JP2008073896A - Image forming apparatus and method for controlling the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image-recording technology for forming a high-quality image not having stripes or density variations by utilizing a quasi-random number formed by another processing section. <P>SOLUTION: This image processor comprises a pattern storage means for storing a dot pattern by each gradation, a setting means for setting a plurality of sets of continuous bits during outputting of a random number generation circuit, a standard deviation deriving means for deriving a standard deviation value of each value designated by L bits in K bits of the random number generation circuit with respect to each set of the L bits by generating a random number for the number of times set by the random number generation circuit beforehand, and a determination means for determining the L bits for selecting the dot pattern from the derived result by the standard deviation deriving means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that performs recording using a dot pattern and a control method thereof.

  With the spread of information processing equipment such as personal computers (PCs) in recent years, recording devices as image forming terminals have also been rapidly developed and spread. In particular, among various recording apparatuses, an inkjet apparatus that performs recording on a recording medium such as paper, cloth, a plastic sheet, and an OHP sheet by ejecting ink from an ejection port has been widespread. Inkjet devices have excellent characteristics such as low-noise, non-impact recording system, high-density and high-speed recording operation, easy compatibility with color recording, and low cost. Have. Therefore, it has become the mainstream of personal use recording devices. Furthermore, in recent years, in an ink jet recording apparatus, the resolution of recording has been improved, and the accompanying reduction in the size of recording droplets has progressed drastically, making it possible to output higher quality images. .

  However, higher resolution and higher definition of recorded images increase the amount of data to be processed in the recording system. Along with this, the image processing time and the transfer time are increased, and the image output time of the entire recording system is reduced. Therefore, a configuration and a processing method for performing data processing at a resolution lower than the recording resolution of the recording apparatus are disclosed.

  For example, Patent Document 1 discloses a recording system configured to input quinary image data at a resolution of 300 dpi from a host apparatus to a recording apparatus that performs binary recording with a recording resolution of, for example, 600 dpi (dots / inch). ing. Since image processing requires various and complicated processes such as luminance density conversion and quantization, even if it is executed by a host device such as a personal computer, the processing load and processing time are The number of pixels to be greatly affected. Therefore, by executing processing at a resolution lower than the recording resolution in this way, image processing can be completed in a shorter time with a smaller amount of data. However, in a binary recording apparatus that forms an image by dot recording / non-recording, it is necessary to perform resolution conversion for outputting image data received at 300 dpi 5 values as binary values at 600 dpi. Therefore, so-called dot arrangement patterning processing is applied at this stage.

  FIG. 1 is a schematic diagram for explaining dot arrangement patterning processing. The left side of the figure represents a five-value image signal input to the recording apparatus at 300 dpi, and the right side shows a dot pattern that is an output pattern in which dot recording / non-recording is associated with each image signal. ing. Each output pattern corresponding to one pixel of 300 dpi is composed of four 600 dpi areas shown in a small grid, 2 × 2 in the horizontal direction. Each part indicates an area where no dot is recorded. For level 0 and level 4, only one kind of dot pattern is prepared, but for level 1 to level 3, a plurality of kinds of dot patterns are prepared. Japanese Patent Application Laid-Open No. 2004-228561 discloses the content of selecting and arranging these plural dot patterns sequentially or randomly. As a result, the dot positions to be formed are not fixed even in an image having a uniform density, and it is described that there is an effect of reducing the “rushing phenomenon” associated with the pseudo halftone process.

  On the other hand, in Patent Document 2, any dot pattern corresponding to the gradation value of input image data is selected and assigned from a plurality of dot patterns based on a random value consisting of a predetermined number of bits. And the content which forms a binary image with the allocated dot pattern is disclosed. As described above, the dot arrangement patterning process is a process for determining a dot pattern that is actually recorded on the recording medium. Therefore, not only the burden of image processing before the dot arrangement patterning process is reduced, but also the arrangement method is devised to make the unevenness, streaks, pseudo contours, etc. peculiar to the recording apparatus inconspicuous. Further, it can contribute to the image quality and the reliability of the recording apparatus.

By performing the dot arrangement patterning process described above, it is possible to output a high-definition and high-resolution recording as a uniform image without unevenness at a relatively high speed.
Japanese Patent No. 3423491 JP 2000-141617 A

  However, when a plurality of dot patterns are randomly selected and assigned as described above, a circuit for generating random numbers or a memory for holding random values of a certain size is required. In general, an image processing apparatus performs processing using random values, such as processing for adding noise to an input image. Therefore, it is not useful in terms of cost or performance to hold a random number generation circuit or a random value of a certain size for each processing unit using random numbers as well as the dot patterning processing unit.

  In addition, when the dot pattern corresponding to the five gradation values shown in FIG. 1 is selected using the random value generated from the random number generation circuit of another processing unit, the selection is made according to the gradation value. It is difficult to select all possible dot patterns without bias. As a result of being biased toward a certain dot pattern in an image having the same gradation value, the recorded image may be an image with noise.

  The present invention has been made in view of such problems, and an image recording technique for creating a high-quality image free from streaks and density unevenness using pseudo-random values generated by other processing units. The purpose is to provide.

  In order to solve the above-described problems, the image forming apparatus of the present invention has the following configuration. That is, when an N-gradation pixel data value is input, one of the M dot patterns is selected at random, so that the range M in the random number data generated by the K-bit random number generation circuit is set. An image processing apparatus that allocates a value represented by the required number of bits L and M dot patterns, and associates M dot patterns with L bit values for each of N gradations. Pattern storing means for storing the data, setting means for setting a plurality of sets of consecutive L bits during the K bit output of the K bit random number generating circuit, and random numbers for the number of times set in advance by the K bit random number generating circuit. And a standard deviation deriving means for deriving a standard deviation value of each value represented by L bits in the K bits of the K bit random number generation circuit for each set of L bits, and the standard deviation deriving means Based on the derivation result, the K-bit output of said K-bit random number generating circuit, and a determining means for determining a L bits for selecting the dot pattern.

  Here, the determining means determines a set of L bits that minimizes the standard deviation value derived by the standard deviation deriving means as L bits for selecting the dot pattern. Further, the setting means sets the L bit to be equal to the N gradations. Alternatively, the setting means sets the L bit to be different for the N gray levels.

  In order to solve the above-described problems, a control method for an image forming apparatus of the present invention has the following configuration. That is, when an N-gradation pixel data value is input, one of the M dot patterns is selected at random, so that the range M in the random number data generated by the K-bit random number generation circuit is set. A pattern storage means for assigning a value represented by the required number of bits L and M dot patterns and storing M dot patterns in association with L bit values for each of N gradations A setting step of setting a plurality of sets of consecutive L bits during the K-bit output of the K-bit random number generation circuit, and a preset method in the K-bit random number generation circuit A standard deviation derivation step for generating a random number of times, and deriving a standard deviation value of each value represented by L bits in K bits of the K-bit random number generation circuit for each set of L bits; Based on the derivation result of the quasi-deviation obtaining step, from the K-bit output of said K-bit random number generating circuit, and a determination step of determining the L bits for selecting the dot pattern.

  According to the present invention, it is possible to provide an image recording technique for creating a high-quality image without streaks or density unevenness by using a pseudo random number value generated by another processing unit.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the constituent elements described in this embodiment are merely examples, and are not intended to limit the scope of the present invention only to them.

(First embodiment)
An image forming apparatus according to a first embodiment of the present invention will be described below by taking an ink jet recording apparatus as an example.

  In this specification, “recording” (sometimes referred to as “printing”) is not limited to the case of forming significant information such as characters and graphics, but may be significant. It also represents the case where an image, a pattern, a pattern, etc. are widely formed on a recording medium, or the medium is processed, regardless of whether it is manifested so that humans can perceive it visually. .

<Description of inkjet recording apparatus>
FIG. 10 is an external perspective view showing an outline of the configuration of an ink jet recording apparatus which is a typical embodiment of the present invention.

  As shown in FIG. 10, an ink jet recording apparatus (hereinafter referred to as a recording apparatus) reciprocates a carriage 102 in the direction of arrow A. This is done by transmitting the driving force generated by the carriage motor M1 from the transmission mechanism to the ink cartridge 110 on which the recording head 111 that performs recording by discharging ink in accordance with the ink jet method. At the same time, for example, a recording medium 150 such as recording paper is fed through the paper feeding mechanism 104, conveyed to a recording position, and recording is performed by discharging ink from the recording head 111 to the recording medium at the recording position. .

  Further, in order to maintain the state of the recording head 111 satisfactorily, the carriage 102 is moved to the position of the recovery device 106, and discharge recovery processing of the recording head 111 is intermittently performed.

  An ink tank 112 that stores ink to be supplied to the recording head 111 is attached to the ink cartridge 110 of the recording apparatus 100. The ink tank 112 is detachable from the ink cartridge 110.

  The recording apparatus 100 shown in FIG. 10 can perform color recording. For this reason, the ink cartridge 112 contains magenta (M), cyan (C), yellow (Y), and black (K) inks, respectively. Equipped with two ink tanks. These four ink tanks can be attached and detached independently.

  The carriage 102 and the ink cartridge 110 can achieve and maintain a required electrical connection by properly contacting the joint surfaces of both members. The recording head 111 records by selectively ejecting ink from a plurality of ejection ports by applying energy according to a recording signal. In particular, the recording head 111 of this embodiment employs an ink jet system that ejects ink using thermal energy, and includes an electrothermal transducer to generate thermal energy. The electrical energy applied to the electrothermal transducer is converted into thermal energy, and pressure changes due to bubble growth and contraction caused by film boiling caused by applying the thermal energy to the ink. Using this pressure change, ink is ejected from the ejection port. The electrothermal transducer is provided corresponding to each of the ejection ports, and ink is ejected from the corresponding ejection port by applying a pulse voltage to the corresponding electrothermal transducer in accordance with the recording signal.

  As shown in FIG. 10, the carriage 102 is connected to a part of the drive belt of the transmission mechanism that transmits the driving force of the carriage motor M1, and is slidably guided in the direction of arrow A along the guide shaft. It has come to be supported. Accordingly, the carriage 102 reciprocates along the guide shaft by forward and reverse rotations of the carriage motor M1. A scale is provided for indicating the absolute position of the carriage 102 along the direction of movement of the carriage 102 (arrow A direction). In this embodiment, the scale uses a transparent PET film with black bars printed at the required pitch, one of which is fixed to the chassis 103 and the other is supported by a leaf spring (not shown). .

  Further, the recording apparatus 100 is provided with a platen (not shown) facing the discharge port surface where the discharge port (not shown) of the recording head 111 is formed. The ink cartridge 110 on which the recording head 111 is mounted is reciprocated by the driving force of the carriage motor M1, and at the same time, a recording signal is given to the recording head 111 to eject ink, thereby causing the recording medium 150 conveyed on the platen. Recording is performed across the entire width.

  Further, in FIG. 10, a transport roller driven by a transport motor M2 for transporting the recording medium 150 is illustrated. A pinch roller that abuts the recording medium 150 against the conveyance roller by a spring (not shown), a pinch roller holder that rotatably supports the pinch roller, and a conveyance roller gear that is fixed to one end of the conveyance roller are illustrated. Then, the conveyance roller is driven by the rotation of the conveyance motor M2 transmitted to the conveyance roller gear via an intermediate gear (not shown).

  Furthermore, there is a discharge roller for discharging the recording medium 150 on which the image is formed by the recording head 111 to the outside of the recording apparatus, and is driven by the rotation of the transport motor M2. The discharge roller abuts on a spur roller (not shown) that presses the recording medium 150 with a spring (not shown). There is also a spur holder that rotatably supports the spur roller.

  Further, the recording device 100 is provided with a recovery device 106 as shown in FIG. This is provided at a desired position (for example, a position corresponding to the home position) outside the range of reciprocating motion (outside the recording area) for the recording operation of the ink cartridge 110 on which the recording head 111 is mounted. Recover defects.

  The recovery device 106 includes a capping mechanism for capping the ejection port surface of the recording head 111 and a wiping mechanism for cleaning the ejection port surface of the recording head 111. In conjunction with capping of the ejection port surface by the capping mechanism, ink is forcibly discharged from the ejection port by a suction means (suction pump or the like) in the recovery device. Thereby, an ejection recovery process such as removing ink or bubbles with increased viscosity in the ink flow path of the recording head 111 is performed.

  Further, when the recording head 111 is not in operation or the like, the recording head 111 can be protected and the ink can be prevented from being evaporated and dried by capping the ejection port surface of the recording head 111 with a capping mechanism. On the other hand, the wiping mechanism is disposed in the vicinity of the capping mechanism, and wipes ink droplets adhering to the ejection port surface of the recording head 111.

  By these capping mechanism and wiping mechanism, the ink discharge state of the recording head 111 can be kept normal.

<Control configuration of inkjet recording apparatus>
FIG. 11 is a block diagram showing a control configuration of the recording apparatus shown in FIG.

  As shown in FIG. 11, the controller 600 includes an MPU 601, a ROM 602 storing a program corresponding to a control sequence described later, a required table, and other fixed data. In addition, a special application integrated circuit (ASIC) 603 that generates control signals for controlling the carriage motor M1, the transport motor M2, and the recording head 3 is provided. A system bus 605 is provided that connects the RAM 604, the MPU 601, the ASIC 603, and the RAM 604, which are provided with an image data development area, a work area for program execution, and the like to exchange data. Furthermore, an analog signal from a sensor group described below is input, A / D converted, and an A / D converter 606 that supplies a digital signal to the MPU 601 is configured.

  In FIG. 11, reference numeral 610 denotes a computer (or an image reading reader, digital camera, or the like) serving as a supply source of image data, and is collectively referred to as a host device. Image data, commands, status signals, and the like are transmitted and received between the host apparatus 610 and the recording apparatus 1 via an interface (I / F) 611.

  Reference numeral 620 denotes a switch group, which includes a power switch 621 and a print switch 622 for instructing the start of printing. Further, it includes a switch for receiving a command input by an operator, such as a recovery switch 623 for instructing start of processing (recovery processing) for maintaining the ink ejection performance of the recording head 3 in a good state. Reference numeral 630 denotes a position sensor 631 such as a photocoupler for detecting the home position h, a temperature sensor 632 provided at an appropriate location of the recording apparatus for detecting the environmental temperature, and the like. It is a sensor group.

  Further, 640 is a carriage motor driver that drives a carriage motor M1 for reciprocating scanning of the carriage 2 in the direction of arrow A, and 642 is a conveyance motor driver that drives a conveyance motor M2 for conveying the recording medium P.

  The ASIC 603 transfers drive data (DATA) of the printing element (ejection heater) to the printing head while directly accessing the storage area of the RAM 602 during printing scanning by the printing head 3.

  The configuration shown in FIG. 10 is a configuration in which the ink cartridge 6 and the recording head 3 can be separated, but a replaceable head cartridge may be configured by integrally forming them.

<Processing flow of image data conversion processing>
FIG. 2 is a functional block diagram relating to image data conversion processing.

  The application 201 generates image data to be recorded by the recording device. Here, the application 201 is a program that operates on an operating system (OS) of a host device such as a PC.

  Thereafter, the image data generated by the application 201 is processed as follows by the processing units of the pre-stage process 202, the post-stage process 203, the γ correction 204, the halftoning 205, and the dot arrangement patterning process 206.

  The pre-stage process 202 is a processing unit that performs color gamut mapping. Thereby, for example, data conversion for mapping a color gamut reproduced by image data of the sRGB standard into a color gamut reproduced by the recording apparatus is performed. For example, by using a three-dimensional LUT, a luminance signal that is configured with a pixel density of 300 dpi and each pixel is represented by a value of R, G, and B (8 bits for each color) in sRGB, R, G, The value is converted into a value of B (8 bits for each color).

  The post-stage process 203 is a processing unit that converts R, G, and B values into Y, M, C, and K values. That is, color separation data Y, M, C, and K (8 bits for each color) corresponding to the combination of inks that reproduce the color represented by this data based on the R, G, and B values to which the color gamut has been mapped by the pre-processing 202. ) Is performed. Here, similarly to the pre-processing 202, it is assumed that interpolation calculation is performed in combination with a three-dimensional LUT.

  The γ correction 204 performs gradation value conversion for each color separation data Y, M, C, and K. Specifically, using the one-dimensional LUT, the color separation data Y, M, C, and K obtained by the post-processing 203 are converted according to the tone characteristics of the corresponding color ink.

  Halftoning 205 is a processing unit that converts (quantizes) color separation data from 8 bits for each color to 3 bits for each color. That is, the image data of color separation data Y, M, C, K (each color 8 bits) configured with a pixel density of 300 dpi is converted into color separation data (each color 3 bits) similarly configured with a pixel density of 300 dpi. In the present embodiment, 256-level 8-bit data is converted into 5-level 3-bit data using a multi-level error diffusion method. This 3-bit data serves as an index for indicating a dot pattern in a dot arrangement patterning process to be described later. Here, it is assumed that the halftoning 205 generates an 8-bit random value and uses the random value for image processing in the halftoning.

  The dot arrangement patterning process 206 is a processing unit that assigns a dot pattern of 2 rows and 2 columns (hereinafter referred to as 2 × 2) in which each dot is binary data to each color of color separation data of 3 bits for each color. Specifically, color separation data (3 bits for each color) configured with a pixel density of 300 dpi is converted into dot pattern data (1 bit for each color) configured with a dot density of 600 dpi. Each dot corresponds to recording / non-recording with ink.

  FIG. 3 is a diagram exemplarily showing a storage state of a 2 × 2 dot pattern for each gradation according to the first embodiment. That is, a 2 × 2 dot pattern as shown in FIG. 1 is arbitrarily stored in an 8 × 1 matrix for each of the five gradations.

  Since there is only one type of dot pattern for gradation values 0 and 4, the same dot pattern is stored in the 8 × 1 matrix. On the other hand, since there are four or six dot patterns for the gradation values 1, 2, and 3, respectively, these dot patterns are arbitrarily stored in the 8 × 1 matrix as shown in FIG. Yes.

  The dot arrangement patterning process 206 selects a dot pattern corresponding to the gradation value of each processing pixel from an 8 × 1 matrix from a value obtained by cutting out 3 bits from the 8-bit random value generated in the halftoning 205. . For example, if the extracted 3-bit value is “010” in a pixel with a gradation value of 1, a 2 × 2 dot pattern with gradation value 1 and matrix number 3 in FIG. 3 is selected. That is, the dot pattern corresponding to the dot array number having a value obtained by adding 1 to the decimal representation of the cut out 3-bit value is selected. In the following, details of a method for selecting a 3-bit value cut out from an 8-bit random value generated in halftoning 205 will be described.

<Dot pattern selection flow>
As described above, the dot arrangement patterning process 206 cuts out 3 bits from the 8-bit random value generated in the halftoning 205, regards it as a random value, and uses it for selecting a dot pattern. However, the cut out 3-bit value is not necessarily a random value depending on the range of values that the 8-bit random value can take.

  In the following description, it is assumed that the 8-bit value generated in the halftoning 205 is 0 to 128 (decimal number). That is, in binary notation, 000000000000, 00000001,. . . , 01111111, 10000000, 129 types of values are generated randomly. In the following, “range of random value” means a range defined by the minimum value and the maximum value of the generated random value.

FIG. 4 is a diagram showing the frequency of occurrence of a 3-bit value depending on the cut-out position when a 3-bit value is cut out from an 8-bit random number value. Specifically, from an 8-bit random value,
(1) 3 bits of Bit0, Bit1, and Bit2 (2) 3 bits of Bit1, Bit2, and Bit3 (3) 3 bits of Bit2, Bit3, and Bit4 (4) 3 bits of Bit3, Bit4, and Bit5 (5) Bit4, Bit5 , Bit 6 3 bits (6) The number of selections for each dot pattern number (1 to 8) when 3 bits each of Bit 5, Bit 6, and Bit 7 are cut out is shown. That is, it corresponds to the generation distribution map of 3-bit values (000, 001, ..., 110, 111). It should be noted that the 8-bit value is changed to Bit0, Bit1,. . . It is expressed as Bit 6 and Bit 7, and is an example in the case where an 8-bit random number value is generated 2048 times in halftoning 205.

  As can be seen from FIG. 4, in (1) to (5), the dot pattern numbers (1 to 8) are selected almost equally. On the other hand, when 3 bits of “Bit5, Bit6, Bit7” in (6) are cut out, it is understood that the dot patterns of the dot pattern numbers 1 to 4 are selected in a biased manner. Therefore, it can be seen that the selected dot pattern is also biased depending on the bit position from which the 3-bit value used for selection is cut out.

  FIG. 5 shows a calculation of the standard deviation of the number of selections of each dot pattern for the above-described six types of bit cutout positions. From the nature of the standard deviation, the larger the value, the more the selection frequency varies. In other words, the larger the standard deviation value, the more biased the selection is to some dot patterns. From FIG. 5, it can be seen that the standard deviation value is the smallest when 3 bits of “Bit4, Bit5, Bit6” are cut out. Therefore, it can be seen that by selecting a dot pattern using 3 bits of “Bit4, Bit5, Bit6”, it is possible to select a dot pattern with the least deviation in each gradation value.

Therefore, the dot arrangement patterning process 206 obtains the standard deviation of the frequency of occurrence of each value when 3 bits of the 8-bit random value generated in the halftoning 205 are cut out prior to the dot pattern selection process. Then, the 3-bit position with the smallest standard deviation is determined as the cut-out position. With this configuration, even when the range of random values generated by the halftoning 205 is unknown, it is possible to select dot patterns more evenly (randomly). <Example of head outlet configuration>
FIG. 6 is a view showing an ejection port array of one color in the ink jet recording head. In the figure, the X direction indicates the main scanning direction of recording, and the Y direction indicates the sub scanning direction. One discharge port array is formed by arranging a plurality of discharge port arrays in the Y direction at a predetermined pitch Py. Further, such discharge port arrays are arranged at a distance of Px in the X direction in a state where they are shifted from each other by Py / 2 in the Y direction. When the recording head having such a configuration is used, dots are recorded on the recording medium at a pitch of Py / 2 in the Y direction by moving and scanning in the X direction while ejecting ink from each ejection port at a predetermined frequency. I can do it.

  That is, in the recording head, even if the ejection openings are not arranged in a line at the pitch of the recording resolution, the two lines arranged at a pitch twice the recording resolution are arranged so as to be shifted from each other by a half pitch, thereby achieving a desired recording resolution. This makes it possible to record the images. Such a configuration is applied to a recording head that achieves a particularly high recording resolution.

  In the above configuration, the two nozzle arrays are classified into nozzle arrays (odd nozzles) that record odd rasters and nozzle arrays (even nozzles) that record even rasters. It has been confirmed that deviations in the number of recordings between the odd-numbered raster and the even-numbered raster cause a difference in ejection frequency between the odd-numbered nozzle row and the even-numbered nozzle row, which affects the ejection state between the nozzle rows. ing. In such a situation, the discharge state of the entire recording head also becomes unstable. For this reason, when a recording head having a configuration as shown in FIG. 6 is applied, it is important to make the ejection frequency in each row as uniform as possible.

  Therefore, like the dot pattern stored in the 8 × 1 matrix corresponding to each gradation value in FIG. 3, the dot pattern is set so that the number of dots printed by the even raster and the odd raster in the matrix is equal. Store. By doing so, since the dot pattern is selected without deviation in each gradation value, the effect of averaging the number of recorded dots of even-numbered raster and odd-numbered raster can be obtained more than simply arranging dots randomly. be able to. Therefore, it is possible to further stabilize the image quality and maintain the reliability of the recording head as compared with the conventional case.

  As described above, the bit cutout position at which the dot pattern is selected most evenly is selected by determining the bit cutout position at which the standard deviation is minimized. Thereby, since the dot pattern of each gradation can be selected without deviation, it is possible to obtain a high-quality output image in which density unevenness and streaks are suppressed. Here, the pixel group consisting of 2 × 2 has been described, but the present invention can be similarly applied to, for example, 3 × 3, 4 × 4, and the like.

(Modification)
In the first embodiment, as shown in FIG. 3, eight types of dot patterns in an 8 × 1 matrix are selected for each gradation. However, as shown in FIG. 7, the number of dot patterns that can be selected for each gradation may be different. That is, in the case of gradation values 0 and 4, a unique dot pattern, in the case of gradation values 1 and 3, four different (2-bit) dot patterns, and in the case of gradation value 2, any two different two types You may comprise so that it may select from 8 types (3 bits) dot patterns which added the type.

  At this time, the dot arrangement patterning process 206 does not perform the dot pattern selection operation when the gradation values are 0 and 4. On the other hand, the dot arrangement patterning process 206 selects a dot pattern using a 2-bit value when the gradation value is 1 or 3, and selects a dot pattern using a 3-bit value when the gradation value is 2. That is, the number of bits to be cut out for selecting a 2 × 2 dot pattern may be different depending on the gradation value. The method for determining the 2-bit cutout position is the same as in the case of 3-bit.

FIG. 8 shows the calculated variance of the number of selections of each dot pattern for six types of 3-bit cutout positions. FIG. 9 shows the calculated variance of the number of selections of each dot pattern for seven types of 2-bit cutout positions. Here, the value of the variance is derived. However, since (variance) = (standard deviation) ^2, it is only necessary to select a cut-out position that minimizes the variance. That is, “Bit4, Bit5, Bit6” is selected as the 3-bit clipping position, and “Bit3, Bit4” is selected as the 2-bit clipping position.

  The present invention can be implemented in various forms without departing from the scope of the invention. For example, in the dot arrangement patterning process of the above-described embodiment, 300 dpi quinary input pixels are converted into 600 dpi binary data composed of 2 × 2 areas. However, the present invention is not limited to such a form. Any dot arrangement pattern of any size may be prepared as long as it is a conversion process adaptable to the output resolution of the printing apparatus with respect to the gradation value and resolution of the output data after halftoning.

  In the above embodiment, an 8-bit random value is generated in halftoning and the random value is used for image processing in halftoning. However, the processing unit that generates random numbers is not limited to this. Any processing unit may be used. Furthermore, the number of bits of the generated random number value and the random number generation method may be any bit and method.

  Furthermore, in the above-described embodiment, the dot pattern is stored in an 8 × 1 matrix for each gradation. However, the matrix size is not limited to this, and the matrix size can be various depending on other conditions such as the size of the dot pattern. Further, in the above embodiment, random numbers are generated 2048 times in order to determine the cut bit position from the standard deviation or variance value. However, the number of times the random number is generated is not limited to this, and the number may be changed according to the size of the image or the size that can hold the random number.

(Other embodiments)
Although the embodiments of the present invention have been described in detail above, the present invention may be applied to a system constituted by a plurality of devices or may be applied to an apparatus constituted by one device.

  The present invention can also be achieved by supplying a program that realizes the functions of the above-described embodiments directly or remotely to a system or apparatus, and the system or apparatus reads and executes the supplied program code. The Accordingly, the program code itself installed in the computer in order to realize the functional processing of the present invention by the computer is also included in the technical scope of the present invention.

  In this case, the program may be in any form as long as it has a program function, such as an object code, a program executed by an interpreter, or script data supplied to the OS.

  Examples of the recording medium for supplying the program include a floppy (registered trademark) disk, a hard disk, an optical disk (CD, DVD), a magneto-optical disk, a magnetic tape, a nonvolatile memory card, and a ROM.

  Further, the functions of the above-described embodiments are realized by the computer executing the read program. In addition, based on the instructions of the program, an OS or the like running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments can also be realized by the processing.

  Further, the program read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Thereafter, the CPU of the function expansion board or function expansion unit performs part or all of the actual processing based on the instructions of the program, and the functions of the above-described embodiments are realized by the processing.

It is a schematic diagram explaining a dot arrangement patterning process. It is a functional block diagram of image data conversion processing concerning a 1st embodiment. It is a figure which shows the storage state of the 2 * 2 dot pattern for every gradation which concerns on 1st Embodiment exemplarily. It is a figure which shows the generation frequency of 3 bit value depending on the cut-out position when 3 bit value is cut out from 8-bit random number value. It is a figure which shows what computed the standard deviation of the selection frequency of each dot pattern with respect to six types of 3 bit cut-out positions. FIG. 4 is a diagram illustrating a single color ejection port array in an inkjet recording head. It is a figure which shows the storing state of the 2 * 2 dot pattern for every gradation which concerns on a modification. It is a figure which shows what computed dispersion | distribution of the selection frequency of each dot pattern with respect to six types of 3 bit cut-out positions. It is a figure which shows what computed dispersion | distribution of the selection frequency of each dot pattern with respect to seven types of 2-bit cut-out positions. 1 is an external perspective view showing an outline of a configuration of an ink jet recording apparatus. 3 is a block diagram illustrating a configuration of a control circuit of the recording apparatus. FIG.

Claims (5)

When an N-gradation pixel data value is input, one of the M dot patterns is selected at random, so that it is necessary for the range M in the random number data generated by the K-bit random number generation circuit. An image processing apparatus that assigns a value represented by the number of bits L and M dot patterns,
Pattern storage means for storing M dot patterns in association with L-bit values for each of N gradations;
Setting means for setting a plurality of sets of consecutive L bits during K bit output of the K bit random number generation circuit;
A random number is generated for a preset number of times by the K-bit random number generation circuit, and a standard deviation value of each value represented by L bits in the K bits of the K-bit random number generation circuit is assigned to each set of L bits. Standard deviation deriving means derived for
Determining means for determining L bits for selecting the dot pattern from the K-bit output of the K-bit random number generation circuit based on the derivation result of the standard deviation deriving means;
An image processing apparatus comprising:   2. The image according to claim 1, wherein the determining unit determines a set of L bits that minimizes the standard deviation value derived by the standard deviation deriving unit as L bits for selecting the dot pattern. Processing equipment.   The image processing apparatus according to claim 1, wherein the setting unit sets the L bit to be equal to the N gradations.   The image processing apparatus according to claim 1, wherein the setting unit sets the L bit to be different with respect to the N gradations. When an N-gradation pixel data value is input, one of the M dot patterns is selected at random, so that it is necessary for the range M in the random number data generated by the K-bit random number generation circuit. A pattern storage means for allocating a value represented by the number of bits L and M dot patterns and storing M dot patterns in association with L bit values for each of N gray levels is provided. A control method for an image processing apparatus, comprising:
A setting step of setting a plurality of sets of consecutive L bits during K bit output of the K bit random number generation circuit;
A random number is generated for a preset number of times by the K-bit random number generation circuit, and a standard deviation value of each value represented by L bits in the K bits of the K-bit random number generation circuit is assigned to each set of L bits. A standard deviation derivation process derived for
A determination step of determining an L bit for selecting the dot pattern from a K-bit output of the K-bit random number generation circuit based on a derivation result of the standard deviation derivation step;
A control method comprising:

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