JP2011207136A - Image data processor, liquid ejection device and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine whether each pixel is an edge pixel other than a thin-line edge pixel with less calculation quantity.SOLUTION: An edge determination part calculates, for a first processing area 65 where five pixels in a main scanning direction and three pixels in a sub-scanning direction are arranged in matrix with each of pixels 61 of averaged image data as its center, an edge determination value by use of a Sobel filter while multiplying an image density value of each pixel 61 located the closest to the outside in the main scanning direction with the center pixel 61a as its center by the image density value of the pixel 61 inwardly adjacent to the above pixel 61 in the main scanning direction. The edge determination part determines, when the edge determination value exceeds a first threshold, the center pixel 61a as a first edge pixel. The first threshold is equal to or more than the edge determination value in the first processing area 65 when the edge pixel of a thin-line pixel group is the center pixel 61a.

Description

  The present invention relates to an image data processing apparatus that processes image data relating to an image recorded on a recording medium by discharging liquid to form an image from a plurality of discharge ports, a liquid discharge apparatus including the image data processing apparatus, and a program.

  In an inkjet printer, a technology that does not reduce the amount of ink ejected for edge pixels of thin characters that are difficult to bleed, while reducing the amount of ink ejected to suppress bleeding for thick character edge pixels that tend to bleed. Is known (see, for example, Patent Document 1).

JP 2005-153157 A

  In the above-described technique, the inkjet printer performs the two-step process of determining whether or not all pixels determined to be edge pixels are thin line edge pixels after determining the edge pixels for all pixels. The amount of calculation increases.

  An object of the present invention is to provide an image data processing device, a liquid ejection device, and a program that can determine whether each pixel is an edge pixel other than a thin line with a small amount of calculation.

  The image data processing apparatus of the present invention is an image data processing apparatus related to a liquid ejection apparatus having a liquid ejection head for ejecting liquid for forming an image from a plurality of ejection openings, in a first direction and the first direction. Image data storage means for storing image data having image density values of a plurality of pixels arranged in a matrix in a second direction orthogonal to each other; change means for changing the image data stored in the image data storage means; Each of the plurality of pixels is arranged in a matrix of 1 or more in the first direction and n (n is an integer of 1 or more) × 2 + 1 or more in the second direction, with the pixel as a central pixel. The image density value of the pixel related to the first processing area is extracted from the image data storage means, and a differential filter is applied to the image density value of the pixel related to the first processing area. When the edge determination value exceeds a predetermined first threshold value relating to the second direction obtained by, and an edge determination means for determining the center pixel according to the first process area and the edge pixel. The first threshold is an outer end of the thin line pixel group in which pixels having the image density value equal to or larger than a predetermined value are continuous in the number of n in the second direction and extend in the first direction. A value greater than or equal to the edge determination value for the second direction obtained by performing processing by the edge determination unit on the first processing region having one of the pixels as the central pixel; The image data is changed so as to reduce the image density value of the pixel determined to be the edge pixel by the edge determination unit among the pixels.

  A liquid discharge apparatus according to the present invention includes a liquid discharge head that discharges liquid to form an image from a plurality of discharge ports, and the above-described image data processing apparatus.

  A program according to the present invention is a program that causes a computer to function as an image data processing apparatus related to a liquid ejection apparatus having a liquid ejection head that ejects liquid to form an image from a plurality of ejection openings. Image data storage means for storing image data having image density values of a plurality of pixels arranged in a matrix in a second direction orthogonal to the direction, change means for changing the image data stored in the image data storage means, For each of the plurality of pixels, a matrix arrangement in which the pixel is a central pixel and the number of pixels is 1 or more in the first direction and n (n is an integer of 1 or more) × 2 + 1 or more in the second direction. The image density value of the pixel related to the first processing area is extracted from the image data storage means, and the pixel related to the first processing area Edge determination for determining the center pixel of the first processing region as an edge pixel when an edge determination value for the second direction obtained by applying a differential filter to the image density value exceeds a predetermined first threshold value. Make a computer function as a means. The first threshold is an outer end of the thin line pixel group in which pixels having the image density value equal to or larger than a predetermined value are continuous in the number of n in the second direction and extend in the first direction. A value greater than or equal to the edge determination value for the second direction obtained by performing processing by the edge determination unit on the first processing region having one of the pixels as the central pixel; The image data is changed so as to reduce the image density value of the pixel determined to be the edge pixel by the edge determination unit among the pixels.

  According to the present invention, the number of pixels from the central pixel in the first processing region to the outer edge pixel in the second direction is made larger than the number of pixels (n) in the width direction of the thin line pixel group, and the first threshold is set to By making the edge determination value equal to or greater than the edge determination value when the outer end pixel of the thin line pixel group is the central pixel, the determination of the edge pixel and the determination of whether the edge pixel is an edge pixel of the thin line can be performed simultaneously. it can. This makes it possible to determine whether each pixel is an edge pixel other than a thin line with a small amount of calculation.

  In the present invention, the first threshold value is the thick line pixel group in which pixels having the image density value equal to or greater than the predetermined value are continuous in the number of n + 1 in the second direction and extend in the first direction. It is preferable that the value is less than the edge determination value obtained by performing processing by the edge determination unit using one of the outer end pixels in the second direction as the central pixel. According to this, since the edge determination unit reliably determines the edge pixel of the thick line pixel group as the edge pixel, the changing unit decreases the image density value of the edge pixel, and the image related to the image data is recorded on the recording medium. It is possible to suppress the bleeding of the thick line edge.

  In the present invention, it is preferable that the first processing region includes a plurality of pixels arranged in a matrix of 3 in the first direction and n × 2 + 1 in the second direction with the central pixel as the center. . According to this, it is possible to determine the edge pixel without reducing the accuracy and with a small amount of calculation.

  In the present invention, it is preferable that the predetermined value is not less than the third smallest image density value among three or more image density values having different liquid volumes to be ejected. According to this, since the edge determination unit does not determine the edge pixel having the second smallest image density value as the edge pixel, it is possible to prevent the dot corresponding to the edge pixel from disappearing due to the processing of the changing unit. it can.

  In addition, in the present invention, the changing unit is configured so that the image density value of the pixel determined as the edge pixel by the edge determining unit becomes an image density value in which the volume of liquid to be ejected is reduced. It is preferable to change the data. According to this, the volume of the liquid to be ejected can be surely reduced with respect to the dots corresponding to the edge pixels.

  Further, in the present invention, for each of the plurality of pixels, the image density value of the pixel is arranged in a matrix with the pixel being a central pixel and 3 or more in the first direction and 3 or more in the second direction. A moving average calculating means for calculating an average value of the image density values in the average area, wherein the edge determining means calculates the image density value of each of the plurality of pixels by the moving average means. It is preferable to determine an edge pixel as the image density value. According to this, since the image density value of each pixel is averaged, it is possible to suppress erroneous determination regarding the edge pixel due to the influence of noise such as an independent point adjacent to the edge pixel.

  Furthermore, in the present invention, the edge determination means determines the image density value of each pixel located outside the second direction with the central pixel as the center with respect to the first processing region, with respect to the second direction of the pixel. It is preferable to apply the differential filter after multiplying the image density value of the adjacent pixel on the inside. According to this, the image density value of the pixel located outside in the second direction of the central pixel in the first processing area is multiplied by the image density value of the pixel adjacent inside in the second direction, thereby obtaining the image density value. It is easy to emphasize (enlarge) an area with a low value. Therefore, in the application result of the differential filter, it becomes easy to determine an edge pixel adjacent to a thin line space (thin line having a low density value) as an edge pixel.

  In addition, in the present invention, for each of the plurality of pixels, the edge determination unit has one or more in the second direction and n (n is n in the first direction) of the plurality of pixels with the pixel as a central pixel. The image density value of the pixel related to the second processing area arranged in a matrix with an integer of 1 or more) × 2 + 1 or more is extracted from the image data storage means and differentiated into the image density value of the pixel related to the second processing area When the edge determination value related to the first direction obtained by applying the filter exceeds a predetermined second threshold value, the center pixel related to the second processing region is further determined as an edge pixel, and the second threshold value is One of the pixels at the outer end in the first direction in the thin line pixel group in which the pixels having the image density value equal to or larger than a predetermined value are continuous in the number of n in the first direction and extend in the second direction. Before center pixel It is preferably the edge determination value or more values related to the first direction obtained by performing the processing of the edge determination means to the second processing region. According to this, it is possible to determine whether each pixel is an edge pixel in the first and second directions.

  In the present invention, the differential filter is preferably a Sobel filter. According to this, determination of an edge pixel can be performed efficiently.

  According to the present invention, the number of pixels from the central pixel in the first processing region to the outer edge pixel in the second direction is made larger than the number of pixels (n) in the width direction of the thin line pixel group, and the first threshold is set to By making the edge determination value equal to or greater than the edge determination value when the outer end pixel of the thin line pixel group is the central pixel, the determination of the edge pixel and the determination of whether the edge pixel is an edge pixel of the thin line can be performed simultaneously. it can. This makes it possible to determine whether each pixel is an edge pixel other than a thin line with a small amount of calculation.

1 is a schematic plan view of an inkjet printer according to an embodiment of the present invention. It is a functional block diagram of the control apparatus shown in FIG. It is an example of the image data memorize | stored in the image data memory | storage part shown in FIG. It is a figure for demonstrating the function of the moving average calculation part shown in FIG. It is a figure for demonstrating the 1st edge process which concerns on the edge judgment part shown in FIG. It is a figure for demonstrating the 2nd edge process which concerns on the edge judgment part shown in FIG. 3 is a flowchart illustrating an operation procedure of preprocessing according to the image data processing unit illustrated in FIG. 2.

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

  As shown in FIG. 1, the ink jet printer 101 includes a transport unit 20 that transports the paper P from the upper side to the lower side of FIG. 1, and inks of magenta, cyan, yellow, and black on the paper P transported by the transport unit 20. There are four inkjet heads 1 that respectively eject droplets, and a control device 16 that controls the entire inkjet printer 101. In the present embodiment, the sub-scanning direction is a direction parallel to the transport direction when the paper P is transported by the transport unit 20, and the main scanning direction is a direction orthogonal to the sub-scanning direction and along the horizontal plane. Direction.

  The transport unit 20 includes two belt rollers 6 and 7 and an endless transport belt 8 wound around the rollers 6 and 7. The belt roller 7 is a driving roller, and rotates when a driving force is applied from a conveyance motor (not shown). The belt roller 6 is a driven roller and rotates as the conveyor belt 8 travels due to the rotation of the belt roller 7. The paper P placed on the outer peripheral surface of the transport belt 8 is transported downward in FIG.

  The four inkjet heads 1 each extend along the main scanning direction and are arranged in parallel to each other in the sub-scanning direction. That is, the ink jet printer 101 is a line type color ink jet printer in which a plurality of ejection openings for ejecting ink droplets are arranged in the main scanning direction.

  The outer peripheral surface of the upper loop of the conveyor belt 8 and the discharge surface are parallel to each other while facing each other. When the paper P transported by the transport belt 8 passes immediately below the four ink jet heads 1, ink droplets of each color are sequentially ejected from the respective ink jet heads 1 toward the upper surface of the paper P, and are then onto the paper P. A desired color image is formed.

  Next, the control device 16 will be described with reference to FIG. The control device 16 includes a CPU (Central Processing Unit), a program executed by the CPU, and an EEPROM (Electrically Erasable and Programmable Read Only Memory) that stores data used for these programs in a rewritable manner. It includes RAM (Random Access Memory) for temporary storage. Each functional unit constituting the control device 16 is constructed by cooperation of these hardware and software in the EEPROM. As illustrated in FIG. 2, the control device 16 includes a conveyance control unit 31, an image data processing unit 33, and a head control unit 32.

  The transport control unit 31 controls the transport motor of the transport unit 20 so that the paper P is transported along the transport direction.

  The image data processing unit 33 performs preprocessing of the image data so that the image density value of the edge pixel that forms an edge other than the fine line related to the image printed on the paper P becomes small. The image data processing unit 33 includes an image data storage unit 41, a moving average calculation unit 42, an edge determination unit 43, and a change unit 44. The image data storage unit 41 stores image data 50 relating to an image printed on the paper P. As shown in FIG. 3, the image data 50 includes four colors of magenta, cyan, yellow, and black for each pixel 51 arranged in a matrix in the main scanning direction and the sub-scanning direction so as to correspond to the print area of the paper P. Each has an image density value. The image density value is a value quantized into four values (no ink ejection, small droplet ink, medium droplet ink, large droplet ink) according to the ink ejection amount. In FIG. 3, black image density values relating to some pixels 51 of the image data 50 are shown. Further, the image density value of medium-drop ink or higher is indicated by “1”, and the other image density values are indicated by “0”.

  As shown in FIGS. 3 and 4, the moving average calculation unit 42 sets 3 pixels in the main scanning direction for each pixel 51 of the image data 50 stored in the image data storage unit 41 with the pixel 51 as the central pixel 51 a. An average area 55 in which the pixels 51 are arranged in a matrix with 3 in the scanning direction is defined, and an average value of image density values in each average area 55 is calculated. The moving average calculating unit 42 uses the average value calculated for each pixel 51 as the image density value of the pixel 61 corresponding to the pixel 51, and the image density values of the pixels 61 arranged in a matrix in the main scanning direction and the sub-scanning direction. The averaged image data 60 is created.

  For each pixel 61 of the averaged image data 60 created by the moving average calculation unit 42, the edge determination unit 43 has more than two (n) pixels 51 having an image density value equal to or greater than the middle droplet in the main scanning direction. A first edge determination process for determining whether or not the pixel is a first edge pixel that is an outer edge pixel of an edge having a continuous width and extending in the sub-scanning direction; and a pixel 51 having an image density value equal to or greater than a medium droplet A second edge determination process for determining whether or not the pixel is a second edge pixel that is an outer edge pixel of an edge extending in the main scanning direction while having a width that exceeds two (n) and continues in the sub-scanning direction; Repeat in order.

  The first edge determination process will be described. As shown in FIGS. 4 and 5A, the edge determination unit 43 sets 5 (n × 2 + 1: n = n) in the main scanning direction for each pixel 61 of the averaged image data 60 with the pixel 61 as the central pixel 61a. 2) The first processing region 65 in which the pixels 61 are arranged in a matrix of 3 in the sub-scanning direction is extracted. The edge determination unit 43 adjoins the extracted first processing region 65 with the image density value of each pixel 61 located on the outermost side in the main scanning direction around the center pixel 61 a on the inner side in the main scanning direction of the pixel 61. A reflection process for multiplying the image density value of the pixel 61 to be performed is performed. In FIG. 5A, the image density values of the pixels 61 of D11, D21, D31, D15, D25, and D35 are multiplied by the image density values of the pixels 61 of D12, D22, D32, D14, D24, and D34, respectively. .

  Furthermore, the edge determination unit 43 performs main scanning by applying a Sobel filter (primary differential filter) 71 in the main scanning direction shown in FIG. 5B to the first processing region 65 on which the reflection processing has been performed. Filter processing for calculating the edge judgment value Δg0 related to the direction is performed. The edge determination unit 43 determines that the center pixel 61a is the first edge pixel when the calculated edge determination value Δg0 exceeds the first threshold value.

The edge determination unit 43 simultaneously performs the reflection process and the filter process described above by using the following equation (1).
Δg0 = 1 · D11 + 2 · D21 + 1 · D31 + 2 · (D12 · D11) + 4 · (D22 · D21) + 2 · (D32 · D31) -2 (D14 · D15) -4 · (D24 · D25) -2 · (D34 · D35) -1, D15-2, D25-1, D35 (1)

  Here, as shown in FIG. 5C, the first threshold value is an image density value equal to or greater than a predetermined value (in this embodiment, the image density value related to the medium drop ink, which is the third smallest image density value). In the thin line pixel group in which two pixels 51 are continuous in the main scanning direction (n = 2) and extend in the sub scanning direction, one outer pixel 51c in the main scanning direction (an edge pixel forming the edge of the thin line) ) Is the edge determination value Δg0 obtained by performing the above-described first edge determination processing for the first processing region 65 having the pixel 61 corresponding to) as the central pixel 61a. At this time, the first threshold is the main scanning in the thick line pixel group in which the number of pixels 51 having an image density value equal to or larger than a predetermined value is continuous in the number of three (n + 1 = 3) in the main scanning direction and extends in the sub scanning direction. It is obtained by performing the above-described first edge determination processing on the first processing region 65 having the pixel 61 corresponding to one pixel 51c (edge pixel forming a thick line edge) at the outer end in the direction as the central pixel 61a. The edge determination value is less than Δg0.

  Next, the second edge determination process will be described. As shown in FIG. 6A, the edge determination unit 43 sets 5 (n) in the sub-scanning direction for each pixel 61 of the averaged image data 60 created by the moving average calculation unit 42 with the pixel 61 as the central pixel 61b. × 2 + 1: n = 2), the second processing region 66 in which the pixels 61 are arranged in a matrix of 3 in the main scanning direction is extracted. For the extracted second processing region 66, the edge determination unit 43 adjoins the image density value of each pixel 61 located on the outermost side in the sub-scanning direction around the center pixel 61 b on the inner side in the sub-scanning direction of the pixel 61. A reflection process for multiplying the image density value of the pixel 61 to be performed is performed. In FIG. 6A, the image density values of the pixels 61 of D41, D42, D43, D81, D82, and D83 are multiplied by the image density values of the pixels 61 of D51, D52, D53, D71, D72, and D73, respectively. Match.

  Further, the edge determination unit 43 applies the Sobel filter 72 regarding the sub-scanning direction shown in FIG. 6B to the second processing region 66 on which the reflection process has been performed, thereby determining the edge determination value regarding the sub-scanning direction. Filter processing for calculating Δg90 is performed. The edge determination unit 43 determines that the center pixel 61b is the second edge pixel when the calculated edge determination value Δg90 exceeds the second threshold value.

The edge determination unit 43 simultaneously performs the reflection process and the filter process described above by using the following expression (2).
Δg90 = 1 · D41 + 2 · D42 + 1 · D43 + 2 · (D51 · D41) + 4 · (D52 · D42) + 2 · (D53 · D43) -2 (D71 · D81) -4 · (D72 · D82) -2 · (D73 · D83) -1, D81-2, D82-1, D83 (2)

  Here, as shown in FIG. 6C, the second threshold value is an image density value equal to or greater than a predetermined value (in this embodiment, the image density value related to the medium drop ink which is the third smallest image density value). One pixel 51d at the outer end in the sub-scanning direction (an edge pixel forming an edge of a thin line) in a thin-line pixel group in which two pixels 51 are continuous in the sub-scanning direction (n = 2) and extend in the main scanning direction ) Is the edge determination value Δg90 obtained by performing the above-described second edge determination processing for the second processing region 66 having the pixel 61 corresponding to) as the central pixel 61b. At this time, the second threshold value is a sub-scan in a thick line pixel group in which three pixels 61 having an image density value equal to or larger than a predetermined value are continuous in the sub-scan direction (n + 1 = 3) and extend in the main scan direction. It is obtained by performing the above-described second edge determination processing for the second processing region 66 having the pixel 61 corresponding to one pixel 51d (edge pixel forming a thick line edge) at the outer edge in the direction as the central pixel 61b. The edge determination value is less than Δg90.

  The changing unit 44 determines that the image density value of the pixel 51 corresponding to the pixel 61 determined as the first edge pixel or the second edge pixel by the edge determination unit 43 is the image density value that decreases the volume of the ejected ink droplet. Thus, the image data 50 is changed. Specifically, if the image density value of the pixel 51 corresponding to the pixel 61 determined to be the first edge pixel or the second edge pixel is the image density value related to the large drop ink, the image density value is set to the medium drop ink. If the image density value of the pixel 51 corresponding to the pixel 61 determined to be the first edge pixel or the second edge pixel is the image density value related to the medium drop ink, the image density value Is changed to the image density value relating to the small droplet ink. As described above, the predetermined value is determined by the edge determination unit 43 so that only the pixel 61 having an image density value equal to or higher than that of the medium drop ink is determined as the first edge pixel and the second edge pixel. Therefore, the image density value is not changed for the edge pixel having the image density value related to the small drop ink.

  Based on the image data changed by the changing unit 44, the head control unit 32 drives each inkjet head 1 so that an ink droplet of a desired volume is ejected from the ejection port at a desired timing. At this time, since the image density value of the pixel 51 corresponding to the pixel 61 determined to be the first edge pixel or the second edge pixel is reduced, the ink ejection related to the dot corresponding to the first edge pixel or the second edge pixel The amount is reduced, and blurring of edges in the printed image is suppressed. Further, since the edge pixel of the thin line is not determined as the first edge pixel or the second edge pixel, the ink discharge amount relating to the dot corresponding to the edge pixel is not reduced. Thereby, it is prevented that the visibility of a thin line falls.

  Next, an operation procedure of preprocessing according to the image data processing unit 33 will be described. As shown in FIG. 7, when the image data 50 is transmitted together with the print command from the host computer, the transmitted image data 50 is stored in the image data storage unit 41 (S101). The moving average calculation unit 42 demarcates the average region 55 for each pixel 51 of the image data 50 stored in the image data storage unit 41 and calculates the average value of the image density values in each average region 55 to obtain the average. The converted image data 60 is created (S102).

  The edge determination unit 43 extracts the first processing region 65 having each pixel 61 of the averaged image data 60 created by the moving average calculation unit 42 as the central pixel 61a, and the above-described first processing region 65 is described above. By applying the equation (1), the edge determination value Δg0 related to each pixel 61 is calculated. The edge determination unit 43 determines that the corresponding pixel 61 is the first edge pixel when the calculated edge determination value Δg0 exceeds the first threshold (S103). Further, the edge determination unit 43 extracts the second processing region 66 having each pixel 61 of the averaged image data 60 as the central pixel 61b, and the above formula (2) is applied to the extracted second processing region 66. By applying this, an edge determination value Δg90 for each pixel 61 is calculated. When the calculated edge determination value Δg90 exceeds the second threshold value, the edge determination unit 43 determines that the corresponding pixel 61 is a second edge pixel (S104).

  The changing unit 44 determines that the image density value of the pixel 51 corresponding to the pixel 61 determined as the first edge pixel or the second edge pixel by the edge determination unit 43 is the image density value that decreases the volume of the ejected ink droplet. Thus, the image data 50 is changed (S105). Thus, the preprocessing is completed, and the flowchart of FIG. 7 ends.

  As described above, according to the inkjet printer 101 of the present embodiment, in the first edge determination process, the outer edge in the main scanning direction (sub-scanning direction) from the center pixel 61a in the first processing region 65 (second processing region 66). The number of pixels up to the pixel 61 is made larger than the number of pixels (n) in the width direction of the fine line pixel group, and the first threshold value (second threshold value) corresponds to one pixel 51 at the outer end of the fine line pixel group. In order to obtain the edge determination value Δg0 (Δg90) when the pixel 61 to be processed is the center pixel 61a (center pixel 61b), the edge determination unit 43 determines whether or not it is the first edge pixel (second edge pixel). It is possible to simultaneously determine whether or not the first edge pixel (second edge pixel) is a thin line edge pixel. This makes it possible to determine whether each pixel 61 is a first edge pixel (second edge pixel) other than the thin line pixel group with a small amount of calculation.

  Further, since the first and second threshold values are less than the edge determination values Δg0 and Δg90 when the pixel 61 corresponding to one pixel 51 at the outer end of the thick line pixel group is the central pixel 61a, the edge determination unit 43 When the pixel 61 determines that the outer edge pixel of the thick line pixel group is surely the first and second edge pixels, the changing unit 44 determines the image density related to the first and second edge pixels of the thick line pixel group. Make sure the value is small. Thereby, it is possible to suppress the bleeding of the thick line edge in the printing result.

  The first processing area 65 is composed of pixels 61 arranged in a matrix of 3 in the sub-scanning direction and n × 2 + 1 in the main scanning direction with the center pixel 61a as the center, and the second processing area 66 is the center pixel. Since the pixel 61 is arranged in a matrix of 3 in the main scanning direction and n × 2 + 1 in the sub-scanning direction with the 61b as the center, each pixel 61 has the first and Whether or not the pixel is the second edge pixel can be determined.

  Furthermore, since the predetermined value related to the first and second edge determination processing is equal to or higher than the image density value related to the medium drop ink, the edge determination unit 43 sets the edge pixel having the image density value related to the small drop ink to the first value. And it is not determined as the second edge pixel. Thereby, it is possible to prevent the dot corresponding to the edge pixel having the image density value of the droplet ink from disappearing due to the processing of the changing unit 44.

  In addition, the change unit 44 causes the image density value of the pixel 51 determined as the first edge pixel or the second edge pixel by the edge determination unit 43 to be an image density value that reduces the volume of the ejected ink droplet. In addition, since the image data 50 is changed, it is possible to reliably reduce the ink discharge amount related to the first and second edge pixels. Thereby, it can suppress reliably that an edge bleeds in a printed image.

  Further, after the moving average calculation unit 42 calculates an average area 55 for each pixel 51 of the image data 50 stored in the image data storage unit 41 and calculates an average value of image density values in each average area 55, The edge determination unit 43 performs first and second edge determination processing. As described above, by averaging the image density values of the respective pixels 61, it is possible to suppress erroneous determination of the first and second edge pixels due to the influence of noise such as an independent point adjacent to the edge pixel. .

  Further, since the edge determination unit 43 performs reflection processing in the first and second edge determination processing, the main scanning direction (sub scanning) of the center pixel 61a (61b) in the first processing region 65 (second processing region 66). The image density value of the pixel 61 located on the outer side in the direction) is multiplied by the image density value of the pixel 61 adjacent on the inner side in the main scanning direction (sub-scanning direction), and the region having a low image density value is emphasized (enlarged). It becomes easy. Therefore, it becomes easy to determine an edge pixel adjacent to a thin line space (a pixel group having a low image density value) as an edge pixel.

  In addition, the edge determination unit 43 can determine whether each pixel 61 is an edge pixel in the main scanning direction and the sub-scanning direction by performing the first and second edge determination processes.

  Further, since the Sobel filter that is a first-order differential filter is used in the first and second edge determination processes, the edge pixel can be determined efficiently.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made as long as they are described in the claims. In the above-described embodiment, each pixel 51 of the image data 50 has an image density value quantized to four values, but each pixel 51 is quantized with two values, three values, or five values or more. A configuration having an image density value or a configuration having an unquantized image density value may be used.

  In the above-described embodiment, the first and second edge determination processes are performed separately. However, both determination processes may be performed simultaneously. In this case, the first and second processing regions 65 and 66 are used. Instead, a third processing region is set, which is composed of pixels 61 arranged in a matrix with n × 2 + 1 or more in the main scanning direction and n × 2 + 1 or more in the sub-scanning direction with the center pixel 61 as the center. Instead of the two threshold values, a value obtained by adding the square of Δg0 to the square of Δg0 may be calculated, and a value obtained by raising the value to the half power (third threshold value) may be used. In this case, the calculation time can be shortened. Note that the smaller value of Δg0 and Δg90 may be used as the third threshold value.

  Further, in the above-described embodiment, when the first and second threshold values are the central pixels 61a and 61b, the pixel 61 corresponding to the pixel 51 at the outer end of the thin line pixel group having a width in which two pixels 51 are continuous. However, the first and second threshold values may be equal to or greater than the edge determination values Δg0 and Δg90. At this time, the edge determination value Δg0 when the first and second threshold values are the pixel 61 corresponding to the outer end pixel 51 of the thick line pixel group having a width in which three pixels 51 are continuous as the central pixels 61a and 61b, Although it is less than Δg90, the first and second threshold values are less than the edge determination values Δg0 and Δg90 when the pixel 61 at the outer edge of the thick line pixel having a width in which four or more pixels 61 are continuous is the central pixel 61a. It may be. Thus, by setting the first and second thresholds to be high, it is possible to reliably exclude the edge of the thin line pixel group from the image data change target (the target of density value reduction processing).

  Furthermore, in the above-described embodiment, the first processing region 65 is configured by the pixels 61 arranged in a matrix of 3 in the sub-scanning direction and n × 2 + 1 in the main scanning direction, and the second processing region 66 is the main processing region 66. It is composed of pixels 61 arranged in a matrix of 3 in the scanning direction and n × 2 + 1 in the sub-scanning direction, but the first processing area is 1, 2 or 4 or more in the sub-scanning direction and n × 2 + 1 in the main scanning direction. The pixel 61 may be arranged in a matrix as described above, or the second processing region may be composed of pixels 61 arranged in a matrix of 1, 2 or 4 or more in the main scanning direction and n × 2 + 1 or more in the sub-scanning direction. May be. In this case, in the first edge processing, the image density value of at least the nth pixel from the center pixel in the main scanning direction may be multiplied by the density value of the pixel adjacent to the outside of the pixel. In the second edge processing, it is only necessary to multiply the image density value of at least the nth pixel from the center pixel by the density value of the pixel adjacent to the outside of the pixel in the sub-scanning direction.

  Further, the predetermined value related to the first and second edge determination processing is equal to or higher than the image density value related to the medium drop ink, but the predetermined value may be equal to or higher than the image density value related to the large drop ink. . Further, it may be an arbitrary value of the intermediate gradation in the image density value.

  In addition, in the above-described embodiment, the change unit 44 determines that the image density value of the pixel 51 determined as the first edge pixel or the second edge pixel by the edge determination unit 43 is small in the volume of the ejected ink droplet. The image data 50 is changed so that the image density value becomes the same, but the image density value may be reduced regardless of the volume of the ejected ink droplet.

  In the above-described embodiment, the moving average calculation unit 42 defines an average region 55 for each pixel 51 of the image data 50 stored in the image data storage unit 41 and sets the image density value in each average region 55. Although the edge determination unit 43 performs the first and second edge determination processing after calculating the average value, the first and second edge determination processing may be performed without averaging the image data 50. Good. Note that the processing (moving average processing) performed by the moving average calculation unit 42 reflects the image density value of the pixels included in the average region 55 in addition to the noise removal effect described above (adjacent to the first processing region). The image density value of the pixel to be reflected is reflected in the pixel density value of the first processing area), so it is also possible to reduce the value of n to reduce the range of the first processing area. It is also possible to determine edge pixels with a small amount of calculation.

  Furthermore, in the above-described embodiment, the edge determination unit 43 is configured to perform the reflection process in the first and second edge determination processes, but may be configured not to perform the reflection process.

  In the above-described embodiment, the first and second edge determination processes use a Sobel filter that is a first-order differential filter. However, other first-order differential filters may be used, or a Lablacian filter. A second order differential filter may be used.

  In addition, in the above-described embodiment, an example in which the present invention is applied to a line-type inkjet printer has been described. However, the present invention can also be applied to a serial-type inkjet printer.

  The present invention is also applicable to a recording apparatus that ejects liquid other than ink. Further, the present invention is not limited to a printer, and can be applied to a facsimile, a copier, and the like.

  In the above-described embodiment, an example in which the present invention is applied to the inkjet printer 101 has been described. However, the present invention can also be applied to an image data processing apparatus that processes image data. The present invention is also applicable to application software or driver software installed on a computer.

DESCRIPTION OF SYMBOLS 1 Inkjet head 16 Control apparatus 31 Conveyance control part 32 Head control part 33 Image data processing part 41 Image data storage part 42 Moving average calculation part 43 Edge judgment part 44 Change part 50 Image data 51 Pixel 51a Center pixel 55 Average area 60 Averaging Image data 61 Pixel 61a, 61b Center pixel 65 First processing area 66 Second processing area 72 Sobel filter 101 Inkjet printer

Claims (11)

An image data processing apparatus relating to a liquid ejection apparatus having a liquid ejection head for ejecting liquid for forming an image from a plurality of ejection openings,
Image data storage means for storing image data having image density values of a plurality of pixels arranged in a matrix in a first direction and a second direction orthogonal to the first direction;
Changing means for changing the image data stored in the image data storage means;
Each of the plurality of pixels is arranged in a matrix of 1 or more in the first direction and n (n is an integer of 1 or more) × 2 + 1 or more in the second direction, with the pixel as a central pixel. The edge in the second direction obtained by extracting the image density value of the pixel relating to the first processing area from the image data storage means and applying a differential filter to the image density value of the pixel relating to the first processing area. Edge determination means for determining, when the determination value exceeds a predetermined first threshold, the center pixel of the first processing region as an edge pixel;
The first threshold is an outer end of the thin line pixel group in which pixels having the image density value equal to or larger than a predetermined value are continuous in the number of n in the second direction and extend in the first direction. A value equal to or greater than the edge determination value related to the second direction obtained by performing processing by the edge determination means on the first processing region with one of the pixels as the central pixel;
The image data processing apparatus characterized in that the changing means changes the image data so as to reduce the image density value of a pixel determined as an edge pixel by the edge determining means among the plurality of pixels.   The first threshold is an external value related to the second direction in a group of thick line pixels in which pixels having the image density value equal to or greater than the predetermined value continue in the second direction by the number n + 1 and extend in the first direction. The image data processing apparatus according to claim 1, wherein the image data processing apparatus has a value less than the edge determination value obtained by performing processing by the edge determination unit using one of the end pixels as the central pixel.   3. The first processing region includes a plurality of pixels arranged in a matrix of 3 in the first direction and n × 2 + 1 in the second direction with the central pixel as a center. The image data processing device described in 1.   The said predetermined value is more than the 3rd smallest image density value among 3 or more image density values from which the volume of the discharged liquid differs, The any one of Claims 1-3 characterized by the above-mentioned. Image data processing device.   The changing unit changes the image data so that an image density value of a pixel determined as an edge pixel by the edge determining unit becomes an image density value in which a volume of liquid to be ejected becomes small. The image data processing apparatus according to any one of claims 1 to 4. For each of the plurality of pixels, the image density value of the pixel is the image density in an average region in which pixels are arranged in a matrix of 3 or more in the first direction and 3 or more in the second direction with the pixel as a central pixel. A moving average calculating means for calculating an average value of the values;
6. The edge determination unit according to claim 1, wherein the edge determination unit determines an edge pixel using the image density value of each of the plurality of pixels as the image density value calculated by the moving average unit. The image data processing apparatus according to claim 1.   The edge determination means determines the image density value of each pixel located outside in the second direction with the center pixel as the center with respect to the first processing region, and the image of the pixel adjacent to the inside in the second direction of the pixel. The image data processing apparatus according to claim 1, wherein the differential filter is applied after multiplying the density value. For each of the plurality of pixels, an edge determination unit has 1 or more in the second direction and n (n is an integer of 1 or more) × 2 + 1 or more in the first direction of the plurality of pixels. The image density values of the pixels related to the second processing area arranged in a matrix are extracted from the image data storage means, and the image density values of the pixels related to the second processing area are obtained by applying a differential filter. When the edge determination value related to the first direction exceeds a predetermined second threshold, the center pixel related to the second processing region is further determined as an edge pixel;
The second threshold is an outer end of the thin line pixel group in which pixels having an image density value equal to or larger than a predetermined value are continuous in the number of n in the first direction and extend in the second direction. The value of the edge determination value related to the first direction obtained by performing processing by the edge determination unit on the second processing region having one of the pixels as the central pixel. 7. The image data processing device according to any one of items 7.   The image data processing apparatus according to claim 1, wherein the differential filter is a Sobel filter. A liquid discharge head that discharges liquid to form an image from a plurality of discharge ports;
A liquid ejection apparatus comprising: the image data processing apparatus according to claim 1. A program that causes a computer to function as an image data processing apparatus related to a liquid ejection apparatus having a liquid ejection head that ejects liquid to form an image from a plurality of ejection openings,
Image data storage means for storing image data having image density values of a plurality of pixels arranged in a matrix in a first direction and a second direction orthogonal to the first direction;
Changing means for changing the image data stored in the image data storage means; and
Each of the plurality of pixels is arranged in a matrix of 1 or more in the first direction and n (n is an integer of 1 or more) × 2 + 1 or more in the second direction, with the pixel as a central pixel. The edge in the second direction obtained by extracting the image density value of the pixel relating to the first processing area from the image data storage means and applying a differential filter to the image density value of the pixel relating to the first processing area. When the determination value exceeds a predetermined first threshold value, the computer functions as an edge determination unit that determines the center pixel of the first processing region as an edge pixel,
The first threshold is an outer end of the thin line pixel group in which pixels having the image density value equal to or larger than a predetermined value are continuous in the number of n in the second direction and extend in the first direction. A value equal to or greater than the edge determination value related to the second direction obtained by performing processing by the edge determination means on the first processing region with one of the pixels as the central pixel;
The change means changes the image data so as to reduce the image density value of a pixel determined as an edge pixel by the edge determination means among the plurality of pixels.

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