constant (recording rate of small droplets = TH2, recording rate of large droplets = 0), and medium droplets The output gradation is increased by increasing the recording rate (medium droplet recording rate = 0 to threshold TH1). The recording rate of the droplets is not constant and may be increased or decreased.

  In the gradation area c having the next largest gradation value after the gradation area b, the medium droplet and large droplet recording ratios are kept constant (medium droplet recording ratio = TH1 and large droplet recording ratio = 0). The output gradation is increased by increasing the droplet recording rate (small droplet recording rate = threshold value TH2 to threshold value TH3). The recording rate of the medium droplet may be decreased so as not to fall below a predetermined value.

  In the gradation area d having the second highest gradation value after the gradation area c, the medium droplet recording ratio is decreased (the medium droplet recording ratio is maintained while the droplet recording ratio is constant (TH3 recording ratio = TH3)). The output gradation is increased by increasing the recording rate of large droplets (recording rate = threshold value TH1 to 0) and large droplet recording rate = 0 to threshold value TH1. The recording rate of the droplets may be increased instead of being constant.

  In the gradation range with the highest gradation value after the gradation value d and the gradation area e with the highest gradation value, the higher the gradation value, the smaller the droplet recording rate (the recording of the droplet). Rate = threshold TH3-0), and the large drop recording rate is increased (large drop recording rate = threshold TH1-100).

  As described above, the relationship between the recording rates of the small droplet and the medium droplet in the gradation region a to the gradation region c is the same as the relationship between the recording rate of the small droplet and the large droplet in the first embodiment. The present embodiment is characterized in that the recording rate of small droplets is fixed to a predetermined value when medium droplets and large droplets are used. Note that the recording rate of the droplets at this time may be increased. Conventionally, it has been usual to use large droplets by reducing small droplets or stopping the use of small droplets.

  In this way, the relative proportion of droplets is increased by using a relatively small size dot to the maximum while using a relatively large size dot sufficient to suppress streaking. . Therefore, the ink amount can be further suppressed in the shadow area.

(Third embodiment)
Next, the case of five values of extra large drops, large drops, medium drops, small drops, and no drops will be described as an example. FIG. 7 is a graph showing the relationship between the gradation value and the recording rate of each dot size according to the third embodiment.

  As shown in FIG. 7, in the gradation range a having the lowest gradation value, the recording rate of medium drops, large drops and extra large drops is set to 0, and the output gradation is increased by increasing the recording rate of small drops. .

  In the gradation area b having the next highest gradation value after the gradation area a, the output gradation is increased by keeping the recording rate of small droplets, large droplets and extra large droplets constant and increasing the recording rate of medium droplets. In the gradation area c, which has the next largest gradation value after the gradation area b, the output gradation is increased by increasing the recording ratio of the small droplets while keeping the recording ratios of the medium drops, large drops, and extra large drops constant. Raise.

  Further, in the gradation area d having the next highest gradation value after the gradation area c, the output gradation is increased by decreasing the recording rate of the medium droplet and increasing the recording rate of the small droplet and the large droplet.

  Further, in the gradation area e having the next highest gradation value after the gradation area d, the output gradation is increased by decreasing the recording rate of large droplets and increasing the recording rate of small droplets and extra large droplets.

  In the gradation range f having the highest gradation value, the output gradation is increased by decreasing the recording rate of small droplets and increasing the recording rate of extra large droplets.

  Thus, the maximum proportion of droplets increases the relative proportion of droplets. Therefore, the ink amount can be further suppressed in the shadow area. Also, in the gradation area d and gradation area e (corresponding to the “third gradation area”), the dots used other than the small droplets are changed to large dots in order, so that The gradation can be increased.

  Further, in order to suppress streaks, it is sufficient that there is a recording rate that can cover the whole. When the dot size is large, the whole can be covered with fewer dots. Accordingly, assuming that the maximum recording rates of medium droplets, large droplets, and extra large droplets in the gradation range d and gradation range e are TH_M, TH_L, and TH_LL, respectively, the relationship TH_M> TH_L> TH_LL may be satisfied. Good. In this way, by reducing the maximum recording rate of each dot as the size increases, it is possible to suppress the use of dots having a large dot size that consumes more ink per density. As a result, the amount of ink can be suppressed by maintaining or increasing efficient droplets, and the color reproduction range can be expanded.

At this time, the ratio of medium drops, large drops, and extra large drops, which are relatively large dots, is set so as not to fall below the recording rate covering the whole. Here, “not lower than the recording rate covering the whole” means that the recording rates r _M , r _L , and r _{LL of} medium droplets, large droplets, and extra large droplets satisfy the following formula 2 in each gradation.

Here, L _x and L _y are horizontal and vertical recording unit pixel sizes, and R _l is an ideal dot radius of each droplet. The sum is taken for relatively large dots.

  Here, TH_M, TH_L, and TH_LL are set as shown in Equation 3.

  As described above, by fixing the recording rate of relatively small size dots and introducing a relatively large size dot, and then increasing the recording rate of relatively small size dots again, the same The amount of ink in density can be suppressed. In addition, by setting the recording rate of the relatively large size dots when increasing the recording rate of the relatively small size dots again so as not to fall below the recording rate covering the entire recording medium, The occurrence of gradation shift can be suppressed.

  In the prior art, various image quality improvements by actively replacing droplets are discussed. The replacement with droplets is effective for suppressing the amount of ink as shown in this specification. However, the conventional technology cannot realize the suppression of the ink amount in the single-tone halftone and the shadow area, which is important for the suppression of the ink amount.

  For example, in the dot recording rate disclosed in Patent Document 1, small droplets are reduced or completely eliminated at the recording rate at which large droplets are introduced. In such a gradation, in this embodiment, the recording rate of small droplets is increased, or small droplets are fixed, and medium droplets that consume a relatively large amount of ink than small droplets are replaced with large droplets. Perform key expression. Accordingly, the amount of ink can be more effectively suppressed, and at the same time, there is a sufficient recording rate of relatively large dots that is dominant with respect to the streak, and thus streak does not occur.

  Patent Document 2 discloses a method for increasing the recording rate of small droplets, but does not disclose a method for reducing relatively large droplets that consume more ink. Since these large droplets cannot be reduced, the amount of ink cannot be effectively suppressed even with these techniques.

  FIG. 8 is a graph showing the relationship between the optical density and the ink amount, and shows the density characteristic obtained by the conventional control and the density characteristic when the printing rate of each dot size is controlled based on the present embodiment. As shown in the figure, when the optical density is 1.9, the conventional ink amount is 3.4 [pl / px], whereas the ink amount when the control of this embodiment is performed is 3. 0.0 [pl / px]. As described above, as a result of using a relatively small size dot, it is possible to more effectively suppress the ink amount at the same density.

[Configuration of Image Forming Apparatus According to the Present Embodiment]
FIG. 9 is a block diagram showing a main configuration of the image forming apparatus according to the present embodiment. The image forming apparatus 50 includes a recording head 60 and a head control device 70 that controls a recording operation by the recording head 60.

  The recording head 60 includes a plurality of piezoelectric elements 62 serving as ejection energy generating elements provided corresponding to the respective nozzles, and a switch IC 64 that switches driving / non-driving of each piezoelectric element 62.

  The head control device 70 includes an original image data input unit 72 that functions as an input interface unit that receives original image data of an image to be recorded, and a halftone processing unit 74 that performs a quantization process on the input original image data ( Equivalent to “quantization means”). The head control device 70 includes a drive waveform generation unit 76 and a head driver 78.

  The original image data may be image data converted for each ink color, or RGB image data before conversion for each ink color. As necessary, color conversion processing, pixel number conversion processing, and γ conversion processing are performed on the original image data.

  The halftone processing unit 74 is a signal processing means for converting original image data (density data) into binary or multivalued dot data. As the means for the halftone processing, the aspect using the dither matrix described above, the aspect combining the dither and the error diffusion method, or the like can be applied. In the halftone process, generally, gradation image data having an M value (M ≧ 3) is converted into gradation image data having an N value (N <M). In the simplest example, the image data is converted into binary (dot on / off) dot image data. However, in the halftone process, the dot size type (for example, three types such as a large dot, a medium dot, and a small dot) is converted. It is also possible to perform corresponding multi-level quantization.

  That is, the halftone processing unit 74 of this example has n values (n−1 droplet sizes) corresponding to n−1 (n is an integer of n> 2) droplet sizes different from each other. Quantize to + no drop). A recording rate indicating how much each n different size dots are printed in each printable pixel is uniquely determined for each gradation.

  The binary or multi-valued image data (tot data) obtained in this way controls the drive (on) / non-drive (off) of each nozzle, and in the case of multi-value, controls the droplet amount (dot size). Used as ink ejection control data (droplet ejection control data). The dot data (droplet ejection control data) generated by the halftone processing unit 74 is given to the head driver 78, and the ink ejection operation of the recording head 60 is controlled.

  The drive waveform generator 76 is a means for generating a drive voltage signal waveform for driving the piezoelectric element 62 corresponding to each nozzle of the recording head 60. The waveform data of the drive voltage signal is stored in advance in storage means such as a ROM, and waveform data to be used is output as necessary. The signal (drive waveform) generated by the drive waveform generation unit 76 is supplied to the head driver 78. Note that the signal output from the drive waveform generator 76 may be digital waveform data or an analog voltage signal.

  The inkjet image forming apparatus 50 shown in this example supplies a common drive power waveform signal to each piezoelectric element 62 of the recording head 60 via the switch IC 64, and the corresponding piezoelectric power is output according to the ejection timing of each nozzle. A driving method is employed in which ink is ejected from nozzles corresponding to each piezoelectric element 62 by switching on / off the switching elements connected to the individual electrodes of the elements 62.

  The combination of the original image data input unit 72 and the halftone processing unit 74 in FIG. 9 corresponds to an “image generation device”.

<Specific Configuration Example of Image Forming Apparatus>
FIG. 10 is an overall configuration diagram illustrating a configuration example of the ink jet recording apparatus according to the embodiment of the present invention. The ink jet recording apparatus 100 of this example mainly includes a paper feeding unit 112, a treatment liquid application unit (precoat unit) 114, a drawing unit 116, a drying unit 118, a fixing unit 120, and a paper discharge unit 122. The inkjet recording apparatus 100 includes a plurality of colors from the inkjet heads 172M, 172K, 172C, and 172Y on a recording medium 124 (hereinafter, also referred to as “paper” for convenience) held on the drum (drawing drum 170) of the drawing unit 116. Is a single-pass ink jet recording apparatus that forms a desired color image by ejecting the ink of the ink, and a treatment liquid (here, an aggregating treatment liquid) is applied onto the recording medium 124 before the ink is ejected. 2 is a drop-on-demand type image forming apparatus to which a two-liquid reaction (aggregation) method in which an ink liquid is reacted to form an image on a recording medium 124 is applied.

(Paper Feeder)
A recording medium 124 that is a sheet is stacked on the paper feeding unit 112, and the recording medium 124 is fed one by one from the paper feeding tray 150 of the paper feeding unit 112 to the processing liquid application unit 114. In this example, a sheet (cut paper) is used as the recording medium 124, but a configuration in which continuous paper (roll paper) is cut to a required size and fed is also possible.

(Processing liquid application part)
The processing liquid application unit 114 is a mechanism that applies the processing liquid to the recording surface of the recording medium 124. The treatment liquid contains a color material aggregating agent that agglomerates the color material (pigment in this example) in the ink applied by the drawing unit 116, and the ink comes into contact with the treatment liquid and the ink. And the solvent are promoted.

  The processing liquid application unit 114 includes a paper feed cylinder 152, a processing liquid drum (also referred to as “precoat cylinder”) 154, and a processing liquid coating device 156. The treatment liquid drum 154 is a drum that holds and rotates the recording medium 124. The processing liquid drum 154 includes a claw-shaped holding means (gripper) 155 on the outer peripheral surface thereof, and the recording medium 124 is sandwiched between the claw of the holding means 155 and the peripheral surface of the processing liquid drum 154. The tip can be held. The treatment liquid drum 154 may be provided with a suction hole on the outer peripheral surface thereof and connected to a suction unit that performs suction from the suction hole. As a result, the recording medium 124 can be held in close contact with the peripheral surface of the treatment liquid drum 154.

  The processing liquid coating device 156 includes a processing liquid container in which the processing liquid is stored, an anix roller (measuring roller) partially immersed in the processing liquid in the processing liquid container, the anix roller and the processing liquid drum 154. A rubber roller that is pressed against the upper recording medium 124 and transfers the measured processing liquid to the recording medium 124. In the present embodiment, the configuration in which the application method using the roller is exemplified, but the present invention is not limited to this. For example, various methods such as a spray method and an ink jet method can be applied.

  The recording medium 124 to which the processing liquid is applied by the processing liquid applying unit 114 is transferred from the processing liquid drum 154 to the drawing drum 170 of the drawing unit 116 via the intermediate transport unit 126.

(Drawing part)
The drawing unit 116 includes a drawing drum (also referred to as “drawing cylinder” or “jetting cylinder”) 170, a sheet pressing roller 174, and inkjet heads 172M, 172K, 172C, and 172Y. As the ink jet heads 172M, 172K, 172C, 172Y for the respective colors and the control devices thereof, the configurations of the recording head 60 and the head control device 70 described in FIG. 9 are employed.

  Similar to the treatment liquid drum 154, the drawing drum 170 includes a claw-shaped holding means (gripper) 171 on the outer peripheral surface thereof. A large number of suction holes (not shown) are formed in a predetermined pattern on the peripheral surface of the drawing drum 170, and the recording medium 124 is sucked and held on the peripheral surface of the drawing drum 170 by sucking air from the suction holes. The In addition, the recording medium 124 is not limited to be sucked and sucked by negative pressure suction, but may be configured to suck and hold the recording medium 124 by electrostatic suction, for example.

  Each of the inkjet heads 172M, 172K, 172C, and 172Y is a full-line inkjet recording head having a length corresponding to the maximum width of the image forming area in the recording medium 124, and image formation is performed on the ink ejection surface thereof. A nozzle row (two-dimensional array nozzle) in which a plurality of nozzles for ejecting ink are arranged over the entire width of the region is formed. Each inkjet head 172M, 172K, 172C, 172Y is installed so as to extend in a direction orthogonal to the conveyance direction of the recording medium 124 (the rotation direction of the drawing drum 170).

  A corresponding color ink cassette (ink cartridge) is attached to each of the inkjet heads 172M, 172K, 172C, and 172Y. Ink droplets are ejected from the inkjet heads 172M, 172K, 172C, and 172Y toward the recording surface of the recording medium 124 held on the outer peripheral surface of the drawing drum 170.

  As a result, the ink comes into contact with the treatment liquid previously applied to the recording surface, and the color material (pigment) dispersed in the ink is aggregated to form a color material aggregate. As an example of the reaction between the ink and the treatment liquid, in this embodiment, an acid is contained in the treatment liquid, and the pigment dispersion is destroyed and aggregated by the PH down. Avoids droplet ejection interference due to liquid coalescence. Thus, the color material flow on the recording medium 124 is prevented, and an image is formed on the recording surface of the recording medium 124.

  The droplet ejection timing of each of the inkjet heads 172M, 172K, 172C, and 172Y is synchronized with an encoder (not shown in FIG. 10, reference numeral 294 in FIG. 14) that detects the rotational speed disposed on the drawing drum 170. A discharge trigger signal (pixel trigger) is generated based on the detection signal of the encoder. Thereby, the landing position can be determined with high accuracy. In addition, it learns the speed fluctuation due to the deflection of the drawing drum 170 in advance, corrects the droplet ejection timing obtained by the encoder, and depends on the deflection of the drawing drum 170, the accuracy of the rotation axis, and the speed of the outer peripheral surface of the drawing drum 170 In this case, it is possible to reduce the droplet ejection unevenness. Furthermore, maintenance operations such as cleaning the nozzle surfaces of the inkjet heads 172M, 172K, 172C, and 172Y and discharging the thickened ink may be performed by retracting the head unit from the drawing drum 170.

  In this example, the configuration of CMYK standard colors (four colors) is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink, dark ink, and special color ink are used as necessary. May be added. For example, it is possible to add an inkjet head that discharges light-colored ink such as light cyan and light magenta, and the arrangement order of the color heads is not particularly limited.

  The recording medium 124 on which an image is formed by the drawing unit 116 is transferred from the drawing drum 170 to the drying drum 176 of the drying unit 118 via the intermediate conveyance unit 128.

(Drying part)
The drying unit 118 is a mechanism that dries moisture contained in the solvent separated by the color material aggregating action, and includes a drying drum (also referred to as “drying cylinder”) 176 and a solvent drying device 178. Similar to the processing liquid drum 154, the drying drum 176 includes a claw-shaped holding unit (gripper) 177 on the outer peripheral surface thereof, and the holding unit 177 can hold the leading end of the recording medium 124.

  The solvent drying device 178 is disposed at a position facing the outer peripheral surface of the drying drum 176, and includes a plurality of halogen heaters 180 and hot air ejection nozzles 182 disposed between the halogen heaters 180. Various drying conditions can be realized by appropriately adjusting the temperature and air volume of the hot air blown toward the recording medium 124 from each hot air ejection nozzle 182 and the temperature of each halogen heater 180. The recording medium 124 that has been dried by the drying unit 118 is transferred from the drying drum 176 to the fixing drum 184 of the fixing unit 120 via the intermediate conveyance unit 130.

(Fixing part)
The fixing unit 120 includes a fixing drum (also referred to as “fixing cylinder”) 184, a halogen heater 186, a fixing roller 188, and an in-line sensor 190. Like the processing liquid drum 154, the fixing drum 184 includes a claw-shaped holding unit (gripper) 185 on the outer peripheral surface, and the leading end of the recording medium 124 can be held by the holding unit 185.

  With the rotation of the fixing drum 184, the recording medium 124 is conveyed with the recording surface facing outward. The recording surface is preheated by the halogen heater 186, fixing processing by the fixing roller 188, and by the inline sensor 190. Inspection is performed.

  The fixing roller 188 is a roller member that heats and pressurizes the dried ink to weld the self-dispersing polymer fine particles in the ink to form a film of the ink, and is configured to heat and press the recording medium 124. The The recording medium 124 is sandwiched between the fixing roller 188 and the fixing drum 184 and nipped at a predetermined nip pressure (for example, 0.15 MPa), and a fixing process is performed.

  The fixing roller 188 is configured by a heating roller in which a halogen lamp is incorporated in a metal pipe such as aluminum having good thermal conductivity, and is controlled to a predetermined temperature (for example, 60 to 80 ° C.). By heating the recording medium 124 with this heating roller, thermal energy equal to or higher than the Tg temperature (glass transition temperature) of the latex contained in the ink is applied, and the latex particles are melted. As a result, pressing and fixing are performed on the unevenness of the recording medium 124, and the unevenness of the image surface is leveled to obtain glossiness.

  The inline sensor 190 is a reading unit for measuring an ejection defect check pattern, image density, image defect, and the like for an image (including a test pattern) recorded on the recording medium 124. Applied.

  According to the fixing unit 120 configured as described above, the latex particles in the thin image layer formed by the drying unit 118 are heated and pressurized by the fixing roller 188 and are melted. Can be made.

  In addition, instead of the ink containing the high boiling point solvent and the polymer fine particles (thermoplastic resin particles), a monomer component that can be polymerized and cured by ultraviolet (UV) exposure may be contained. In this case, the inkjet recording apparatus 100 includes a UV exposure unit that exposes the ink on the recording medium 124 to UV light instead of the heat-pressure fixing unit (fixing roller 188) using a heat roller. As described above, when ink containing an actinic ray curable resin such as a UV curable resin is used, an actinic ray such as a UV lamp or an ultraviolet LD (laser diode) array is used instead of the fixing roller 188 for heat fixing. Means for irradiating are provided.

(Output section)
Subsequent to the fixing unit 120, a paper discharge unit 122 is provided. The paper discharge unit 122 includes a discharge tray 192. Between the discharge tray 192 and the fixing drum 184 of the fixing unit 120, a transfer drum 194, a conveyance belt 196, and a stretching roller 198 are in contact with each other. Is provided. The recording medium 124 is sent to the conveyor belt 196 by the transfer drum 194 and discharged to the discharge tray 192. Although the details of the paper transport mechanism by the transport belt 196 are not shown, the recording medium 124 after printing is held at the front end of the paper by a gripper (not shown) gripped between the endless transport belt 196, and the transport belt 196. Is carried above the discharge tray 192.

  Although not shown in FIG. 10, in addition to the above-described configuration, the ink jet recording apparatus 100 of this example includes an ink storage / loading unit that supplies ink to each of the ink jet heads 172M, 172K, 172C, and 172Y, and a processing liquid. A means for supplying a processing liquid to the applying unit 114 and a head maintenance unit for cleaning each ink jet head 172M, 172K, 172C, 172Y (nozzle surface wiping, purging, nozzle suction, etc.) Are provided with a position detection sensor for detecting the position of the recording medium 124 and a temperature sensor for detecting the temperature of each part of the apparatus.

[Configuration example of inkjet head]
Next, the structure of the inkjet head will be described. Since the inkjet heads 172M, 172K, 172C, and 172Y corresponding to the respective colors have the same structure, the heads are represented by the reference numeral 250 in the following.

  FIG. 11A is a plan perspective view showing an example of the structure of the head 250, and FIG. 11B is an enlarged view of a part thereof. FIG. 12 is a diagram illustrating an arrangement example of a plurality of head modules constituting the head 250. 13 is a cross-sectional view (A- in FIG. 11) showing a three-dimensional configuration of a droplet ejection element (an ink chamber unit corresponding to one nozzle 251) for one channel serving as a recording element unit (ejection element unit). It is sectional drawing which follows the A line.

  As shown in FIG. 11, the head 250 of this example has a matrix of a plurality of ink chamber units (droplet discharge elements) 253 including nozzles 251 serving as ink discharge ports and pressure chambers 252 corresponding to the nozzles 251. The nozzle spacing (projection nozzle pitch) is projected (orthogonally projected) so as to be aligned along the longitudinal direction of the head (direction perpendicular to the paper feed direction). High density is achieved.

  Corresponds to the entire width Wm of the drawing area of the recording medium 124 in a direction (arrow M direction; corresponding to “second direction”) substantially orthogonal to the feeding direction (arrow S direction; corresponding to “first direction”) of the recording medium 124. In order to configure a nozzle array longer than the length, for example, as shown in FIG. 12A, a short head module 250 ′ in which a plurality of nozzles 251 are two-dimensionally arranged is arranged in a staggered manner. Construct a line-type head. Alternatively, as shown in FIG. 12B, a mode in which the head modules 250 ″ are connected in a line is also possible. Each head module 250 ′ or 250 ″ shown in FIG. 12 is the recording head described in FIG. 60.

  Note that the full-line print head for single pass printing is not limited to the case where the entire surface of the recording medium 124 is set as the drawing range, but when a part of the surface of the recording medium 124 is the drawing area (for example, paper In the case of providing a non-drawing area (margin part) around the periphery, it is only necessary to form nozzle rows necessary for drawing in a predetermined drawing area.

  The pressure chamber 252 provided corresponding to each nozzle 251 has a substantially square planar shape (see FIGS. 11A and 11B), and the nozzle 251 is provided at one of the diagonal corners. An outlet for supplying ink (supply port) 254 is provided on the other side. Note that the shape of the pressure chamber 252 is not limited to this example, and the planar shape may have various forms such as a quadrangle (rhombus, rectangle, etc.), a pentagon, a hexagon, other polygons, a circle, and an ellipse.

  As shown in FIG. 13, a head 250 (head modules 250 ′, 250 ″) includes a nozzle plate 251A in which nozzles 251 are formed, and a flow path plate 252P in which flow paths such as a pressure chamber 252 and a common flow path 255 are formed. The nozzle plate 251A constitutes a nozzle surface (ink ejection surface) 250A of the head 250, and a plurality of nozzles 251 communicating with the respective pressure chambers 252 are two-dimensionally formed. .

  The flow path plate 252P forms a side wall of the pressure chamber 252 and a flow path that forms a supply port 254 as a narrowed portion (most narrowed portion) of an individual supply path that guides ink from the common flow path 255 to the pressure chamber 252. It is a forming member. For convenience of explanation, FIG. 13 is illustrated in a simplified manner, but the flow path plate 252P has a structure in which one or more substrates are stacked.

  The nozzle plate 251A and the flow path plate 252P can be processed into a required shape by a semiconductor manufacturing process using silicon as a material.

  The common flow channel 255 communicates with an ink tank (not shown) as an ink supply source, and ink supplied from the ink tank is supplied to each pressure chamber 252 via the common flow channel 255.

  A piezo actuator (piezoelectric element) 258 having individual electrodes 257 is joined to a diaphragm 256 constituting a part of the pressure chamber 252 (the top surface in FIG. 13). The diaphragm 256 of this example is made of silicon (Si) with a nickel (Ni) conductive layer functioning as a common electrode 259 corresponding to the lower electrode of the piezoelectric actuator 258, and is arranged corresponding to each pressure chamber 252. It also serves as a common electrode for the actuator 258. It is also possible to form the diaphragm with a non-conductive material such as resin. In this case, a common electrode layer made of a conductive material such as metal is formed on the surface of the diaphragm member. Moreover, you may comprise the diaphragm which serves as a common electrode with metals (conductive material), such as stainless steel (SUS).

  By applying a driving voltage to the individual electrode 257, the piezo actuator 258 is deformed and the volume of the pressure chamber 252 is changed, and ink is ejected from the nozzle 251 due to the pressure change accompanying this. When the piezo actuator 258 returns to its original state after ink ejection, new ink is refilled into the pressure chamber 252 from the common channel 255 through the supply port 254.

  As shown in FIG. 11B, the ink chamber unit 253 having such a structure has a constant arrangement pattern along a row direction along the main scanning direction and an oblique direction having a constant angle θ that is not orthogonal to the main scanning direction. Thus, the high-density nozzle head of this example is realized by arranging a large number in a grid pattern. In this matrix arrangement, when the interval between adjacent nozzles in the sub-scanning direction is Ls, in the main scanning direction, each nozzle 251 is substantially equivalent to a linear arrangement with a constant pitch P = Ls / tan θ. It can be handled.

  In the implementation of the present invention, the arrangement form of the nozzles 251 in the head 250 is not limited to the illustrated example, and various nozzle arrangement structures can be applied.

  The means for generating discharge pressure (discharge energy) for discharging droplets from each nozzle in the inkjet head is not limited to a piezo actuator (piezoelectric element), but an electrostatic actuator or a thermal system (by heating a heater). Various pressure generating elements (discharge energy generating elements) such as heaters (heating elements) in a system in which ink is ejected using the pressure of film boiling) and various actuators in other systems can be applied. Corresponding energy generating elements are provided in the flow path structure according to the ejection method of the head.

[Explanation of control system]
FIG. 14 is a principal block diagram showing the system configuration of the inkjet recording apparatus 100. The ink jet recording apparatus 100 includes a communication interface 270, a system controller 272, a print controller 274, an image buffer memory 276, a head driver 278, a motor driver 280, a heater driver 282, a processing liquid application controller 284, a drying controller 286, and a fixing control. 288, a memory 290, a ROM 292, an encoder 294, and the like.

  The communication interface 270 is an interface unit that receives image data sent from the host computer 350. As the communication interface 270, a serial interface such as USB (Universal Serial Bus), IEEE 1394, Ethernet (registered trademark), a wireless network, or a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted. Image data sent from the host computer 350 is taken into the inkjet recording apparatus 100 via the communication interface 270 and temporarily stored in the memory 290.

  The memory 290 is a storage unit that temporarily stores an image input via the communication interface 270, and data is read and written through the system controller 272. The memory 290 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

  The system controller 272 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 100 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. . That is, the system controller 272 controls each unit such as the communication interface 270, the print control unit 274, the motor driver 280, the heater driver 282, the treatment liquid application control unit 284, the communication control with the host computer 350, and the memory 290. In addition to performing read / write control, a control signal for controlling the motor 296 and the heater 298 of the transport system is generated.

  The ROM 292 stores programs executed by the CPU of the system controller 272 and various data necessary for control. The ROM 292 may be a non-rewritable storage unit or a rewritable storage unit such as an EEPROM. The memory 290 is used as a temporary storage area for image data, and is also used as a program development area and a calculation work area for the CPU.

  The motor driver 280 is a driver that drives the motor 296 in accordance with an instruction from the system controller 272. In FIG. 14, various motors arranged in each unit in the apparatus are represented by a reference numeral 296. For example, the motor 296 shown in FIG. 14 includes a drawing drum 170, a motor that drives rotation of the paper feed drum 152, the processing liquid drum 154, the drawing drum 170, the drying drum 176, the fixing drum 184, the transfer drum 194, and the like. A pump drive motor for sucking negative pressure from the suction hole, a retraction mechanism motor for moving the head units of the inkjet heads 172M, 172K, 172C, and 172Y to the maintenance area outside the drawing drum 170, and the like. .

  The heater driver 282 is a driver that drives the heater 298 in accordance with an instruction from the system controller 272. In FIG. 14, various heaters arranged in each part in the apparatus are represented by reference numeral 298 as a representative. For example, the heater 298 shown in FIG. 14 includes a preheater (not shown) for heating the recording medium 124 to an appropriate temperature in the paper feeding unit 112 in advance.

  The print control unit 274 has a signal processing function for performing various processes and corrections for generating a print control signal from the image data in the memory 290 according to the control of the system controller 272, and the generated print A control unit that supplies data (dot data) to the head driver 278.

  As described with reference to FIG. 9, dot data is generated by performing color conversion processing and halftone processing on multi-tone image data. In the color conversion process, image data expressed in sRGB or the like (for example, 8-bit image data for each color of RGB) is converted into color data for each color of ink used in the inkjet recording apparatus 100 (in this example, color data of KCMY). It is a process to convert.

  Necessary signal processing is performed in the print control unit 274, and the ejection amount and ejection timing of the ink droplets of the head 250 are controlled via the head driver 278 based on the obtained dot data. Thereby, a desired dot size and dot arrangement are realized. The dot data referred to here corresponds to “nozzle control data”.

  The print control unit 274 includes an image buffer memory (not shown), and image data, parameters, and other data are temporarily stored in the image buffer memory when the print control unit 274 processes image data. Also possible is an aspect in which the print control unit 274 and the system controller 272 are integrated to form a single processor.

  The encoder 294 detects the rotation speed of the drawing drum 170, and for example, a photoelectric rotary encoder is used. The system controller 272 calculates the rotation speed of the drawing drum 170 based on the signal from the encoder 294, and generates the discharge timing signal of the nozzles 251 of the ink jet heads 172M, 172K, 172C, 172Y of each color based on the calculated rotation speed. And supplied to the print controller 274.

  An overview of the flow of processing from image input to print output is as follows. Image data to be printed is input from the outside via the communication interface 270 and stored in the memory 290. At this stage, for example, RGB image data is stored in the memory 290. In the inkjet recording apparatus 100, a pseudo continuous tone image is formed by changing the droplet ejection density and the dot size of fine dots by ink (coloring material) to the human eye. It is necessary to convert to a dot pattern that reproduces the gradation (shading of the image) as faithfully as possible. Therefore, the original image (RGB) data stored in the memory 290 is sent to the print control unit 274 via the system controller 272, and is converted into dot data for each ink color by the halftoning process in the print control unit 274. The In other words, the print control unit 274 performs processing for converting the input RGB image data into dot data of four colors K, C, M, and Y. Thus, the dot data generated by the print control unit 274 is stored in an image buffer memory (not shown).

  The head driver 278 outputs a drive signal for driving an actuator corresponding to each nozzle of the head 250 based on print data (that is, dot data stored in the image buffer memory 276) given from the print control unit 274. . The head driver 278 may include a feedback control system for keeping the head driving condition constant.

  When the drive signal output from the head driver 278 is applied to the head 250, ink is ejected from the corresponding nozzle. An image is formed on the recording medium 124 by controlling ink ejection from the head 250 while conveying the recording medium 124 at a predetermined speed.

  The treatment liquid application controller 284 controls the operation of the treatment liquid application device 156 (see FIG. 10) according to an instruction from the system controller 272. The drying control unit 286 controls the operation of the solvent drying device 178 (see FIG. 10) according to an instruction from the system controller 272.

  The fixing control unit 288 controls the operation of the fixing pressure unit 299 including the halogen heater 186 and the fixing roller 188 (see FIG. 10) of the fixing unit 120 according to an instruction from the system controller 272.

  As described with reference to FIG. 10, the inline sensor 190 is a block including an image sensor. The inline sensor 190 reads an image printed on the recording medium 124, performs necessary signal processing, etc. Variation, optical density, etc.) are detected, and the detection results are provided to the system controller 272 and the print controller 274.

  The print controller 274 performs various corrections (non-ejection correction, density correction, etc.) on the head 250 based on information obtained from the in-line sensor 190, and cleaning operations (nozzles, etc.) such as preliminary ejection, suction, and wiping as necessary. Control to implement recovery operation).

  The system controller 272, print controller 274 (with built-in image buffer memory), and head driver 278 in FIG. 14 correspond to the head controller 70 described in FIG. Note that a mode in which all or part of the processing functions performed by the system controller 272 described in FIG. 14 is mounted on the host computer 350 side is also possible.

[Appendix]
As will be understood from the description of the embodiment described in detail above, this specification includes disclosure of various technical ideas including the invention described below.

  (Invention 1): Image data of M gradations (M ≧ 4) is quantized into (N−1) types of dots having different sizes and N values (M> N> 2) corresponding to no dots. In the image generating apparatus that performs gradation expression by changing the recording rate of each dot for each gradation, the recording rate of the first dot is set to a value other than 0 in the first gradation range, The output gradation is increased by increasing the recording rate of the second dot having a size larger than that of the first dot, and in the second gradation area higher than the first gradation area, the second gradation area has the second gradation area. An image generation comprising: quantization means for increasing the output gradation by increasing the recording rate of the first dot while reducing the recording rate of 2 dots to a fixed value or a value other than 0 apparatus.

  According to the first aspect, the ink amount can be suppressed by using the first dot having a relatively small size as much as possible.

  (Invention 2): In the image generation apparatus according to Invention 1, the quantization means fixes or increases the recording rate of the first dot in a third gradation region higher than the second gradation region. In addition, the output gradation is increased by sequentially setting dots to be used other than the first dot to dots having a large size.

  As a result, in the third gradation region, it is possible to earn a gradation using a large size dot.

  (Invention 3): In the image generation apparatus according to Invention 2, the quantization means calculates a recording rate of dots other than the first dots used in the second gradation region and the third gradation region. The recording rate is set so as not to fall below a recording rate that can cover substantially the entire recording target.

  As a result, even when the recording rate of the relatively small first dots, in which streaks are conspicuous, is increased, the generation of streaks can be suppressed.

  (Invention 4): In the image generation apparatus according to Invention 2 or 3, the quantization means sets the maximum recording rate of each dot in the third gradation region to be smaller as the dot is larger in size. .

  Thereby, the amount of ink can be suppressed and the color reproduction range can be expanded.

  (Invention 5): In the image generating apparatus according to any one of Inventions 1 to 4, the first dot is a dot of the smallest size among the (N-1) types of dots, and the second dot Is a dot having a size next to the first dot.

  Thereby, the ink amount can be appropriately suppressed.

  (Invention 6): In the image generation apparatus according to Invention 5, the quantization means sets the recording rate of the second dots to 0 in a gradation region lower than the first gradation region, and The output gradation is increased by increasing the recording rate of one dot, and in the first gradation region, the recording rate of the first dot is made constant and the recording rate of the second dot is set to be constant. The output gradation is increased by increasing the output gradation. In the second gradation range, the recording rate of the second dot is made constant, and the recording rate of the first dot is increased to increase the output gradation. It is characterized by raising the key.

  Thereby, the ink amount can be appropriately suppressed.

  (Invention 7): In the image generation apparatus according to any one of Inventions 1 to 6, the quantization means sets the first dot recording rate to the first dot in a gradation range equal to or less than the third gradation range. It is characterized in that it is set to be larger than the recording rate of dots other than dots.

  Thereby, the ink amount can be appropriately suppressed.

  (Invention 8): In the image generation apparatus according to any one of Inventions 1 to 7, the quantization means performs quantization using a dither matrix.

  Thereby, the recording rate of each dot can be controlled appropriately.

  (Invention 9): In the image generation apparatus according to Invention 8, the quantization means determines the recording rate of the first dots and the recording rate of the second dots according to a threshold for the dither matrix determined for each gradation. It is characterized by determining.

  Thereby, the recording rate of each dot can be controlled appropriately.

  (Invention 10): In the image generation device according to any one of Inventions 1 to 7, the quantization means performs quantization by using a dither matrix and an error diffusion process in combination.

  Thereby, the recording rate of each dot can be controlled appropriately.

  (Invention 11): A recording head having a recording element capable of forming dots of (N-1) types of sizes, a relative movement means for relatively moving the recording head and the recording medium, and Inventions 1 to 10 One of the image generation apparatuses, and a recording control unit that controls a recording operation of the recording element of the recording head based on the N-value image data generated by the image generation apparatus. Image forming apparatus.

  According to the eleventh aspect, it is possible to provide an image forming apparatus in which the amount of ink is suppressed.

  (Invention 12): Image data of M gradations (M ≧ 4) is quantized into (N−1) types of dots of different sizes and N values (M> N> 2) corresponding to no dots. In the image generation method that performs gradation expression by changing the recording rate of each dot for each gradation, the recording rate of the first dot is set to a value other than 0 in the first gradation region, and The output gradation is increased by increasing the recording rate of the second dot having a size larger than that of the first dot, and in the second gradation area higher than the first gradation area, the second gradation area has the second gradation area. An image generation method characterized by increasing or decreasing an output gradation by fixing or decreasing the recording rate of 2 dots to a predetermined value and increasing the recording rate of the first dot.

  DESCRIPTION OF SYMBOLS 10 ... Nozzle, 20 ... Two-dimensional nozzle arrangement, 21-24 ... Nozzle row, 50 ... Image forming apparatus, 60 ... Recording head, 62 ... Piezoelectric element, 70 ... Head controller, 74 ... Halftone processing part, 78 ... Head Driver, 100 ... Inkjet recording device, 124 ... Recording medium, 170 ... Drawing drum, 172M, 172K, 172C, 172Y ... Inkjet head (recording head), 250 ', 250 "... Head module, 251 ... Nozzle, 272 ... System controller 280 ... Print control unit

Claims (10)

The image data of M gradation (M ≧ 4) is quantized into image data of N values (M>N> 2) corresponding to (N−1) types of dots having different sizes and no dots, and for each gradation. In an image generation apparatus that performs gradation expression by changing the recording rate of each dot,
In the first gradation area, the recording ratio of the first dot is set to a value other than 0, and the output gradation is increased by increasing the recording ratio of the second dot having a size larger than that of the first dot. In the second gradation region higher than the first gradation region, the recording rate of the second dots is fixed or decreased to a value other than 0, and the recording of the first dots is performed. Quantization means to increase the output gradation by increasing the rate ,
The quantization means fixes or increases the recording rate of the first dots in a third gradation range higher than the second gradation range, and uses dots other than the first dots. The output gradation is increased by sequentially increasing the size of the dots, and the recording rate of each dot other than the first dots used in the second gradation area and the third gradation area is further increased. R _l (l = 1 to N−2), ideal dot radii of dots other than the first dot are R _l , and horizontal and vertical recording unit pixel sizes are Lx and Ly, respectively. Sometimes the recording rate r _l is

Is set so as not to fall below a recording rate that satisfies the above and covers the entire recording target . The image generation apparatus according to claim 1 , wherein the quantization unit sets the maximum recording rate of each dot in the third gradation range to be smaller as the dot is larger in size. The first dot is a dot of the smallest size among the (N-1) types of dots, and the second dot is a dot having a size next to the first dot. the image generating apparatus according to claim 1 or 2, characterized. The quantization means sets the recording rate of the second dots to 0 in the gradation range lower than the first gradation range, and increases the recording rate of the first dots to increase the output level. In the first gradation range, the recording rate of the first dots is made constant, and the recording rate of the second dots is increased to increase the output gradation, thereby increasing the first gradation. 4. The output gradation is increased by increasing the recording rate of the first dots in the gradation range of 2, while increasing the recording rate of the second dots. 5 . The image generating apparatus described. The quantization means sets the recording rate of the first dot to be larger than the recording rate of dots other than the first dot in the gradation region below the third gradation region. the image generating apparatus according to any one of claims 1, wherein 4. The quantization means, the image generating apparatus according to any one of claims 1-5, characterized in that quantization is performed using the dither matrix. The quantization means according to claim 6, characterized in that to determine the recording rate and the recording rate of the second dots of the first dot in accordance with a threshold value for said dither matrix determined for each gradation Image generation device. The quantization means, the image generating apparatus according to any one of claims 1 to 5, in combination with a dither matrix and an error diffusion processing and performing quantization. (N-1) a recording head having a recording element capable of forming dots of various sizes;
Relative movement means for relatively moving the recording head and the recording medium;
The image generation apparatus according to any one of claims 1 to 8 ,
Recording control means for controlling a recording operation of the recording element of the recording head based on the N-value image data generated by the image generating device;
An image forming apparatus comprising: The image data of M gradation (M ≧ 4) is quantized into image data of N values (M>N> 2) corresponding to (N−1) types of dots having different sizes and no dots, and for each gradation. In an image generation method for expressing gradation by changing the recording rate of each dot,
In the first gradation area, the recording ratio of the first dot is set to a value other than 0, and the output gradation is increased by increasing the recording ratio of the second dot having a size larger than that of the first dot. In the second gradation region higher than the first gradation region, the recording rate of the second dots is fixed or reduced to a predetermined value, and the recording rate of the first dots To increase the output gradation ,
In the third gradation area higher than the second gradation area, the recording rate of the first dots is fixed or increased, and dots used in addition to the first dots are sequentially increased in size. To increase the output gradation, and in the second gradation area and the third gradation area, the recording rate of each dot other than the first dot to be used is set to r _l ( l = 1 to N-2), where the ideal dot radius of each dot other than the first dot is R _l , and the horizontal and vertical recording unit pixel sizes are Lx and Ly, respectively. the recording rate _{r l,}

Is set so as not to fall below a recording rate that satisfies the above and covers the entire recording target .

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