CN100439103C - Image reproduction and forming device, printer driver and data processing device - Google Patents

Abstract

An image reproducing and forming apparatus comprises a recording head (14) configured to eject liquid droplets of at least one color and capable of bidirectional recording, and a controller (100) configured to control the amount of. liquid adhering to a recording paper (3) so as to reduce color difference occurring in the bidirectional recording. The controller includes a gamma correction unit (133) configured to selectively perform a controlled gamma correction using a controlled gamma value adjusted so as to reduce the color difference or an ordinary gamma correction using an ordinary gamma value.

Description

Image reproduction and forming device, printer driver and data processing device

technical field

The present invention generally relates to an image reproducing and forming device, a printer driver, and a data processing device, and more particularly, the present invention relates to an image reproducing and forming device capable of bidirectional printing while preventing occurrence of chromatic aberration. The present invention also relates to an inkjet type image reproducing and forming apparatus that prevents leakage of charges in a statically attracted paper conveying mechanism. The present invention also relates to a printer driver for processing data in order to prevent chromatic aberration and/or charge leakage in bidirectional recording, and to a data processing device loaded on the printer driver.

Background technique

An "inkjet recording device" is a type of image reproducing and forming device. Examples of inkjet recording devices include inkjet printers and facsimile machines or copiers that record using an inkjet mechanism. An inkjet recording device reproduces an image by ejecting ink droplets or other liquid droplets onto a recording medium such as paper, an OHP sheet, or any other medium to which droplets can adhere. The inkjet recording apparatus is advantageous in that it is capable of high-speed, high-resolution recording operations. Other advantages of inkjet recording devices are relatively low running costs, low noise, and easy color printing with a variety of ink colors.

In the beginning, the inkjet recording apparatus was rapidly developed for personal use because it was cheaply priced and high-quality images were obtained while using dedicated paper. It has been used in recent years and continues to be used also in offices as a color recording device, occupying the mainstream instead of electrophotographic laser printers.

In order to allow inkjet recording devices to be developed for office use, two problems must be solved. The first problem is that it can be applied to plain paper, which is a question of cost. When using dedicated paper, the inkjet recording device reproduces high-quality printed images as beautiful as photos.

Special purpose paper is generally expensive, and this makes it difficult for offices and companies to introduce inkjet recording devices where strict cost management is required. Typically, printed materials used in the office do not require the same high image quality as photos and pictures. However, another disadvantage of inkjet recording devices is that high image quality cannot be obtained unless dedicated paper is used.

At the same time, the ink composition has been improved to be suitable and suitable for printing on plain paper. In fact, many attempts have been made, including the development of dye inks with low water permeability, the use of ink fixing aids, and the development of pigment inks. As a result of these efforts, inkjet printers can reproduce images on plain paper used in offices or copy paper recently with the same image quality as that obtained by laser printers.

The second problem is recording speed. Generally, an inkjet recording apparatus performs a recording operation by ejecting ink droplets onto paper while repeatedly driving the recording head back and forth multiple times. This is the so-called "line by line" basic printing technology. One disadvantage of serial-based printing is the slow recording rate compared to electrophotography, which performs printing operations on a "side-by-side" or "page-by-page" basis, since the recording head is smaller than the paper size.

In order to overcome the shortcomings of the recording rate, attempts have been made to improve the efficiency of the scanning sequence; for example, increasing the ink ejection cycle to shorten the printing time, increasing the size of the recording head, adopting bidirectional printing technology to reduce the number of scans, and those that only scan the image data to actually print the scan area (minimum path control). For small or medium volume print jobs, some machines have achieved print speeds faster than electrophotographic printing.

Together with the aforementioned efforts to improve image quality and recording speed, inkjet recording devices have become extremely attractive office products. In particular, an inkjet recording apparatus has a cost advantage compared with a laser printer, and since it is manufactured compactly, its use as a desktop printer is being realized.

However, unlike a laser printer or an offset printing machine with a mechanism for fixing color additives onto a paper surface, an inkjet recording device uses a liquid color additive capable of penetrating or penetrating paper when fixing ink. Thus, problems and constraints associated with the infiltration process always accompany inkjet recording devices.

Examples of such problems and constraints include swelling of paper under the influence of water contained in the ink. When the swollen or waved paper comes into contact with the printhead, a defective image is formed on the paper due to subsequent secondary ink transfer. From the viewpoint of improving the accuracy of the ink droplet ejection position, it is necessary to set the distance between the print head and the paper as small as possible. However, unlike inkjet-specific paper, plain paper for office use is not subjected to anti-blowing treatment. Thus, if the gap setting scheme is too strict, a smooth recording operation is hindered due to paper swelling.

There is a time lag between the ink drop landing and beginning to expand, which corresponds to the time it takes for the ink to penetrate the paper. Thus, secondary ink transfer problems can be avoided by increasing the recording speed, compensating for slight image degradation, because recording speed is prioritized over image quality in image output for office use.

Another problem is that ink that adheres to the paper earlier will be brighter in color than ink that lands later on the same spot. This problem is related to the ink fusing process. In bidirectional printing mode, which allows the printhead to print as it moves from left to right and right to left, the order in which ink adheres to the paper is on the outbound (left to right) and return (right to left) changes between. For this reason, a color difference may occur between the outbound swath and the return swath. This phenomenon can be observed when bands cover the actual image to be printed. (It should be noted that the terms printing, imaging, image reproduction and recording are used synonymously in this context).

To date, no aggressive action has been taken to address chromatic aberration because image quality degradation due to chromatic aberration is less severe than secondary ink transfer damage to prints, and because such banding occurs primarily at high speed recording mode, where recording speed is prioritized in high-speed recording mode, a certain degree of image quality degradation is acceptable.

JP11-320926A discloses a method for solving the problem of chromatic aberration generated in bidirectional recording operation (it is called "chromatic aberration in bidirectional recording"). In this publication, the recording head has two units whose colors are set oppositely. The two units are set offset by one resolution pitch from each other, imaging every other row while overlapping colored inks on the outbound and return passes. Therefore, no color difference occurs regardless of whether a one-way recording operation or a bidirectional recording operation is performed.

Another method for correcting chromatic aberration is disclosed in JP07-29423B. With this method, the recording operation is performed at every other point on the outbound trip, and the skipped points are compensated on the return trip.

Since the technique disclosed in JP11-320926A employs two head units, the subsystem units for maintaining and restoring the recording heads become doubled, resulting in an unnecessary cost increase. The head cleaning time is also doubled, and the possibility of ink intermixing by the scraper used to clean the nozzle surface increases.

With the technique disclosed in JP07-29423B, the same line is scanned twice due to alternate recording (skipping every other dot), and the actual recording time is substantially the same as in the unidirectional recording mode. This means that the high speed feature, which is one of the advantages of bi-directional printing, cannot be achieved.

Turning now to the problem of swelling of the woody fibers (pulp) contained within the paper due to moisture or the water component of the ink, the areas of the paper where ink droplets adhere become wavy. This phenomenon is called wrinkled appearance. Because of the wrinkled appearance, the surface of the paper becomes uneven, and the distance between the paper and the nozzle surface of the recording head varies depending on the position within the paper. Where the wrinkled appearance is severe, the paper can contact the nozzle surface in the worst case, as described above. In this case, both the nozzle surface and the paper are stained, and the reproduced image quality is extremely degraded. In addition, the ink landing position changes and shifts from the correct position due to the wrinkle appearance effect, and the image cannot be accurately reproduced on the paper.

In order to overcome this problem, JP2000-190473A, JP2001-235945A and JP2001-305873A propose the use of charging belts to keep paper flat by electrostatic attraction in inkjet recording devices (or electrophotographic devices). The charging belt rotates to feed the paper to the recording position. By holding the paper using electrostatic attraction, the paper is prevented from floating on the charging belt, and the surface of the paper can be kept flat.

In JP2000-190473A, an image recording device employs a conveyor belt that conveys paper using electrostatic attraction, and a voltage applying device is in contact with the conveyor belt. The conveyor belt is charged by the voltage applying means, so that a belt-shaped charge distribution pattern is formed on the conveyor belt. In JP2001-235945, electric charge is applied to the paper or the recording medium held on the conveyor belt by the charging means.

However, if charges leak from the paper due to some reason during paper conveyance, the electrostatic attraction between the paper and the conveyor belt becomes weak, and the paper conveyance state deteriorates.

To overcome this, in JP2001-190473A, a moving device is provided to move at least a part of a power source for applying a voltage to an electrostatic generator located above a paper holding surface of a conveyor belt. This setup helps prevent ink from getting into the power supply and preventing unwanted short circuits.

Since ink droplets are ejected onto a recording medium such as paper in an inkjet type image reproducing and forming apparatus, there is always a possibility that charge leakage may occur due to wet components contained in the ink, wherein the ink absorbs Inside the paper held by the electrostatic attraction tape. The degree of charge leakage depends on the amount of ink adhered to the paper.

Although the image reproducing/forming apparatus disclosed in JP2000-190473A is suitable for preventing electric charge leakage from a conveyor belt, it does not aim at preventing electric charge leakage occurring due to ink itself ejected or absorbed into paper.

Contents of the invention

The present invention was made in view of the above-mentioned problems in the prior art, and an object of the present invention is to realize high-speed, high-quality image reproduction by effectively correcting chromatic aberration in a bidirectional recording operation without cost increase or speed decrease.

Another object of the present invention is to prevent charge leakage caused by liquid droplets landing on a recording medium while maintaining stable sheet conveyance performance and reproducing high image quality on the recording medium.

In order to achieve these objects, the amount of ink adhering to the recording medium can be effectively controlled so as to prevent one of color shift and charge leakage in bidirectional recording when an electrostatic attraction tape is used.

In one aspect of the present invention, an image reproduction and forming apparatus includes a recording head capable of ejecting liquid droplets of at least one color and capable of bidirectional recording, and a controller for controlling adhesion to the recording head. The amount of liquid on the paper in order to reduce the color difference produced in bidirectional operation.

Preferably, the controller has a determination unit that determines whether the object to be output is text. When the object to be output is text, the controller does not perform the process of reducing the color difference. Alternatively, the determination unit determines the object to be output and the number of colors used in the bidirectional recording. In this case, when the object to be output is not text and the number of colors is one, the controller does not perform the process of reducing the color difference.

In a preferred example, based on the determination result of the determination unit, the controller selectively performs controllable gamma correction for controlling the amount of liquid adhesion in order to reduce chromatic aberration, or performs ordinary image correction not for correcting chromatic aberration .

In a preferred example, the controller uses controllable grayscale values to perform controllable image correction and normal grayscale values to perform normal image correction.

The controllable gray value is the product of the normal gray value and the coefficient K, wherein K is set in the range of 0.35 to 0.65. More preferably, the coefficient K ranges from 0.5 to 0.6.

When performing duplexing in bidirectional recording, the controllable grayscale value is obtained by multiplying the above product by a coefficient M, where M is less than 1.0.

In another aspect of the present invention, there is provided a printer driver installed in a computer and configured to process image data to be supplied to an image reproducing and forming apparatus capable of utilizing a recording head Bi-directional recording, the recording head is used to eject droplets of at least one color onto the recording medium. The printer driver includes a control unit for controlling the amount of liquid adhering to the recording medium in order to reduce chromatic aberration generated in bidirectional recording.

In a preferred example, the printer driver determines whether the object to be output is text, wherein the control unit does not perform the process of reducing the color difference when the object to be output is text. Alternatively, the printer driver determines the object type and the number of colors employed in the image data, and when the object type is not text and the number of colors is one, the control unit does not perform color difference reducing processing.

Preferably, the printer driver includes a gradation correction unit that selectively performs controllable gradation correction for controlling the amount of liquid adhesion or normal gradation correction not for controlling the amount of liquid adhesion based on the determination result of the determination unit.

In yet another aspect of the present invention, there is provided a data processing apparatus for processing image data to be supplied to an image reproduction and forming apparatus capable of bidirectional recording using a recording head that converts at least one color The droplets are ejected onto the recording medium. In the data processing device, the above-mentioned printer driver is installed.

In still another aspect of the present invention, there is provided an image reproducing and forming apparatus capable of preventing charge leakage. The image reproducing and forming apparatus includes a conveying mechanism that conveys a recording medium using electrostatic attraction, an image recording unit that ejects liquid droplets onto the recording medium, and a control unit that generates a liquid on the recording medium. An image is formed, and the control unit is used to control the amount of liquid adhering to the recording medium in order to prevent electric charges from leaking from the recording medium.

In a preferred example, the control unit includes a gradation correction processing unit that controls the amount of liquid adhered to the recording medium by gradation correction.

For example, the gradation correction processing unit may selectively perform a first gradation correction for preventing charge leakage and a second gradation correction not for preventing charge leakage.

When controlling the amount of liquid adhesion, or when performing the first grayscale correction, the controllable grayscale value is obtained by multiplying the ordinary grayscale value by a coefficient K (K<1.0).

The value of the coefficient K can be selected according to the object type of image data to be recorded. Alternatively, the value of the coefficient K may vary according to environmental conditions, or according to the amount of data to be output on a sheet.

When performing the above printing, the second controllable grayscale value obtained by multiplying the controllable grayscale value by the coefficient M (M<1.0) is used.

Description of drawings

After reading the following detailed description in conjunction with the accompanying drawings, other objects, features and advantages of the present invention will become more apparent, wherein:

1 is a schematic view of a printing mechanism of an inkjet recording apparatus according to an embodiment of the present invention;

2A is a plan view of a main part of the inkjet printing mechanism shown in FIG. 1, and FIG. 2B is a perspective view of a recording head unit used in the inkjet recording apparatus shown in FIG. 1;

3 shows a conveying belt for conveying a recording medium and a charging roller pressed against the conveying belt used in the inkjet recording apparatus shown in FIG. 1;

4A and 4B are schematic views for explaining the recording operation of the inkjet recording apparatus shown in FIG. 1;

5 is a block diagram of a control unit of the inkjet recording apparatus shown in FIG. 1, and a printer driver connected to the apparatus according to the first embodiment of the present invention;

6 is a functional block diagram showing an example of a printer driver installed in a data processing apparatus to perform gradation correction;

7 is a functional block diagram showing another example of a control unit of a printer driver installed in a data processing device to perform gradation correction, and an image reproducing and forming device connected to on the data processing device;

Fig. 8 is a schematic graph for explaining the generation of chromatic aberration;

9A to 9C are schematic diagrams illustrating penetration of pigmented ink droplets onto paper;

Figures 10A to 10C are schematic diagrams illustrating penetration of pigmented ink droplets onto paper;

Figure 11 is an example of banding formed on paper due to chromatic aberration;

12 is a graph showing color differences of mixed colors expressed on L ^* a ^* b ^* chromaticity coordinates;

Figure 13 is an enlarged view of the circular portion A shown in the chromaticity table of Figure 12;

Figure 14 is a graph of the color difference ΔE for red, green and blue as a function of functional gray scale (%);

Figure 15A is the original image at 100% tone, Figure 15B is the image after halftone processing;

Figure 16A is the original image with 20% tone, and Figure 16B is the image after halftone processing;

Figure 17A is the original image with 60% tone, and Figure 17B is the image after halftone processing;

Figure 18 shows a block diagram of data flow in a printer driver;

FIG. 19 is a graph showing an example of gradation correction according to the first embodiment;

FIG. 20 is a graph showing another example of grayscale correction;

Figure 21 is a diagram illustrating different types of data processing performed for different data objects, and analysis of these data objects;

22 is a block diagram of a control unit of an image reproduction and forming apparatus according to a second embodiment of the present invention;

23 is a graph of an example of gray scale correction according to the second embodiment of the present invention;

FIG. 24 is a graph showing another example of grayscale correction;

Fig. 25 is a graph showing the amount of ink adhesion and the data components in the ink adhesion, which is used to process the grayscale ratio (or coefficient K) of graphic data variable;

FIG. 26 is a graph showing another example of grayscale correction, which is applicable to the image analysis shown in FIG. 24;

FIG. 27 is a graph showing still another example of grayscale correction;

FIG. 28 is a graph showing still another example of grayscale correction;

FIG. 29 is a graph showing still another example of grayscale correction;

Fig. 30 is a block diagram of a host computer in which a printer driver according to a second embodiment of the present invention is incorporated.

Detailed ways

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing the overall structure (including a printing mechanism) of an inkjet recording apparatus, which is an example of an image reproducing and forming apparatus according to an embodiment of the present invention. 2A is a plan view of a main part of a printing mechanism, and FIG. 2B is a perspective view showing a head structure of an inkjet recording apparatus. 3 is a schematic diagram illustrating a conveyor belt that conveys a recording medium using electrostatic attraction, according to an embodiment of the present invention.

The inkjet recording device 1 comprises an image recording unit 2, a paper feed tray 4 and a transport mechanism 5, wherein the paper supply tray 4 is placed at the bottom of the inkjet recording device, and accommodates paper 3 (as a recording medium), and the transport mechanism 5 is used for The paper 3 supplied from the paper feed tray 4 is conveyed to the image recording unit 2 . When the image is recorded on the paper, the paper is output to the output tray 6 attached to the side panel of the main body of the inkjet recording apparatus 1 .

The inkjet recording device 1 also includes a double-sided recording unit 7 which is detachably attached to the main body of the inkjet recording device 1 . When a duplex printing operation is performed, an image is printed on the first side (upper side) of the paper 3, and then the paper 3 is conveyed in the backward direction by the conveyance mechanism 5 toward the duplex unit 7 where the paper 3 is recorded. Turn it upside down so that the back is facing up. The inverted paper 3 is fed to the image recording unit 2 again to print an image on the back side. The double-sided paper 3 is output to an output tray 6 .

The image recording unit 2 includes a carriage 13 held by guide shafts 11 and 12 to slide along the guide shafts 11 and 12 . The character carriage 13 is driven by a fast scanning motor (not shown) to move in a fast scanning direction perpendicular to the paper feeding direction. The recording head 14 is mounted on the carriage 13 . The recording head 14 has a plurality of nozzle holes 14n for ejecting liquid droplets, as shown in FIG. 2B. An ink cartridge 15 is also detachably mounted on the carriage 13 to supply liquid ink to the recording head 14 . The ink tank 15 is replaceable by a sub tank to supply ink to the recording head 14 from a main tank (not shown).

The recording head 14 has, for example, four independent inkjet heads 14y, 14m, 14c, and 14k for ejecting ink droplets of yellow (Y), magenta (M), cyan (C) and black (B), respectively, as Figures 2A and 2B. Alternatively, the recording head 14 may have an inkjet head having a plurality of nozzle arrays for ejecting ink droplets of respective colors. It should be noted that the structure, ink color, and number of colors of the recording head 14 are not limited to these examples.

The inkjet head constituting the recording head 14 has an energy generator to generate energy for ejecting ink droplets. Examples of such energy generators include piezoelectric actuators using piezoelectric elements, thermal actuators using electrothermal conversion elements (such as heating resistors) that produce phase changes due to film boiling of liquids, thermal actuators using Shape memory alloy actuators with metal phase transitions and electrostatic actuators using electrostatic forces.

A sheet of paper 3 is drawn out from a stack of paper sheets stacked on the paper feed tray 4 using a pickup roller (rough-convex roller) 21 and a separation pad (not shown), and is fed to the main body of the inkjet recording apparatus 1. Conveying mechanism 5.

The conveying mechanism 5 includes a conveying guide 23, which is provided with a guide surface 23a and a guide surface 23b, wherein the guide surface 23a is used to guide the paper 3 to be fed upward from the paper supply tray 4, and the guide surface 23b is used to guide the paper 3 from the double-sided Paper 3 delivered by unit 7. The conveying mechanism 5 also includes a paper feed roller 24 for feeding the paper 3, a pressure roller 25 for pressing the paper 3 against the paper feed roller 24, a guide device 26 for guiding the paper 3 to the paper feed roller 24, A guide 27 for guiding the paper 3 backward to the duplex unit 7 and a platen roller 28 for pressing the paper 3 fed from the paper feed roller 24 .

The conveying mechanism 5 may also include a conveying belt 33 wound on the driving roller 31 and the tension roller 32 to convey the paper 3 while keeping the paper 3 under the recording head 14 flat. A charging roller 34 and a guide roller 35 for charging the conveying belt 33 are disposed on either side of the conveying belt 33 so that the conveying belt 33 is held between the charging roller 34 and the guiding roller 35 . Although not shown in FIG. 1 , a pressing plate for holding the conveying belt 33 so as to face the image recording unit 2 and a cleaning roller made of a porous material to remove adhesion to the conveying belt 33 are also provided. ink on.

The conveyance belt 33 is an endless belt, and rotates around the drive roller 31 and the tension roller 32 in the sheet feeding direction.

FIG. 3 shows an example of the structure of the conveyor belt 33 . In this example, the conveyor belt 33 has a first layer (top layer) 33a and a second layer (bottom layer) 33b. The first layer (top layer) 33a is made of, for example, a pure resin film having a thickness of about 40 μm, such as ETFE pure material, which has not been subjected to resistance control. The second layer (bottom layer) 33b is made of the same material as the first layer, and undergoes resistance control using carbon. The first layer (top layer) 33a is used as a paper absorbent surface, and the second layer (bottom layer) 33b is used as a grounding layer or intermediate resistance layer.

The charging roller 34 is in contact with the top layer 33a of the conveyor belt 33, and rotates as the conveyor belt rotates. A high voltage is applied to the charge roller 34 from a high voltage power source (not shown) in a predetermined voltage application pattern.

Turning to FIG. 1 , output rollers 38 are provided downstream of the transport mechanism 5 to output the image-formed paper 3 to the output tray 6 .

In the image reproducing and forming apparatus shown in FIG. 1 , a rotary conveyor belt 33 rotates in a predetermined direction and is charged by a charging roller 34 pressed against the conveyor belt 33 under an applied high voltage. By switching (reversing) the polarity at predetermined time intervals, the charging pitch of the conveyor belt 33 charged with the charging roller 34 can be controlled within a desired pitch.

When the paper 3 is fed to the conveying belt 33 charged at a high voltage, the inside of the paper 3 is polarized, and charges having opposite polarities are generated on the interface between the conveying belt 33 and the paper 3 . The charges on the conveyance belt 33 and the opposite charges induced on the paper 3 attract each other, and thus the paper 3 electrostatically adheres to the conveyance belt 33 . Since the paper 3 is firmly adhered to the conveyor belt 33, the curved or corrugated surface of the paper 3 is corrected into a highly flat surface.

In response to the pixel signal, the recording head 14 is driven to perform one-way or two-way scanning by moving the carriage 13 , and the paper 3 on the rotating conveyor belt 33 is transported at the same time. Ink droplets 14 i are ejected from the recording head 14 toward the stationary paper 3 as shown in FIG. 4A , thereby forming a row of dots Di of an image on the paper 3 . Then, the paper 3 is fed by a predetermined distance, thereby performing a recording operation for the next line of the image. When the recording head 14 receives the job end signal or detects the end of the paper 3 within the recording area, the recording operation for the sheet is completed. The dots Di formed on the paper are shown in the enlarged view of FIG. 4B. The paper 3 on which the image has been recorded is output onto the output tray 6 by output rollers 38 .

FIG. 5 is a block diagram of the control unit 100 of the inkjet recording apparatus (or image reproducing/forming apparatus) 1 . The control unit 100 includes a CPU 101, a ROM 102, a RAM 103, a non-volatile memory (NVRAM) 104, and an ASIC 105, wherein the CPU 101 is used to control the overall operation of the inkjet recording device 1, and the ROM 102 is used to store The CPU 101 executes programs and other fixed data, the RAM 103 is used to temporarily store pixel data, and the nonvolatile memory 104 is used to retain data when the power is turned off. The ASIC 105 processes input and output signals for performing image processing (including various types of signal processing and data rearrangement), and for controlling the entire operation of the device.

The control unit 100 also includes an interface (I/F) 106 for transferring data between the control unit 100 and a host computer 90, for example, a personal computer used for data processing according to the present invention. device. The control unit 100 also includes a head driver 108 for driving the recording head 14 and a head drive controller 107 for controlling the head driver 108 . The control unit 100 also includes a fast scan motor driving unit 111 for driving the fast scan motor 110 and a slow scan motor driving unit 113 for driving the slow motor 112 . The control unit 100 has an input/output unit 116 for receiving various detection signals from an environmental sensor 118 for detecting ambient temperature or humidity, as well as other sensors (not shown).

An operation panel 117 is connected to the control unit 100 . Necessary information is displayed on the operation panel 117 , and it allows the user to input input information necessary for the operation of the inkjet recording apparatus 1 . A high voltage circuit (or power source) 114 for applying high voltage to the charging roller 34 is connected to the control unit 100 , and the control unit 100 controls the ON/OFF switch and the polarity of the high voltage circuit 114 .

The control unit 100 receives print data on the interface 106 from the host computer 90 via a cable or a network, and temporarily stores the print data in a buffer (not shown) of the interface 106 . The host computer 90 includes a data processing device (such as a personal computer), an image recognizer (such as an image scanner), and an image pickup device (such as a digital camera). Print data to be supplied to the controller 10 of the inkjet recording apparatus is generated by a printer driver 91 stored in the host computer 90, and the data is output from the printer driver.

The CPU 101 reads out the print data from the buffer of the interface 106, and analyzes the print data. The ASIC 105 performs necessary image processing operations such as data rearrangement, and supplies the processed pixel data to the head drive controller 107. An operation of converting print data into bitmap data for outputting an image is performed by the printer driver 91 of the host computer 90, thereby developing the image data into bitmap data. Alternatively, using font data stored in the ROM 102, the print data may be converted into bitmap data by the controller 100 of the inkjet recording apparatus.

The head drive controller 107 receives one line of pixel data (dot pattern data) corresponding to the scanning line of the recording head 14, and outputs serial data to the head driver 108 synchronized with a clock signal. The head drive controller 107 also outputs a latch signal to the head driver 108 at predetermined timing.

The head drive controller 107 includes a ROM for storing pattern data for driving pulses and a driving pulse generating circuit for generating driving pulses based on the pattern data read from the ROM. Pattern data for driving pulses may be stored in ROM 102 . The driving pulse generation circuit includes a digital-to-analog converter for converting pattern data read from the ROM into an analog form, and a multiplier.

The head driver 108 includes a shift register, a latch circuit and a level shifter, wherein the shift register receives a clock signal and serial pixel data from the head drive controller 107, and the latch circuit is supplied from the head drive controller 107. The timing of the lock signal of the shift register locks the register value of the shift register, and the level shifter is used to shift the level of the output value from the latch circuit. The head driver 108 also includes an array of analog switches whose ON/OFF operation is controlled by level shifters. Based on the ON/OFF control of the analog switch array, required drive pulses are selectively supplied to the actuators of the recording head 14 to drive the recording head.

6 and 7 show examples of how image data is processed. In FIG. 6, most data processing is performed in the printer driver 91 of the data processing device (or host computer) 90, and data processing is performed jointly by the printer driver 91 and the controller 100 of the inkjet recording device shown in FIG.

In the example shown in FIG. 6, the printer driver 91 has a controller 120 including a color management module (CMM) processing unit 131, a black generation/under color removal (BG/UCR) processing unit 132, a gradation correction unit 133 , scaling unit 134 (zooming unit) and halftone processing unit 135 . The CMM processing unit 131 receives the image data 130 from the application software, and converts the RGB color space for the monitor display into the CMY color space for the inkjet recording device. The BG/UCR processing unit 132 performs black generation and under color removal on CMY spatial image data. The gradation correction unit 133 includes an ink adhesion control unit for adjusting or reducing the amount of ink adhering to paper, and it enables correction of input and output signals depending on machine characteristics and user preference of the inkjet recording apparatus. The scaling unit 134 performs an enlarging operation according to the resolution of the inkjet recording device. The halftone processing unit 135 includes a multivariate/binary matrix (not shown) for setting image data into a dot pattern reproduced by ink droplets ejected from the recording head.

In the example shown in FIG. 7 , the printer driver 91 has a controller 140 including a color management module (CMM) processing unit 131 , a black generation/under color removal (BG/UCR) processing unit 132 , and a gradation correction unit 133 . With the configuration shown in FIG. 6 , the CMM processing unit 131 converts the RGB color space of the image data 130 supplied from the application software into the CMY color space. The BG/UCR processing unit 132 performs black generation and under color removal on image data in the CMY space. The gradation correction unit 133 includes an ink adhesion control unit, and enables correction of input and output signals depending on machine characteristics and user preferences of the inkjet recording apparatus.

The image data subjected to gradation correction is supplied to the controller 100 of the inkjet recording apparatus, where the controller 100 includes a scaling unit 134 and a halftone processing unit 135 . The image data is subjected to scaling processing at the scaling unit 134 and developed into a dot pattern using a multivariate/binary matrix (not shown) within the halftone processing unit 135 .

Next, chromatic aberration in bidirectional recording, which problem can be solved by the present invention, is explained with reference to FIGS. 8 to 13 .

In FIG. 8, the recording head 14 includes head units 14k, 14c, 14m, and 14y corresponding to black (K), cyan (C), magenta (M), and yellow (Y), and are arranged in this order at the fast scanning direction. Of course, the recording head 14 is not limited to this example, and different arrangements of head units and more colors may be employed.

In bidirectional printing (or recording), the printing operation is performed in the outbound and inbound trips of the carriage, and thus the number of reciprocating movements of the carriage and the recording time for each sheet are greatly reduced. On the other hand, the recording positions in the return trip may be shifted in the reciprocating movement from those in the out trip. In addition, unwanted color differences may occur due to the different order of color overlap between the outbound and inbound passes, which degrades the quality of the printed image. For this reason, bidirectional printing is employed in a recording mode in which recording speed is preferred over image quality.

In the example shown in FIG. 8 , ink droplets are ejected in the order of black (K), cyan (C), magenta (M), and yellow (Y) on the way out. On the return pass, the ink droplets are ejected in reverse order, ie yellow (Y), magenta (M), cyan (C) and black (K). Due to the colorant fixation feature, if ink droplets of different colors are attached to the same point on the paper, the color of the ink droplet attached to that point first is the dominant color.

9A to 9C are graphs showing the distribution of colorants within paper when dye inks of different colors are jetted onto the same spot on the paper. The ink droplet of color A and the ink droplet of color B are ejected onto the paper 3 in this order, as shown in FIG. 9A . The ink droplet of color A is jetted through the paper 3 first, as shown in FIG. 9B . In this case, if the next ink droplet of color B is ejected to the same point, the ink droplet of color B penetrates only inside the transmission area of the first ink droplet of color A, as shown in FIG. 9C. In other words, the area where the first ink droplet of color A is distributed is wider than the area where the second ink droplet of color B is distributed, and thus there is a different fusing area of the colorant. For example, when printing is performed by a mixed color produced by a combination between cyan and magenta (C+M) or magenta and yellow (M+Y), the color of the first ejected ink droplet is the main color component.

10A to 10C are graphs showing the distribution of colorants within the paper when different colored pigmented inks are jetted onto the same spot on the paper. The ink droplet of color A and the ink droplet of color B are ejected onto the paper 3 in this order, as shown in FIG. 10A . The ink droplet of color A penetrates the paper 3 first, as shown in FIG. 10B . Then, if the ink droplet of color B is ejected onto the same point next, the ink droplet of color B completely penetrates the penetration area of the first ink droplet of color A, and penetrates deeper into the inside of the paper 3, as shown in FIG. 10C . In this case, the colorant of the first ink drop A remains on the surface area of the paper 3 , while the colorant of the second ink drop B sinks into the paper 3 . As a result, the character of the colorant (first ejected ink droplet A) remaining near the surface becomes stronger, and this colorant becomes the main color component.

Returning to FIG. 8 , since the ink droplets are ejected on the way out in the order of K→C→M→Y, the degree of dominance in the composite color tone becomes K>C>M>Y. In contrast, ink droplets are ejected in the order of Y→M→C→K in the return pass, and the degree of dominance in the composite color tone becomes Y>M>C>K.

When using bidirectional recording to increase the recording rate, it is necessary to take into account the change in hue in the mixed color or three primary colors (C+M+Y, etc.) due to ink penetration characteristics. Especially when the paper is fed by a certain distance in each stroke (each outgoing and returning stroke), the change in color tone can lead to banding, as shown in FIG. 11 .

In order to reduce chromatic aberration in bidirectional printing, in a preferred embodiment of the present invention, the amount of ink adhering to the paper is controlled or reduced. For example, the amount of ink adhesion is controlled by gradation correction in order to reduce color difference in bidirectional printing.

Color differences in bidirectional printing tend to become more noticeable as color saturation increases. Fig. 12 is a chromaticity diagram plotting color change of mixed colors, usually red (R), green (G) and blue (B), produced in L ^* a ^* b ^* chromaticity coordinates in bidirectional recording, and Fig. 13 is an enlarged view of the circular portion A. As the saturation of a color increases, this means that as the position moves further away from the origin, the shift between the outbound and the backhaul of each color increases.

In Figure 12, the closer to the origin, the lighter the color, and the farther away from the origin, the stronger the color. As the color becomes more intense, the offset between outbound and inbound becomes larger. When the a ^* value and b ^* value reach a certain level, the hue phase line returns toward the origin, as shown in Figure 13.

Usually, color difference is represented by ΔE represented by L ^* , a ^* , b ^* values. The ^color difference ΔE is represented by Equation (1) represented by a ^* , b ^* , and L ^* , which is a luminance component, as shown in FIG. 12 .

ΔE＝[(L ^* ₀ -L ^* ₁ )2+(a ^* ₀ -a ^* ₁ )2+(b ^* ₀ -b ^* ₁ ) ² ]1/2(1)

Among them, L ^* ₀ , a ^* ₀ and b ^* ₀ are the L ^* , a ^* and b ^* values of the reference color, L ^* ₁ , a ^* ₁ and b ^* ₁ are the L ^* , a ^* and b ^* of the comparison color value.

Fig. 14 is a graph of the color difference ΔE of red, green and blue as a function of gray level (%) obtained by experimental bidirectional recording using the above-described inkjet recording apparatus. As shown in FIG. 12, as the hue level (or color saturation) increases, the color difference ΔE increases among the three primary colors.

The inventors of the present invention focused attention on the tendency of color aberration to increase with increasing hue (color saturation) and found that the color aberration in bidirectional recording could be reduced by controlling or reducing the output color level. In order to control or reduce the color scale, a certain coefficient K (K<1.0) is multiplied by the input value in the gray scale correction.

When chromatic aberration correction (or control) is not performed, input values are actually supplied to the gradation correction table. On the other hand, when performing chromatic aberration correction, the product of the input value and the coefficient K is input into the grayscale correction table, and the output value of the grayscale table is used for further processing.

When reducing the amount of ink adhesion, special extraction processing or forced changes in dot size can be used to reduce the color level. However, these processes can cause serious damage to image quality, such as degradation of the gray balance of the recorded image, lack of information due to decimation, or the creation of unique texture patterns.

In contrast, controlling the gradation using the coefficient K in gradation correction maintains the gradation balance, and the adhesion amount of ink forming dots can be increased or decreased within the tone range. Also prevents unwanted textures.

The coefficient K is set to an optimum value depending on the action and reaction obtained. Table 1 is the estimated value of the color difference ΔE.

Table 1

type Chromatic difference ΔE Ratio steps Unpredictable range 0.0-0.2 Not perceptible to the naked eye; the error range of color measurement equipment under special conditions perceivable boundaries 0.2-0.4 The range of reproducible accuracy of color measuring equipment under basic conditions; the perceptual limit of reproducibility of the sighted human eye AAA Tolerance 0.4-0.8 From the point of view of observation and judgment, the set limited color difference standard range JIS L0804JIS L0805 AA Tolerance 0.8-1.6 Perceive the color difference by adjacent comparison; the error range of general color measurement equipment including machine differences  Precautionary Standards: National Police Agency Standards; General Shipping Inspection Standards A tolerance 1.6-3.2 Barely perceived in separate comparisons; perceives the same color B tolerance 3.2-6.5 Treated as the same color at the representation level; for pigments, interpreted as the wrong color Color Management Tolerance for Heterogeneous Materials; JIS E3305 C tolerance 6.5-13 Corresponding to the color difference between color systems (such as JIS color system and Munsell color system) JIS S6016JIS S6024JIS S6037 D tolerance 13-25 Different shades of color named as color systems; otherwise, called different colors

As can be seen from Table 1, the color difference ΔE is set to be less than or equal to 0.8 (ΔE≦0.8) in order to sufficiently remove the color difference from bidirectional recording. Referring to the relationship between the color difference ΔE and the gray scale (%) shown in FIG. 14, the gray scale must be reduced to 20% or less of the theoretical value. However, in this case, most of the original image information will be lost and the image quality will be extremely degraded.

If halftone processing is performed on the original image at the 100% tone level, as shown in FIG. 15A, the output image becomes the one shown in FIG. 15B. If halftone processing is performed after the gray scale is lowered to 20% from the original image, as shown in FIG. 16A, the output image cannot be regarded as the image shown in FIG. 16B.

In order to maintain the A tolerance level defined in Table 1, the color difference ΔE was set from 1.6 to 3.2, where the color difference range was barely perceived in the separation comparison. Referring again to the relationship between the color difference ΔE and the gray level (%) shown in FIG. 14, a satisfactory image is obtained by setting the gray level to 35% to 65% of the original image.

By conducting experiments and analyzes in consideration of image quality degradation and chromatic aberration improvement, the inventors of the present invention found that by setting the gray level to 50% to 60% (or setting the coefficient K within the range of 0.5 to 0.6), bidirectional recording can be achieved. A balance between the improvement of chromatic aberration and the degradation of image quality in .

FIG. 17A shows an image formed after grayscale control of setting the grayscale to 60% of the original image. When halftone processing is performed on an image whose gradation is controllable, image quality perceived satisfactorily by the user can be obtained, as shown in FIG. 17B .

As can be seen from the foregoing description, the coefficient K used in grayscale correction should be set within the range of 0.35 to 0.65, more preferably, within the range of 0.5 to 0.6, in order to prevent chromatic aberration in bidirectional recording. The above range is an appropriate range for obtaining satisfactory image quality, although it varies slightly depending on the original image. Utilizing this range of grayscale levels, a color difference reduction effect corresponding to at least the A-level tolerance shown in Table 1 can be expected, and high-speed, high-quality inkjet recording devices can be realized under the influence of slight color differences in bidirectional recording Log actions.

In this embodiment, the input data value is multiplied by a factor K in order to obtain the improvement. However, as already mentioned above, the influence of image quality may vary depending on the content of the image data. In FIGS. 15 to 17, the gradation correction using the coefficient K is performed on the captured image data. For text data, the degradation in image quality can become more pronounced.

This is because text data is reproduced in terms of "lines" as compared with image data in terms of "planes". Even if text data is accurately reproduced by halftone processing as expected, letters and symbols are blurred by decimating a few dots. Furthermore, when estimating printed text from the viewpoint of color difference in bidirectional recording, such color difference is not conspicuous in printed text, which is captured as "line" unlike a photographic image captured as "surface".

This means that, if the object of input data is text, it is desirable not to perform a control process for reducing the ink adhesion amount. There are other types of objects, such as graphics, including diagrams or figures that are often used in the industry concerned. Since graphic data expresses information with "planes" like a picture or a photo, it is processed into image data, which is similar to the picture and photo in the embodiment.

FIG. 18 is a block diagram showing the flow of data in the printer driver 91 that executes the ink adhesion amount control process. When the "print" command is generated by application software operating on the data processing device 90 (such as a personal computer), the object determination unit 201 of the printer driver 91 determines the object type of the input data 200, such as text 202, line drawing 203, graphics 204 and images (pictures) 205. Each object undergoes relevant processing through a corresponding process.

Text data 202 , line drawing data 203 , and graphics data 204 are subject to color control 206 . Text data 202 is also subjected to color matching 207 , BG/UCR processing 209 , volume control 211 , gradation correction 213 , and text shading (halftone) processing 215 . The line drawing data 203 and graphic data 204 are also subjected to color matching 208 , BG/UCR processing 210 , volume control 212 , gradation correction 214 , and graphic shading (halftone) processing 216 .

For the image data 205 , color determination and expression scheme determination are performed in the determination unit 221 . In regular mode, image data 205 also undergoes color control 222 , color matching 223 , BG/UCR processing 224 , total amount control 225 , gray scale correction 226 and error diffusion (halftone) processing 227 . If the number of colors of the image data 205 is two or less, image decimation and color control 232 is performed. Then, color matching 233a or no-index processing (in order not to perform color matching) 233b is performed. Image data 205 including two or fewer colors is also subjected to BG/UCR processing 224 , total amount control 225 , gradation correction 226 , and error diffusion (halftone) processing 227 .

The line drawing data 203 and the graphics data 204 may be applied to the image color control unit 232 via the ROP processing unit 241 instead of the color control unit 206 .

The image data items processed for the respective objects are synthesized and applied to the recording device.

In an embodiment, the amount of ink adhesion for graphic data and image data is controlled or reduced by the gradation correction units 214 and 226 to reduce color difference in bidirectional recording. On the other hand, for text data, the gradation correction unit 213 performs ordinary gradation correction without reducing the ink adhesion amount.

Fig. 19 shows an example of gradation correction performed by the printer driver 91 according to the first embodiment of the present invention. In order to perform ink adhesion control for reducing color difference in bidirectional recording, input data is supplied to the coefficient K multiplier 303 . The input data value is multiplied by the coefficient K, and then supplied to the gradation correction table 301 . On the other hand, if the input data does not require ink adhesion control, the input data is directly applied to the gradation correction table 301 . The selector 303 determines whether input data is directly supplied to the gradation correction table 301 or the coefficient K multiplier 302 .

Gray scale correction is a process for converting the gray scale of input data into different gray scales depending on the imaging characteristics of the recording device. Input data is gray scale corrected data, which may or may not undergo necessary processing (such as CMM processing or BG/UCR processing). The output data is data that has undergone gradation correction.

If color difference control is not performed in bidirectional recording, input data is directly supplied to the gradation correction table 301, and it is gradation-corrected using normal gradation values, and data that has undergone normal gradation correction is output. On the other hand, in order to control or reduce chromatic aberration in bidirectional recording, at the coefficient K multiplier 302, the input data value is multiplied by the coefficient K, and the adjusted input data is supplied to the gradation correction table 301, in which an ordinary gradation correction value is used to perform grayscale correction. Composite output data has been adjusted to reduce chromatic aberration in bidirectional recording. This process is equivalent to performing gradation correction on input data using a gradation value multiplied by the coefficient K (that is, a controllable gradation value) in order to reduce chromatic aberration in bidirectional recording.

The coefficient K is set in the range of 0.35 to 0.65. Since the input data value is multiplied by the coefficient K, the data values to be grayscale corrected have been reduced in the grayscale correction table 301 compared with those directly supplied to the grayscale correction table 301, and adhesion to the paper can also be reduced. The amount of ink adhesion on the

In the example shown in FIG. 19, a single gradation correction table 301 is commonly used for both the color difference control process and the normal gradation correction process, and the data values input to the gradation correction table 301 vary depending on whether color difference control is performed on the input data. Make adjustments. However, two different grayscale tables with different grayscale values may be used.

Fig. 20 shows optimization of the gradation correction table for reducing chromatic aberration in bidirectional recording. The gradation correction part includes an ordinary gradation correction unit 401 , a controllable gradation correction unit 402 , a gradation value storage unit 403 , a coefficient K multiplier 404 and a selector 303 . The normal gradation correction unit 401 performs normal gradation correction on input data without controlling the ink adhesion amount to reduce color difference in bidirectional recording. The controllable gradation correction unit 402 performs controllable gradation correction to adjust the amount of ink adhesion so as to reduce color difference in bidirectional recording. The gradation value storage unit 403 stores gradation values used in normal gradation correction (which are referred to as “normal gradation values”). The coefficient K multiplier 404 multiplies the normal gray value stored in the gray value storage unit 403 by the coefficient K, and applies the controllable gray value to the controllable gray value correction unit 402 . The selector 303 applies the input data to the normal gradation correction unit 401 or the controllable gradation correction unit 402 .

The selector 303 is installed in the printer driver 91, and thus the user can adjust the installation of the selector 303. For example, if the decrease in gray scale is more serious than the color difference, the user can set the selector 303 so as not to select the controllable gray scale correction.

If a suggested setting mode or an automatic setting mode is loaded in the printer driver 91, the selector may be configured to determine whether there is "color difference control in bidirectional recording" in its selection operation, wherein the suggested setting mode is used for Optimum image quality as determined by the manufacturer is achieved, and the automatic setting mode is used for optimum installation as determined by the printer driver through image data analysis.

If a single-color ink (black or other colors) is used, in principle, there will be no color difference due to bidirectional recording. In this case, a mode for "not performing color difference control in bidirectional recording" can be automatically set.

If the object type determined by the object type determination unit is text, ordinary gradation correction is performed without color difference control in bidirectional recording. Likewise, if the number of ink colors used in recording is one, ordinary gradation correction is performed without reducing color difference in bidirectional recording.

Fig. 21 shows a diagram of different types of data processing performed on different types of data objects and image composition of these data objects. In FIG. 21, graphic halftone processing for graphics is performed using a controllable gradation value obtained by multiplying an ordinary gradation value by a coefficient K, and color text data (except black) is performed using an ordinary gradation value. Text halftone processing. For monochrome (or black) text, only jaggy correction (ie, anti-aliasing) is performed. Then, graphics, color text, and monochrome (black) text are composited to reproduce an image.

By controlling the amount of ink adhesion to reduce chromatic aberration in bidirectional recording, image quality can be maintained while preventing chromatic aberration in the bidirectional printing mode for increasing the recording rate. In other words, high-speed, high-quality recording can be achieved, achieving a balance between image quality and recording rate.

When the object to be output is text, ordinary gradation correction is performed without multiplying by the coefficient K, thereby preventing the image quality of the text from degrading to an undesired level. Also, when the object to be output is not text, and when monochrome ink is used, ordinary gradation correction is performed again without reducing the amount of ink adhesion, because in principle there will be no gradation in monochrome recording operation. Chromatic aberration occurs in bidirectional recording.

By controlling the amount of ink adhesion using gradation correction with a controllable gradation value, the gradation level can be adjusted while maintaining the gradation balance. Points are increased or decreased within the range of gradation representation while preventing unwanted textures.

A controllable grayscale value can be obtained by multiplying the normal grayscale value by a coefficient K (K<1), wherein the controllable grayscale value is used for controllable grayscale correction to reduce color difference in bidirectional recording. By setting the coefficient K in the range of 0.35 to 0.65, chromatic aberration in bidirectional recording can be effectively reduced while preventing image quality from degrading due to gray scale degradation. In particular, by setting the K value between 0.5 and 0.6, chromatic aberration in bidirectional recording is substantially eliminated, while the negative effect of gray level drop is minimized, and satisfactory high-quality recorded images can be reproduced .

The total ink consumption of the color inks is set approximately equal to the ink consumption of the black ink. This setup extends color cartridge replacement intervals and reduces costs. In offices, so-called business documents containing text and graphics are mainly output. With the inkjet recording apparatus in this embodiment, ink consumption can be reduced when printing graphics such as charts and pictures such as photographs, while printing text portions without deteriorating image quality.

Typically, text is printed in black and graphics and pictures are printed in colored inks. With the present invention, since the ink consumption of the black ink is substantially to the total ink consumption of the color inks (C+M+Y), it is not necessary to always replace the color ink cartridges (which is different from the conventional art).

Some known devices are equipped with an ink saving mode and change the image processing for each object. The inkjet recording apparatus of this embodiment does not require such an ink saving mode, but as a side effect of the color difference control in bidirectional recording, ink consumption can be reduced.

The first embodiment of the present invention is applicable not only to inkjet recording apparatuses but also to printers, facsimile machines, copiers, and printing/fax/copy multifunction machines that reproduce images using ink. The first embodiment of the present invention is also applicable to an image reproducing/forming device, a data processing device, and a printer driver loaded in a data processing device using liquids other than ink.

In the above-described embodiments, the gradation correction and controllable gradation correction for reducing color difference in bidirectional recording are performed by the printer driver installed in the host computer. However, gradation correction and controllable gradation correction can be performed by the ink recording device. In this case, a gradation correction process 133 as shown in FIG. 7 is added to the controller 100 of the inkjet recording apparatus. Alternatively, the entire data flow as shown in FIG. 18 may be performed in an inkjet recording apparatus.

FIG. 22 is a block diagram of a controller 500 of an inkjet recording apparatus (as an example of an image reproducing/forming apparatus) according to a second embodiment of the present invention. In the second embodiment, the amount of ink adhesion is controlled in order to reduce charge leakage and perform satisfactory double-sided printing. Thus, the inkjet recording device does not have to be a bidirectional recording device.

Similar to the first embodiment, the recording head 14 is driven in response to a pixel signal while conveying paper on the carousel belt 33 . More precisely, as shown in FIG. 2A, an image of one line is recorded by ejecting ink droplets onto a sheet of paper which is held stationary at a prescribed position by a conveying belt. Then, the paper 3 is fed at a prescribed distance for the next image recording operation. When the recording head 14 receives the job end signal or detects the end of the paper 3 in the recording area, the recording operation for this page is completed.

Returning to FIG. 22, the control unit 500 includes a CPU 101, a ROM 102, a RAM 103, a nonvolatile memory (NVRAM) 104, and an ASIC 520, wherein the CPU is used to control the entire operation of the inkjet recording apparatus 1, and the ROM 102 is used for For storing programs and other fixed data executed by the CPU 101, RAM for temporarily storing pixel data, and the non-volatile memory 104 for retaining data when the power is turned off. The ASIC 520 performs various types of signal processing, including gradation (γ) correction, which is used to adjust the amount of ink adhered to the recording medium at the gradation correction processing unit 119 according to the present invention. The ASIC 520 performs image processing, processes rearrangement of print data, signal processing of input/output control signals, and the like.

The control unit 100 also includes an interface (I/F) 106 for performing Data exchange with a host (not shown). The control unit 100 also includes a fast scan motor driving unit 111 for driving the fast scan motor 110 and a slow scan motor driving unit 113 for driving the slow scan motor 112 . The control unit 100 has an input/output unit 116 for receiving various detection signals from an environmental sensor 118 for detecting ambient temperature or humidity, as well as other sensors (not shown).

An operation panel 117 is connected to the control unit 100 . Necessary information is displayed on the operation panel 117 , and it allows the user to input input information required to operate the inkjet recording apparatus 1 . A high voltage circuit (or power source) 114 for applying high voltage to the charging roller 34 is connected to the control unit 100 , and the control unit 100 controls the ON/OFF switch and the polarity of the high voltage circuit 114 .

The control unit 100 receives print data from an external device on the interface 106 via a cable or a network, and temporarily stores the print data in a buffer (not shown) of the interface 106 . The external devices include data processing devices such as personal computers, image recognizers such as image scanners, and image pickup devices such as digital cameras.

The CPU 101 reads out the print data from the buffer of the interface 106, and analyzes the print data. The ASIC 520 (including the grayscale correction processing unit 530) performs necessary image processing operations such as CCM processing, BG/UCR processing, and grayscale correction. Then, the ASIC 520 rearranges the processed print data (pixel data), and supplies the pixel data to the head drive controller 107. Using the font data stored in the ROM 102, the print data can be converted into bitmap data for outputting images.

Alternatively, the image data may be developed into bitmap data by a printer driver of the host computer, and the bitmap data may be externally supplied to the control unit 100 of the inkjet recording apparatus 1 .

The head drive controller 107 receives pixel data (dot pattern data) corresponding to the scanning line of the recording head 14, and outputs serial data to the head driver 108 in synchronization with a clock signal. The head drive controller 107 also outputs a latch signal to the head driver 108 at predetermined timing.

The head drive controller 107 includes a ROM for storing pattern data for driving pulses and a driving pulse generating circuit for generating driving pulses based on the pattern data read from the ROM. Pattern data for driving pulses may be stored in ROM 102 . The driving pulse generation circuit includes a digital-to-analog converter for converting pattern data read from the ROM into an analog form, and a multiplier.

The head driver 108 includes a shift register, a latch circuit and a level shifter, wherein the shift register receives a clock signal and a serial pixel signal from the head drive controller 107, and the latch circuit is supplied from the head drive controller 107. The lock signal of the shift register locks the register value (register value) of the shift register at regular intervals, and the level shifter is used for shifting the level of the output value from the latch circuit. The head driver 108 also includes an array of analog switches whose ON/OFF operation is controlled by level shifters. Based on the ON/OFF control of the analog switch array, required drive pulses are selectively supplied to the actuators of the recording head 14 to drive the recording head.

FIG. 23 is a schematic block diagram of a grayscale correction processing unit 530 according to an embodiment of the present invention. The gradation correction processing unit 530 includes an ordinary gradation correction unit 501 and a controllable (or leak-proof) gradation correction unit 502, wherein the ordinary gradation correction unit 501 is configured to perform ordinary gradation correction regardless of preventing Charge leakage occurs on the paper or recording medium, and the controllable grayscale correction unit 502 is configured to perform grayscale correction for reducing the amount of liquid droplets adhering to the paper, thereby preventing charge leakage from occurring on the paper. The grayscale value storage unit 503 stores ordinary grayscale values used in ordinary grayscale correction. The coefficient K multiplier 504 multiplies the normal grayscale value by the coefficient K (K<1), and outputs the obtained value (controllable grayscale value) to the controllable grayscale correction unit 502 . The selector 505 selects the first grayscale correction data of the normal grayscale correction unit 501 or the second grayscale correction data of the controllable grayscale correction unit 502 as output data.

In this context, gradation correction is a process for converting a gradation level of input data into another gradation level in which factors of image pickup characteristics of an inkjet recording apparatus are considered. The input data is data that has not been subjected to grayscale correction, and which may or may not have undergone other types of data processing, such as CCM processing or BG/UCR processing. Output data of the gradation correction processing unit 530 is data that has undergone gradation correction.

In the second embodiment, the controllable gradation correction unit 502 performs gradation correction on input data using a controllable gradation value, wherein the controllable gradation value is obtained by setting It is obtained by multiplying the ordinary gray value with the coefficient K (K<1). The controllable grayscale value used by the controllable grayscale correction unit 502 is generally smaller than the normal grayscale value, and thus reduces the amount of ink adhering to the paper.

By reducing the amount of ink (liquid) adhering to the paper, it is possible to prevent charge leakage due to excessive moisture content of the paper. Thus, the electrostatic attraction between the paper and the conveyance belt 33 is properly maintained, and the paper is conveyed in a stable manner. In addition, the landing position of the ink drop is also maintained with high accuracy, and the image quality is improved.

In forming an image on paper held by electrostatic attraction by ejecting ink droplets or other types of liquid droplets onto the paper, there is always the possibility of charge leakage due to the moisture of the ink droplets adhering to the paper. Even if a drying device for promoting the evaporation of moisture components is equipped, the electric charge which has been lost during the recording (printing) operation cannot be recovered. Thus, it is more advantageous to reduce the amount of ink that adheres. This arrangement can be preferably applied in the prior art, as disclosed in JP2001-235945A and JP2000-190473A, regardless of being equipped with means for supplying charge to paper (JP2001-234945A) or not equipped with such means ( JP2000-190473A).

Even though the image density is slightly reduced by the use of controllable gray values, which are achieved by normal gray values and Multiplied by a coefficient K less than 1.0, the color brightness has a greater impact on visual characteristics than image density.

Although in the example shown in FIG. 23, whether the pixel data undergoes normal gradation correction at normal gradation correction unit 501 or undergoes controllable gradation correction at controllable gradation correction unit 502 is selected by selector 505, the input data It is optionally supplied to the normal grayscale correction unit 501 or the controllable grayscale correction unit 502 .

By allowing a selection between normal and controllable gamma correction, gamma correction is performed in an appropriate manner according to paper type and/or material. For example, when using thick paper or paper with a surface coating, the image quality is prioritized, and the normal gray value is used for normal gray correction at the original density, because this paper prevents the moisture component of the ink from reaching the back side , and no charge leakage can occur. On the other hand, when using plain paper that tends to cause charge leakage, select Controlled Gamma Correction with a controlled gradation value to prevent image quality from deteriorating due to charge leakage and electrostatic attraction reduction in advance.

FIG. 24 shows another example of the gradation correction processing unit 530 according to the second embodiment. In this example, the data type determination unit 506 is provided to determine the type of input data. According to the data type, perform a more appropriate one of ordinary grayscale correction and controllable grayscale correction.

In the specific example shown in FIG. 24 , the data type determination unit 506 determines whether the input data is text data or graphic data, and at the same time supplies the graphic data to the controllable grayscale correction unit 502 .

In addition, an image synthesizer 507 is provided to synthesize the output data output by the ordinary grayscale correction unit 501 (the output data has been subjected to ordinary grayscale correction) and the output data output by the controllable grayscale correction unit 502 (the output data has been subjected to the controllable grayscale correction unit 502 ). control grayscale correction).

Although in this example, the graphic data is always supplied to the controllable gradation correction unit 502, the gradation correction processing unit 530 may be constructed such that, depending on, for example, the type of paper, ordinary gradation correction or controllable gradation correction is selectively performed on the graphic data. Control grayscale correction, as described with reference to FIG. 4 in the first example. In addition, the value of the coefficient K may vary according to the data type.

When multiplying the normal grayscale value by a constant factor K (K<1.0), the pattern density of the print data is slightly lowered because the amount of ink adhering to the paper is reduced based on the controllable grayscale value. The effect of image density reduction varies depending on the data subject. For example, image density degradation is more dangerous when printing text data because image quality or sharpness is more prone to degradation, and is less effective in preventing leakage because the amount of ink used to print data text is inherently small ( leaving more non-printable area on the paper). On the other hand, in printing graphic data, as long as the brightness balance is maintained, the visual characteristics are not greatly degraded. It has a greater effect on preventing leakage, because the ink consumption is larger when printing graphics, and there are few non-printing areas on the paper.

Thus, print data objects are grouped according to types such as text data and graphic data items, wherein the information value of text data items tends to degrade with a decrease in density, and graphic data items allow the density to be reduced to a certain extent. Different gray values are used, that is to say, the normal gray value and the controllable gray value are used for gray correction, wherein the controllable gray value is obtained by multiplying the normal gray value by the coefficient K. The value of the coefficient K itself can be varied to produce a controllable gray scale.

Printing of data items that prioritize image quality (such as text data) without reducing the amount of ink adhering to the paper, printing that can accept a reduction in color density to A certain level of data items prevents charge leakage and keeps image quality balanced.

Typically, text data is printed using a single color ink (usually black ink), while graphic data is printed using cyan, magenta, yellow, and black inks at the same time. By switching the gamma correction mode between normal gamma correction and controllable gamma correction according to the object type, satisfactory output images can be obtained with less ink consumption while maintaining image quality and reducing running costs.

An example of a development mode of this example is explained with reference to FIGS. 21 and 25 . In FIG. 21, like the first embodiment, graphic halftone processing for graphic data is performed using controllable gradation values, and text halftone processing for color text data is performed using ordinary gradation values, wherein the The controllable gray value is obtained by multiplying the normal (original) gray value by the coefficient K. For monochrome (or black) text, only jaggy correction (ie, anti-aliasing) is done. Then, graphics, color text, and monochrome (black) text are synthesized to reproduce an image.

FIG. 25 is a graph showing the ink adhesion amount and the data composition in the ink adhesion in the case of changing the gradation ratio (coefficient K) for processing graphic data. As the gradation value (or coefficient K) decreases, the amount of ink adhesion of graphic data decreases.

FIG. 26 shows a modification of the gradation correction processing unit of the second example, which is applicable to the development mode shown in FIG. 21 . The data type determination unit 506 determines the text type among, for example, graphics, determination, color text, and monochrome (black) text. The color text data is supplied to the normal gradation correction unit 501 and subjected to normal gradation correction using the normal gradation value stored in the gradation value storage unit 503 . The graphic data is provided to the controllable grayscale correction unit 502 , and the controllable grayscale correction is performed using the controllable grayscale value supplied from the coefficient K multiplier 504 . Monochrome (black) text data is supplied to the jaggy correction unit 509 . The data items that have been subjected to correlation processing are synthesized by the image synthesizer 507 .

FIG. 27 shows another example of the gradation correction processing unit 530 according to the second embodiment of the present invention. In a third example, the coefficient K modification unit 510 is configured to adjust the value of the coefficient K used by the coefficient K multiplier 504 based on the environmental conditions detected by the environmental sensor 118 ( FIG. 5 ). This setup can be applied in the second example shown in Figure 24 and in the optimization shown in Figure 26.

Leakage of paper charge tends to vary according to environmental conditions. Generally, when the humidity is high, the charge tends to leak due to the moisture absorbed by the paper. On the other hand, when the humidity is low, charge leakage is less likely to occur.

In view of such environmental changes, the value of the coefficient K is optimized (or corrected) according to the environmental conditions. For example, when the humidity is high, the coefficient K is set smaller to reduce the amount of ink adhered to the paper, thereby preventing charge leakage and maintaining electrostatic attraction between the paper 3 and the conveying belt 33 . On the other hand, when the humidity is low, the value of the coefficient K is set close to 1.0, thereby maintaining high image quality.

The selector 505 can selectively output data items that have been subjected to controllable grayscale correction or data items that have been subjected to ordinary grayscale correction, wherein the controllable grayscale correction is performed using a controllable grayscale value, the controllable grayscale The value is obtained by multiplying by the correction factor K.

Fig. 28 shows still another example of the gradation correction processing unit according to the second embodiment of the present invention. In this example, the gradation correction processing unit 530 is provided with a data amount determination unit 511 that determines the data output amount output to a page and a coefficient K correction unit 512 that responds to The value of the coefficient K used by the coefficient K multiplier 504 is adjusted based on the determination result of the data amount determination unit 511 .

When the total amount of data output for a page is small, charge leakage due to ink sticking does not greatly affect electrostatic attraction or a composite printed image. For example, when an image is printed only at the corner of the paper, the amount of ink adhesion itself is small, and thus the charge leakage is not serious.

In view of this situation, the data output amount for a page is determined to adjust the coefficient K value according to the data amount. When the amount of data used for the page is small, the coefficient K is set close to 1.0 (in this way, the controllable gray value is close to the normal gray value), so as to improve the image quality. This arrangement allows balancing printed image quality with charge leakage prevention.

Fig. 29 shows still another example of the gradation correction processing unit according to the second embodiment of the present invention. In this example, the coefficient K multiplier 514 is provided to the grayscale correction processing unit 530 to generate a controllable grayscale value. In this case, when double-sided printing is performed, the ordinary gray value multiplied by the coefficient K can be multiplied by the coefficient M (M<1.0). The coefficient M multiplier 514 passes the controllable grayscale value output from the coefficient K multiplier 504 to the controllable grayscale correction unit 502 as it is without performing multiplication by the coefficient M when a simplex print job is performed.

In double-sided printing, the amount of ink adhesion is doubled, and multiplying by the coefficient K is not enough to prevent charge leakage. Therefore, another coefficient M (M<1.0) is used to multiply the controllable grayscale value to further reduce the total amount of ink adhered to both sides of the paper. Prevents charge leakage on each side of the paper and properly maintains electrostatic attraction between the paper and the conveyor belt.

In this example, normal grayscale values are used for normal grayscale correction mode. The first controllable grayscale value multiplied by the coefficient K is used for single-sided printing in the controlled grayscale correction mode. The second controllable grayscale correction value multiplied by the coefficient K and the coefficient M is used for duplex printing in the controllable grayscale correction mode.

In the inkjet recording apparatus, the gradation correction mode and the corresponding gradation values are set as follows in this example.

Normal Grayscale Correction Mode: γ

Controllable grayscale correction (single-sided printing): γ×K

Controllable grayscale correction (duplex printing): γ×K×M.

The preferred range for the coefficient M is between 0.8 and 0.95 to avoid problems in duplex printing. The product K×M is adjusted so as to obtain the optimum effect of preventing charge leakage in duplex printing.

Although the first to fifth examples of gradation correction have been described as being applied to ink recording devices, the present invention can be applied to other image reproduction/forming devices such as printers, facsimile machines, copiers, or multifunctional image forming devices (used as printer, facsimile machine or copier), the device is equipped with a paper transport mechanism using electrostatic attraction. In addition, the present invention can be used in an image reproducing/forming device which reproduces an image on a recording medium using a liquid material other than ink.

In the above-described example of the second embodiment, gradation correction for preventing charge leakage is performed in the image reproduction/forming apparatus; however, gradation correction may be performed by the printer driver 91 installed in the external host computer 90 (see FIG. 5).

FIG. 30 is an enlarged view of a host machine in which a printer driver 610 is installed according to a second embodiment of the present invention. In this embodiment, the image reproducing/forming device does not have to have a function of generating a dot pattern which is actually recorded on paper based on a print command for printing a picture or text. For example, the printer driver 610 of the host computer generates dot patterns and transfers the dot patterns to the inkjet recording apparatus.

In FIG. 30, application software 602 executed by the host supplies a print command (or recording command) to a printer driver 610 installed in the host. The printer driver 610 processes a print command, and generates print data that realizes dot pattern data specified by the print command. The dot pattern data is transmitted to an image recording device (or image reproduction/forming device).

The operating system or application software 602 executed by the CPU 601 of the host computer generates print commands for drawing pictures or text. A printing command is described by a special printing language, and it includes about the position, thickness and length of a line to be recorded, or about the position, font and size of a text to be recorded. Print commands are temporarily stored in the drawing data memory 603 and interpreted by the rasterizer 604 . The rasterizer 604 converts the print command into a dot pattern to be actually recorded based on the interpreted content. For example, a print command for recording lines is converted into dot pattern data according to prescribed positions, thicknesses, and lengths. A print command for recording text is converted into dot pattern data according to a specified position and size, using text outline information extracted from font outline data 608 stored in the host computer. These dot pattern data are stored in the raster data memory 605 .

When generating dot pattern data, the printer driver 310 executes the gradation correction described in the first, second, fourth, or fifth example at the gradation correction processing unit 607 . The explanation about the gradation correction performed by the gradation correction processing unit 607 is omitted here because it has been described in the above example.

The dot pattern data stored in the raster data memory 605 is transmitted as pixel data (or print data) to an inkjet recording device or an image reproducing/forming device via an interface 606 .

By performing gradation correction in the printer driver of the external host, the workload of the image reproduction/forming device can be reduced.

Although the present invention has been described based on the preferred embodiments, the present invention is not limited to these embodiments. For example, the coefficient M set for double-sided printing may be combined with the coefficient K to prevent chromatic aberration from occurring in the bidirectional recording described in the first embodiment. In this case, the preferred range for the coefficient M is between 0.8 and 0.95. However, since the gradation value has been adjusted by the coefficient K to reduce the ink adhesion amount in order to reduce the color difference, the coefficient M for duplex printing can be replaced by the coefficient K when both the bidirectional printing mode and the duplex printing mode are set. In this case, the coefficient K for reducing chromatic aberration is slightly adjusted so as to reflect the coefficient M.

It will be obvious to a person skilled in the art that there are many other alternatives and optimizations without departing from the scope of the present invention, which is defined by the appended claims.

Claims (18)

1. an image reproduces and the formation device, has: record head, and it has a plurality of nozzle arrays, is used for spraying the drop of at least a color; Perhaps have a plurality of record heads, be used for spraying the drop of at least a color; Described record head can bidirectional record; And

Controller, it is used for preventing in the pattern at aberration, prevents that with not carrying out aberration the situation of step from comparing, and reduces the amount of liquid that adheres to every kind of color on the recording paper with constant ratio;

To export to as if during text, be not text and number of color when being one perhaps at the object that will export, described controller is not carried out and is reduced the processing that adheres to the amount of liquid on the recording paper.

2. image as claimed in claim 1 reproduces and forms device, and wherein, described controller is controlled the liquid adhesive capacity by the controllable gray scale correction of adopting the controllable gray scale value to be carried out, so that reduce aberration.

3. image as claimed in claim 2 reproduces and the formation device, wherein, described controller is provided with selector, and the common gray scale correction that this selector is used for selecting to adopt common gray value to carry out still adopts the controllable gray scale value to be used to reduce the controllable gray scale correction of aberration.

4. image as claimed in claim 3 reproduces and forms device, and wherein, described controllable gray scale value is the product of common gray value and COEFFICIENT K, and wherein, COEFFICIENT K is arranged between 0.35 to 0.65.

5. image as claimed in claim 1 reproduces and the formation device, wherein, described controller is configured to select controllable gray scale correction or common gray scale correction based on the result of determining unit, wherein, described controllable gray scale correction is used to control the liquid adhesive capacity, to reduce aberration in bidirectional record, described common gray scale correction is not used in the reduction aberration.

6. image as claimed in claim 5 reproduces and forms device, and wherein, described controller uses the controllable gray scale value, with the correction of execution controllable gray scale, and uses common gray value, to carry out common gray scale correction.

7. image as claimed in claim 6 reproduces and forms device, and wherein, described controllable gray scale value is the product of common gray value and COEFFICIENT K, and wherein, COEFFICIENT K is arranged between 0.35 to 0.65.

8. image as claimed in claim 1 reproduces and forms device, and wherein, when carrying out duplex printing in bidirectional record, controller also usage factor M is controlled the liquid adhesive capacity that adheres on the recording paper, and wherein, M is less than 1.0.

9. printer driver, its structure is used for handling and will supplies to the view data that image reproduces and form device, wherein, this image reproduces and forms device and can utilize the record head that has a plurality of nozzle arrays or utilize a plurality of record heads to carry out bidirectional record, this record head can spray the drop of at least a color to recording medium, and this printer driver comprises:

Control module, it prevents in the pattern at aberration when bidirectional record, prevents that with not carrying out aberration the situation of step from comparing, and reduces the amount of liquid that adheres to every kind of color on the recording medium with constant ratio;

To export to as if during text, be not text and number of color when being one perhaps at the object that will export, described control module is not carried out and is reduced the processing that adheres to the amount of liquid on the recording medium.

10. printer driver as claimed in claim 9, wherein, control module comprises the gray scale amending unit, it is used for selectively carrying out the controllable gray scale correction and adopts the common gray scale correction that common gray value carried out, wherein, the controllable gray scale value is adopted in described controllable gray scale correction, so that reduce aberration.

11. printer driver as claimed in claim 10, wherein, described controllable gray scale value is the product of common gray value and COEFFICIENT K, and wherein, COEFFICIENT K is arranged between 0.35 to 0.65.

12. printer driver as claimed in claim 11, wherein, when the view data regulation was carried out double-sided recording modes, control module used the second controllable gray scale value, and wherein, this second controllable gray scale value obtains by multiply by above-mentioned product with coefficient M, and coefficient M is less than 1.0.

13. printer driver as claimed in claim 9, wherein, described control module comprises the gray scale amending unit, and this gray scale amending unit is carried out the common gray scale correction that is used to control the controllable gray scale correction of liquid adhesive capacity or is not used in control liquid adhesive capacity selectively based on the definite result or the outside instruction of supplying with of determining unit.

14. printer driver as claimed in claim 13, wherein, described control module adopts the controllable gray scale value, with the correction of execution controllable gray scale, and uses common gray value, to carry out common gray scale correction.

15. printer driver as claimed in claim 14, wherein, described controllable gray scale value is the product of common gray value and COEFFICIENT K, and wherein, COEFFICIENT K is arranged between 0.35 to 0.65.

16. printer driver as claimed in claim 15, wherein, when the view data regulation is carried out double-sided recording modes, control module adopts the second controllable gray scale value, wherein, this second controllable gray scale value obtains by multiply by described product with coefficient M, and coefficient M is less than 1.0.

17. one kind is used to handle and will supplies to the data processing equipment that image reproduces and form the view data of device, wherein, this image reproduces and forms device and can adopt the record head that has a plurality of nozzle arrays or utilize a plurality of record heads to carry out bidirectional record, and described record head is used for the drop of at least one color is ejected into recording medium; Described data processing equipment comprises:

Control module, it prevents in the pattern at aberration when bidirectional record, prevents that with not carrying out aberration the situation of step from comparing, and reduces the amount of liquid that adheres to every kind of color on the recording medium with constant ratio;

To export to as if during text, be not text and number of color when being one perhaps at the object that will export, described control module is not carried out and is reduced the processing that adheres to the amount of liquid on the recording medium.

18. data processing equipment as claimed in claim 17, wherein, described control module comprises the gray scale amending unit, this gray scale amending unit is used for selectively carrying out controllable gray scale correction or common gray scale correction, wherein, described controllable gray scale correction is used for reducing aberration at bidirectional record, and described common gray scale correction does not reduce the aberration on the view data.

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