JP2010260319A - Image forming apparatus, image forming method and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can make resolution higher by using a color nozzle, and at the same time, can make the density of a black density higher, and to provide an image forming method and a program. <P>SOLUTION: This image forming apparatus has a composite image forming means for forming an image by composing an original image and pattern information in order to control the duplication of the original image. The pattern information is constituted of black dots of a process black which is expressed by the mixing of a plurality of color inks, and black dots of a black ink. Then, at least one black dot of the black ink is adjoined to the black dot of the process black. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, an image forming method, and a program for expressing black by mixing color inks.

  In recent years, personal computers, printers, copiers, multifunction devices, and the like have become cheaper and easier to introduce due to technological advances. For this reason, it is possible to easily duplicate documents, and management of confidential documents that are prohibited from being duplicated has become a problem.

  Therefore, an image forming apparatus having a copying function is required to have a function of controlling the copying of confidential documents. Therefore, for example, in Patent Documents 1 to 3, duplication prohibition information is embedded in a confidential document, the duplication prohibition information is detected from the image read by the copier, and the copying operation of the copier is performed according to the detection result. Techniques for controlling are disclosed.

  However, in these methods, unless the resolution of printing and the resolution of reading are the same, the copy prohibition information cannot be accurately detected, and the copying operation of the copying machine cannot be controlled. With the increase in resolution of reading devices, it has become possible to read at a resolution higher than the printing resolution. In some cases, these methods cannot prevent unauthorized copying.

  Recently, an ink jet recording apparatus employing an ink jet recording method is known. This ink jet recording apparatus is capable of recording with high image quality and is relatively inexpensive, and is widely used as a color image output apparatus with the spread of personal computers. The ink jet recording head used in this ink jet recording apparatus has a plurality of nozzles in the sub-scanning direction (paper traveling direction) and is moved in the main scanning direction (direction perpendicular to the paper traveling direction) by the carriage mechanism. The Each nozzle ejects ink droplets at a timing according to the dot pattern data obtained by developing the recording data. As a result, ink droplets from the respective nozzles adhere to the recording medium and printing is performed.

  Since such an ink jet recording apparatus is used as an output device of a personal computer, it is required to increase the speed, improve the image quality, reduce the size, and reduce the cost. The increase in speed can be realized by increasing the ink ejection driving frequency, increasing the number of nozzles, low-resolution printing when the printing resolution is higher than the nozzle resolution, and the like. Further, high image quality can be realized by dot miniaturization and high resolution printing. In order to achieve both high speed and high image quality, high-resolution printing is performed with a large number of nozzles and small dots. However, as the number of nozzles increases, the inkjet recording head becomes larger and costs increase. There is a problem of being connected. Increasing the size of the head also increases the overall size of the ink jet recording apparatus, and also increases vibration and noise when the head moves and increases power consumption. Both of these are in a trade-off relationship. Also, as one of the forms of the ink jet recording apparatus, the ink jet recording head is formed in a long shape arranged at the length of the substantially maximum printing width of the recording medium, and is a line head fixed to the apparatus main body. There is. According to this configuration, it is not necessary to move the inkjet recording head in the main scanning direction, and image formation can be performed only by transporting the recording medium perpendicular to the main scanning direction in the sub-scanning direction, so that high-speed image formation is performed. be able to.

  When these ink jet recording apparatuses are printed with an inexpensive structure at high speed, the printing resolution is lowered, and in some cases, printing is performed at a resolution lower than the reading resolution. In this case, even if an image in which the copy prohibition information is embedded as described above is printed, the copy prohibition information cannot be accurately detected, and the copying operation of the copying machine cannot be controlled.

  Therefore, as a method of increasing the resolution without increasing the number of nozzles in the serial scanning type ink jet printer, a technique of artificially increasing the resolution by devising the arrangement of the nozzles as disclosed in Patent Documents 4 to 6 is also used. Has come to be. In this technique, nozzles of three primary colors (magenta, cyan, and yellow) are arranged on the same scanning line shifted by half the pitch of the black ink nozzles. Recording is performed by using a process black that expresses black by overlaying and mixing color inks, and realizes twice the resolution of color recording without reducing the recording speed.

  Further, even in an ink jet recording apparatus using a line head, nozzles of three primary colors (magenta, cyan, yellow) are arranged on the same scanning line shifted by 1/2 of the pitch of the black ink nozzles to reduce the recording speed. In contrast, when recording monochrome data, it is possible to realize twice the resolution of color recording.

  However, in these methods, the process black expressed by the color mixture of the color inks has a lower density than the black ink single color, so that the copy prohibition information cannot be accurately detected.

  The reason why the density does not increase is that the dominant color changes depending on the order of the ink color layers in accordance with the ink landing order. When another ink is superimposed on the ink that has landed first, the ink that has been deposited after the ink that has landed earlier tends to sink in the depth direction of the paper. Since printing of copy prohibition information in monochrome (gray) printing is an important element for accurately detecting information, it is not preferable that the density is low even at high resolution.

  Therefore, the present invention has been made in view of the above problems, and provides an image forming apparatus, an image forming method, and a program capable of increasing the resolution using a color nozzle and simultaneously increasing the black density. For the purpose.

  In order to solve the above problems, an image forming apparatus according to the present invention includes a composite image forming unit that forms an image by combining an original image and pattern information for controlling reproduction of the original image, and the pattern information is The process black black dots and the black ink black dots expressed by the color mixture of a plurality of color inks, and at least one black ink black dot is adjacent to the process black black dots. Features.

  The image forming method of the present invention forms an image by synthesizing an original image and pattern information for controlling reproduction of the original image, and the pattern information is expressed by a color mixture of a plurality of color inks. The black dot of black ink and the black dot of black ink are characterized in that at least one black dot of the black ink is adjacent to the black dot of the process black.

  The program according to the present invention causes the image forming apparatus to function as a unit that forms an image by combining an original image and pattern information for controlling reproduction of the original image, and the pattern information includes a plurality of color inks. The process black is represented by black dots of process black and black ink, and at least one black dot of black ink is adjacent to the black dot of process black.

  According to the present invention, the color nozzle can be used to increase the resolution and at the same time increase the black density.

1 is a diagram illustrating an example of a configuration of an image forming apparatus according to an embodiment of the present invention. 3 is a block diagram illustrating an example of a configuration of a control unit of the image forming apparatus according to the embodiment of the present invention. FIG. FIG. 2 is a block diagram illustrating an example of a configuration of a head driver of the image forming apparatus according to the embodiment of the present invention. It is a figure which shows an example of the drive waveform at the time of discharging a droplet. It is a figure which shows an example of the drive waveform at the time of discharging a droplet. FIG. 2 is a diagram illustrating an example of a configuration of a recording head of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating an example of a configuration of a recording head of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating an example of a configuration of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the osmosis | permeation to the paper of an ink drop. FIG. 6 is a diagram illustrating an operation in the image forming apparatus according to the embodiment of the present invention. 1 is a diagram illustrating an example of a configuration of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the position of CMYK on color space. It is a figure which shows the position of the process black on color space. FIG. 3 is a diagram illustrating an example of a configuration of nozzle rows in a recording head of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a diagram illustrating an example of a configuration of nozzle rows in a recording head of an image forming apparatus according to an embodiment of the present invention. FIG. 6 is a diagram illustrating an example of a printing result by an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating an example of a configuration of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows an example of formation of the pattern information by the image forming apparatus which concerns on embodiment of this invention. It is a figure which shows an example of formation of the pattern information by the image forming apparatus which concerns on embodiment of this invention.

  Next, embodiments for carrying out the invention will be described in detail with reference to the drawings.

  FIG. 1 is a perspective view showing an example of the configuration of an image forming apparatus according to an embodiment of the present invention. A carriage 4 is movably mounted on guide rails 2 and 3 horizontally mounted on the frame 1, a recording head unit 10 is mounted on the carriage 4, and the carriage 4 is shown in the drawing by a drive source of a motor or the like (not shown). A platen 8 provided with a feed knob 8a that is movable in the direction A and that rotates a recording paper 15 set on the guide plate 5 via a drive gear 6 and a sprocket gear 7 by a drive source (not shown). , And can be conveyed in the B direction in the figure by the pressure roller 9 that presses against the periphery of the platen 8. Further, while the recording head unit 10 is moved and scanned in the main scanning direction (A direction), the recording paper 15 is conveyed in the sub scanning direction (B direction), and ink droplets are ejected from the recording head unit 10 to thereby record the recording paper 15. Print an image on.

  Next, an outline of the control unit of the image forming apparatus will be described with reference to the block diagram of FIG. The control unit 200 also serves as a means for correcting the contour part (means for performing jaggy correction), which controls the entire apparatus, a program including the program according to the present invention executed by the CPU 211, and other fixed items. ROM 202 for storing data, RAM 203 for temporarily storing image data and the like, rewritable non-volatile memory 204 for holding data even while the apparatus is powered off, various signal processing for image data, It includes an ASIC 205 that processes input / output signals for performing image processing for switching and other control of the entire apparatus.

  The control unit 200 includes an I / F 206 for transmitting and receiving data and signals to and from the host side, a data transfer unit for driving and controlling the recording head unit 10, and a drive waveform generating unit for generating a drive waveform. A printing control unit 207 including the head driver (driver IC) 208 for driving the recording head unit 10 provided on the carriage 4 side, and a motor driving unit 210 for driving the main scanning motor 20 and the sub-scanning motor 31. Various sensors such as an AC bias supply unit 212 for supplying an AC bias to the charging roller 34, detection signals from the encoder sensors 43 and 35, and a temperature sensor 215 for detecting an environmental temperature as a factor causing a shift in the dot formation position I / O 213 and the like for inputting a detection signal from. The control unit 200 is connected to an operation panel 214 for inputting and displaying information necessary for the apparatus.

  Here, the control unit 200 transmits image data from the host side such as an information processing device such as a personal computer, an image reading device such as an image scanner, an imaging device such as a digital camera, etc. via an I / F 206 via a cable or a network. Receive. Then, the CPU 201 of the control unit 200 reads and analyzes the print data in the reception buffer included in the I / F 206, performs necessary image processing, data rearrangement processing, and the like in the ASIC 205, and drives the image data to the head drive. The data is transferred from the control unit 207 to the head driver 208. Note that generation of dot pattern data for outputting an image is performed by a printer driver on the host side as will be described later.

  The print control unit 207 transfers the above-described image data to the head driver 208 as serial data, and transmits a transfer clock, a latch signal, a droplet control signal (mask signal), and the like necessary for the transfer of the image data and confirmation of the transfer. In addition to the output to the head driver 208, a drive waveform generator and a head driver composed of a D / A converter, a voltage amplifier, a current amplifier, etc. for D / A converting the pattern data of the drive signal stored in the ROM Drive waveform selection means for generating a drive waveform composed of one drive pulse (drive signal) or a plurality of drive pulses (drive signal) and outputting the drive waveform to the head driver 208.

  The head driver 208 selectively selects a drive signal constituting a drive waveform supplied from the print control unit 207 based on image data corresponding to one line of the print head unit 10 input serially. The recording head unit 10 is driven by applying to a driving element (for example, a piezoelectric element as described above) that generates energy for ejecting droplets. At this time, by selecting a driving pulse constituting the driving waveform, for example, dots having different sizes such as large droplets (large dots), medium droplets (medium dots), and small droplets (small dots) can be distinguished. it can.

  Further, the CPU 201 detects a speed detection value and a position detection value obtained by sampling a detection pulse from the encoder sensor 43 constituting the linear encoder, and a speed target value and a position target value obtained from a previously stored speed / position profile. Based on the above, a drive output value (control value) for the main scanning motor 20 is calculated, and the main scanning motor 20 is driven via the motor driving unit 210. Similarly, based on the speed detection value and position detection value obtained by sampling the detection pulse from the encoder sensor 35 constituting the rotary encoder, and the speed target value and position target value obtained from the previously stored speed / position profile. Then, a drive output value (control value) for the sub-scanning motor 31 is calculated, and the sub-scanning motor 31 is driven via the motor driver 210 and the motor driver.

  Next, an example of the print control unit 207 and the head driver 208 will be described with reference to FIG. As described above, the print control unit 207 generates a drive waveform (common drive waveform) composed of a plurality of drive pulses (drive signals) within one printing cycle, and outputs a print waveform. And a data transfer unit 302 that outputs a clock signal, a latch signal (LAT), and droplet control signals M0 to M3. The droplet control signal is a 2-bit signal that instructs each droplet to open and close an analog switch 317, which will be described later, of the head driver 208. The droplet control signal is a waveform to be selected according to the printing cycle of the common drive waveform. State transition is made to level (ON), and state transition is made to L level (OFF) when not selected.

  The head driver 208 receives a transfer clock (shift clock) and serial image data (gradation data: 2 bits / CH) from the data transfer unit 302, and each register value of the shift register 311 by a latch signal. A latch circuit 312 for latching, a decoder 313 that decodes gradation data and control signals M0 to M3 and outputs the result, and a logic level voltage signal of the decoder 313 is converted to a level at which the analog switch 315 can operate. Level shifter 314, and an analog switch 316 that is turned on / off (opened / closed) by the output of the decoder 313 provided via the level shifter 314.

  The analog switch 316 is connected to the selection electrode (individual electrode) 154 of each piezoelectric element 121, and the common drive waveform from the drive waveform generation unit 301 is input thereto. Therefore, when the analog switch 316 is turned on in accordance with the result of decoding the serially transferred image data (gradation data) and the control signals MN0 to MN3 by the decoder 313, a required drive signal constituting the common drive waveform is obtained. Passing (selected) is applied to the piezoelectric element 121.

  Next, an example of the drive waveform will be described with reference to FIGS. As shown in FIG. 4, the drive waveform generation unit 301 includes a waveform element that falls from the reference potential Ve and a waveform element that rises from the state after the fall within one printing cycle (one drive cycle). A drive signal (drive waveform) composed of eight drive pulses P1 to P8 is generated and output. On the other hand, the driving pulse to be used is selected by the droplet control signals M0 to M3 from the data transfer unit 302.

  Here, the waveform element in which the potential V of the drive pulse falls from the reference potential Ve is a drawing waveform element in which the piezoelectric element 121 contracts and the volume of the pressurized liquid chamber 106 expands. Further, the waveform element that rises from the state after the fall is a pressurizing waveform element that causes the piezoelectric element 121 to expand and the volume of the pressurized liquid chamber 106 to contract.

  Then, when forming a small droplet (small dot) by the droplet control signals M0 to M3 from the data transfer unit 302, the drive pulse P1 is selected as shown in FIG. 5A to form a medium droplet (medium dot). When driving, the driving pulses P4 to P6 are selected as shown in FIG. 5B, and when forming large droplets (large dots), the driving pulses P2 to P8 are selected as shown in FIG. In this case (when the meniscus is vibrated without droplet ejection), the fine drive pulse P2 is selected and applied to the piezoelectric element 121 of the recording head unit 10 as shown in FIG.

  FIG. 6 is a diagram illustrating an example of the configuration of the recording head unit according to the embodiment of the invention. This recording head unit is mounted on the image forming apparatus shown in FIG. In FIG. 6A, the recording head unit 10 includes recording heads 11 and 12 corresponding to the respective colors. Usually, recording is performed by ejecting ink droplets on the surface of the paper from the recording head unit 10 in which the recording heads 11 and 12 are integrated. These recording heads 11 and 12 have a plurality of ink ejecting nozzles, and can eject a plurality of sizes of ink having different droplet amounts. FIG. 6B shows a state in which the droplets ejected from the recording head unit 10 are recorded on the recording paper 15.

  FIG. 7 is a diagram illustrating an example of a recording head according to an embodiment of the present invention. The head is composed of two heads 11 and 12, and each head is arranged in a row in the main scanning direction with nozzle rows N1 and N2 each composed of a plurality of nozzles 16n that discharge droplets arranged in a direction perpendicular to the main scanning direction. is doing. Here, the nozzle row K (N1) that discharges the black ink is arranged so as to be shifted in the sub-scanning direction by 1/2 pitch (nozzle pitch) between the nozzles 16n with respect to the other nozzle rows.

  FIG. 8 is a diagram for explaining an operation example of the recording head unit 10 at the time of recording on the recording paper 15. Ejection units 11 and 12 having ink ejection nozzles are configured in the order of black, cyan, magenta, and yellow (hereinafter referred to as K, C, M, and Y) with respect to the main scanning forward recording direction. However, it is not necessarily limited to this arrangement order, color, and number of colors. Depending on the characteristics and design philosophy of the ink, a unit with a different arrangement order or more colors may be used. . For example, other combinations capable of expressing black by color mixing, such as a combination of R, G, and B, or a combination of light cyan, light magenta, and light yellow can be used. In addition, when black is expressed by a mixed color, two or more colors of CMY ink, light cyan ink, light magenta ink, and light yellow ink may be combined.

  FIG. 9 is a cross-sectional view showing an example of the colorant distribution inside the recording paper 15 when the pigment-based ink is driven into the same location. The colorant contained in the ink that was previously ejected (A color drop in this example) stays on the surface of the paper, and the colorant that was ejected later (B color drop in this example) is inside the paper. It ’s sinking in. As a result, the characteristics of the colorant on the recording surface of the recording paper 15 become stronger, and the A color becomes the dominant color. The colorant fixing characteristics described above tend to be stronger in the pigment-based ink shown in this example than in the dye-based ink. In other words, when performing process black image formation in which a plurality of color inks are juxtaposed or recorded at the same position to represent black, it is necessary to consider changes in density and tone due to the overlapping order of colors. In particular, when bi-directional recording is employed in order to improve the printing speed, the dominant color differs between forward recording and backward recording, which may result in a density or color tone that is not suitable for black expression.

FIG. 10 is a diagram showing an example of the arrangement of each color recording head and the dominant / subject color in one-way recording, and shows the superiority or inferiority of each color component in process black. The control strength expected when recording is performed only when the recording head unit that reciprocates on the recording paper 15 moves in the forward direction, and when recording is performed only when the recording head unit moves in the backward direction is shown below. Note that the following relational expressions are simplified for the sake of explanation. The expected strength of control is
When recorded during movement in the forward direction: C>M> Y (1)
When recording when moving in the backward direction: Y>M> C (2)
It is. It should be noted that the equations (1) and (2) also hold for the dominant color / subject color during bidirectional recording in which recording is performed in both the forward and backward directions.

FIG. 11 is a diagram showing an example of the alignment of each color recording head and the dominant / subjected color in the ink jet recording apparatus using the above-described line head, and shows the superiority or inferiority of each color component in process black. In a recording apparatus using a line head, the color ink overlap order is uniquely determined by the arrangement order of the color recording heads and the paper discharge direction of the recording paper 15, and the relational expression indicating the dominant strength is also shown below. It is. Note that the following relational expressions are simplified for the sake of explanation.
Expected strength of control: C>M> Y (3)

  The above-mentioned dominant strength is established in the overlapping portion of the ink. In addition to the overlap of the inks ejected at the same position, in the portion where the spread of the landed ink and the ink landed in the vicinity thereof overlaps. Also holds.

  In order to realize a density and color tone suitable for the expression of black by process black, it is important to use an ink having a high black density as a dominant color, but the method of realizing it differs depending on the configuration and recording method of the head.

  In the above-described one-way recording or ink jet recording apparatus using a line head, the order of ink overlap is uniquely determined, so the arrangement order of the nozzles that eject each ink is determined so that the density and color tone are suitable for process black. There is a need.

  For example, considering that ink with high black density is the dominant color contributes to making process black with high black density, if C, M, and Y are three colors, C or M is landed first. It is desirable to land Y having a low black density last. Here, the black density is a value obtained by measuring an arbitrary ink through a black density measurement filter, and each ink has a black density. For example, black ink has a large black density, and Y ink has a black density. Small.

  Similarly, considering that ink having a color difference distance from ideal black as the dominant color contributes to making process black whose color tone is close to ideal black, for example, C, M, Y In the case of three colors, it is desirable that C or M is landed first, and Y that is the farthest from the ideal black color difference distance is landed last. Here, “ideal black” means black recorded with black ink or black with high black density.

  For example, the color difference distance in the L * a * b * color space may be used as the color difference distance. FIG. 12 is a diagram illustrating an example of a colorimetric value distribution of C, M, Y, and K inks on the a * b * plane in the L * a * b * color space. Here, including L * not shown in FIG. 12, the L * component of the C ink colorimetric value is Cl, the a * component is Ca, the b * component is Cb, and the L * component of the M ink colorimetric value is Ml. The a * component is Ma, the b * component is Mb, the L * component of the Y ink colorimetric value is Yl, the a * component is Ya, and the b * component is Yb. At this time, if the color difference distance between C ink and black (gray) is ΔEc, the color difference distance between M ink and black (gray) is ΔEm, and the color difference distance between Y ink and black (gray) is ΔEy, each color C , M, Y and the color difference distance between black (gray) in the L * a * b * color space is established by the following relational expression.

  Further, the L * component of the K ink colorimetric value is Kl, the a * component is Ka, the b * component is Kb, the color difference distance between the C ink and the K ink is ΔEck, and the color difference distance between the M ink and the K ink is If ΔEmk, the color difference distance between Y ink and K ink is ΔEyk, the color difference distance between each color C, M, Y ink and K ink is expressed by the following relational expression.

  Further, when printing is performed using an ink head whose ink droplet size can be changed, the gray balance may be adjusted by adjusting the droplet size of the color ink so as to be close to the ideal black. For example, the ink that is landed first, the density and color tone of process black is closer to the ideal black, the ink that is landed later, the density and color tone of process black is kept away from the ideal black, and the ink is landed last. The amount of droplets is equal to or less than that of other color inks.

  In the above-described bidirectional recording, since the ink overlap order is reversed between the forward path and the backward path, even if a process black having a density and color tone close to ideal black can be configured in the forward path, There may be a large color difference from process black, which is composed of the reversed stacking order. In this case, the color difference between the process black in the forward path and the backward path is conspicuous, leading to deterioration in image quality. Therefore, the arrangement order of the nozzles that discharge each ink so that the color difference between the process black according to the ink stacking order in the forward path and the process black according to the ink stacking order in the return path is small and the density and color tone are suitable for the process black. It is necessary to adjust the amount of ink ejected.

  FIG. 13 is an example of the colorimetric value distribution of each color mixing dot when the overlapping order of the C, M, and Y inks on the a * b * plane in the L * a * b * color space is changed. .

  When obtaining the color difference distance with the reverse superposition order in each color mixture dot, the L * component of any color mixture dot F is Fl, the a * component is Fa, the b * component is Fb, and the ink constituting the F The color difference distance ΔEfg between F and G is expressed by the following relational expression when the L * component of the mixed color dot G configured in the overlapping order and the overlapping order of reverse order is G1, the a * component is Ga, and the b * component is Gb. It holds.

  In addition, when an L * component of an arbitrary color mixing dot H is H1, an a * component is Ha, and a b * component is Hb, a color difference distance ΔEh from black (gray) in the L * a * b * color space is The following relational expression holds.

  Further, the color difference distance ΔEhk between an arbitrary mixed color dot H and K ink is established by the following relational expression.

  Also, as in the case of the one-way recording described above, considering that ink having a color tone close to ideal black is the dominant color, it contributes to creating process black whose color tone is close to ideal black. Alternatively, if there are three colors C, M, and Y on the return path, it is desirable to land C or M first, and finally land Y that is farthest from the ideal black tone. At this time, the ink that is landed first improves the density and color tone of process black, and the ink that landes later deteriorates, so the amount of ink droplets that land last is equal to or less than that of other color inks. It is also good.

  However, since the ink stacking order is reversed in the forward path or the backward path, Y furthest from the ideal color tone of black is landed first, and C or M is landed thereafter. At this time, the ink to be landed first, the density and color tone of the process black are kept away from the ideal black, and the ink to be landed later, the density and color tone of the process black are brought close to the ideal black, so that they are landed first. The amount of ink drops is equal to or less than that of other color inks.

  In addition, black dots due to process black made by superimposing multiple colors of color ink tend to bleed more easily than black dots due to black ink alone, and the density and color tone are also completely black (achromatic). It is difficult and may be slightly tinted. Therefore, the amount of drops of the color ink constituting the process black may be smaller than the amount of drops of the black ink so that it is less noticeable than the black dots formed by the black ink.

  In addition, the selection range of the ink droplet size includes a selection that ink is not applied. Even if the droplet size is adjusted, the deterioration of quality due to the conspicuousness of process black dots at the end of a monochrome image is unavoidable. It can also be avoided.

  Hereinafter, a recording head capable of carrying out the present invention will be described. In FIG. 14A, the nozzles of the recording head that discharge each of a plurality of color inks capable of forming black dots by mixing colors are arranged side by side in the direction in which the recording head moves relative to the recording medium. Is a recording head in which the nozzles of the recording head for discharging the ink are arranged with a ½ pixel pitch shift in the vertical direction with respect to the nozzle array of the color ink group.

  Further, the K ink may have different components from other color inks, for example, the K ink may be a pigment ink and the other ink may be a dye. From the discharge mechanism, as shown in FIG. The nozzle row that discharges may be arranged at a position away from other nozzle rows. This is not limited to K ink, but may be a nozzle that ejects other ink, or may be an ink ejection mechanism that is not limited to pigment or dye ink but is composed of other components.

  When recording black dots of black ink and process black black dots that are expressed by overlapping color inks, if the distance between nozzles that discharge the same color is 150 dpi pitch, 300 dpi in one scan. Images can be recorded. It is also possible to record an image of 300 dpi in the first scan and record an image of 600 dpi so as to fill the gap in the second scan.

  FIG. 15 shows the arrangement of the recording head nozzles that discharge a plurality of color inks capable of forming black dots by color mixing in a direction in which the recording head moves relative to the recording medium, and discharges black ink. This is a recording head in which the nozzles of the recording head are arranged with a ¼ pixel pitch shifted in the vertical direction with respect to the arrangement of the nozzles of the existing color ink group.

  When using this recording head to record black dots of black ink and black dots of process black that are expressed by overlapping color ink, if the distance between nozzles that discharge the same color is 150 dpi pitch, A 600 dpi image can be recorded so that the interval recorded in the first scan is filled in in the second scan. In addition, a 1200 dpi image can be recorded by four scans.

  As described above, when the recording head performs recording n times on the recording area equal to or less than the recording width of the recording head, the shift amount between the nozzle that ejects the black ink and the nozzle that ejects the color ink is set to 1 / n pixels. By setting the pitch (n is an integer greater than or equal to 2) or 1 / (2n) pixel pitch (n is an integer greater than or equal to 1), the print head scans the print medium multiple times to form an image. In the ink jet recording apparatus, the recording method in the present invention is realized.

  Note that black ink lines and process black lines may be alternately recorded as shown in FIG. 16A in a direction perpendicular to the direction in which the recording head scans the recording medium a plurality of times. However, it may be recorded for each of a plurality of lines as shown in FIG.

  In addition, when the recording head performs recording on the recording area equal to or smaller than the recording width of the recording head by performing n scans, recording is performed not only when all nozzles are used but also when all nozzles are not used for printing control. May be performed.

  Furthermore, in an inkjet recording apparatus using a line head, a plurality of elongated recording heads may be arranged in the paper feed direction as shown in FIG. 17A, or as shown in FIG. A plurality of recording heads having a size used for a serial head may be arranged in a zigzag pattern and arranged in the paper discharge direction. By doing so, the recording method of the present invention can be realized.

  Further, as a shape of a recording apparatus using the above-described line head, one having a mechanism for transporting a recording medium in a plane, or one having a mechanism for rotating a recording medium using a drum-shaped transporting means is available. Can be mentioned.

  Further, when the recording head is scanned relative to the recording medium, if the recording apparatus includes a mechanism for transporting the recording medium in a plane, the recording is mainly performed by one scanning. By transporting the sheet in the reverse direction later, the second scanning / recording can be performed, and the operation / recording can be performed a plurality of times in the same manner.

  In addition, if the recording apparatus has a mechanism for rotating a recording medium using a drum-shaped transport unit, after the first scanning / recording, the recording medium is returned to the start position of the first scanning. Therefore, a plurality of times of scanning / recording can be easily performed.

  Also in such a recording apparatus, the nozzles of the recording head that discharge each of a plurality of color inks that can form black dots by mixing colors are arranged in the paper feed direction, and the nozzles of the recording head that discharge black ink are arranged as color inks. The recording method according to the present invention can be realized by disposing 1 / n (n is an integer of 2 or more) pixel pitch in the vertical direction with respect to the arrangement of the nozzles of the group.

  In the example of the recording head described above, the distance between nozzles that discharge the same color is set to 150 dpi pitch, and the arrangement of the ink discharge nozzles is K, C, M, and Y. However, this arrangement order, color, number of colors, and nozzles are not necessarily limited. It is not limited to the pitch width, but may be a different arrangement order, a unit to which more colors are added, or a narrower nozzle pitch width depending on the characteristics and design concept of the ink.

  Note that the monochrome (gray) image has a high resolution and a high density by using the control of the stacking order or the drop amount of the color inks constituting the process black as described above when the monochrome printing mode is selected. Can do.

  In the above description, an inkjet image forming apparatus that discharges liquid ink has been described as a representative example. However, as its discharge mechanism, film boiling using a piezoelectric element using a piezoelectric element or a heating element that generates heat when energized is used. The present invention can be applied to an image forming apparatus that uses an equation. Further, as described above, the present invention can be applied not only to a serial head but also to a line head type image forming apparatus.

  Next, a pattern for controlling replication in the present invention will be described. In the recording head according to the present invention, in order to increase the resolution in one scan, the black nozzle and the color nozzle have a 1 / n pixel pitch (n is 2 as shown in FIGS. 14 and 15, for example). The nozzle position is shifted by 1 / (2n) pixel pitch (n is an integer of 1 or more). Therefore, the pattern image for controlling duplication is composed of black and white black dots as shown in FIG. 18 and a combination of black dots using the color inks described so far. To do.

  As the duplication control information pattern, as shown in A of FIG. 18, a pattern in which black dots of black ink of black ink are arranged one by one vertically, or B and C of FIG. A pattern in which a plurality of patterns A are arranged, and a pattern in which black dots by color ink are sandwiched between black dots by black ink in the nozzle row direction as shown in FIG. This is because black ink dots are placed next to black dots by color ink, and the black ink blots contribute to improving the black density of the black dots of color ink, and the pattern information detection accuracy at the time of reading It is because it can raise.

  Therefore, examples that are not suitable as a plurality of control information patterns include a pattern of only black dots of color ink as shown in E of FIG. 18, a black dot pattern of only black ink as shown in F of FIG. As in H, there is a pattern in which black dots by black ink and black dots by color ink are not adjacent.

  As the pattern image, for example, an image as shown in FIG. In addition to the triangle in FIG. 19A and the circle in FIG. 19B, the pattern image may be a straight line, a square, a circle, an ellipse, or the like. In FIG. 19, two types are prepared for each pattern image, but the number of types of pattern images representing the prohibited copy code is not limited to two, and may be three or more types. However, these patterns are configured by using a pattern in which black dots made of black ink and black dots made of color ink are adjacent to each other. Here, the pixel size of one pattern image is 12 × 12 pixels, but there are various other pixel sizes.

  As a pattern image printing method, the pattern image may be repeatedly printed on the paper.

  Next, print control that can be used in the present invention will be described. Here, a case where cross control is applied will be described. “Cross control” refers to control in which both driving are cooperatively overlapped in driving in the main scanning direction of the carriage on which the recording head is mounted and in driving in the sub-scanning direction when transporting the recording medium. To speed up the printing process, ideally, the main scan (CR) is started before the sub-scan (LF) is completed, and the LF is stopped just when the CR reaches the recording area. The timing is managed. If such time management is not performed, the CR reaches the recording area while the LF is operating, causing skew recording, and conversely, no recording is performed without overlapping with the LF driving. Will cause an unacceptable section of CR.

  The image forming method and the image forming apparatus of the present invention have been described above. However, the application of the present invention is not limited to such a configuration, and the above-described image forming method is applied to the host computer and the image forming apparatus. Either of them may be provided, or an image forming system in which everything is integrally formed may be used.

  In the above embodiment, the CPU of the host computer may perform all of the series of image processing, or a part or all of the processing may be performed by the image forming apparatus.

  Further, the present invention may be in the form of a program for causing a computer to execute the above-described image forming method, or in the form of a computer-readable recording medium on which the program is recorded. Here, the program includes a printer driver that can be incorporated into a computer.

  The present invention has been described above by the preferred embodiments of the present invention. While the invention has been described with reference to specific embodiments thereof, various modifications and changes can be made to these embodiments without departing from the broader spirit and scope of the invention as defined in the claims. is there.

  In the image forming apparatus according to the present invention, the composite image forming unit includes a recording head unit including a plurality of recording heads in which a plurality of nozzles for ejecting ink are arranged, and the plurality of nozzle rows include: 1 / n pitch with respect to the nozzle pitch of the plurality of color ink nozzle rows, including the black ink nozzle row and the plurality of color ink nozzle rows, where n is an integer. It may be shifted.

  In the image forming apparatus according to the present invention, when forming the process black black dots included in the pattern information, a difference in black density between the process black black dots and the black ink black dots is minimized. As described above, at least one of the control of the color ink stacking order and the control of the drop amount of each color ink may be performed.

  Further, in the image forming apparatus according to the present invention, when forming the process black black dots included in the pattern information, the color difference between the process black black dots and the black ink black dots is minimized. You may make it perform at least one of control of the stacking order of the said color ink, and control of the drop amount of each said color ink.

  Further, the image forming apparatus according to the present invention may overlap the color inks in descending order of black density when forming the process black black dots.

  In the image forming apparatus according to the present invention, when forming the process black black dots, the color inks may be stacked in order of increasing color difference from the black ink.

  The image forming apparatus according to the present invention may repeatedly print the pattern information on a sheet.

DESCRIPTION OF SYMBOLS 10 Recording head unit 11 Recording head 12 Recording head 15 Recording paper

JP 2000-76458 A JP 2001-189855 A JP 2001-346032 A Japanese Patent Laid-Open No. 02-026753 Japanese Patent No. 3533771 JP 2001-171153 A

Claims (9)

A composite image forming unit that forms an image by combining the original image and pattern information for controlling reproduction of the original image;
The pattern information is composed of black dots of process black and black dots of black ink expressed by a mixed color of a plurality of color inks,
An image forming apparatus, wherein at least one black dot of the black ink is adjacent to the black dot of the process black. The composite image forming unit has a recording head unit on which a plurality of recording heads in which a plurality of nozzles for ejecting ink are arranged are mounted,
The plurality of nozzle rows include the black ink nozzle row and the plurality of color ink nozzle rows,
2. The image forming apparatus according to claim 1, wherein the nozzle row of the black ink is shifted by 1 / n pitch with respect to the nozzle pitch of the plurality of color ink nozzle rows when n is an integer. .   When forming the process black black dots included in the pattern information, the color inks are stacked in order to minimize the difference in black density between the process black black dots and the black ink black dots. The image forming apparatus according to claim 1, wherein at least one of control and control of a drop amount of each color ink is performed.   When the black dots of the process black included in the pattern information are formed, the color ink overlap order is controlled so that the color difference between the black dots of the process black and the black ink is minimized. The image forming apparatus according to claim 1, wherein at least one of the control of the drop amount of each color ink is performed.   5. The image forming apparatus according to claim 1, wherein when forming the process black black dots, the color inks are superposed in descending order of black density. 6.   5. The image forming apparatus according to claim 1, wherein when forming black dots of the process black, the color inks are stacked in order of increasing color difference from the black ink. 6.   The image forming apparatus according to claim 1, wherein the pattern information is repeatedly printed on a sheet. An image is formed by combining the original image and pattern information for controlling reproduction of the original image,
The pattern information is composed of black dots of process black and black dots of black ink expressed by a mixed color of a plurality of color inks,
An image forming method, wherein at least one black dot of the black ink is adjacent to the black dot of the process black. The image forming apparatus
The original image and the pattern information for controlling the reproduction of the original image are combined to function as a means for forming an image,
The pattern information is composed of black dots of process black and black dots of black ink expressed by a mixed color of a plurality of color inks,
A program characterized in that at least one black dot of the black ink is adjacent to the black dot of the process black.

Images