JP2011156691A - Printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve quality of image while reducing the increase of ink consumption when performing a printing on a paper with small dot gain. <P>SOLUTION: When performing the printing on the paper with small dot gain such as a paper only for inkjet print, an edge detecting part 191 detects the pixel of edge part in image data to be printed, and a drop data forming section 193 forms the drop data which shows the ink amount discharged from an inkjet head to each pixel of the image data, and a drop data correcting section 194 corrects the drop data formed in the drop data forming section 193 so that the ink amount discharged to the pixel of the edge part is increased according to the type of the paper used for printing. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a printing apparatus that performs printing on paper or the like.

  2. Description of the Related Art Conventionally, in an ink jet printing apparatus, the ink discharge amount is changed according to the type of paper used for printing.

  For example, since plain paper has a large dot gain of ink, when printing on plain paper, the amount of ink discharged is suppressed to prevent characters and lines from becoming thick and blurring. On the other hand, since the ink-dedicated paper has a smaller dot gain than plain paper, a large amount of ink can be placed thereon, thereby widening the color gamut. For this reason, the amount of ink discharged is larger when printing on inkjet dedicated paper than when printing on plain paper.

  However, since there are many types of inkjet dedicated paper, and the dot gain may differ depending on the type, the ink discharge amount set by the printing apparatus corresponding to the inkjet dedicated paper is insufficient, and printing is performed. Characters etc. were sometimes faded.

  Therefore, there is a method of performing printing by increasing the ink discharge amount uniformly over the entire surface of the paper. When this method is used, blurring of characters and the like is improved, but the amount of ink consumption increases. Also, there is a tendency for the paper to show through.

  On the other hand, Patent Document 1 discloses a technique for thickening an image by adding an image dot to a blank portion adjacent to an image dot that forms an image, in response to a disadvantage that printed characters become thin. . Thereby, it is possible to improve blurring of characters without excessively increasing the ink consumption.

Japanese Patent Laid-Open No. 2007-125827

  However, as in the technique described in Patent Document 1, when an image dot is added to a blank portion adjacent to an image dot with respect to a fine character portion or a fine line portion, the line of the fine character portion printed on the paper becomes thick. The characters were crushed and the thin lines became thicker, resulting in a deterioration in image quality.

  The present invention has been made in view of the above, and an object of the present invention is to provide a printing apparatus capable of improving image quality while reducing an increase in ink consumption when printing on a sheet having a small dot gain. To do.

  In order to achieve the above object, a printing apparatus according to the present invention includes an inkjet head that prints an image by ejecting ink onto a sheet, and an ink ejection that is ejected from the inkjet head to each pixel of image data to be printed. A drop data generation unit that generates drop data indicating an amount; an edge detection unit that detects pixels in an edge portion of the image data; and an ink discharge amount for at least one of the pixels in the edge portion is increased. A drop data correction unit configured to correct the drop data; and a print control unit configured to control ejection of ink from the inkjet head based on the corrected drop data. The drop data correction unit is a sheet used for printing. Depending on the type of ink, the corrected ink discharge amount for the pixels at the edge is set. And wherein the door.

  According to the printing apparatus of the present invention, the drop data is corrected so as to increase the ink discharge amount for at least one of the pixels in the edge portion of the image data, and the corrected ink is used according to the type of paper used for printing. Since the ejection amount is set, it is possible to improve the image quality by suppressing the blurring of characters and the like while suppressing an excessive increase in the ink consumption amount with respect to paper having various dot gains.

1 is a schematic configuration diagram of a printing apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a functional configuration of the printing apparatus illustrated in FIG. 1. 6 is a diagram illustrating an example of a paper feed tray selection screen. FIG. It is a figure which shows an example of an edge density correction instruction | indication screen. 2 is a flowchart illustrating an operation of the printing apparatus illustrated in FIG. 1. It is a figure which shows the differential filter for edge detection. It is a figure which shows the coefficient of a differential filter. It is a figure which shows the coordinate of the pixel in image data. It is a figure which shows an example of image data. It is a figure for demonstrating a conversion table. It is a figure which shows an example of the enlarged view of a printing image.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a printing apparatus according to an embodiment of the present invention. As shown in FIG. 1, the printing apparatus 1 according to the present embodiment includes a paper feed unit 2, a transport unit 3, and a head unit 4.

  The sheet feeding unit 2 includes a plurality of sheet feeding mechanisms. In the present embodiment, the sheet feeding unit 21, the first sheet feeding tray 22a, the second sheet feeding tray 22b, the third sheet feeding tray 22c, and the fourth sheet feeding mechanism are provided. There are five paper feed mechanisms for the paper tray 22d. A plurality of sheets can be set in each sheet feeding mechanism in a stacked state.

  Further, the paper feed unit 2 picks up the paper one by one from the paper feed roller 23 that picks up and conveys the paper one by one from the paper feed tray 21 and the first paper feed tray 22a to the fourth paper feed tray 22d. The sheet feeding rollers 24a to 24d to be conveyed and the sheet conveyed from any one of the sheet feeding table 21 and the first sheet feeding tray 22a to the fourth sheet feeding tray 22d are skew-corrected and conveyed at a predetermined timing. 3 and a registration roller 25 that feeds out the toner.

  The paper has a size such as A4 and B4, and paper types such as plain paper and inkjet paper, and the same paper size and paper type are set in one paper feed mechanism. There are various types of paper, such as plain paper and inkjet paper.

  The transport unit 3 transports the paper fed from the paper feed unit 2 toward the head unit 4 side by an annular transport belt 31.

  The head unit 4 includes a plurality of line-type inkjet heads 4a to 4d in which a plurality of nozzles are arranged in a direction orthogonal to the paper transport direction, and ejects ink transported by the transport unit 3 onto the paper to generate an image. To print. The ink jet heads 4a to 4d are arranged above the transport unit 3 at a predetermined interval, and ink of each color of C (cyan), K (black), M (magenta), and Y (yellow) is sequentially applied from the paper supply side to the paper. To be discharged.

  The paper printed by the head unit 4 is transported by the transport unit 3 and discharged as it is to the face-up discharge tray 5 or is transported through the circulation transport path 6 and discharged to the face-down discharge tray 7. .

  At the time of double-sided printing, the paper on which single-sided printing has been performed is transported through the circulation transport path 6 and is guided to a switchback path 8 provided using the space in the face-down paper discharge tray 7 to perform switchback. The sheet is sent to the transport unit 3 by the registration roller 25 with the surface facing downward. Then, the single-side printed paper is printed on the non-printed surface by the head unit 4 while being transported by the transport unit 3, and is then discharged to the face-up discharge tray 5 or the face-down discharge tray 7.

  FIG. 2 is a block diagram illustrating a functional configuration of the printing apparatus 1. As illustrated in FIG. 2, the printing apparatus 1 includes an operation panel unit 10, a conveyance drive unit 11, an image reading unit 12, a conversion table storage unit 13, a print execution unit 14, and a control unit 15.

  The operation panel unit 10 includes various operation keys and a touch panel (both not shown), receives a user operation, and outputs an operation signal based on the user operation. The user can perform an input operation by pressing an operation key or touching the surface of the touch panel with a finger or the like.

  The conveyance driving unit 11 conveys a sheet by driving driving rollers in the conveyance unit 3 and the circulation conveyance path 6.

  The image reading unit 12 includes a CCD (Charge Coupled Device) image sensor, optically reads a document, and outputs image data of the read document. The image reading unit 12 may be installed in the printing apparatus 1 or may be installed outside the printing apparatus 1.

  The conversion table storage unit 13 includes a non-volatile storage medium, and stores conversion tables 131a, 131b,... Used for correcting drop data in a drop data correction unit 194 described later.

  The print execution unit 14 includes a head unit 4 and prints an image on a sheet by ejecting ink from each of the inkjet heads 4 a to 4 d of the head unit 4.

  The control unit 15 includes a CPU (Central Processing Unit), a memory, an image processing device, and the like. The operation panel control unit 16 and the paper feed control unit 17 are operated by the CPU operating according to a program stored in the memory. A conveyance control unit 18, an image processing unit 19, and a print control unit 20 are configured.

  The operation panel control unit 16 performs screen display control of the touch panel of the operation panel unit 10 and processing for interpreting a user operation based on an operation signal from the operation panel unit 10.

  The paper feed control unit 17 performs control to send the paper from the paper feed mechanism selected by the user operation to the transport unit 3 at a predetermined timing.

  The conveyance control unit 18 controls paper conveyance by the conveyance driving unit 11.

  The image processing unit 19 includes an edge detection unit 191, a color conversion unit 192, a drop data generation unit 193, and a drop data correction unit 194.

  The edge detection unit 191 uses the G image data among the R (red), G (green), and B (blue) image data obtained by reading the document with the image reading unit 12, so that characters, lines, etc. Detect pixels at the edge of the image. Further, the edge detection unit 191 performs an edge enhancement process for enhancing the edge portion of the G image data.

  The color conversion unit 192 converts R, G, and B image data into C, K, M, and Y image data. The image data of each color is represented by a gradation of 8 bits for each pixel, and is represented by a value of 0 to 255 from the darker side to the brighter side.

  The drop data generation unit 193 performs gamma conversion processing for each color of C, K, M, and Y, and then performs multi-value error diffusion processing to generate drop data indicating the amount of ink discharged to each pixel. To do. The drop data is data indicating the number of ink drops of a predetermined amount ejected to each pixel.

  The drop data correction unit 194 corrects the drop data generated by the drop data generation unit 193 so as to increase the ink discharge amount for the pixels at the edge portion.

  The print control unit 20 controls the printing process in the print execution unit 14 by controlling the ink ejection operation in each of the inkjet heads 4a to 4d of the head unit 4 based on the drop data.

  Next, the operation of the printing apparatus 1 will be described.

  When printing is performed by the copy function of the printing apparatus 1, the user performs printing from each paper feed mechanism (the paper feed table 21, the first paper feed tray 22a to the fourth paper feed tray 22d) prior to execution of printing. A paper feed mechanism in which the paper size and paper type to be used are set can be selected.

  An example of a paper feed tray selection screen for the user to select a paper feed mechanism is shown in FIG. As shown in FIG. 3, a selection button group 41 for selecting a paper feed mechanism is displayed on the paper feed tray selection screen 40. Each selection button of the selection button group 41 displays the size and paper type set in each paper feed mechanism. The user can select a paper feed mechanism on which desired paper is set from a selection button group 41 on the paper feed tray selection screen 40 displayed on the touch panel of the operation panel unit 10.

  When a paper feed mechanism on which inkjet paper is set is selected from the paper feed tray selection screen 40, that is, in the example of FIG. 3, one of the first paper feed tray 22a to the third paper feed tray 22c is selected. In this case, the operation panel control unit 16 displays an edge density correction instruction screen 50 as shown in FIG. 4 on the touch panel of the operation panel unit 10.

  The edge density correction instruction screen 50 is a screen for the user to set whether or not to correct the ink discharge amount of the pixels in the edge portion in order to increase the density of the edge portion of the image. The edge density correction instruction screen 50 includes an “up” button 51 for setting the user to increase the density of the edge portion of the image and an “not up” button 52 for setting not to increase. Is displayed. The user can set to increase the ink discharge amount for the pixels at the edge portion of the image by selecting the “Up” button 51.

  FIG. 5 is a flowchart showing the operation of the printing apparatus 1 during printing.

  When the start of printing is instructed by a user operation, in step S10, the edge detection unit 191 uses G image data among R, G, and B image data obtained by reading an original with the image reading unit 12. Detect pixels at the edge of the image such as characters and lines.

  An example of an edge detection method in the edge detection unit 191 will be described. First, the edge detection unit 191 calculates four provisional edge amounts corresponding to each differential filter for each pixel using four differential filters of a 3 × 3 matrix as shown in FIGS. To do. Here, FIG. 6 (a) detects the horizontal direction, FIG. 6 (b) detects the vertical direction, FIG. 6 (c) detects the right-up diagonal direction, and FIG. 6 (d) detects the left-up diagonal edge. It is a filter for.

  The calculation of the provisional edge amount will be described. The coefficients of the differential filter are expressed as shown in FIG. 7, the coordinates of the pixel in the image data are expressed as shown in FIG. 8, and the pixel value at the position (x, y) is expressed as D (x, y). The provisional edge amount E of the target pixel 60 at the position y) is calculated by the following (Equation 1).

E = a * D (x-1, y-1) + b * D (x, y-1) + c * D (x + 1, y-1)
+ D × D (x−1, y) + e × D (x, y) + f × D (x + 1, y)
+ G × D (x−1, y + 1) + h × D (x, y + 1)
+ I × D (x + 1, y + 1) (Formula 1)
For example, in the image data as shown in FIG. 9, the provisional edge amount E of the target pixel 60 is calculated as follows using the above (Formula 1).

E = 129a + 85b + 47c + 24d + 5e + 57f
+ 199g + 207h + 230i
With such a calculation, the edge detection unit 191 calculates, for each pixel, four provisional edge amounts corresponding to the four differential filters shown in FIGS. A large provisional edge amount is set as the edge amount of the pixel.

  Then, the edge detection unit 191 compares the calculated edge amount of each pixel with a predetermined threshold Eth, and determines a pixel having an edge amount equal to or greater than the threshold Eth as a pixel in the edge portion.

  In the case of the example in FIG. 9, assuming that the temporary edge amounts corresponding to the differential filters in FIGS. 6A to 6D of the target pixel 60 are E1 to E4, E1 = 375, E2 = −18, E3 = 256, E4 = 241, of which E1 = 375 having the maximum absolute value is the edge amount of the target pixel 60. For example, if the threshold Eth = 210, since E1> Eth, it is determined that the target pixel 60 is an edge portion pixel.

  After detection of the edge portion, in step S20, the edge detection portion 191 performs edge enhancement processing for enhancing the edge portion on the G image data. The edge enhancement processing may be performed using a general high frequency enhancement filter such as Laplacian.

  Next, in step S30, the color conversion unit 192 converts the R, G, and B image data into C, K, M, and Y image data.

  Next, the drop data generation unit 193 performs gamma conversion processing of each color of C, K, M, and Y in step S40, and then performs multi-value error diffusion processing in step S50, and discharges each pixel. Drop data indicating the number of ink drops to be generated is generated.

  Next, in step S60, the drop data correction unit 194 determines whether or not the setting is to correct the ink discharge amount with respect to the edge portion. Here, the drop data correction unit 194 is a setting for correcting the ink discharge amount when the “Up” button 51 is selected by the user operation on the edge density correction instruction screen 50 prior to the instruction to start printing. Judge.

  When the setting is to correct the ink discharge amount (step S60: YES), in step S70, the drop data correction unit 194 applies the drop data of each color generated by the drop data generation unit 193 to the pixels in the edge portion. Correction for increasing the ink discharge amount (number of ink drops) is performed.

  The method for correcting the drop data is not particularly limited, but in the present embodiment, conversion tables 131a, 131b,... Are used.

  Each of the conversion tables 131a, 131b,... Shows the relationship between the drop data (input drop data) generated by the drop data generation unit 193 and the corrected drop data (output drop data) as shown in FIG. keeping. The relationship between the input drop data and the output drop data as shown in FIG. 10 is defined according to the type of ink jet dedicated paper, and the conversion tables 131a, 131b,. Are prepared for each type of ink-jet dedicated paper set.

  The example of FIG. 10 shows a case where the maximum number of drops when printing on inkjet dedicated paper is 5, and 1 drop in the input drop data is 3 drops, 2 drops are 4 drops, 3 drops and 4 drops. Each is increased to 5 drops.

  The drop data correction unit 194 refers to one of the conversion tables 131a, 131b,... Based on the type of the dedicated inkjet paper corresponding to the paper feed mechanism selected by the user operation from the paper feed tray selection screen 40. Then, correction processing for converting input drop data into output drop data is performed.

  In step S80, the paper feed control unit 17 controls the paper feed unit 2 to send the paper from the paper feed mechanism selected by the user operation to the transport unit 3, and the print control unit 20 drops the drop data correction unit 194. Based on the drop data of each color corrected in step (i), the ink ejection operation in each of the inkjet heads 4a to 4d of the head unit 4 is controlled, and printing is performed on the paper conveyed by the conveyance unit 3.

  If it is not set to correct the ink ejection amount (step S60: NO), the drop data correction unit 194 does not correct the drop data and outputs the drop data generated by the drop data generation unit 193 to the print control unit 20. In this case, in step S80, the print control unit 20 controls the printing operation based on the drop data generated by the drop data generation unit 193.

  FIG. 11 is an example of an enlarged view of a print image. FIG. 11A is an enlarged view of the print image when the ink discharge amount is not corrected for the edge portion, and FIG. FIG. 6 shows an enlarged view of a printed image when the ink discharge amount is increased. When the correction is performed in step S70, the ink discharge amount of the pixels of the edge portion 61 is increased as shown in FIG. 11B, so that the edge portion is clearly expressed. Thus, by increasing the ink discharge amount to the edge portion, it is possible to suppress the occurrence of blurring of characters, lines, and the like.

  As described above, in the present embodiment, when printing on a paper having a small dot gain such as an inkjet-dedicated paper, the ink discharge amount for the pixels at the edge portion is increased, and the ink discharge is uniformly performed for all the pixels. Do not increase the amount or add image dots to the blank. For this reason, it is possible to improve image quality by suppressing blurring of characters and the like while suppressing an excessive increase in ink consumption.

  Further, by using the conversion tables 131a, 131b,... According to the paper type, the corrected ink ejection amount is set for each paper type, so that it is possible to deal with papers with various dot gains.

  In the above description, the case where printing is performed based on the image data of the original read by the image reading unit 12 using the copy function has been described. However, the personal computer connected to the printing apparatus 1 via the communication line or the like using the printer function. The present invention is also applicable when printing is performed using print data transmitted from (PC). In this case, the selection of the paper type and the setting of whether or not to correct the ink discharge amount for the edge portion are performed by the printer driver of the PC.

DESCRIPTION OF SYMBOLS 1 Printing apparatus 2 Paper feed part 3 Conveyance part 4 Head unit 4a-4d Inkjet head 10 Operation panel part 11 Conveyance drive part 12 Image reading part 13 Conversion table memory | storage part 14 Print execution part 15 Control part 16 Operation panel control part 17 Paper feed Control unit 18 Conveyance control unit 19 Image processing unit 20 Print control unit 21 Paper feed table 22a First paper feed tray 22b Second paper feed tray 22c Third paper feed tray 22d Fourth paper feed tray 40 Paper feed tray selection screen 50 Edge Density correction instruction screen 131a, 131b, ... conversion table 191 edge detection unit 192 color conversion unit 193 drop data generation unit 194 drop data correction unit

Claims (1)

An inkjet head that prints an image by ejecting ink onto paper;
A drop data generation unit that generates drop data indicating the amount of ink discharged from the inkjet head for each pixel of image data to be printed;
An edge detection unit for detecting pixels of an edge part in the image data;
A drop data correction unit that corrects the drop data so as to increase an ink ejection amount for at least one of the pixels of the edge portion;
A print control unit that controls to eject ink from the inkjet head based on the corrected drop data;
The printing apparatus according to claim 1, wherein the drop data correction unit sets a corrected ink ejection amount for the pixels of the edge portion according to a type of paper used for printing.

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