JP5747976B2 - Printing apparatus, printing program, and printing method - Google Patents

Description

  The present invention relates to a printing apparatus, a printing program, and a printing method, and more particularly to a printing apparatus, a printing program, and a printing method that print on a printing medium based on image data.

  Improvement of print image quality is an essential issue in a printing apparatus. Conventionally, the generation ratio of dark ink and light ink is adjusted according to the gradation value of image data (see Patent Document 1), and printing / colorimetric conditions Various devices have been devised, such as providing a correction table to be referred to when compensating for color misregistration due to the difference between them (see, for example, Patent Document 2).

JP 2004-291459 A JP 2008-72366 A

  In recent years, printing of images on printing media other than white (such as transparent media) with a printing apparatus has been increasing. When printing on such a print medium, in order to improve the color reproducibility in the print result of the color image that forms the main image on the print medium, a background image that is a base in advance in the area where the color image is printed May be printed. As the background image, not only a solid white image but also a color image or a gradation image having a color component to be printed using a color ink such as CMYK is used. Thus, the technique of printing a plurality of images in duplicate at the same location has not yet matured, and further improvement in image quality has been desired.

  SUMMARY An advantage of some aspects of the invention is that it provides a printing apparatus, a printing program, and a printing method capable of improving the image quality of a background image.

  In order to solve the above-described problem, in the printing apparatus of the present invention, each pixel has a first image data having a white ink dot recording rate, and each pixel has a non-white ink dot recording rate. Image data acquisition means for acquiring two image data is provided. The halftone processing means generates first halftone data and second halftone data indicating whether or not each pixel records at least a dot based on the first image data and the second image data, respectively. To do. In the halftone processing, the halftone processing means records the first halftone data and the second halftone data so that the white ink dots and the non-white ink dots are overlapped on the print medium. Generate halftone data. Then, the printing unit records the white ink dots and the non-white ink dots on a print medium based on the first halftone data and the second halftone data.

  According to this configuration, the white ink dots and the non-white ink dots can be overlapped and recorded on the print medium. Therefore, the graininess caused by the non-white ink dots can be alleviated by the white ink dots. The effect of alleviating the graininess due to the white ink dots becomes significant when the white ink dots are superimposed on the viewer side. Accordingly, it is desirable that the white ink dots are overlapped with the non-white ink dots from the observer side of the print medium and recorded. Of course, even if the non-white ink dots are overlapped and recorded from the observer side of the print medium with respect to the white ink dots, the graininess can be reduced.

  As a method suitable for recording a plurality of the non-white ink dots, the non-white ink dots having a greater granularity than the other non-white inks among the non-white inks, and the white The first halftone data and the second halftone data may be generated so that ink dots are recorded on the print medium in an overlapping manner. For example, this method is preferably applied when there is a limit to the number of ink dots that can be recorded on a print medium in an overlapping manner due to bleeding characteristics or the like. Even in the case where there is such a limitation, it can be considered that if the recording rate is small, even if many ink dots are overlapped, there is a low possibility of occurrence of problems such as bleeding. Therefore, when the recording rate is small, the number of colors of the non-white ink to be overlapped with the white ink dots may be increased.

As a specific halftone processing method for generating the first halftone data and the second halftone data, there are a dither method and an error diffusion method. In the case of the dither method, by using the same dither mask with respect to the ink to overlap the dots, the white ink dots and the non-white ink dots are overlapped and recorded on the print medium. One halftone data and the second halftone data can be generated. On the other hand, in the case of the error diffusion method, the white ink dots and the non-white ink dots are overlapped and recorded on the print medium by adjusting the diffusion error or a threshold value to be compared with the diffusion error. In addition, the first halftone data and the second halftone data can be generated.
The printing apparatus according to the present invention is a printing apparatus that prints a background image on a print medium, and includes the first image data that is the recording rate of white ink dots of each pixel and the recording rate of non-white ink dots. An image data acquisition means for acquiring at least one second image data; and a first half indicating whether or not each pixel records at least a dot based on the first image data and the second image data. When the tone data and the second halftone data are generated, the first halftone data and the second halftone data are recorded so that the white ink dots and the non-white ink dots are overlapped on the print medium. Based on the halftone processing means for generating the second halftone data, the first halftone data and the second halftone data, the white ink is applied to the print medium. The dots and the above non-white ink dots comprising a printing unit for recording, the.

  The above-described printing apparatus includes various modes such as being implemented in a state of being incorporated in another device or being implemented together with another method. The present invention also provides a printing system including the printing apparatus, a printing method and a printing control method having steps corresponding to the configuration of the apparatus described above, a printing program for causing a computer to realize a function corresponding to the configuration of the apparatus described above, and the printing It can also be realized as a computer-readable recording medium on which a program is recorded. The inventions of these printing system, printing method, printing control method, printing program, and medium on which the printing program is recorded also have the above-described operations and effects. Of course, the inventions described in claims 2 to 6 are also applicable to the system, the method, and the program.

It is explanatory drawing which showed the schematic structure of the printing apparatus. It is the block diagram which showed the hardware constitutions of PC. FIG. 2 is a block diagram illustrating a hardware configuration of a printer. FIG. 2 is a block diagram illustrating a software configuration of a printing apparatus. It is explanatory drawing which showed the main image and the background image notionally. It is explanatory drawing which showed an example of the combination of main image data and background image data. 6 is a flowchart illustrating a flow of printing processing executed by a printer driver. It is explanatory drawing which showed an example of the color conversion table LUTm partially. It is the figure which showed partially an example of the correspondence of color conversion table LUTb. It is a figure which illustrates the process of S125 typically. It is a figure explaining a dither mask and a dither method. It is a schematic diagram which shows the procedure of an error diffusion method. It is explanatory drawing which shows an example of the control command produced in print data creation processing. 5 is a flowchart of print processing executed by a printer. It is explanatory drawing which shows the detailed structure of a raster buffer and a head buffer. It is explanatory drawing which shows the structure of the print head of a printer. It is explanatory drawing which shows a printing result. It is explanatory drawing which shows the structure of the print head of the printer of a modification.

Hereinafter, embodiments of the present invention will be described in the following order.
(1) Configuration of the present embodiment:
(2) Printing process by printer driver:
(3) Printing process on the printer:
(4) Print result:
(5) Modification:

(1) Configuration of the present embodiment:
FIG. 1 is an explanatory diagram schematically illustrating the configuration of the printing apparatus according to the present embodiment. In the figure, the printing apparatus of the present embodiment includes a printer 100 and a personal computer 200 (PC 200). The printer 100 is an ink jet printer that discharges ink to form an image on a print medium. The PC 200 functions as a print control apparatus that causes the printer 100 to perform printing by outputting print control data including image data for printing, control commands, and the like to the printer 100. The printer 100 and the PC 200 are communicably connected via a communication cable, a wireless communication line, or the like.

  The printer 100 according to the present exemplary embodiment uses a total of seven ink colors, cyan (C), magenta (M), yellow (Y), black (K), light cyan (lc), light magenta (lm), and white (W). It is mounted and printing is performed using ink of a color appropriately selected from these. In other words, the printer 100 uses W ink to perform printing to form a white or near-white background on the print medium, print a color image, or place the background and the color image in a predetermined order. Duplicate printing is possible.

(1-1) Hardware configuration:
FIG. 2 is an explanatory diagram schematically showing the configuration of the PC 200. As shown in the figure, the PC 200 includes a CPU 205, a RAM 210, a ROM 215, a display interface 225 (DIF 225), an operation input device interface 230, a hard disk 235 (HD 235), and a USB interface 240. The units 205 to 230 are connected via a communication line such as a bus, and can communicate with each other under the control of a control controller such as a chip set. A display 225a as a display device is connected to the display interface 225. The operation input device interface 230 is connected with a mouse and a keyboard as the operation input device 230a. The USB interface 240 can communicate with the USB interface 155 of the printer 100.

  FIG. 3 is an explanatory diagram schematically showing the configuration of the printer 100. As shown in the figure, the printer 100 includes a CPU 105, a RAM 110, a ROM 115, a print head 120, a head controller 125, a carriage on which ink tanks of each color of CMYKlclmW are mounted, a carriage controller 135, a carriage motor 140, a print medium feed motor 145, A print medium feed controller 150 and a USB interface 155 are provided. Each part 105,110,115,125,135,150,155 is connected via communication lines, such as a bus | bath, and can mutually communicate according to control of control controllers, such as a chipset. The CPU 105 functions as a control unit for controlling the entire printer 100 by performing arithmetic processing according to the program while appropriately using the RAM stored in the ROM 115 as a work area.

  The print head 120 includes a group of nozzles that eject ink droplets, and is mounted on a carriage. The ink droplets land on the print medium and are fixed, whereby dots are recorded. The carriage motor 140 is a drive mechanism that moves the carriage in a predetermined direction (main scanning direction), and operates according to the control of the carriage controller 135. The print medium feed motor 145 is a drive mechanism that transports the print medium in a direction orthogonal to the main scanning direction (sub-scanning direction), and operates according to the control of the print medium feed controller 150. Each nozzle of the print head 120 is arranged so as to correspond to the ink tank of each color. Under the control of the head controller 125, the color ink is acquired from the corresponding ink tank and discharged. The controller forms an image on the print medium by controlling the carriage controller 135, the print medium feed controller 150, and the head controller 125 in conjunction with each other.

(1-2) Software Configuration FIG. 4 is an explanatory diagram schematically showing the software configuration of the printing apparatus. The HD 235 of the PC 200 stores an application program APL and a printer driver PDrv, a main image color conversion table LUTm, a background image color conversion table LUTb, a main image dither mask DMm, and a background image dither mask DMb. By executing the application program APL and the printer driver PDrv on the PC 200, the software configuration shown in FIG. 4 is realized.

<Application>
The application program APL is an application program that creates image data of an image to be printed on a print medium such as a transparent film and outputs the image data to a printer driver. As such application programs, there are various programs such as an application for processing and correcting an image like a retouch program, an application for drawing an image on a computer like a draw program, and an application for creating a document like word processing software. Applicable.

  It is assumed that the application program APL can adjust a main image representing an image or document itself and a background image representing a background of the image or document. The application program APL has a function of creating image data corresponding to each of the main image and the background image and outputting the image data to the printer driver. In this embodiment, the image data corresponding to the main image is the main image data MID, the image data corresponding to the background image data is the background image data BID (if there are a plurality of background image data, “first”, “second” ..., Etc., and the symbols are “BID1”, “BID2”, etc.).

In this embodiment, the main image data is composed of a combination of gradation values of each color data of CMYK, and the background image data is a gradation value of density of white (W) in addition to the gradation value of each color data of CMYK. It is comprised by the density value T which shows. In this embodiment, the description will be made by adopting four colors of CMYK as the color data, but the color data is not limited to the combination of CMYK, and RGB data represented by the three primary colors of RGB or L ^* a Lab data represented by each value of ^* b ^* may be used.

The names “main image” and “background image” are not necessarily limited to those having a master-slave relationship in which one is a main image and the other is a subordinate image. It is only a name determined according to the printing order when printing and the observation direction assumed for the printing result.
FIG. 5 is an explanatory diagram conceptually showing a main image and a background image. As shown in FIG. 5 (a), for example, by first printing a "background image" on a printing medium such as a transparent film and then printing a "main image", the image is observed from the printing surface side of the printing medium. The background image is printed as a background when the image is printed, and the main image is formed on the front side of the background image.
In addition, as shown in FIG. 5B, the “main image” was first printed on the transparent film, and then the “background image” was printed, which was observed from the non-printed surface side of the print medium. A background image is printed as a background, and a main image is formed on the front side of the background image.
Further, as shown in FIG. 5C, assuming that one surface of the printing medium is observed from the front surface, a “main image” is printed on the front surface and a “background image” is printed on the back surface. Thus, when viewed from the observation direction, the “background image” is printed as the background of the “main image”. It is also conceivable that the print medium in FIG. 5C is observed from the back side.
In FIGS. 5A to 5C, focusing only on the “background image”, when the “background image” is printed on the viewer side (surface background type), the “background image” is the opposite of the viewer. When printing on the side (back side background type), it can be classified.

  The user selects which of the main image and the background image is printed first according to the usage of the printed matter. That is, if the printed material is observed from the printing surface side, the background image is designated to be printed first, and if the printed material is observed from the back surface side, the main image is designated to be printed first. Become. The application program APL generates printing order designation data POD including printing order designation data s that designates the printing order. Further, the application program APL determines whether it is classified into the front background type or the back background type, and sets the scanning direction designation data m for designating the main scanning direction of the print head 120 according to the classification to the printing order designation data. Store in POD. The application program outputs the print data PD including the main image data MID, background image data BID, and print order designation data POD created as described above to the printer driver PDrv.

  The main image data and the background image data may each be one image data, but may be composed of a combination of a plurality of image data. For example, when main image data is created by dividing it into a plurality of image layers, this corresponds to the case where each layer data is output as one image data.

  FIG. 6 is an explanatory diagram showing an example of a combination of main image data and background image data. This figure shows an example in which main image data MID including main image MI, first background image data BID1 including background image BI1, and second background image data BID2 including background image BI2 are output from application program APL. .

  In FIG. 6, the first background image data BID1 represents a gradation image as the background image BI1 composed of colors other than white. That is, the first background image data BID1 is a background image printed with CMYKlclm ink (non-white ink) other than W ink. In FIG. 6, the first background image data BID <b> 1 is an image that gradually becomes darker as it approaches the right edge of the image.

  In FIG. 6, the second background image data BID2 represents a background image BI2 composed of a white image, and the white density, that is, the recording rate of the white ink dots and the ink coverage are designated for each pixel. Image data. That is, the second background image data BID2 is a background image that is printed with only W ink without using CMYKlclm ink. FIG. 6 shows an image created so that the density of the white image is different for each part of the image. The left half of the image has a density of N% of the maximum density of the white image, and the middle to the right 4 from the middle of the image. The density up to one-quarter is M% of the highest density, and the density of the right quarter of the image is P% of the highest density.

<Printer driver>
As shown in FIG. 4, by executing a printer driver program of the printer 100 on basic software such as operating software in the PC 200, an image data acquisition unit M1, a color conversion unit M2, a halftone setting unit M3, and a halftone processing unit Functions corresponding to the modules of M4 and the print data creation unit M5 are realized. In addition, when a control program such as firmware is executed by the control unit of the printer 100, a function corresponding to the command processing unit M11 is realized.

  The color conversion unit M2 refers to the color conversion tables LUTm and LUTb stored in advance in the HD 235 as appropriate, and provides the printer 100 with the gradation values of the CMYK colors of the pixels constituting the main image data MID and the background image data BID. It is converted into a gradation value representing the ink amount of each ink color mounted. The gradation value of each ink amount means the amount of ink attached to the print medium and the dot recording rate. The gradation value of each ink amount is a value proportional to the amount of ink taken out from the nozzle of the print head within a range corresponding to each pixel, and is also called a dot recording rate. Further, although the ink amount has a non-linear correspondence, it also uniquely corresponds to the ink coverage on the print medium. The color conversion unit M2 is configured to perform so-called color separation processing for distributing light ink, dark ink, and gradation values of the same color at the same time.

  The halftone setting unit M3 sets a dither mask for each ink to be used by the halftone processing unit M4 based on the result of color conversion of the background image data BID. The halftone processing unit M4 binarizes the gradation value generated for each ink color for each pixel, ink ejection / non-ejection, with reference to the dither masks DMm and HTRb stored in advance in the HD 235 as appropriate. Then, halftone image data specifying the amount of ink to be ejected is generated. The print data creation unit M5 receives the halftone image data and rearranges the data in the order used by the printer 100, and sequentially outputs the halftone image data to the printer 100 in units of data used in one main scan.

(2) Printing process by printer driver:
(2-1) First Embodiment of Print Processing:
FIG. 7 is a flowchart showing a flow of printing processing executed by the printer driver PDrv. In the printing process shown in the figure, printing is performed based on print data PD composed of main image data MID, first background image data BID1, second background image data BID2, and print order designation data POD. At this time, if the print range overlaps between the main image data MID and the first background image data BID1, or between the main image data MID and the second background image data BID2, the first background image data for the overlapping portion. BID1 and second background image data BID2 are corrected. As a result, the print result is corrected to match the intention of the user who created the print data PD. In the printing process according to the first embodiment, the main image data MID is not corrected.

  The printing process of the first embodiment is started when print data PD is input from the application program APL. When the process is started, in step S100 (hereinafter, “step” is omitted), the image data acquisition unit M1 receives the main image data MID input from the application program APL and the first background image data BID1. Second background image data BID2 and printing order designation data POD are acquired.

  In step S105, the color conversion unit M2 creates ink amount data M_ink of the main image (corresponding to the first image data of the present invention) from the main image data MID. That is, the color conversion unit M2 selects one pixel data M_Pix from the main image data MID, refers to the color conversion table LUTm, and converts each pixel data M_Pix of the main image data MID to a gradation value for each ink color. Is converted into ink amount data (tone value for each ink color). As described above, in this embodiment, printing is performed using CMYKlclmW inks of a total of seven colors. Therefore, in the color conversion process of S105, the CMYK values are converted into the respective tone values of the seven ink colors with reference to the color conversion table LUTm.

  FIG. 8 is an explanatory diagram partially showing an example of the color conversion table LUTm. As shown in the figure, the color conversion table LUTm defines a correspondence relationship between preset CMYK values and CMYKlclm gradation values indicating the ink amounts of the respective ink colors. In the color conversion table LUTm shown in the figure, the gradation value of each color data of CMYK is defined in the range of 0 to 100, and the gradation value of the ink amount is defined in the range of 0 to 255. ing. Also, as shown in FIG. 8, in this embodiment, six inks of CMYKlclm are used in the ink amount data generated by conversion from the main image data MID, and W ink is not used.

  In S110, the halftone processing unit M4 extracts the gradation value for each ink color from the ink amount data M_ink of the main image, and performs halftone processing (halftone processing) with reference to the dither mask DMm for each ink color. Do. The halftone process is executed with reference to a preset main image dither mask DMm. Then, the halftone processing unit M4 sequentially extracts halftone values for each ink color from the ink amount data M_ink of the main image and repeats the halftone processing until the halftone processing of S110 is performed for all pixels and all ink colors. When the halftone process of S110 is completed for the ink color gradation values constituting the ink amount data M_ink of the main image, the halftone data of the main image is created. In step S115, synthesized background image data BID 'obtained by synthesizing the first background image data BID1 and the second background image data BID2 is created, and the color conversion unit M2 performs color conversion processing on the synthesized background image data BID'.

  FIG. 9 is a diagram partially showing an example of a correspondence relationship of the color conversion table LUTb that is referred to when the color conversion unit M2 performs color conversion of the background image data. As shown in the figure, in the color conversion table LUTb, the amount of white ink can be specified by the density value T. The color conversion unit M2 converts each pixel data of the composite background image data BID ′ into ink amount data with reference to the color conversion table LUTb, thereby generating ink amount data B_ink of the composite background image (corresponding to the second image data of the present invention). Is created and stored in the RAM 210. The color conversion unit M2 corresponds to the image data acquisition unit of the present invention.

  The ink amount data B_ink is created for each of the seven colors CMYKlclmW, and the corresponding ink amount (dot recording rate) is stored in each pixel. The ink amount data B_ink (W) for W ink that is white ink corresponds to the first image data of the present invention, and the ink amount data B_ink (C) to (lm) for CMYKlclm ink that is non-white ink is the present invention. Corresponds to the second image data.

  In S120, the halftone setting unit M3 detects the maximum ink amount IKU from the ink amounts of all the pixels of the ink amount data B_ink (C) to (lm) for all the non-white inks, and the maximum ink The quantity IKU is compared with the threshold value ITH. When the maximum ink amount IKU is larger than the threshold value ITH, the overlapping ink number limit ND is set to 1. On the other hand, when the maximum ink amount IKU is less than or equal to the threshold value ITH, the overlapping ink number limit ND is set to 4, for example. The threshold value ITH is set according to the ink bleed characteristic in the print medium, and it is guaranteed that the print result will not break down due to bleed or the like even if all the ink dots are recorded with the ink amount below the threshold value ITH.

  In S125, the halftone setting unit M3 acquires the ink amount data B_ink (C) to (lm) for the non-white ink, and sets the ink amount of each pixel of the ink amount data B_ink (C) to (lm) to the granularity. Convert to exponent GI. At this time, the graininess table GTB is referred to. As the graininess index GI, index values disclosed in JP-A-2005-103921, JP-A-2005-310098, and JP-A-2007-281724 can be used. The graininess index GI is an index that means that the larger the value, the more noticeable graininess is.

  FIG. 10 is a diagram schematically illustrating the process of S125. FIG. 10A shows an example of the ink amount data B_ink, and FIG. 10B shows an example of the graininess table GTB. The graininess table GTB is a lookup table that defines the correspondence between the ink amount and the graininess index GI for each non-white ink. Since the tendency of the graininess index GI varies depending on the print medium, the graininess table GTB corresponding to the print medium to be printed is referred to. In general, the darkness of the ink tends to increase the granularity index GI. Further, with a single ink, as shown in FIG. 10C, the graininess index GI tends to increase in the low to medium ink amount region. This is because when dots of ink are filled to some extent on the print medium, it is difficult to visually recognize individual dots. The graininess index GI defined in the graininess table GTB can be measured by printing a gradation color patch of each ink alone on a target print medium and using the method described in the above-mentioned publication.

  In S125, as shown in FIG. 10D, when the image data in which each pixel shows the graininess index GI is obtained by each non-white ink, in S130, the halftone setting unit M3 determines all pixels for each non-white ink. The graininess average value GIave is calculated by averaging the graininess index GI. In S135, the halftone setting unit M3 compares the graininess average value GIave and the graininess threshold GTH for each non-white ink. Then, the non-white ink whose graininess average value GIave is larger than the graininess threshold GTH is set as the overlap candidate ink. The overlap candidate ink may be determined based on the maximum value of the graininess index GI, not the average value of the graininess average value GIave. In S140, the halftone setting unit M3 determines the number of overlapping candidate inks in which the graininess average value GIave is larger than the graininess threshold GTH.

  If there is no overlap candidate ink, in S145, the halftone setting unit M3 does not set any ink as the overlap target ink. When there is one overlap candidate ink, in S150, the halftone setting unit M3 sets the only overlap candidate ink as the overlap target ink. When there are a plurality of overlapping candidate inks, in S155, the halftone setting unit M3 selects the overlapping candidate inks in the descending order of the average graininess value GIave by the number of overlapping ink number limit ND, and selects the selected overlapping candidate inks. Ink. When the overlap ink number limit ND is 4, four overlap candidate inks are set as the overlap target ink, and when the overlap ink number limit ND is 1, one overlap candidate ink is the overlap target ink. Set as Data indicating whether or not each non-white ink is an overlay target ink is stored in the RAM 210.

  In S160, the halftone setting unit M3 selects whether the halftone process is performed by the dither method or the error diffusion method. For example, the halftone processing method is selected in accordance with the printing conditions such as the type of printing medium on which printing is performed and the printing mode (fast, clean) set by the user. The dither method is selected when printing on plain paper or when the print mode (fast) is set. On the other hand, the error diffusion method is selected when printing on dedicated paper or when the print mode (clean) is set. Thereafter, the halftone processing unit M4 executes halftone processing by a dither method and an error diffusion method, respectively. Here, the dither method will be described first.

  In S165, the halftone processing unit M4 acquires data indicating whether or not each non-white ink is an overlay target ink from the RAM 210, and the dither mask DMb for the overlay target ink is replaced with the dither mask DMb for the W ink. Set to the same one.

  FIGS. 11A and 11B are diagrams for explaining a dither mask DMb and a dither method using the dither mask DMb. As shown in the figure, in this embodiment, a different dither mask DMb is prepared for each ink. The dither mask DMb is composed of a plurality of pixels, and each pixel has a mask threshold value MTH for comparison with the gradation value of the ink amount. The smaller the mask threshold value MTH, the higher the probability that ink dots will be recorded. In this embodiment, the mask threshold value MTH of the dither mask DMb for each ink is optimized by the method disclosed in Japanese Patent Laid-Open No. 2007-15359. According to the dither mask DMb created by this method, it is possible to prevent dots from being concentrated locally, and as a result, graininess can be suppressed.

  As shown in FIG. 11A, a different dither mask DMb is prepared for each ink. However, for the overlay target ink, the dither mask DMb of white ink is used instead of the original dither mask DMb of the overlay target ink. Will be. Therefore, when the four non-white inks are set as the overlay target inks, the four overlay target inks and the W ink are subjected to halftone processing using the same dither mask DMb. In S170, the halftone processing unit M4 compares the ink amount gradation value of each pixel of the ink amount data B_ink of each ink with the mask threshold value MTH of the corresponding pixel of the dither mask DMb, and determines the ink amount gradation. If the value is larger, it is determined to record a dot, and if the gradation value of the ink amount is not larger, it is determined not to record a dot. Thereby, the gradation value of the ink amount of each pixel is binarized. That is, halftone data indicating whether or not each pixel records a dot can be generated for each ink. In the halftone data, a gradation value “1” is given to a pixel that records a dot, and a gradation value “0” is given to a pixel that does not record a dot. The halftone data for the W ink corresponds to the first halftone data of the present invention, and the halftone data for the overlapping target ink corresponds to the second halftone data of the present invention.

  Here, with respect to the overlapping target ink binarized using the same dither mask DMb as the W ink, the probability of determining that dots are recorded for each pixel is the same as that of the W ink. That is, for pixels in which dots are easily recorded in W ink, dots for ink to be superimposed are easily recorded. Therefore, there is a high possibility that a pixel in which dots are recorded in the first halftone data of W ink is also recorded in dots in the second halftone data of the overlay target ink. Next, a case where the error diffusion method is performed will be described.

  FIG. 12A is a schematic diagram showing a basic procedure of the error diffusion method. In the error diffusion method, for the target pixel, a determination value JV is calculated by adding the gradation value (IK) of the ink amount and the total value te of the diffusion error ER diffused from surrounding pixels existing in the left direction and the upward direction. Then, the determination value JV is compared with the determination threshold value T (127). When the determination value JV is larger than the determination threshold value T, a dot is recorded for the target pixel. When the determination value JV is not larger than the determination threshold value T, no dot is recorded for the target pixel. When dots are formed, a diffusion error ER having a value obtained by subtracting the maximum ink amount (255) from the determination value JV is generated, and the diffusion error ER is diffused to surrounding pixels. When dots are not formed, a diffusion error ER having a value obtained by subtracting the minimum ink amount (0) from the determination value JV is generated, and the diffusion error ER is diffused to surrounding pixels. By performing the above processing while sequentially scanning the target pixel, each pixel can be binarized in order. First, in S175, the halftone setting unit M3 sets a reference ink for each ink.

  The setting of the reference ink differs depending on the number of overlapping target inks. When there is one overlap target ink, the overlap target ink is set as a reference ink. In the case where there are four overlap target inks, the ink having the maximum graininess average value GIave is set as the reference ink among the overlap target inks. If there is no overlap target ink, none of the inks is set as the reference ink. It can be said that the reference ink is the ink that produces the most granular feeling among the non-white inks.

  When the reference ink is set as described above, the halftone processing unit M4 executes halftone processing by the error diffusion method for the reference ink in S177. If there is no overlap target ink and the reference ink is not set, S177 is skipped. When the halftone process is performed for the reference ink, the offset of the determination value JV is invalidated. As a result, the error diffusion method is uniformly performed as shown in FIG. When the halftone process is completed for the reference ink, halftone data for the ink can be generated. This halftone data is stored in the RAM 210 as reference halftone data (S180). The reference halftone data corresponds to the second halftone data of the present invention.

  In S182, the halftone processing unit M4 executes halftone processing for the W ink by an error diffusion method. When halftone processing is performed for W ink, the offset of the determination value JV is validated. When the offset of the determination value JV is valid, the offset process shown in FIG. 12B is executed for each target pixel. First, in S182a, by referring to the reference halftone data stored in the RAM 210, it is determined whether or not the reference ink dot is recorded at the same position as the target pixel. When the reference ink dot is recorded at the same position as the target pixel, the determination value JV is offset (S182b). In this embodiment, as shown in FIG. 12C, the determination value JV is offset by adding a certain offset amount OS (positive value) to the determination value JV.

  On the other hand, when the reference ink dot is not recorded at the same position as the target pixel, the determination value JV is not offset (S182c). Thereby, it is possible to increase the probability that dots of W ink are recorded for pixels on which the reference ink is recorded. That is, there is a high possibility that a pixel for which dots are recorded in the reference halftone data is also recorded for dots in the halftone data for W ink. The halftone data obtained for the W ink in S182 corresponds to the first halftone data of the present invention.

  In S185, the halftone processing unit M4 executes halftone processing for the overlapping target ink (other than the reference ink) by the error diffusion method. If there is no overlapping target ink other than the reference ink, S185 is skipped. When there are a plurality of overlapping target inks other than the reference ink, halftone processing is sequentially executed for each overlapping target ink. In this case, the processing order of the respective overlapping target inks may be any. The offset of the determination value JV is also valid when halftone processing is performed for ink to be superimposed other than the reference ink. Therefore, there is a high possibility that a pixel in which dots are recorded in the reference halftone data is also recorded in dots in the halftone data for the overlapping target ink other than the reference ink. Further, according to S182 and S185, when dots are recorded at the same pixel between the reference halftone data, the halftone data for the target ink other than the reference ink, and the halftone data for the W ink, It can be said that there is a high possibility of being.

  In S187, the halftone processing unit M4 performs halftone processing by the error diffusion method for the remaining non-white ink that is neither the overlay target ink nor the W ink. If there is no remaining non-white ink, step S187 is skipped, and if there are a plurality of non-white inks, halftone processing is sequentially performed on each remaining non-white ink. Also in this case, the processing order of each remaining non-white ink may be any. When the halftone process is performed on the remaining non-white ink, the offset of the determination value JV is invalidated. As a result, the error diffusion method is uniformly performed as shown in FIG. As described above, the halftone processing by the error diffusion method is completed for all inks.

  As described above, when even one overlay target ink exists, the halftone data for the overlay target ink having the largest graininess average value GIave is set as the reference halftone data, and at least the halftone for the W ink is used. The offset of the judgment value JV is valid for the process. Accordingly, it is possible to record the dots of the ink to be overlapped and the dots of the W ink that are most likely to produce a grainy feeling in the same pixel. Further, when there are four overlapping target inks, not only the W ink but also other overlapping target ink dots can be recorded in the same pixel as the reference ink dots.

  That is, according to the present embodiment, it is possible to increase the probability that the dot of the ink to be overlapped is recorded at the same position as the dot of the W ink. Note that when there is no overlapping target ink, a normal error diffusion method that does not depend on the halftone processing results of other inks is performed for all inks. Note that it is only necessary that the halftone process can be performed so that dots are recorded in the same pixel for the W ink and the overlap target ink, and the halftone process for the overlap target ink is not necessarily performed first. That is, halftone data for W ink may be first generated as reference halftone data, and halftone processing for ink to be overlapped may be executed with reference to the reference halftone data.

In S190, the print data creation unit M5 adds the halftone data of each ink for the main image, the halftone data (first halftone data and second halftone data) for the background image, and the print order designation data POD. Based on this, a control command for causing the printer 100 to print the main image MI and the background images BI1 and BI2 is created. In the following description, a case where a control command for causing the printer 100 to print the main image MI will be described as an example. However, a control command for causing the printer 100 to print a composite background image is also created by performing similar processing. Shall be.
FIG. 13 is an explanatory diagram illustrating an example of a control command created in the print data creation process. The control command includes a printing order designation command, a vertical position designation command, a horizontal position designation command, each dot data (raster data), and an ink code.

The print order designation command is created based on the print order designation data POD input from the application program APL.
FIG. 13A shows an example of a print order designation command. As shown in the figure, the print order designation command includes an identifier Esc indicating the head of the command, an identifier “j” indicating the print order designation command, and a command length (2 bytes in this embodiment) nL, nH. , Printing order designation data s, and scanning direction designation data m. For example, the value of the printing order designation data s is “0” when the printing order designation data POD indicates “MB printing”, and “1” when the printing order designation data POD indicates “BM printing”. ". “MB printing” means that the main image is printed first and the background image is printed later, and “MB printing” means that the background image is printed first and the main image is printed later. Means that. Further, for example, the value of the scanning direction designation data m is “0” when the printing order designation data POD indicates “forward printing”, and “1” when the printing order designation data POD indicates “reverse printing”. ".

  Here, “forward printing” means that each ink dot is recorded while the print head 120 performs main scanning in the forward direction, whereby non-white ink (color ink) is recorded first. , W ink will be recorded later. On the other hand, “reverse printing” means that the dots of each ink are recorded while the print head 120 is main-scanned in the reverse direction. As a result, the W ink tip is recorded, and the non-white ink is recorded later. The application program APL sets the printing order to “forward printing” in the case of the surface background type (see FIG. 5). On the contrary, in the case of the back surface background type (see FIG. 5), the printing order is “reverse direction printing”. In this embodiment, the printing order designation data POD is created by the application program APL. However, the printing order designation data POD may be created by the printer driver PDrv, or the printing order designation data created by the application program APL. The POD may be corrected by the printer driver PDrv.

  The vertical position designation command is created based on the halftone data of the main image created corresponding to the main image data MID output from the halftone processing unit M4. The vertical position designation command is a command for designating a start position of an image in the vertical direction (sub-scanning direction: print medium conveyance direction). The vertical position designation command is created as a command common to all inks.

  The horizontal position designation command is a command for designating the image formation start position in the horizontal direction (main scanning direction) for one ink color during main image formation. The horizontal position designation command is generated for each ink color of the halftone data of the main image output from the halftone processing unit M4. The print data creation unit M5 refers to the halftone data for one ink color, specifies the start position of the halftone data of the main image for the one ink color in the horizontal direction, and designates this start position Create a horizontal positioning command for.

  FIG. 13B is a diagram illustrating an example of a raster command. As shown in the figure, the raster command includes an identifier Esc indicating the head of the command, an identifier i indicating the raster command, an ink code r, a bit number b per pixel, and a horizontal direction (X direction). Length (2 bytes in this embodiment) nL, nH, vertical (Y direction) length (2 bytes in this embodiment) mL, mH, raster data (dot data) d1, d2,. ., Dn. Dot data is created for each raster. The ink code r is a code unique to each ink color. The HD 235 stores an ink code table in which an ink abbreviation unique to each ink color is associated with an ink code. By referring to the ink code table, an ink code of each ink color is searched for, and a raster command is stored. Ink cords to be applied to can be obtained.

  In step S195, the printer driver PDrv transmits the main image print control data (print order designation command, vertical position designation command, horizontal position designation command, raster command) and background image print data created in step S190 to the printer 100. . This completes the processing by the printer driver PDrv.

(3) Printing process on the printer:
When the print control command created and output in each embodiment as described above is input to the printer 100, the printer 100 executes printing based on the print control command.
FIG. 14 is a flowchart of printing processing executed by the printer 100. The processing shown in the figure is executed by the command processing unit M11 executed in the control unit of the printer 100.
In step S505, print control data received from the printer driver PDrv of the PC 200 is received.
In S510, the type of the received command is determined, and any one of S515 to S530 is performed according to the type of command. That is, if the received command is a printing order designation command, the process proceeds to S515. If the received command is a horizontal position designation command, the process proceeds to S520. If the received command is a vertical position designation command, the process proceeds to S525. If is a raster command, the process proceeds to S530.

  In S515, the printing order designation data POD designated by the received printing order designation command is stored in the RAM 110. In S520, the horizontal position designated by the received horizontal position designation command is updated as the horizontal print start position X. In step S525, the vertical position designated by the received vertical position designation command is updated as the print start position Y in the vertical direction. In S530, the raster data included in the received raster command is stored in the raster buffer 132 for each ink code.

FIG. 15 is an explanatory diagram showing detailed configurations of the raster buffer 132 and the head buffer 127. The color image raster buffer 132c is shown in the upper part of the figure, and the background image raster buffer 132w is shown in the middle part of the figure. As shown in the figure, the raster buffer 132 is assigned a region for each ink code. The color image raster buffer 132c is configured as a set of regions corresponding to each color ink code, and the background image raster buffer 132w is also a set of regions corresponding to each background image ink code. It is configured as.
The size in the X direction of each area of the raster buffer 132 corresponds to the image size, and the size in the Y direction is more than half the height of the print head 120.
The raster buffer 132 has a raster buffer pointer in the Y direction that indicates how far raster data has been received.

In the lower part of FIG. 15, the head buffer 127 is shown. As shown in FIG. 15, the head buffer 127 is allocated with areas for seven ink colors. That is, the head buffer 127 includes a cyan area (for C and WC), a magenta area (for M and WM), a yellow area (for Y and WY), and a black area (for K and WK). ) Area and a white area (for W, WW area).
The size in the X direction of each area of the head buffer 127 corresponds to the scanning distance of the carriage, and the size in the Y direction corresponds to the number of nozzles constituting the nozzle row 146 of the print head 120. Each region of the head buffer 127 for each ink color is divided into an upstream head buffer 127u and a downstream head buffer 127l.

FIG. 16 is an explanatory diagram illustrating a configuration of the print head 120 of the printer 100. As shown in FIGS. 16A and 16B, the print head 120 is provided with nozzle rows 146 corresponding to each of the seven ink colors. The nozzle row 146 is formed so as to extend along the Y direction (print medium feeding direction).
Further, as shown in FIG. 16C, each nozzle row 146 is composed of 32 nozzle groups arranged in the Y direction. In this embodiment, among the nozzle groups constituting the nozzle row 146, the nozzle group (nozzle 1 to nozzle 16) located in the upstream half in the print medium feed direction is defined as the upstream nozzle group, and the downstream side in the print medium feed direction. Let the nozzle group (nozzle 17-nozzle 32) located in a half be a downstream nozzle group. In the present embodiment, the nozzles of the respective inks having the same rank in the print medium feed direction are arranged at the same position with respect to the print medium feed direction.

  As shown in FIG. 16A, when the background image is first printed on the print medium, the background image is formed using the upstream nozzle group of each nozzle row 146 of the print head 120, and the downstream nozzle group is formed. Is used to form a main image. Further, as shown in FIG. 16B, when the main image is printed on the print medium first, the main image is formed using the upstream nozzle group of each nozzle row 146 of the print head 120, and the downstream side. A background image is printed using a nozzle group.

  As shown in FIG. 15, the upstream head buffer 127u is a head buffer corresponding to the upstream nozzle group, and the downstream head buffer 127l is a head buffer corresponding to the downstream nozzle group.

  In S535, it is determined whether or not a raster buffer is stored in the raster buffer 132 corresponding to half the height of the print head 120. If not stored, the process proceeds to S580, and the buffer pointer is updated in S580. On the other hand, if it is stored, the process proceeds to S540.

In S540, based on the print order specifying data s of the print order specifying data POD stored in the RAM 130, it is determined which of the main image and the background image is to be printed first. If the main image is printed first, the process proceeds to S545. If the background image is printed first, the process proceeds to S550.
In S545, the raster data is transferred from the main image raster buffer 132c to the upstream head buffer 127u, and the raster data is transferred from the background image raster buffer 132w to the downstream head buffer 127l. Accordingly, the main image is formed using the upstream nozzle group of each nozzle row 146 of the print head 120, and the background image is formed using the downstream nozzle group.
In S550, the raster data is transferred from the raster buffer 132c for the main image to the downstream head buffer 127l, and the raster data is transferred from the raster buffer 132w for the background image to the upstream head buffer 127u. Therefore, the background image is formed using the upstream nozzle group of each nozzle row 146 of the print head 120, and the main image is formed using the downstream nozzle group.
Since the upstream nozzle group and the downstream nozzle group have different physical printing positions on the paper, when the raster data is transferred from the raster buffer 132, the raster data corresponding to the upstream nozzle group and the downstream nozzle group is stored. The transfer start data position on the raster buffer is determined by giving a timing difference corresponding to the difference in print position so that printing is performed at a corresponding position on the paper.

In S555, the print medium feed controller 150 is controlled to transport the print medium PM so that the print start position of the print medium PM and the position of the print head 120 coincide with each other in the sub-scanning direction.
In S560, the carriage controller 135 is controlled to move the print head 120 so that the print start position of the print medium PM matches the position of the print head 120 in the main scanning direction.

  In S565, whether “forward printing” or “reverse printing” is designated is specified based on the value of the scanning direction designation data m of the printing order designation data POD stored in the RAM 130. When main scanning is performed in the specified direction, printing for a range corresponding to the length of the print head 120 in the sub-scanning direction is executed. At this time, dot recording by the upstream nozzle group and dot recording by the downstream nozzle group are executed in parallel. As shown in FIG. 16A, when the print head 120 performs main scanning in the forward direction, the CMYKlclm ink (non-white ink) is located upstream of the W ink in the main scanning direction, and the dots of the CMYKlclm ink are the W ink. It is recorded on the print medium before the dots.

  On the other hand, if “reverse direction printing” is designated, in S567, when performing main scanning in the reverse direction, dot recording by the upstream nozzle group and dot recording by the downstream nozzle group are executed. As shown in FIG. 16A, when the print head 120 performs main scanning in the reverse direction, the W ink is located upstream of the CMYKlclmK ink (non-white ink) in the main scanning direction, and the W ink dots are the CMYKlclmK ink. It is recorded on the print medium before the dots.

In S570, the raster buffer pointer of the raster buffer 132 is cleared.
In S575, it is determined whether printing of the entire print image PI has been completed. If printing has not been completed, the processes of S505 to S570 are repeatedly executed until it is determined that printing has been completed. If printing has been completed, the printing process in FIG. 14 ends.

(4) Print result:
FIGS. 17A and 17B are schematic diagrams showing printing (dot recording) results for the background images BI1 and BI2 for the front and back background types, respectively. The main image MI is not printed. As described above, in the case of the front surface background type, the printing order for the background images BI1 and BI2 is “forward printing”, and in the case of the back surface background type (see FIG. 5), the background images BI1 and BI2 are used. The printing order for is “reverse printing”. Therefore, when the dots of the respective inks are overlapped, the dots of the W ink are present on the observer side with respect to the non-white ink in any type of printing. As described above, in both cases of the dither method and the error diffusion method, a pixel for which dots are recorded in the first halftone data of the W ink is supposed to record dots in the second halftone data of the overlapping target ink. Therefore, it is possible to cause many dot overlaps as shown in FIGS. 17 (a) and 17 (b).

  FIG. 17C is a schematic diagram illustrating a state in which the state where the W ink is overlapped with the overlapping target ink is observed. As shown in the drawing, when the W ink dot overlaps on the non-white ink dot (observer side), the outline of the non-white ink dot can be partially erased by the non-white ink dot. . Therefore, it is possible to suppress the graininess due to the outline of the non-white ink dots, particularly in the background with high overall brightness. Further, the contour shape of the non-white ink dot is complicated by the non-white ink dot, and the spatial frequency of the color change due to the non-white ink dot contour can be increased. If the color change becomes higher in frequency, it becomes difficult for humans to perceive it, so that it is possible to make it difficult to feel graininess. In addition, since the overlay target ink is limited to non-white ink that produces a graininess larger than a certain graininess index GI, the graininess can be efficiently suppressed.

(5) Modification:
In the error diffusion method of the above embodiment, the dot of the W ink and the dot of the overlapping target ink are overlapped by offsetting the determination value JV, but the same effect can be obtained by offsetting the determination threshold T. Can be obtained. That is, in the offset process of FIG. 12B, when a dot of W ink is recorded at the same position as the target pixel, an offset amount OS proportional to the ink amount of the target pixel is used instead of offsetting the determination value JV. Is subtracted from the determination threshold T. Thereby, the probability that dots are formed for the target pixel can be increased. In addition, about the offset of the determination threshold value T, the method of Unexamined-Japanese-Patent No. 2000-6444 can be used.

  In the error diffusion method of the above embodiment, the offset amount OS for offsetting the determination value JV is constant, but the size of the offset amount OS may be switched for each ink. The larger the offset amount OS, the higher the probability that the W ink dot and the overlap target ink dot overlap. For example, by setting an offset amount OS that is proportional to the size of the graininess index GI for each ink, it is possible to reliably overlap the dots of the W ink on the dots of the target ink that are likely to cause graininess. it can.

  In the above-described embodiment, the printer 100 that records only a single size dot for each ink is illustrated, but the present invention can also be applied to a printer that records a plurality of sizes of dots for each ink. For example, for each ink, the present invention may be applied to a printer in which three types of dots, a large size dot, a medium size dot, and a small size dot are formed. In this case, the ink amount obtained by the color conversion process is divided into a half-size dot recording rate, a medium-size dot recording rate, and a small-size dot recording rate. Tone processing is performed. In this dot distribution process, it is desirable that the recording rate at which non-white ink is distributed to small-sized dots is higher for the background image than for the normal main image. By doing so, it is possible to reduce the size of the white ink that is recorded over the non-white ink, and to suppress the graininess in the background image.

  Further, when halftone processing by the error diffusion method is performed in order to record dots of a plurality of sizes, the ease of dot overlap can be adjusted according to the dot size. In the above-described embodiment, the fixed offset amount OS is added to the determination value JV for the target pixel on which the dot of the overlay target ink that is most likely to produce a graininess is formed. By changing according to the dot size of the ink, it is possible to adjust the ease of overlapping of the dots according to the dot size. If the offset amount OS is increased as the dot size is larger, the dots of the W ink can be surely overlapped and recorded on the dots that give a strong grain feeling.

  FIG. 18 is an explanatory diagram showing a configuration of a print head 620 according to this modification. As shown in the figure, each nozzle row 646 is composed of 32 nozzle groups arranged in the Y direction. In the print head 120 shown in FIG. 16C, the nozzles of the respective inks in the same order in the print medium feeding direction are arranged at the same position in the print medium feeding direction, but in the print head 620, adjacent nozzle rows. The position in the print medium feeding direction of the entire 646 is alternately shifted by a half pitch of the nozzle arrangement. That is, the nozzles are arranged in a staggered pattern so as to be enlarged in FIG. In the odd-numbered nozzle rows 646 (four rows) counted from the left side of the drawing, the positions of the nozzles in the print medium feeding direction are the same. Similarly, in the even-numbered nozzle rows 646 (3 rows) counted from the left side of the drawing, the positions of the nozzles in the print medium feeding direction are the same.

  In the print head 620 as described above, when the nozzle row 646 for recording the W ink dots is the rightmost nozzle row 646, the odd-numbered three rows in which the positions of the nozzles in the print medium feeding direction are the same. The nozzle row 646 is assigned non-white ink (CMYKlclmK) ink that is most likely to produce graininess. For example, when it is experimentally found that a certain amount of CMK ink is more likely to produce a graininess than Ylclm ink, the CMK ink is assigned to the odd-numbered three nozzle rows 646. The remaining Ylclm ink is assigned to the even-numbered three nozzle rows 646. In this way, the nozzle for ejecting the non-white ink that strongly causes the graininess is set at the same position in the print medium feeding direction as the nozzle for ejecting the W ink, so that the interlace scan of the print medium (half pitch feed of the nozzle array) is performed. Regardless of the presence or absence of (), white ink dots and non-white ink dots that strongly generate graininess can be recorded in the same position. That is, the effects of the present invention can be obtained in a wide range of printing modes.

  In the above embodiment, the main scanning direction of the print head 120 for recording dots is switched between the front and back background types so that the dots of W ink overlap from the viewer side. Ink dots may be overlapped from the observer side. For example, W ink dots may be recorded in the nozzle rows at both ends of the print head in the print head, and the nozzle rows for recording W ink dots may be switched according to the main scanning direction. By doing so, the dots of W ink can be overlapped from the observer side even in bidirectional printing. The same printing can be performed even if a print head in which the array of nozzle rows is symmetrical with respect to the main scanning direction is used.

  Note that the present invention is not limited to the above-described embodiments and modifications, and the configurations disclosed in the above-described embodiments and modifications are mutually replaced, the combinations are changed, the known technology, and the above-described implementations. Configurations in which the configurations disclosed in the embodiments and modifications are replaced with each other or combinations are also included.

  DESCRIPTION OF SYMBOLS 100 ... Printer, 105 ... CPU, 110 ... RAM, 115 ... ROM, 120 ... Print head, 125 ... Head controller, 135 ... Carriage controller, 140 ... Carriage motor, 145 ... Print medium feed motor, 150 ... Print medium feed controller, 155 ... USB interface, 200 ... personal computer, 205 ... CPU, 210 ... RAM, 215 ... ROM, 225 ... display interface, 225a ... display, 230 ... operation input device interface, 230a ... operation input device, 235 ... hard disk, 240 ... USB interface, APL ... application program, PDrv ... printer driver, M1 ... image data acquisition unit, M2 ... color conversion unit, M3 ... halftone M4 ... halftone processing unit, M5 ... print data creation unit, PD ... print data, POD ... print order designation data, MID ... main image data, M_ink ... ink amount data of main image, BID ... background image data BID1 ... first background image data, BID2 ... second background image data, B_ink ... background ink amount data, DMm, DMb ... dither mask, LUTm ... color conversion table, LUTb ... color conversion table.

Claims (8)

A printing apparatus for printing a background image on a print medium,
A first image data is a dot recording rate of the white ink in each pixel, and the image data acquisition means for acquiring at least one of the second image data is a dot recording rate of non-white ink,
In generating each of the first halftone data and the second halftone data indicating whether or not each pixel records at least a dot based on the first image data and the second image data, the print medium Halftone processing means for generating the first halftone data and the second halftone data so that the white ink dots and the non-white ink dots are overlapped on each other;
Printing apparatus characterized by comprising a printing unit for printing the dots of the dot and the non-white ink of the white ink to the printing medium based on the first half-tone data and the second halftone data .   The printing apparatus according to claim 1, wherein the printing unit superimposes the white ink dots on the non-white ink dots from the viewer side of the print medium. The image data acquisition means acquires the second image data having recording rates of a plurality of the non-white inks in which each pixel has a different color,
The halftone processing means includes the non-white ink dots that are more noticeable than the other non-white inks in the non-white ink, and the white ink dots that overlap on the print medium. The printing apparatus according to claim 1, wherein the first halftone data and the second halftone data are generated so as to be recorded.   The printing apparatus according to claim 3, wherein the halftone processing unit increases the number of colors of the non-white ink that overlaps the dots of the white ink as the recording rate decreases.   The halftone processing means performs halftone processing by a dither method using the same dither mask, so that the white ink dots and the non-white ink dots are overlapped and recorded on the print medium. The printing apparatus according to any one of claims 1 to 4, wherein the first halftone data and the second halftone data are generated as described above.   The halftone processing means adjusts a diffusion error or a threshold value to be compared with the diffusion error in halftone processing by an error diffusion method, so that the white ink dots and the non-white ink dots are formed on the print medium. The printing apparatus according to any one of claims 1 to 4, wherein the first halftone data and the second halftone data are generated so as to be recorded in an overlapping manner. A print program for causing a computer to realize a function of printing a background image on a print medium,
An image data acquisition function for acquiring first image data that is a recording rate of white ink dots of each pixel and at least one second image data that is a recording rate of non-white ink dots;
In generating each of the first halftone data and the second halftone data indicating whether or not each pixel records at least a dot based on the first image data and the second image data, the print medium A halftone processing function for generating the first halftone data and the second halftone data so that the white ink dots and the non-white ink dots are overlapped on each other;
A computer is configured to realize a printing function for recording the white ink dots and the non-white ink dots on a print medium based on the first halftone data and the second halftone data. Printing program. A printing method for printing a background image on a print medium,
Acquiring first image data that is a recording rate of white ink dots of each pixel and at least one second image data that is a recording rate of non-white ink dots;
In generating each of the first halftone data and the second halftone data indicating whether or not each pixel records at least a dot based on the first image data and the second image data, the print medium Generating the first halftone data and the second halftone data so that the white ink dots and the non-white ink dots are recorded on top of each other;
A printing method comprising: recording the white ink dots and the non-white ink dots on a print medium based on the first halftone data and the second halftone data.

Images