JP2011194832A - Printing method and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the consumption of white ink while maintaining image quality.SOLUTION: The printing method intended for a printer comprising a color ink nozzle array having a plurality of nozzles discharging color ink and a white ink nozzle array having a plurality of nozzles discharging white ink includes the formation of a color image on a medium by using the color ink and the formation of a background image to be the background of the color image on the medium by using the white ink. At that time, the density of white is corrected to vary the density in accordance with the distances to the color image to form the background image.

Description

  The present invention relates to a printing method and a program.

  2. Related Art Inkjet printing apparatuses that perform printing on a medium (paper, cloth, OHP paper, etc.) by discharging ink from a head in which a large number of nozzles are arranged are known. As such a printing apparatus, a line printer that moves a medium with respect to a fixed head, a serial printer that repeats an operation of moving the head to eject ink and an operation of conveying the medium alternately are known. Yes. As a method for ejecting ink from the head, a piezoelectric method using a piezoelectric element such as a piezo element, a thermal method using a heater that generates bubbles, and the like are known.

  A printing apparatus using not only color inks such as cyan, magenta, yellow, and black but also white ink is known (for example, see Patent Document 1). The white ink is used mainly for the purpose of forming a background of a printed image formed with color inks.

JP 2009-241419 A

  When the background of a color image formed with color ink is formed with white ink, a large amount of white ink is consumed. For this reason, there is a demand for suppressing the amount of white ink used. In particular, when white ink is expensive, there is a strong demand for suppressing the amount of white ink used in order to produce printed matter at low cost.

  However, simply reducing the amount of white ink used reduces the density of the white image, resulting in large deterioration of the printed image.

  An object of the present invention is to suppress the amount of white ink used while maintaining image quality.

  A main invention for achieving the above object is a printing method for a printing apparatus comprising: a color ink nozzle row having a plurality of nozzles for discharging color ink; and a white ink nozzle row having a plurality of nozzles for discharging white ink. When forming a color image on the medium using the color ink and forming a background image as a background of the color image on the medium using the white ink, the distance to the color image is increased. In this printing method, the background image is formed by correcting the white density so that the density changes accordingly.

  Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

1 is a block diagram of an overall configuration of a line printer 1. FIG. 1 is a schematic diagram of an overall configuration of a printer. 4 is an explanatory diagram of an arrangement of a plurality of heads on the lower surface of the first white head group. FIG. FIG. 4A is an explanatory diagram of the surface printing mode. FIG. 4B is an explanatory diagram of the reverse printing mode. It is explanatory drawing of an original image. FIG. 6A is a printed image when the original image is printed as usual. FIG. 6B is an explanatory diagram of a print image when white ink reduction processing is performed. FIG. 7A is a setting screen for white ink reduction processing. FIG. 7B is a graph of correction values used in the white ink reduction process. It is a flowchart of a white ink reduction process. FIG. 9A is a printed image when the original image is printed as usual. FIG. 9B is an explanatory diagram of a print image when another white ink reduction process is performed. It is a graph of the correction value used for another white ink reduction process.

  At least the following matters will become clear from the description of the present specification and the accompanying drawings.

A printing method for a printing apparatus comprising: a color ink nozzle row having a plurality of nozzles that discharge color ink; and a white ink nozzle row having a plurality of nozzles that discharge white ink, wherein the color image is obtained using the color ink. Is formed on the medium, and when forming a background image as the background of the color image using the white ink on the medium, the white density is changed so that the density changes according to the distance to the color image. A printing method characterized by forming the background image after correction is made clear.
With such a printing method, the amount of white ink used can be suppressed while maintaining the image quality.

  It is desirable to correct so that the density of white becomes lighter as the distance to the color image becomes longer. As a result, the amount of white ink used can be suppressed without impairing the contrast of the color image.

  It is desirable to correct so that the density of white becomes lighter as the distance to the color image becomes shorter. As a result, the amount of white ink used can be suppressed while the white image is easily visually recognized at a uniform density.

  It is desirable to be able to set the minimum white density. As a result, the degree of image quality degradation can be adjusted.

  If the white gradation value is not constant in the background image before correction, it is desirable not to correct the white density. As a result, the image quality of the image before correction is not significantly deteriorated.

  It is desirable to calculate the distance to the area surrounding the color image as the distance to the color image. Thereby, the gradation change that the white image undulates does not occur.

A printing apparatus including a color ink nozzle row having a plurality of nozzles for discharging color ink and a white ink nozzle row having a plurality of nozzles for discharging white ink causes a color image to be formed on a medium using the color ink. A function of forming a background image as a background of the color image using the white ink on the medium, and correcting the white density so that the density changes according to the distance to the color image, A program characterized by realizing the function of forming a background image becomes clear.
According to such a program, the amount of white ink used can be suppressed while maintaining the image quality.

=== Printer configuration ===
<Overall configuration>
FIG. 1 is a block diagram of the overall configuration of the line printer 1. FIG. 2 is a schematic diagram of the overall configuration of the printer 1. Hereinafter, the basic configuration of the printer of this embodiment will be described.

  A printer driver is installed in the computer 110. The computer 110 in which the printer driver is installed becomes a print control device for controlling the printer 1. The printer driver receives image data from the application program, converts it into print data in a format that can be interpreted by the printer 1, and outputs the print data to the printer.

  The line printer 1 of the present embodiment includes a transport unit 20, a head unit 40, a sensor group 50, and a controller 60. The printer 1 that has received print data from the computer 110 that is an external device controls each unit (the transport unit 20 and the head unit 40) by the controller 60. The controller 60 controls each unit based on the received print data and prints on paper (medium). The situation in the printer 1 is monitored by a sensor group 50, and the sensor group 50 outputs a detection result to the controller 60. The controller 60 controls each unit based on the detection result output from the sensor group 50.

  The transport unit 20 is for transporting a medium (for example, paper S) in the transport direction. The transport unit 20 includes a transport motor (not shown), an upstream roller 22A and a downstream roller 22B, and a belt 24. When a conveyance motor (not shown) rotates, the upstream roller 22A and the downstream roller 22B rotate, and the belt 24 rotates. The fed paper S is conveyed by the belt 24 while facing the head. The paper S that has passed through the printing area is discharged to the outside by the belt 24. The paper S being conveyed is electrostatically attracted or vacuum attracted to the belt 24.

  The head unit 40 is for ejecting ink onto the paper S. The head unit 40 includes four head groups 41 that discharge color ink. These four head groups 41 eject cyan ink (C), magenta ink (M), yellow ink (Y), and black ink (K), respectively. A first white head group 42 that discharges white ink is provided on the upstream side in the transport direction of the four head groups 41 that discharge color ink. A second white head group for ejecting white ink is also provided on the downstream side in the transport direction of the four head groups 41 for ejecting color ink. Each head group (41, 42, 43) can form dots for the paper width at a time.

FIG. 3 is an explanatory diagram of an arrangement of a plurality of heads on the lower surface of the first white head group 42. As shown in the figure, the first white head group 42 has a plurality of heads 421. The plurality of heads are arranged in a staggered pattern along the paper width direction. Each head 421 is formed with a nozzle row. The nozzle row is composed of a plurality of nozzles (for example, 360 nozzles) that eject ink. The plurality of nozzles constituting the nozzle row are arranged at a constant nozzle pitch in the paper width direction. With such a configuration, the first white head group 42 can form dots corresponding to the paper width at a time.
Although the configuration of the first white head group 42 has been described here, the configurations of the other head groups (41, 43) are the same.

  The sensor group 50 includes a rotary encoder (not shown), a paper detection sensor, and the like. A rotary encoder (not shown) detects the amount of rotation of the upstream roller 22A and the downstream roller 22B. Based on the detection result of the rotary encoder, the transport amount of the paper S can be detected. A paper detection sensor (not shown) detects the position of the leading edge of the paper being fed. The position of the paper S in the transport direction can also be detected by detecting the transport amount of the paper S after the paper detection sensor detects the paper with a rotary encoder.

  The controller 60 is a control unit (control unit) for controlling the printer. The controller 60 controls each unit according to a program stored in the memory 61. The memory 61 stores various correction values.

=== Front printing mode and reverse printing mode ===
When a color image is simply printed on a transparent medium, the periphery of the color image is seen through, so that the visibility of the color image is deteriorated. Specifically, when characters are printed on a transparent film, the characters are difficult to see. Therefore, a white image is formed on the background of the color image.

  There are “front printing mode” and “back printing mode” as printing modes for printing a color image and a white image as a background image on a transparent medium. FIG. 4A is an explanatory diagram of the surface printing mode. FIG. 4B is an explanatory diagram of the reverse printing mode. Here, the white image is illustrated in black (in the following description, the white image may be illustrated in black).

  The front printing mode is a printing mode for viewing a color image from the direction of the printing surface of the medium (the arrow direction in FIG. 4A). In the front printing mode, the first white head group 42 on the upstream side in the transport direction is used. The controller 60 ejects white ink from the first white head group 42 while transporting the medium S in the transport direction, and forms a white image as a background image on the medium S. Then, the controller 60 discharges the color ink from the head group 41 while further transporting the medium S, and forms a color image on the white image.

  The reverse printing mode is a printing mode for viewing a color image through a transparent medium from a direction opposite to the printing surface of the medium (the arrow direction in FIG. 4B). In the reverse printing mode, the second white head group 43 on the downstream side in the transport direction is used. The controller 60 discharges color ink from the head group 41 while transporting the medium S in the transport direction, and forms a color image on the medium S. Note that in the reverse printing mode, a color image is seen through the transparent medium, so that a mirror image is printed from the direction of the printing surface. Then, the controller 60 ejects white ink from the second white head group 43 while further transporting the medium S, and forms a white image as a background image on the color image.

  The printer 1 of the present embodiment includes the head groups (42, 43) that discharge white ink on the upstream side and the downstream side in the transport direction of the head group 41 that discharges color ink. "And" back printing mode "can be realized.

  A white image as a background image is often set in a wider range than a color image. For this reason, if the original image is printed as it is, the amount of white ink used increases. Therefore, the printer driver of the present embodiment causes the computer 110 to execute white ink reduction processing for reducing the amount of white ink used.

=== White Ink Reduction Processing (1) ===
<About images>
FIG. 5 is an explanatory diagram of an original image. Here, the white ink reduction process of the original image for the front printing mode as shown in the drawing will be described.

  The original image has a white image layer and a color image layer. A white image serving as a background image is set in the white image layer. The white image is composed of 256 gradation pixels. In the white image of the original image in the figure, the gradation value of every pixel is uniform and indicates the darkest gradation value. A color image is set in the color image layer. The color image is composed of, for example, pixels of 256 gradations in the RGB color space. Such an original image is drawn by the user with application software.

  When the user instructs printing of the original image on the application, the printer driver is read, and the original image data is transferred from the application software to the printer driver.

  FIG. 6A is a printed image when the original image is printed as usual. FIG. 6B is an explanatory diagram of a print image when white ink reduction processing is performed. Here, the darker the white image, the darker the black.

  When the white ink reduction process is performed, a gradation is applied to the white image as the background image so that the density gradually changes according to the distance to the color image. Here, the density of white is the same as that of the original image in the region close to the color image, but becomes lighter as it goes away from the color image.

By changing the white density lighter than the original image, it is possible to reduce the amount of white ink used when a printed image is formed on a medium.
However, since the density of white in the area close to the color image is maintained as the original image, the influence of the contrast of the color image when the print image is viewed is small. On the other hand, since the area where the white density is lighter is separated from the color image, the influence of the contrast of the color image is small. That is, even if such white ink reduction processing is performed, the contrast of the color image is hardly affected.

<About processing>
FIG. 7A is a setting screen for white ink reduction processing. The printer driver can display a setting screen on a display as a user interface.

  When the check box of “Perform white ink reduction” is not checked, the printer driver is set not to execute white ink reduction processing during printing. When the user checks this check box, the printer driver is set to execute white ink reduction processing during printing.

  In addition, when this check box is checked, a predetermined item for white ink reduction processing can be set. Here, “gradation width” and “minimum white density” can be set. By setting the minimum white density, the degree of image quality deterioration can be adjusted.

  FIG. 7B is a graph of correction values used in the white ink reduction process. When the setting item for the white ink reduction process is set, a correction value for the distance L is set.

  Here, the correction value is set to 1.0 at the distance L = 0. Then, the correction value is set to gradually decrease as the distance L increases. The correction value gradually decreases as the distance L increases so that the correction value becomes 0.7 (corresponding to the value set in “minimum white density”) at the distance L = 50 mm of “gradation width”. Further, the correction value is set so as not to be lower than the value set in the “minimum white density”. For this reason, when the distance L exceeds 50 mm, the correction value becomes a constant value.

  In the above description, “gradation width” and “minimum white density” are set items, but the setting items are not limited to these. For example, for example, a gradation of gradation (corresponding to θ in FIG. 7B) may be set.

  FIG. 8 is a flowchart of the white ink reduction process.

  First, the printer driver determines whether or not the gradation value of a pixel (white pixel) constituting the white image is a constant value (S101). When this determination is NO, it is considered that the white image of the original image is not a simple filled image but an image on which gradation expression aiming at a visual effect is applied. When the gradation value of such a white image is changed by the white ink reduction process, the image quality of the original image is expected to be significantly deteriorated. Accordingly, when the gradation value of the white image is not constant (NO in S101), the printer driver ends the process without performing the white ink reduction process on the white image. Note that the printer driver may display a warning screen on the display indicating that the white ink reduction process has not been performed, if necessary.

  When the gradation value of the white image is constant (YES in S101), the printer driver calculates the distance L to the color image for each white pixel (S102). The printer driver calculates the distance L based on the coordinates of the target white pixel (target pixel) and the coordinates of the color image closest to the target pixel.

  Incidentally, in the case of a color image of the original image as shown in FIG. 5, the calculation of the distance L is complicated on the right side of the color image “E”. Further, if the gradation value of the white pixel is corrected according to the distance L, the gradation changes so that the white image on the right side of the color image “E” ripples, and the image quality after the white ink reduction process is expected to deteriorate. Is done. For this reason, the printer driver defines a rectangular area surrounding a pixel having a gradation value (a pixel constituting “E”) in the color image layer as a color image area, and sets the distance between the rectangular area and the white pixel as a distance. It may be calculated as L. If the color image area is defined in this way, even if the gradation value of the white pixel is corrected according to the distance L, the gradation change in which the white image undulates does not occur. In addition, since the shape of a normal medium is a quadrangle, if a color image area is defined as a rectangle, gradation is applied along the shape of the medium, so that the appearance of the printed image is improved. Note that the rectangular area surrounding the pixel having the gradation value obtains the maximum value and the minimum value of the coordinate in the X direction and the maximum value and the minimum value of the coordinate in the Y direction from the pixels having the gradation value, respectively. The coordinates ((X direction minimum value, Y direction minimum value), (X direction maximum value, Y direction minimum value), (X direction minimum value, Y direction maximum value) and (X direction maximum value, Y direction) It is good to define from the maximum value)).

  Next, the printer driver corrects the gradation value of the white pixel according to the distance L (S103). Since the correction value is determined when the distance L is determined (see FIG. 7B), the printer driver corrects the gradation value of the white pixel by multiplying the gradation value of the white pixel in the original image by the correction value. . Since the correction value is smaller as the distance L is larger (see FIG. 7B), the density of the white image is maintained as it is closer to the color image, but the density of the white image becomes lighter as it is farther from the color image.

  The printer driver performs the processes of S102 and S103 for all the white pixels, and ends the white ink reduction process (S104).

  Thereafter, the printer driver performs a halftone process on the 256 gradation white image data after the white ink reduction process, and converts the white gradation data into four gradation white image data that can be expressed by one pixel. Then, the printer driver causes ink to be ejected from each nozzle of the first white head group 42 based on the white image data of four gradations, and dots (large dots, medium dots, small dots) are formed on each pixel on the medium. Dot / no dot) and print a white image on the medium. In the area where the gradation value is corrected to be light by the white ink reduction process, the number of dots formed on the medium is reduced or the size of the dots is reduced, so that the amount of white ink used is reduced.

  The printer driver performs color conversion processing for converting a color image in the RGB color space of the original image into image data in the CMYK color space, and performs halftone processing on the image data after color conversion. Then, the printer driver ejects cyan ink, magenta ink, yellow ink, and black ink from the four head groups 41 based on the four gradation image data in the CMYK color space, respectively, and a color image on the white image. To print.

  If the original image is printed after performing the white ink reduction process in this way, as shown in FIG. 6B, the white image as the background image is changed so that the density gradually changes according to the distance to the color image. Gradation is applied.

=== White ink reduction processing (2) ===
In the white ink reduction process described above, the white image is corrected so that the density of white becomes lighter as the distance to the color image becomes longer. However, it is not limited to this. As described below, the white image may be corrected so that the density of white becomes lighter as the distance to the color image becomes shorter. In the following description, the white ink reduction process of the original image for the front printing mode as shown in FIG. 5 will be described.

  FIG. 9A is a printed image when the original image is printed as usual. FIG. 9B is an explanatory diagram of a print image when another white ink reduction process is performed. Also here, the darker the white image, the darker the black.

  Even when this white ink reduction process is performed, gradation is applied to the white image as the background image so that the density gradually changes according to the distance to the color image. However, here, the density of white is the density of the original image in a region sufficiently away from the color image, but becomes lighter as it approaches the color image.

By changing the white density lighter than the original image, it is possible to reduce the amount of white ink used when a printed image is formed on a medium.
However, since the white density in a region sufficiently away from the color image is maintained as in the original image, the whiteness of the white image as the background image is as in the original image. In addition, since the area where the density of white is light is close to the color image, it is visually recognized while being compared with the color of the color image. Therefore, it is easy to visually recognize white and it is difficult to visually recognize that it has become light. For this reason, even if such white ink reduction processing is performed, the white image is easily visually recognized with a uniform density.

  FIG. 10 is a graph of correction values used for the white ink reduction process. When white ink reduction processing is set as in FIG. 7A, a correction value for the distance L is set.

  Here, at the distance L = 0, the correction value is set to 0.7 (corresponding to the value set for “minimum white density”). The correction value is set to gradually increase as the distance L increases. Further, the correction value is gradually increased as the distance L is increased so that the correction value becomes 1.0 at the distance L = 50 mm of the “gradation width”. When the distance L exceeds 50 mm, the correction value is 1.0 and becomes a constant value.

  When white ink reduction processing is performed in the same manner as in FIG. 8 according to such correction values, as shown in FIG. 9B, the background image has a density that gradually changes according to the distance to the color image. A gradation is applied to a white image.

=== Other Embodiments ===
The above-described embodiments are for facilitating the understanding of the present invention, and are not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof.

<About line printers>
The above-described printer 1 is a so-called line printer, in which a medium is conveyed to a fixed head, and a dot row is formed on the medium along the conveyance direction. However, the printer 1 is not limited to a line printer. For example, a printer having a head mounted on a carriage movable in the main scanning direction, which ejects ink from the moving head to form a dot row along the main scanning direction, and transports the medium It may be a printer (so-called serial printer) that alternately repeats the carrying operation.

  In the case of such a serial printer, it is possible to form dot rows at an interval narrower than the nozzle pitch. That is, the printing resolution can be made higher than the nozzle pitch. For this reason, the resolution of the above-described image data is not the same resolution as the nozzle pitch, but may be a resolution higher than the nozzle pitch.

<About white ink>
In the above embodiment, “white” is not limited to white in the strict sense that is the surface color of an object that reflects 100% of all wavelengths of visible light. , Including a color called white. “White” means, for example, (1) Color measurement mode: Spot color measurement, Light source: D50, Backing: Black, Print medium: Measured with transparent film, using x-rite colorimeter eye-one Pro If it is colored, the label in the Lab system is on the a * b * plane within the circumference of the radius 20 and inside thereof, and L * is in the hue range represented by 70 or more, or (2) Minolta When using the colorimeter CM2022 manufactured by the company with color measurement in the measurement mode D502 ° field of view, SCF mode, and white background, the label in the Lab system is on the circumference of the radius 20 and inside it on the a * b * plane. , And L * is in the hue range represented by 70 or more, or (3) the color of the ink used as the background of the image as described in JP-A-2004-306591, as the background If it is used, it is not limited to pure white.

<About print mode>
In the above-described white ink reduction process, the original image in the front printing mode has been described. However, the white ink reduction process may be performed in the back printing mode.

  Further, white ink reduction processing may be performed when printing on a medium such as opaque paper instead of a transparent medium. For example, when a white image is formed on paper and a color image is formed on the white image, the paper color may be adjusted to white and printed. May be performed.

<About gradation settings>
In the above-described embodiment, the user sets “gradation width”, “minimum white density”, and the like on the setting screen. However, the present invention is not limited to this. For example, default setting values may be prepared in advance, and setting by the user may be unnecessary.

  Further, the set value may be automatically set based on the size of the image. For example, the “gradation width” may be automatically set so as to increase as the white image or the color image increases. Alternatively, the “gradation width” may be automatically set such that the size (ratio) of the color image with respect to the white image increases.

<About the white ink reduction process 1>
In the above-described embodiment, when the gradation value of the white image is not constant (NO in S101), the printer driver ends the process without performing the white ink reduction process on the white image. However, if NO in S101, the amount of white ink used may be reduced uniformly instead of reducing the amount of white ink used according to the distance to the color image. For example, in the case of NO in S101, the amount of white ink used may be reduced uniformly by uniformly setting the correction value to 0.9. In this case, it is possible to print a white image while reducing as much as possible the gradation expression aiming at the visual effect while reducing the amount of white ink used.

<About white ink reduction processing 2>
In the above-described embodiment, the printer driver realizes a reduction in the amount of white ink used by correcting the gradation value of the 256 gradation white pixels to be light. However, the present invention is not limited to this. For example, the printer driver corrects the gradation value of the four gradation white pixels after halftone processing to reduce the number of dots or reduce the size of the dots, thereby reducing the amount of white ink used. May be reduced.

1 printer (line printer), 20 transport unit,
40 head units, 41 head groups,
42 1st white head group, 43 2nd white head group,
421 heads,
50 sensor groups, 60 controllers, 61 memories,
110 computer

Claims (7)

A printing method of a printing apparatus comprising: a color ink nozzle row having a plurality of nozzles that discharge color ink; and a white ink nozzle row having a plurality of nozzles that discharge white ink,
When forming a color image on the medium using the color ink and forming a background image serving as a background of the color image on the medium using the white ink,
A printing method, wherein the background image is formed by correcting white density so that density changes according to the distance to the color image. The printing method according to claim 1, comprising:
A printing method, wherein correction is performed so that the density of white becomes lighter as the distance to the color image becomes longer. The printing method according to claim 1, comprising:
A printing method, wherein correction is performed so that the density of white becomes lighter as the distance to the color image becomes shorter. The printing method according to any one of claims 1 to 3,
A printing method characterized in that a minimum density of white can be set. The printing method according to any one of claims 1 to 4,
A printing method characterized by not correcting a white density when a white gradation value is not constant in a background image before correction. A printing method according to any one of claims 1 to 5,
A printing method comprising calculating a distance to an area surrounding the color image as a distance to the color image. In a printing apparatus provided with a color ink nozzle row having a plurality of nozzles for discharging color ink and a white ink nozzle row having a plurality of nozzles for discharging white ink,
A function of forming a color image on the medium using the color ink and forming a background image serving as a background of the color image on the medium using the white ink;
A program for realizing the function of correcting the white density so that the density changes according to the distance to the color image and forming the background image.