JP2019098700A - Controller and control method - Google Patents

Abstract

To improve sharpness even for an input image including an area with unclear boundary with a configuration having a low processing load.SOLUTION: A controller for controlling a recording apparatus for relatively reciprocating a recording head and a recording medium to form an image on the recording medium comprises: acquisition means for acquiring a sharpness recovery amount for recovering deterioration of spacial frequency characteristics of the image formed on the recording medium; and determination means for determining a scanning direction when forming dots for each pixel based on the acquired sharpness recovery amount.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a control apparatus and control method for improving the sharpness of an image.

  As an image forming method for forming an image on a recording medium, for example, an inkjet method is used. In the inkjet method, a desired image is formed on a recording medium by ejecting ink droplets from a plurality of recording elements to form a large number of dots on the recording medium. At this time, the ink ejected from the recording element is divided into a plurality of droplet groups when flying toward the recording medium, and a plurality of dot groups having a substantially constant separation distance are formed on the recording medium There is. Among such a plurality of dot groups, a dot which is attached (landed) temporally earlier on the recording medium and whose dot size is relatively large is also referred to as a main droplet (also referred to as a main dot), temporally later on the recording medium Dots that are attached and whose dot size is relatively small are called satellite dots (hereinafter referred to as satellites). The generation degree and the generation number of satellites on the recording medium are variously varied depending on the ejection control of the recording head, the composition of the ink, the distance between the recording head and the recording medium, and the scanning and conveying accuracy of the recording head and the recording medium. The satellite is not a dot that should be originally formed on the recording medium, and causes a reduction in the sharpness of the image when the satellite is formed in the vicinity of a character or an edge. Therefore, it is necessary to minimize the influence on satellite image quality.

  Conventionally, Patent Document 1 is known as an image processing technique in which the influence on satellite image quality is taken into consideration. Patent Document 1 is a technique of extracting a predetermined area of an input image and determining a recording direction when forming the extracted boundary portion based on information on sharpness. Specifically, in order to suppress the influence of the satellite on the image quality, the recording direction of the boundary is determined so that the satellite lands on the dark part side of the boundary when importance is given to the sharpness of the boundary.

JP, 2006-27181, A

  However, the technology described in Patent Document 1 requires a process for extracting a predetermined area, and there is a problem that the processing load is large. Further, for example, when the technique described in Patent Document 1 is applied to an input image including halftone edges in which the boundary of the region is unclear, the region of the boundary may be extracted erroneously. As described above, in the prior art represented by Patent Document 1, there is a problem that the adhesion position of the satellite can not be controlled, and the improvement of the sharpness is insufficient.

  The present invention has been made in view of these problems, and its object is to provide an input image including an area with unclear boundaries, with a configuration having a smaller processing load than a conventional method of extracting a predetermined area. Also to provide a technology capable of improving sharpness.

  One aspect of the present invention relates to a control device. This control device is a control device that controls the recording apparatus for forming an image on the recording medium by relatively reciprocating the recording head and the recording medium, and the spatial frequency of the image formed on the recording medium The image processing apparatus includes an acquisition unit that acquires a sharpness recovery amount for recovering the deterioration of the characteristic, and a determination unit that determines a scanning direction when forming a dot for each pixel based on the acquired sharpness recovery amount.

  According to the present invention, as compared with the conventional method of extracting a predetermined area, the sharpness can be improved even for an input image including an area where the boundary is unclear, with a configuration with less processing load.

FIG. 1 is an external perspective view showing an overview of the configuration of a printer according to a first embodiment that performs recording using an inkjet recording head. FIG. 1 is a block diagram showing the configuration of an image forming system according to a first embodiment. FIG. 3 is a flowchart showing the flow of a series of processes in the image forming system of FIG. 2; The figure which shows an exemplary measurement chart. The figure which shows an example of P (u) and Ra (u). The flowchart which shows the flow of a series of processes in the scanning direction determination process. FIGS. 7A and 7B are diagrams showing an example of binary image data and an amount of sharpness recovery. The figure which shows the relationship between the determination condition in pre-processing of scanning direction determination, and the scanning direction calculated according to it. 9 (a) to 9 (f) are explanatory diagrams for illustrating the reason why the scanning direction is determined by the relationship between the signs of the amount of sharpness recovery. FIGS. 10A to 10C are schematic diagrams for explaining the details of the path data replacement process. FIGS. 11 (a) to 11 (d) are explanatory diagrams showing the effect when the first embodiment is applied in comparison with the conventional example. The flowchart which shows the flow of a series of processes in the scanning direction determination process. The figure which shows the relationship between the determination condition in pre-processing of scanning direction determination, and the scanning direction calculated according to it. The flowchart which shows the flow of a series of processes in the scanning direction determination process. The figure which shows the relationship between the determination condition in pre-processing of scanning direction determination, and the scanning direction calculated according to it. FIG. 14 is a block diagram showing the configuration of an image forming system according to a fourth embodiment. The flowchart which shows the flow of a series of processes in the scanning direction determination process. 18 (a) to 18 (f) are schematic diagrams showing the relationship between the satellite distance and the adhesion position in the reciprocation recording. FIG. 14 is a block diagram showing the configuration of a multifunction peripheral according to a fifth embodiment. FIG. 16 is a block diagram showing the configuration of an image forming system according to a sixth embodiment. FIGS. 21A to 21D are schematic diagrams showing correction processing in the halftone processing unit according to the sixth embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiments do not limit the present invention, and all combinations of the features described in the present embodiment are not necessarily essential to the solution means of the present invention. The same or equivalent constituent elements, members, processes, and signals shown in the drawings are denoted by the same reference numerals, and redundant description will be omitted as appropriate. Moreover, in each drawing, a part of the member which is not important for description is abbreviate | omitted and displayed.

  In this specification, "recording" (hereinafter also referred to as "printing") refers not only to the formation of significant information such as characters and figures, but also to images, patterns, and the like on recording media widely regardless of significance. A case where a pattern or the like is formed or processing of a medium is performed is also shown. In addition, it does not matter whether it is manifested so that humans can perceive it visually.

  Also, "recording medium" refers not only to paper used in general recording devices, but also widely to those that can accept ink, such as cloth, plastic film, metal plate, glass, ceramics, wood, leather, etc. It shall be.

  Also, “ink” should be interpreted broadly as in the above definition of “recording”, and by being applied on the recording medium, formation of an image, a pattern, a pattern, etc. or processing of the recording medium, or Let it represent a liquid that can be subjected to the treatment of the ink. Examples of the treatment of the ink include coagulating or insolubilizing a coloring agent in the ink applied to the recording medium.

  Further, the term "recording element (or nozzle)" generally refers to an ejection port, a liquid path communicating with the ejection port, and an element that generates energy used for ink ejection unless otherwise specified.

First Embodiment
FIG. 1 is an external perspective view showing an outline of a configuration of a printer 1 according to a first embodiment for performing recording using an inkjet recording head. The printer 1 mounts on the carriage 2 a recording head 3 that ejects ink to perform recording in accordance with the inkjet method, and reciprocates the carriage 2 in the scanning direction (the direction indicated by the arrow A) to perform recording. The printer 1 forms an image on a recording medium P by multi-pass printing. The printer 1 feeds a recording medium P such as recording paper through the paper feeding mechanism 5, conveys it to the recording position, and performs recording by discharging ink from the recording head 3 to the recording medium P at the recording position. .

  Not only the recording head 3 is mounted on the carriage 2 of the printer 1, but also an ink tank 6 for storing the ink supplied to the recording head 3 is mounted. The ink tank 6 is configured to be removable from the carriage 2.

  The printer 1 is capable of color recording, so four ink tanks 6 (ink cartridges) each containing magenta (M), cyan (C), yellow (Y) and black (K) inks in the carriage 2 Also called). Each of the four ink tanks 6 is configured to be detachable independently.

  The recording head 3 employs an inkjet method of ejecting ink using thermal energy. For this reason, an electrothermal converter such as an electric heater is provided. The electrothermal transducers are provided corresponding to the respective ejection openings, and a pulse voltage is applied to the corresponding electrothermal transducers according to the recording signal, whereby the ink is ejected from the corresponding ejection openings.

(Configuration of image forming system)
FIG. 2 is a block diagram showing the configuration of the image forming system according to the present embodiment. Hardware-wise, each block shown in this figure and other block diagrams in the present specification can be realized by a device such as a CPU of a computer or a mechanical device, and can be realized by a computer program etc. in software. However, here, the functional block realized by those cooperation is drawn. Therefore, it is understood by those skilled in the art who have been mentioned in the present specification that these functional blocks can be realized in various forms by a combination of hardware and software.

  The image forming system includes an image processing apparatus 10 and a printer 1. The image processing apparatus 10 can be implemented by, for example, a printer driver installed in a general personal computer. In that case, each unit of the image processing apparatus 10 described below is realized by the computer executing a predetermined program. As another configuration, for example, the printer 1 may be configured to include the image processing apparatus 10.

  The image processing apparatus 10 includes an image input terminal 101, a low frequency recovery unit 102, a low frequency storage unit 103, a full frequency recovery unit 110, a full frequency storage unit 111, a color separation storage unit 105, and a color separation unit. A high frequency generation unit 112, an OPG storage unit 107, an OPG processing unit 106, a matrix storage unit 109, a halftone processing unit 108, and an output terminal 113 are provided. The printer 1 includes a carriage 2, a recording head 3, a sheet feeding mechanism 5, a head control unit 204, an ink color selection unit 210, a direction control unit 201, and an input terminal 211.

  The image processing apparatus 10 and the printer 1 are connected by a printer interface or a circuit. The image processing apparatus 10 acquires image data to be recorded (printed) from the image input terminal 101. Image data is data representing an 8-bit RGB color image.

  The low frequency recovery unit 102 performs low frequency recovery processing on the input RGB image data. The low frequency recovery unit 102 acquires the filter coefficient of the low frequency recovery filter stored in the low frequency storage unit 103 in the low frequency recovery processing, and performs a convolution operation on the luminance value of the input image to obtain a low frequency component. Recover. This is a process called so-called filtering. In the present embodiment, a filter of 11 × 11 size is used as the low frequency recovery filter. The method of creating the low frequency recovery filter will be described later.

  The color separation unit 104 generates a 4-plane 8-bit ink value image corresponding to 4-color ink included in the printer 1 from the image data corrected by the low frequency recovery unit 102. In the present embodiment, four color inks of cyan (C), magenta (M), yellow (Y), and black (K) are mounted on the recording head 3, and an ink value image generated by the color separation unit 104 is Four planes correspond to four color inks, respectively. The color separation unit 4 refers to a three-dimensional color separation LUT (Look-Up Table) stored in the color separation storage unit 105 at the time of color separation processing. In the color separation LUT, ink values of four colors are stored on lattice points thinned out to 17 × 17 × 17 points. The values between the grid points are calculated by linear interpolation.

  An OPG (output gamma) processing unit 106 subjects the ink value image generated by the color separation unit 104 to gamma correction processing. The OPG processing unit 106 refers to the one-dimensional OPGLUT stored in the OPG storage unit 107 at the time of gamma correction processing. In the OPG LUT, a value is set in advance for each ink color so that the lightness of the printed matter linearly changes with respect to the signal value of the ink value image when printing is performed using only each ink of CMYK. As the evaluation value of lightness, L * defined by CIELAB is used.

  The halftone processing unit 108 converts the ink value image of each color obtained by the OPG processing unit 106 into a binary image (or an image having a number of gradations and a number of gradations smaller than the number of input gradations). In the present embodiment, the halftone processing unit 108 refers to the dither matrix stored in the matrix storage unit 109, and performs threshold processing for each pixel based on the dither method to cope with ON / OFF of the ink. Generate binary image data.

  The full frequency recovery unit 110 performs full frequency recovery processing on the input RGB image data. The full frequency recovery unit 110 acquires the full frequency recovery filter stored in the full frequency storage unit 111 in the full frequency recovery processing, and recovers all frequency components by performing a convolution operation on the luminance value of the input image. . In the present embodiment, an 11 × 11 size filter is used as the full frequency recovery filter. The method of creating the full frequency recovery filter will be described later.

  The high frequency generation unit 112 generates a high frequency recovery amount image by calculating the difference between the image data corrected by the low frequency recovery unit 102 and the image data corrected by the full frequency recovery unit 112.

  The binary image data (for four colors of ink) generated by the halftone processing unit 108 and the high frequency recovery amount image generated by the high frequency generation unit 112 are output to the input terminal 211 of the printer 1 through the output terminal 113. Be done.

  The direction control unit 201 determines the scanning direction at the time of dot-on for each pixel based on the high frequency recovery amount image acquired from the image processing apparatus 10 via the input terminal 211. The dot on time means that a dot is formed. The direction control unit 201 includes a path replacing unit 209, a path decomposing unit 207, a preprocessing unit 206, and a path mask storage unit 208.

  The preprocessing unit 206 acquires binary image data (for four colors of ink) and a high frequency recovery amount image from the input terminal 211, and performs dot on for at least a part of the pixels of the binary image data. The time scanning direction is determined for each pixel. In the pre-processing unit 206, the scanning direction when the dot is on is one of the forward recording direction (first direction) and the reverse recording direction (second direction) opposite to each other for one pixel of the binary image data. Not determined or not determined at this stage. If not determined, the scanning direction is arbitrary (any of the forward recording direction and the backward recording direction).

  The pass separation unit 207 generates scan data corresponding to each ink color based on the binary image data and the pass mask acquired from the pass mask storage unit 208. The scan data is a pattern that a plurality of divided nozzle groups print in each printing scan. The scan data are complementary to each other, and when the patterns of all the nozzle groups are superimposed, the recording of the entire area is completed. Every time each printing scan is completed, the printing medium is transported in the transport direction by the width of the plurality of divided nozzle groups. The transport direction and the scanning direction are orthogonal to each other.

  The path interchanging unit 209 acquires scan data of each path output from the path disassembling unit 207, and performs the process of exchanging path data while referring to the scanning direction of each pixel determined by the preprocessing unit 206. When the scanning direction at the time of dot on of the pixel determined by the pre-processing unit 206 is different from the scanning direction at the time of dot on of the pixel in the scan data of each pass output by the pass decomposing unit 207, the pass replacing unit 209 , Replace the path data so that the former takes precedence over the latter.

  The ink color selection unit 210 selects a corresponding ink color from the ink colors mounted on the recording head 3 based on the replaced scan data output by the pass replacement unit 209.

  In the printer 1, binary image data generated by the image processing apparatus 10 is formed on the recording medium P by moving the recording head 3 in the vertical and horizontal directions relatively to the recording medium P. In the present embodiment, an inkjet type is used as the recording head 3. The recording head 3 has a plurality of recording elements (nozzles). In the present embodiment, four color inks of cyan (C), magenta (M), yellow (Y) and black (K) are mounted on the recording head 3. The carriage 2 moves the recording head 3 under the control of the head control unit 204. The sheet feeding mechanism 5 conveys the recording medium P under the control of the head control unit 204. In the present embodiment, a multipass printing method is used in which an image is completed by scanning the printing medium P a plurality of times (for example, 4 times) by the printing head 3.

  An image is formed in accordance with the configuration described above.

(Processing flow of image forming system)
Next, a processing flow in the image forming system of the present embodiment provided with the above-described functional configuration will be described. FIG. 3 is a flowchart showing the flow of a series of processing in the image forming system.
First, in step S201, the image processing apparatus 10 acquires an input RGB image from the image input terminal 101.
Next, in S202, the low frequency recovery unit 102 performs low frequency recovery processing on the input RGB image. The low frequency recovery unit 102 uses a two-dimensional filter stored in the low frequency storage unit 103 in the low frequency recovery process.
Next, in S203, the color separation unit 104 generates an ink value image from the image data corrected by the low frequency recovery unit 102. The color separation unit 104 refers to the three-dimensional color separation LUT stored in the color separation storage unit 105 at the time of color separation processing.
Next, in S204, the OPG processing unit 106 performs gamma correction processing on the ink value image generated by the color separation unit 104.
Next, in step S205, the halftone processing unit 108 performs halftone processing to convert the data after the OPG processing into binary data. The halftone processing unit 108 refers to the dither matrix stored in the matrix storage unit 109 in halftone processing.
On the other hand, in S206, the full frequency recovery unit 110 performs full frequency recovery processing on the input image. The full frequency recovery unit 110 uses a two-dimensional filter stored in the full frequency storage unit 111 in the full frequency recovery process.
Next, in S207, the high frequency generation unit 112 performs high frequency recovery amount image generation processing. The high frequency generation unit 112 generates a high frequency recovery amount image by calculating a difference between the image data corrected by the full frequency recovery unit 110 and the image data corrected by the low frequency recovery unit 102 in the high frequency recovery amount image generation process. Generate

  The high frequency recovery amount image may be called a sharpness recovery amount depending on the purpose of use. In the following description, although it is described as the sharpness recovery amount, the high frequency recovery amount image and the sharpness recovery amount represent equivalent data and are only differences in expression. The sharpness recovery amount in the present embodiment is a “compensation over / under distribution” for performing frequency recovery processing, and is a concept different from the edge amount obtained by so-called edge detection. Therefore, unlike the known Laplacian filter etc., it is possible to compensate not only the edge portion but also any frequency deterioration.

  The binary image data after halftone processing obtained in the above steps and the generated sharpness recovery amount have an arbitrary size such as the entire image or the bandwidth of the unit recording area, and the output terminal 113 The signal is output and passed to the pre-processing unit 206 via the input terminal 211.

  Next, in step S208, the preprocessing unit 206 acquires binary image data (for four colors of ink) and the amount of sharpness recovery from the input terminal 211, and at least a part of the pixels of the binary image data. For the dot on, the scanning direction is determined. The scanning direction at dot on time is determined in either the forward recording direction or the reverse recording direction for one pixel of binary image data, or not determined at this stage. If not determined, the scanning direction is arbitrary (any of the forward recording direction and the backward recording direction). Details of the scan direction determination will be described later.

  Next, in S209, the pass decomposing unit 207 performs pass decomposing processing of converting the image data received from the pre-processing unit 206 into scan data based on the pass mask acquired from the pass mask storage unit 208. In the present embodiment, the path decomposition unit 207 decomposes the input image data (binary image data) into four passes. At this time, the pass resolution mask is stored in the pass mask storage unit 208, and an evenness mask in which the implantation amount of each pass is 25% is used. The uniform mask is an example, and for example, a so-called gradation mask may be used in which the amount of impact of the preceding pass and the subsequent path is smaller and the amount of impact of the central pass is larger. In addition to the above, a mask may be used in which the implantation amount of each pass of the pass mask is arbitrary.

  Next, in step S210, the path replacement unit 209 acquires scan data of each pass output from the path decomposition unit 207, and refers to the scan direction of the pixels determined by the pre-processing unit 206, while replacing the path data. I do. When the scanning direction at the time of dot on of the pixel determined by the pre-processing unit 206 is different from the scanning direction at the time of dot on of the pixel in the scan data of each pass output by the pass decomposing unit 207, the pass replacing unit 209 , Replace the path data so that the former takes precedence over the latter. Details of the path data replacement process will be described later.

  Next, in step S211, the ink color selection unit 210 selects an ink color that matches the replaced scan data output from the pass replacement unit 209, and image formation is started. In the image formation, while moving the recording head 3 with respect to the recording medium P, each nozzle is driven at a constant driving interval to record an image on the recording medium P. The recording medium P is transported by a predetermined transport amount for each scan.

  Thus, a series of image forming processes are completed.

(How to create full frequency recovery filter and low frequency recovery filter)
Hereinafter, a method of creating the full frequency recovery filter and the low frequency recovery filter in the present embodiment will be described.
First, a sharpness measurement chart is output using the filter design target printer 1. When outputting the measurement chart, sharpness recovery processing is not performed.

  FIG. 4 is a diagram showing an exemplary measurement chart 301. As shown in FIG. The measurement chart 301 is an example of an image chart including a plurality of sine wave patterns different in frequency and direction and a uniform pattern (for example, solid white and solid black). In the measurement chart 301, the patterns 302, 303, 304 are lateral sine wave patterns of different frequencies, and the patterns 305, 306, 307 are longitudinal sine wave patterns of different frequencies. Further, the pattern 308 is a uniform white solid pattern, and the pattern 309 is a uniform black solid pattern.

Here, the frequency response value P (u) is calculated, for example, as an optical transfer function (MTF) according to the following equation (1).
P (u) = C (u) / C '
... Equation (1)
However, u is a frequency of a sine wave pattern, and C (u) and C 'are denoted by a following formula.
C (u) = {Max (u) -Min (u)} / {Max (u) + Min (u)}
C '= (White-Black) / (White + Black)

  At this time, Max (u) is the maximum brightness of the sine wave pattern changing at frequency u, Min (u) is the minimum brightness of the sine wave pattern changing at frequency u, White and Black are the brightness of the uniform white solid pattern, respectively. And the lightness of a uniform pattern of solid black.

In addition, calculation of an optical transfer function is not limited to this, For example, you may use the following formula (2).
P (u) = {Max (u) -Min (u)} / (White-Black)
... Equation (2)

  Further, in the equation (2), the frequency response value P (u) is calculated with Max (u), Min (u), White and Black as lightness, for example, luminance and density, device RGB values of the measuring apparatus The frequency response value may be calculated using or the like. Also, as the measurement chart, the frequency response value P (u) may be acquired using a rectangular wave pattern instead of a sine wave pattern. In that case, the value of the contrast transfer function (CTF) calculated by applying equation (1) to the rectangular wave pattern is used as the frequency response value P (u). Alternatively, the MTF value obtained by converting the CTF value using a known Coltmann correction equation may be used as the frequency response value P (u).

  Next, based on the frequency response value P (u), the frequency characteristic Ra (u) = 1 / P (u) of the full frequency recovery filter is calculated. FIG. 5 is a diagram showing an example of P (u) and Ra (u). Ra (u) has a strong response in a high frequency region where the value of u is large. On the other hand, the frequency characteristic Rl (u) of the low frequency recovery filter is generated by correcting the response higher than the predetermined frequency ub with respect to Ra (u) so as to be substantially flat.

  Finally, the coefficients of the full frequency recovery filter and the low frequency recovery filter are calculated by performing inverse Fourier transform on the frequency characteristics Ra (u) and Rl (u).

(Details of scan direction determination process)
Hereinafter, the details of the scanning direction determination process of the present embodiment will be described. FIG. 6 is a flowchart showing the flow of a series of processing in the scanning direction determination processing.
First, in step S501, the preprocessing unit 206 acquires an input image. The input image here is binary image data after halftone processing that is input to the preprocessing unit 206 via the input terminal 211.
Next, in step S502, the pre-processing unit 206 acquires the sharpness recovery amount. The sharpness restoration amount is a positive or negative value corresponding to each pixel of the binary image data acquired in S501.

  FIGS. 7A and 7B are diagrams showing an example of binary image data and an amount of sharpness recovery. FIG. 7A shows an example of binary image data. FIG. 7 (b) shows an example of the sharpness recovery amount corresponding to the binary image data shown in FIG. 7 (a). The sharpness recovery amount is an amount for recovering the deterioration of the spatial frequency characteristic of the image formed on the recording medium P. The amount of sharpness recovery represents that the higher the value, the higher the density, and the smaller the value, the lower the density is corrected, in order to restore the sharpness of the image.

  The binary image data of FIG. 7A indicates data obtained by binarizing multi-level data in which the amount of strikes of the left half of the image is 75% and the amount of strikes of the right half of the image is 25%. As shown in FIG. 7B, in a region 750 including pixels in the fourth and fifth columns from the left, the sharpness recovery amount on the left side (fourth column) is a large positive value, and the right side The sharpness recovery amount in column 5) is a large negative value (absolute value). The sharpness recovery amount has a characteristic that a pixel whose positive / negative sign is inverted (zero cross) corresponds to an edge. By referring to the sharpness recovery amount, it is possible to estimate the density relationship between the position of the edge and the density at both ends of the edge even for an edge that can not be clearly separated by binary image data. In the present embodiment, such characteristics of the sharpness recovery amount are used.

Returning to FIG. 6, in step S503, the pre-processing unit 206 has a positive sharpness recovery amount of a pixel adjacent to the processing target pixel (processing point) in the forward recording direction and is adjacent to the processing target pixel in the reverse recording direction. It is determined whether the sharpness recovery amount of the pixel is negative. When the determination result is Yes, the process proceeds to S504, and when the determination result is No, the process proceeds to process S505.
When the process proceeds to step S504, the pre-processing unit 206 determines the scanning direction when the dot of the processing target pixel is on as the forward recording direction.

If the process proceeds to step S505, the pre-processing unit 206 determines that the sharpness recovery amount of the pixel adjacent to the processing target pixel in the forward recording direction is negative, and the sharpness recovery of the pixel adjacent to the processing target pixel in the backward recording direction. Determine if the quantity is positive. When the determination result is Yes, the process proceeds to S506, and when the determination result is No, the process proceeds to S507.
If the process proceeds to step S506, the pre-processing unit 206 determines the scanning direction when the dot of the processing target pixel is on as the backward recording direction.
When the process proceeds to step S <b> 507, the preprocessing unit 206 does not determine, in the preprocessing, the scanning direction at the time when the dot of the processing target pixel is on, that is, arbitrary. Here, “arbitrary” indicates that the pre-processing unit 206 does not designate reciprocation, which may be in any direction.

  After performing the processes of S504, S506, and S507, the process proceeds to S508. In step S508, the pre-processing unit 206 determines whether pre-processing has been performed on all the pixels of the input image acquired in step S501. If the determination result is Yes, the process proceeds to S209. If the determination result is No, the process returns to S502, and the same process is performed on the next processing target pixel. The processes of S209, S210, and S211 are as described with reference to FIG.

  When reference is made to the sign of the sharpness recovery amount, the most significant bit (MSB) of the value corresponding to the corresponding pixel on the memory such as the RAM storing the sharpness recovery amount is referred to. The load on the implementation can be reduced by referencing only the most significant bit. In addition, acquisition of the information of the code | symbol of sharpness recovery amount may be implement | achieved by another means. For example, when the sharpness recovery amount is stored in the memory, only the most significant bit may be stored separately. In this case, memory access when referring to the most significant bit can be significantly reduced.

  Thus, a series of scanning direction determination processes are completed.

(Relationship between satellite generation position in reciprocating recording and scanning direction to be determined)
The relationship between the generation position of the satellites in the round trip recording and the scanning direction to be determined will be described below.

  FIG. 8 is a diagram showing the relationship between the determination condition in the pre-processing of scan direction determination and the scan direction obtained according to the determination condition. In order to simplify the explanation, it is assumed that the sharpness recovery amount of 0 is included in the positive. In the present embodiment, the scanning direction at the time of dot-on is determined based on the sign of the sharpness recovery amount. When the sign of sharpness recovery amount is reversed between the adjacent pixel in the backward recording direction and the adjacent pixel in the forward recording direction, the scanning direction when the dot of the processing target pixel is on is the forward recording direction and the backward recording direction. It is decided on one of them. Hereinafter, the reason for such determination will be described.

  FIGS. 9A to 9F are explanatory diagrams for illustrating the reason why the scanning direction is determined by the relationship of the signs of the amount of sharpness recovery. In the determination of the scanning direction at dot on time, the direction of the satellite generated in each of the two-way recording is considered. Since the satellites are not originally dots to be formed on the recording medium, the scanning direction at dot on time is determined so that the influence on the image quality of the satellites is minimized.

  FIGS. 9A and 9B are schematic diagrams showing the positional relationship between the main droplet and the satellite in the forward recording direction and the positional relationship between the main droplet and the satellite in the reverse recording direction, respectively. In FIG. 9A, when dots are formed in the backward recording direction from the left to the right in the figure (that is, when dots are on), the satellite discharge speed is slower than the main droplet discharge speed. It adheres to the main recording side (right side) of the main drop.

  On the other hand, in FIG. 9 (b), when dots are formed in the right to left backward recording direction in the figure, as in the case of FIG. 9 (a), the discharge speed of the satellite is compared to the discharge speed of the main droplet. Because it is slow, the satellites adhere to the main droplet in the backward direction (left side). This is the reverse of the case of the forward recording. Thus, the attachment position of the satellite to the main drop differs depending on the scanning direction. In the present embodiment, it is assumed that the pixel to which the satellite adheres and the pixel to which the main droplet adheres are always adjacent regardless of the forward recording direction and the reverse recording direction.

  FIGS. 9 (c) and 9 (d) are schematic diagrams representing pixel values of an input image in the scanning direction in one dimension, respectively. In each of FIGS. 9C and 9D, the pixel value of the input image = “255” is a dot on (ON) pixel, and the pixel value of the input image = “0” is a non-dot on (OFF) pixel Represents FIG. 9C shows an edge area having a relatively high density in the forward recording direction, and FIG. 9D shows an edge area having a relatively high density in the reverse recording direction.

  FIGS. 9 (e) and 9 (f) are schematic diagrams showing the amount of sharpness recovery corresponding to the input image of FIGS. 9 (c) and 9 (d), respectively. In both of FIGS. 9E and 9F, the sharpness recovery amount is a large positive value with respect to the pixel on the side where the density of the edge area of the input image is high. Further, for the pixel on the side where the density of the edge region of the input image is low, the sharpness recovery amount is a large negative value of the absolute value.

  Description will be given by focusing on the pixel 801 in FIG. The sharpness restoration amount corresponding to the pixel 801 is the code 802 in FIG. As can be seen from FIG. 9E, the sharpness recovery amount (symbol 805) of the adjacent pixel in the backward recording direction is negative, and the sharpness recovery amount (symbol 806) of the adjacent pixel in the forward recording direction is positive. . This corresponds to the case of the first line of the table of FIG. 8, and the scanning direction at the time of dot on at this time is the forward recording direction. That is, the pixel 801 is dot-on in the forward recording direction shown in FIG. 9A, and the satellite at that time adheres to the right side of the pixel 801 (the high density side of the edge area).

  On the other hand, focusing on the pixel 803 in FIG. 9D, the sharpness recovery amount corresponding to the pixel 803 is the code 804 in FIG. 9F. As can be seen from FIG. 9F, the sharpness recovery amount (symbol 807) of the adjacent pixel in the backward recording direction is positive, and the sharpness recovery amount (symbol 808) of the adjacent pixel in the forward recording direction is negative. . This corresponds to the case of the second line of the table of FIG. 8, and the scanning direction at the time of dot on at this time is the backward recording direction. That is, the pixel 803 is dot-on in the reverse recording direction shown in FIG. 9B, and the satellite at that time adheres to the left side of the pixel 803 (the side having the higher density in the edge area).

  As described above, in the present embodiment, the sign of the sharpness recovery amount is compared between the adjacent pixel in the forward recording direction and the adjacent pixel in the backward recording direction. Then, the scanning direction at the time of the dot-on of the processing target pixel is determined so that the satellite dots corresponding to the main droplet recording the processing target pixel are redundantly attached to the higher density area. This allows the satellites to be attached to the higher density area, reducing the adverse effect of the satellites on the image quality.

(Details of path data replacement process)
FIGS. 10A to 10C are schematic diagrams for explaining the details of the path data replacement process. FIG. 10A shows an example of path data before the path data replacement process is performed. FIG. 10A is a schematic diagram showing each pass data in 4-pass printing for an area of 4 pixels × 8 pixels corresponding to the nozzles of the printing head (represented by 16 nozzles for simplicity); In each pass, dot ON and dot OFF are shown. In FIG. 10A, pass data for the first and third passes are recorded in the forward recording direction (hereinafter, also referred to as forward direction), and pass data for the second and fourth passes are in the reverse recording direction (hereinafter, It shall be recorded in the reverse direction).

  FIG. 10B illustrates an example of the scanning direction determined by the preprocessing unit 206. In this example, the scanning directions of the pixels in the two columns near the center (the fourth and fifth columns from the left) are determined such that the pixels are scanned in the backward direction when the dot of the pixel is turned on. For the other pixels, the scanning direction is arbitrary in the pre-processing stage.

  FIG. 10C shows pass data after the pass data replacement process, and some dots of the pass data before the pass data replacement process shown in FIG. 10A are shown in FIG. It is path data generated by switching ON and OFF according to the scanning direction. When the scanning direction of the pixels in the pass data before the pass data replacement processing is different from the scanning direction determined by the pre-processing unit 206, ON / OFF replacement processing is performed.

  In the example of FIGS. 10A to 10C, first, with regard to the pixels 901, 902, and 903, in the pass data before replacement, the scanning direction at the time of dot-on is the forward direction, and is determined by the preprocessing unit 206. The scanning direction when the dot is on is the reverse direction (the circle of the broken line in FIG. 10B), and it is determined that both are different. For each of the pixels 901, 902, and 903 determined to be different, processing is performed to replace the path in which the dot is turned on so that the scanning direction at the time of dot on is reversed. The pixel 901 is changed from “record in first pass” to “record in second pass”. As a result, as shown in FIG. 10C, with regard to the pixel 901, dot-off occurs in the first pass and dot-on occurs in the second pass. When dot-on is performed in the second pass, the scanning direction when the dot of the pixel 901 is on is the reverse direction, which matches the scanning direction when the dot-on determined by the preprocessing unit 206. The pixel 902 is changed from “record in the third pass” to “record in the fourth pass”. As a result, as shown in FIG. 10C, with regard to the pixel 902, in the third pass dot-off and in the fourth pass dot-on. When dot-on is performed in the fourth pass, the scanning direction at the dot-on time of the pixel 902 is the backward direction, which matches the scanning direction at the dot-on time determined by the preprocessing unit 206. The pixel 903 is similar to the pixel 902. The above process can also be said to be a process of replacing the path in which dots are turned on for pixels in which the scanning direction determined in the preprocessing and the scanning direction of the pass data are different.

  When the number of passes is an even number, the replacement process of the pass data may be a process of replacing the dot ON between the adjacent even pass and the odd pass as described above. When the number of passes is an odd number, the dot ON may be switched between a certain pass and a pass immediately before or after that pass, or between the final pass and the leading pass. Alternatively, replacement may be performed between any pass and pass so that the scanning direction determined by the pre-processing unit 206 is obtained regardless of whether the pass number is even or odd. In either method, replacement is performed so that the number of dots finally recorded is stored.

(effect)
Hereinafter, the effects when the present embodiment is applied will be described. Here, for the sake of simplicity, a case will be described as an example in which an image is formed in two passes where printing in the forward direction is performed in the first pass and printing in the reverse direction is performed in the second pass.

  FIGS. 11 (a) to 11 (d) are explanatory views showing the effect when the present embodiment is applied in comparison with the conventional example. FIGS. 11A and 11B are schematic views showing the scanning direction and the dot pattern to be printed in the present embodiment, respectively. Reference numerals 1001 and 1002 in FIG. 11A indicate the scanning direction determined by the preprocessing unit 206. For all the pixels in the area enclosed by the frame 1001, the scanning direction when the dot is on is the forward direction. For all the pixels in the area enclosed by the reference numeral 1002, the scanning direction when the dot is on is the reverse direction. The dot pattern recorded according to the scanning direction of FIG. 11 (a) is shown in FIG. 11 (b). FIG. 11 (b) schematically shows the main drop 1003 (large black circle in the figure) and the satellite 1004 (small black circle in the figure, the portion where the dots overlap has a dark color) generated accordingly There is.

  11C and 11D are schematic views showing the scanning direction and the dot pattern to be recorded in the conventional example, respectively. In the conventional example, a dot pattern (FIG. 11 (d)) recorded according to a checkered pass mask (FIG. 11 (c)) is shown.

  As can be seen by comparing FIG. 11 (b) and FIG. 11 (d), in the dot pattern shown in FIG. 11 (b), satellites are not attached to the pixels in the area where the main droplet should not be attached. , The edge area is well formed. On the other hand, in FIG. 11D, satellites are attached to some of the pixels in the area, and the sharpness of the edge area is reduced.

  In order to briefly explain the effects of the present embodiment, an example in which the boundaries of the edge regions are relatively clear has been described here. However, since the sharpness recovery amount can be obtained as a continuous value for every input image, even if the present embodiment is applied to an input image including halftone edges where the boundary of the region is unclear, the edge is The sharpness of the area can be improved.

  Further, in the present embodiment, the scanning direction at the time of dot-on is determined by referring to the sharpness recovery amount of the adjacent pixels in the scanning direction, so that the required processing load is required compared to the case of performing the extraction processing of a predetermined area Can be reduced.

  As described above, according to the present embodiment, based on the sign of the sharpness recovery amount of the printer, the scanning direction at the time of dot-on is set so that satellite dots adhere to the image area with high correction density by sharpness recovery. decide. Thereby, as compared with the conventional method of extracting a predetermined region, the sharpness can be improved even for an input image including a region where the boundary is unclear with a simple configuration.

(Modification)
In the above embodiment, an example of using the difference image between the low frequency compensated image data and the full frequency compensated image data as the sharpness recovery amount has been described. However, the present invention is not limited to this. The recovery amount may be processed and used. For example, an arbitrary upper limit value may be set for (the absolute value of) the sharpness recovery amount so that the addition of the sharpness recovery amount does not exceed the range of the input pixel. In this case, when the sharpness recovery amount calculated from the input image exceeds the upper limit value, the sharpness recovery amount may be clipped to a constant value.

  Alternatively, an edge or a thin line may be extracted from the sharpness restoration amount image and used. For example, when the sign of the sharpness recovery amount is reversed between two adjacent pixels, the two pixels may be determined as edge pixels, and only edge pixels may be subjected to path replacement.

  In the embodiment, the scanning direction is based on the sign of the sharpness recovery amount of the pixel adjacent to the processing target pixel in the forward recording direction and the sign of the sharpness recovery amount of the pixel adjacent to the processing target pixel in the backward recording direction. The case of deciding was explained. However, the present invention is not limited to this, and for example, the scanning direction at the time of dot-on of each pixel may be temporarily determined by pass decomposition or the like. After that, the scanning direction may be changed or corrected with reference to the sign of the sharpness recovery amount of the pixel adjacent to the processing target pixel in the temporarily determined scanning direction. In this case, the scanning direction may be changed so as to reverse the scanning direction only when the sign of the sharpness restoration amount of the pixel adjacent to the processing target pixel is negative in the temporarily determined scanning direction.

  In the embodiment, the case where the recording head 3 includes four color inks of cyan (C), magenta (M), yellow (Y), and black (K) has been described, but the type of ink is not limited to these. For example, light ink with low density, special color ink such as red or green, or white ink may be used. Alternatively, clear and colorless clear ink and metallic ink of metallic tone may be used. Alternatively, the technical idea of the present embodiment can be applied to a configuration in which the discharge amount of the ink discharged by the recording head 3 can be controlled. However, in the case of white ink, the scanning direction determination is reversed.

  In the embodiment, although the input image is a RGB color image, the present invention is not limited to this, and the type of the image may be arbitrary, and may be, for example, a monochrome image or a CMYK image. Also, the image may include information other than color, and for example, an image including gloss information may be input.

  In the embodiment, the number of bits of various LUTs, the number of grids, and the interpolation method between grids are arbitrary. Similarly, the number of bits and the size of various filters and dither matrices are arbitrary.

  Although the embodiment has described the case where the dither matrix is used in the halftone processing in the halftone processing unit 108, the present invention is not limited to this and the halftone processing may be arbitrary. For example, known error diffusion methods or other halftoning methods may be used.

  In the embodiment, the case of using the pass mask in the pass decomposition processing in the pass decomposition unit 207 has been described, but the present invention is not limited thereto, and the method of the pass decomposition processing may be arbitrary. For example, the technical idea of the present embodiment can also be applied to a configuration in which a multilevel image for the number of passes is generated in the color separation unit 104 and binarized in the halftone processing unit 108.

  In the embodiment, the case of using multi-pass recording by four passes has been described, but the present invention is not limited to this and the number of passes may be arbitrary. For example, a multipass printing method may be used which performs reciprocating printing including at least one forward scan and at least one backward scan.

Second Embodiment
In the second embodiment, the scanning direction is determined based on both the sign and the magnitude (absolute value) of the amount of sharpness recovery.

  In the first embodiment, an example in which the scanning direction is determined so that satellites adhere to a higher density image area based on the sign of the amount of sharpness recovery to compensate for the reduction in sharpness caused by the printer 1 Explained. In the second embodiment, for example, it is considered that it is better to control the scanning direction even if the signs of the amount of sharpness recovery are the same. The sharpness recovery amount indicates the density correction direction (thin / dense) and the correction amount (how thin / dense). That is, even if the signs are the same, sharpness can be maintained and improved by controlling the attachment position of the satellites so that the difference in density is maintained. For example, if control is performed such that satellites are attached to the pixel having the higher density or the smaller density among the pixels on both sides of the pixel to which the main droplet is attached, the sharpness can be maintained and improved.

  Therefore, in the present embodiment, based on not only the sign of the sharpness recovery amount of the printer 1 but also the size (absolute value) thereof, the scanning direction is determined such that the satellites adhere to the image area having a higher density. An example will be described. The main difference between the present embodiment and the first embodiment is the process of determining the scanning direction, and the other parts are the same as those in the first embodiment, so the description will be omitted. Also in this embodiment, as in the first embodiment, it is assumed that the pixels to which the satellites adhere and the pixels to which the main droplets adhere are always adjacent regardless of the forward recording direction and the backward recording direction. .

(Details of scan direction determination process)
The details of the scanning direction determination process in the present embodiment will be described below. FIG. 12 is a flowchart showing the flow of a series of processing in the scanning direction determination processing. 12, processing steps different from those in FIG. 6 of the first embodiment are three steps S1101, S1102, and S1103, and only these processing steps will be described.

  In step S1101, the preprocessing unit has a positive sharpness recovery amount of a pixel adjacent to the processing target pixel in the forward recording direction, and a positive sharpness recovery amount of a pixel adjacent to the processing target pixel in the backward recording direction. Determine if it is. If the determination result is Yes, the process proceeds to S1102, and if the determination result is No, the process proceeds to S1103.

  In step S1102, the preprocessing unit determines that the magnitude of the absolute value of the sharpness recovery amount of the pixel adjacent to the processing target pixel in the forward recording direction is the magnitude of the sharpness recovery amount of the pixel adjacent to the processing target pixel in the backward recording direction. To determine if it is greater than or equal to the absolute value of When the determination result is Yes, the process proceeds to S504, and when the determination result is No, the process proceeds to S506.

  In step S1103, the preprocessing unit determines that the magnitude of the absolute value of the sharpness recovery amount of the pixel adjacent to the processing target pixel in the forward recording direction is the magnitude of the sharpness recovery amount of the pixel adjacent to the processing target pixel in the backward recording direction. To determine if it is greater than or equal to the absolute value of When the determination result is Yes, the process proceeds to S506, and when the determination result is No, the process proceeds to S504.

  In the present embodiment, an example of processing when referring to the sign and size (absolute value) of the sharpness recovery amount is as follows. The pre-processing unit accesses the RAM memory storing the sharpness recovery amount, obtains the code by referring to the most significant bit (MSB) of the amount, and obtains the size by referring to other than the most significant bit (absolute value Get the value). At this time, when the sign is negative, it is inverted and 1 is added. Alternatively, other means capable of obtaining the magnitude (absolute value) of the sharpness recovery amount in the case of the same sign may be used. For example, when the sign is negative, the magnitude can be determined only by inverting, except when all the bits other than the most significant bit are 0.

  This completes the series of recording direction determination processing in the present embodiment.

(Relationship between satellite generation position in reciprocating recording and scanning direction determined)
The relationship between the satellite generation position in reciprocating printing and the determined scanning direction in the present embodiment will be described below.

  FIG. 13 is a diagram showing the relationship between the determination condition in the pre-processing for determining the scanning direction and the scanning direction obtained according to the determination condition. In order to simplify the explanation, it is assumed that the sharpness recovery amount of 0 is included in the positive. As shown in FIG. 13, in the present embodiment, the scanning direction at the time of dot-on is determined based on the sign and the magnitude (absolute value) of the sharpness recovery amount. Unlike the first embodiment, in the present embodiment, the scanning direction does not optionally depend on the scanning direction of the pass mask. Even if the sign of the sharpness recovery amount is the same between the adjacent pixel in the backward recording direction and the adjacent pixel in the forward recording direction, the scanning direction is more appropriate due to the magnitude relationship (absolute value) of the sharpness recovery amount. Can be determined.

  The determination condition based on the sign and the size (absolute value) of the sharpness recovery amount is not limited to the example of FIG. 13, and the condition for determining the scanning direction according to the size (absolute value) is detailed Thus, the scanning direction may be controlled. For example, the preprocessing unit may be configured not to specify the scanning direction (do not change the scanning direction) when the difference between the absolute values is equal to or less than a predetermined value.

  As described above, according to the present embodiment, at the time of dot-on, satellite dots are attached to an image area having a high correction density due to sharpness recovery based on the signed size of the sharpness recovery amount of the printer. Uniquely determine the scan direction of Thereby, as compared with the conventional method of extracting a predetermined region, the sharpness can be improved even for an input image including a region where the boundary is unclear with a simple configuration.

Third Embodiment
In the third embodiment, the scanning direction is determined based on the magnitude relationship of the sharpness recovery amount.

  In the second embodiment, based on the sign and size (absolute value) of the sharpness recovery amount of the printer, the scanning direction at the time of dot-on so that the satellite dots adhere to the image area with high correction density by the sharpness recovery. An example of determining In the third embodiment, an example will be described in which the scanning direction at the time of dot-on is determined based only on the magnitude relationship of the sharpness recovery amount. The main difference between this embodiment and the first and second embodiments is the process of determining the scanning direction, and the other parts are the same as in the first embodiment, and therefore the description thereof is omitted. Do. Also in this embodiment, as in the first embodiment, it is assumed that the pixels to which the satellites adhere and the pixels to which the main droplets adhere are always adjacent regardless of the backward recording direction and the backward recording direction. .

(Details of scan direction determination process)
The details of the scanning direction determination process in the present embodiment will be described below. FIG. 14 is a flowchart showing the flow of a series of processing in the scanning direction determination processing. In FIG. 14, the processing step different from FIG. 6 of the first embodiment and FIG. 12 of the second embodiment is S1301, and only this processing step will be described.

  In step S1301, the preprocessing unit determines whether the sharpness recovery amount of the pixel adjacent to the processing target pixel in the forward recording direction is larger than the sharpness recovery amount of the pixel adjacent to the processing target pixel in the reverse recording direction. Do. When the determination result is Yes, the process proceeds to S504, and when the determination result is No, the process proceeds to S506.

  This completes the series of scanning direction determination processes in the present embodiment.

(Relationship between satellite generation position in reciprocating recording and scanning direction determined)
The relationship between the satellite generation position in reciprocating printing and the determined scanning direction in the present embodiment will be described below.

  FIG. 15 is a diagram showing the relationship between the determination condition in the pre-process of determining the scanning direction and the scanning direction obtained according to the determination condition. As shown in FIG. 15, in the present embodiment, the scanning direction is determined based on the magnitude relationship of the sharpness recovery amount. Therefore, unlike the first embodiment, in the pre-processing stage, the scanning direction is arbitrary, and there is no pixel whose scanning direction is determined by the pass mask. In addition, since the scanning direction can be determined under the simple condition that only the magnitude comparison of the sharpness recovery amount is performed, the processing load is reduced as compared with the second embodiment.

  The scanning direction may be determined only when the difference in sharpness recovery amount is greater than or equal to a certain threshold, and the scanning direction may be arbitrarily determined according to the scanning direction of the pass mask if the difference is small. By adjusting the threshold, it is possible to adjust the degree of control of the satellite scanning direction according to the present embodiment.

  As described above, according to the present embodiment, based on the magnitude relationship between the amount of sharpness recovery of the printer, the scanning direction at the time of dot-on is set so that the satellite dots adhere to the image area with high correction density due to sharpness recovery. decide. Thereby, as compared with the conventional method of extracting a predetermined area, the sharpness can be improved even for an input image including an area where the boundary is unclear with a simpler configuration.

Fourth Embodiment
In the fourth embodiment, satellite distance information is acquired, and the scanning direction is determined accordingly.

  The first to third embodiments have been described on the premise that the pixel to which the satellite adheres and the pixel to which the main droplet adheres are always adjacent regardless of the forward recording direction and the reverse recording direction. In the fourth embodiment, the case where satellites adhere to a predetermined number of pixel separated positions with respect to the main droplet will be described. Hereinafter, the description of the portions common to the first to third embodiments will be omitted, and only the configuration added in the fourth embodiment will be described.

(Configuration of image forming system)
FIG. 16 is a block diagram showing the configuration of the image forming system according to the present embodiment. The configuration different from FIG. 2 of the first embodiment is the distance storage unit 212 and the distance acquisition unit 213, and the other configurations are the same as those in FIG.

  The distance storage unit 212 stores information on the distance of the satellites. In the present embodiment, the distance storage unit 212 stores information indicating that the satellite distance is 2 (pixels) in both the forward recording direction and the backward recording direction.

  The distance acquisition unit 213 acquires satellite distance information stored in the distance storage unit 212. In the present embodiment, the distance acquisition unit 213 acquires information indicating that the satellite distance is 2 (pixels) in both the forward recording direction and the backward recording direction.

  An image is formed in accordance with the configuration described above.

(Details of scan direction determination process)
Hereinafter, the details of the scanning direction determination process in the present embodiment will be described. FIG. 17 is a flowchart showing the flow of a series of processing in the scanning direction determination processing. In FIG. 17, processing steps different from those in FIG. 6 of the first embodiment are three steps S1601, S1602 and S1603, and only these processing steps will be described.

  In S1601, the distance acquisition unit 213 refers to the distance storage unit 212 to acquire satellite distance information. Here, information in which the satellite distance is 2 (pixels) is acquired in both the forward recording direction and the backward recording direction.

  In step S1602, the pre-processing unit 206 has a positive sharpness recovery amount of pixels to which satellites may adhere in the forward recording direction, and a sharpness recovery amount of pixels to which satellites may adhere in the backward recording direction. Determine if it is negative. The pixels to which satellites may be attached are one or more pixels determined by the satellite distance acquired in S1601 and the diameter of the satellites. The determined pixels are at least partially covered by the satellites. The determined sharpness recovery amount of the pixel is taken as the average value of the sharpness recovery amount corresponding to the determined pixel. In the present embodiment, since the satellite distance is 2, the sharpness recovery amount of the pixel separated by two pixels from the pixel to be processed is used. If the determination result in S1602 is Yes, the process proceeds to S504, and if the determination result is No, the process proceeds to S1603.

  In step S1603, in the pre-processing unit 206, the sharpness recovery amount of pixels to which satellites may adhere in the forward recording direction is negative, and the sharpness recovery amount of pixels to which satellites may adhere in the backward recording direction is negative. Determine if it is positive. When the determination result is Yes, the process proceeds to S506, and when the determination result is No, the process proceeds to S507.

  This completes the series of scanning direction determination processes in the present embodiment.

(Relationship between satellite separation distance and dot position)
18 (a) to 18 (f) are schematic views showing the relationship between the satellite distance and the adhesion position in the reciprocation recording. FIGS. 18A and 18B are schematic views of the main droplets MD and satellite ST in the forward recording direction and the reverse recording direction when the satellite distance is one. FIGS. 18C and 18D are schematic views of the main droplets MD and satellite ST in the forward recording direction and the reverse recording direction when the satellite distance is two. FIGS. 18E and 18F are schematic views of the main drop MD and the satellite ST in the forward recording direction and the backward recording direction when the satellite distance is three.

  As can be seen from FIGS. 18A to 18F, it can be seen that the distance between the main droplet MD and the satellite ST and the direction in which the satellite ST adheres differ depending on the satellite distance and the scanning direction. In the present embodiment, the satellite distance is acquired in S1601, the pixel to which the satellite ST may be attached is identified in the forward recording direction and the backward recording direction, and the sharpness recovery amount value corresponding to the identified pixel is determined. Determine the scan direction based on As a result, as in the first to third embodiments, the satellite ST is controlled to be attached to a region having less influence when the satellite ST is attached.

  As described above, according to the present embodiment, even when satellites adhere to pixels other than the pixels adjacent to the main droplet, an image area having a high correction density due to sharpness recovery based on the sharpness recovery amount of the printer. The scanning direction is determined such that satellite dots are attached to the Thereby, as compared with the conventional method of extracting a predetermined region, the sharpness can be improved even for an input image including a region where the boundary is unclear with a simple configuration.

(Modification)
In the fourth embodiment, the case where the satellite distances are equal in the forward recording direction and the backward recording direction has been described, but the invention is not limited thereto. For example, the satellite distance may be different between the forward recording direction and the backward recording direction depending on the state at the time of image formation such as the relative inclination between the face surface of the recording head and the recording medium. In such a case, the technical idea of the present embodiment can be similarly applied by storing and acquiring different satellite distances in the forward recording direction and the backward recording direction. At this time, the sharpness restoration amount acquired in the forward recording direction and the sharpness restoration amount acquired in the reverse recording direction are asymmetric with respect to the pixel to be processed.

  In the present embodiment, the unit of the satellite distance is described as the number of pixels. However, the present invention is not limited to this. For example, the satellite distance may be stored and acquired in units of distance (for example, μm) on the paper. In this case, the amount of sharpness recovery can be weighted average according to the ratio of the portion covered by the satellite to the size of the pixel. Alternatively, the distance may be converted (for example, rounded up) to the number of pixels in accordance with the pixel pitch of the sharpness recovery amount.

  In addition, when a plurality of satellites are generated, the technical idea of the present embodiment can be obtained by storing and acquiring the distance from the main droplet of the satellite farthest from the main droplet as the satellite distance and determining the sharpness recovery amount. The same applies.

Fifth Embodiment
In the fifth embodiment, the sharpness recovery amount of the scanner is acquired, and the scanning direction is determined.

  In the first to fourth embodiments, the example in which the scanning direction at the time of dot-on is determined using the sharpness recovery amount calculated based on the known frequency deterioration characteristic of the printer 1 has been described. I can not. Other amounts of sharpness recovery may be used as long as the satellites adhere in the direction in which the density is to be increased. Therefore, in the fifth embodiment, copying (copying) of a document by a printer (so-called multifunction machine) provided with document reading means (scanner) is taken as an example. In the present embodiment, the scanning direction is determined using the sharpness recovery amount obtained from the frequency deterioration characteristic of the document reading unit. The description of the parts common to any of the first to fourth embodiments will be omitted.

(Configuration of MFP)
FIG. 19 is a block diagram showing the configuration of the MFP 20 according to the present embodiment. The multi-function device 20 includes a document reading unit 114, a sharpness recovery unit 110, a sharpness storage unit 111, a color separation storage unit 105, a color separation unit 104, a recovery amount generation unit 115, and an OPG storage unit 107. , OPG processing unit 106, matrix storage unit 109, halftone processing unit 108, carriage 2, recording head 3, paper feed mechanism 5, head control unit 204, ink color selection unit 210, direction control And a unit 201. The direction control unit 201 includes a path replacing unit 209, a path decomposing unit 207, a preprocessing unit 206, and a path mask storage unit 208.

The multifunction machine 20 acquires image data of an image to be copied from the document reading unit 114. The image data is an 8-bit RGB color image.
The sharpness recovery unit 110 uses the sharpness filter stored in the sharpness storage unit 111 to perform sharpness recovery processing on the input image data. The sharpness filter is designed based on the spatial frequency deterioration characteristic of the document reading unit 114. The image corrected by the sharpness recovery unit 110 is sent to the color separation unit 104 and the recovery amount generation unit 115.

  The recovery amount generation unit 115 generates a sharpness recovery amount by calculating the difference between the image data corrected by the sharpness recovery unit 110 and the image data before correction. The generated sharpness recovery amount is sent to the pre-processing unit 206.

  The other configuration is the same as any of the first to fourth embodiments, and the description will be omitted. Further, in the present embodiment, the processing after acquiring the sharpness recovery amount is the same as in the first to fourth embodiments, and the description will be omitted.

  As described above, according to the present embodiment, satellite dots are attached to an image area having a high correction density due to sharpness recovery based on the sharpness recovery amount obtained from the spatial frequency degradation characteristic of the document reading unit. The scan direction is determined. Thereby, as compared with the conventional method of extracting a predetermined region, the sharpness can be suitably improved even for an input image including a region where the boundary is unclear with a simple configuration.

Sixth Embodiment
In the first to fifth embodiments, the case where the sharpness is improved by determining the scanning direction at the time of dot-on based on the sharpness recovery amount has been described. In the sixth embodiment, the sharpness is further enhanced by using the amount of sharpness recovery for image processing other than the determination of the scanning direction.

  FIG. 20 is a block diagram showing the configuration of the image forming system according to the present embodiment. The difference from the first embodiment in FIG. 2 is that the sharpness recovery amount generated by the high frequency generation unit 112 is also input to the halftone processing unit 108, and the other configuration is the same as that in FIG. .

  FIGS. 21A to 21D are schematic diagrams showing correction processing in the halftone processing unit 108 according to the present embodiment. FIG. 21A shows multi-valued image data and density distribution processed by the OPG processing unit 106 and input to the halftone processing unit 108. An area of 8 pixels × 8 pixels is shown in FIG. 21A, of which the left half is an area of 50% density and the right half is an area of 25% density (white). The halftone processing unit 108 performs halftone processing on the multivalued image data shown in FIG. 21A using the dither matrix stored in the matrix storage unit 109, and then the halftone pattern shown in FIG. 21B. Generate Since the halftoning process is a process of converting multi-values into binary values, as shown in the density distribution graph of FIG. 21B, the sharpness of the edges is reduced.

  FIG. 21C shows the sharpness restoration amount generated by the high frequency generation unit 112 and the distribution thereof. The halftone processing unit 108 corrects the halftone pattern shown in FIG. 21 (b) based on the sharpness recovery amount shown in FIG. 21 (c). FIG. 21D shows the halftone pattern and the density distribution after the correction based on the sharpness recovery amount is performed. As shown in the density distribution graph of FIG. 21D, the edge sharpness is recovered by the correction based on the sharpness recovery amount.

  As described above, according to the present embodiment, the sharpness of the image can be further enhanced based on the sharpness recovery amount.

  The configuration and operation of the device according to the embodiment have been described above. It is understood by those skilled in the art that these embodiments are exemplifications, and that various modifications can be made to the combination of each component and each process, and such modifications are also within the scope of the present invention.

(Other embodiments)
The present invention supplies a program that implements one or more functions of the above-described embodiments to a system or apparatus via a network or storage medium, and one or more processors in a computer of the system or apparatus read and execute the program. Can also be realized. It can also be implemented by a circuit (eg, an ASIC) that implements one or more functions.

  Reference Signs List 1 printer, 3 recording heads, 10 image processing apparatuses, 112 high frequency generation units, 201 direction control units, 206 pre-processing units, 207 path decomposition units, 208 path mask storage units, 209 path replacement units.

Claims (11)

A control device for controlling a recording apparatus for relatively reciprocating a recording head and a recording medium to form an image on the recording medium, comprising:
Acquisition means for acquiring a sharpness restoration amount for restoring deterioration of spatial frequency characteristics of an image formed on the recording medium;
A control device comprising: determining means for determining a scanning direction at the time of forming a dot for each pixel based on the acquired sharpness restoration amount. The scanning directions include first and second directions opposite to each other,
The determination means is a code or a magnitude or a sharpness recovery amount between pixels to which satellite dots may be attached in the first direction and pixels to which satellite dots may be attached in the second direction. The control device according to claim 1, wherein the control direction is determined in forming the dots so that the satellite dots are attached to the side of the higher density pixel by comparing the both. The pixel to which satellite dots may be attached in the first direction is a pixel adjacent to the pixel to be processed in the first direction,
The control device according to claim 2, wherein the pixel to which satellite dots may be attached in the second direction is a pixel adjacent to a pixel to be processed in the second direction. It further comprises distance acquisition means for acquiring information on the distance between the main drop and the satellite dots,
The determination means is a pixel to which satellite dots may be attached in the first direction and a pixel to which satellite dots may be attached in the second direction based on the information acquired by the distance acquisition means. The control device according to claim 2 or 3, which specifies   The control device according to claim 4, wherein the distance acquiring unit acquires at least one of the distance between the main droplet and the satellite dot in the first direction and the distance between the main droplet and the satellite dot in the second direction.   The determination means uses the average value of the sign and / or the magnitude of the sharpness recovery amount of the identified plurality of pixels for comparison when the plurality of pixels to which the satellite dot may be attached are identified. Item 5. The control device according to item 4 or 5.   The control device according to any one of claims 1 to 6, wherein the sharpness recovery amount is an amount for recovering degradation of spatial frequency characteristics when forming an image on the recording medium.   The control device according to any one of claims 1 to 6, wherein the sharpness recovery amount is an amount for recovering degradation of spatial frequency characteristics when reading an image to be formed on the recording medium.   The data representing the image formed on the recording medium is processed based on the sharpness recovery amount to recover the deterioration of the spatial frequency characteristic separately from the determination processing in the determination means. Control device as described. A control method for controlling a recording apparatus for forming an image on a recording medium by relatively reciprocating a recording head and a recording medium, comprising:
Obtaining a sharpness recovery amount for recovering degradation of spatial frequency characteristics of an image formed on the recording medium;
Determining the scanning direction at the time of forming a dot for each pixel based on the acquired sharpness recovery amount.   The program for functioning a computer as each means of the apparatus as described in any one of Claims 1-9.