JP2008024004A - Print control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve color printing having excellent image quality in multiple tones through overlapping printing by combining a plurality of printing dots having a first color different in printing area and a plurality of printing dots having a second color different in printing area. <P>SOLUTION: In the print control device, printing dots different in printing area are printed with the first color by a first printing part, and printing dots different in printing area are printed with the second color different from the first color by a second printing part. The first printing part and the second printing part are controlled by a print control part, and printing is performed by overlapping a part of the printing dots formed in the different color and different printing area while printing in multiple tones is achieved by combining the printing dots formed in different colors and different printing areas, resulting in color printing having multiple tones excellent in image quality. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a print control apparatus capable of expressing the density of each pixel constituting an image printed on paper or the like with multiple gradations.

  In a printer that exclusively prints characters, each pixel constituting an image may be expressed by a binary value of white or black. However, when printing an image including a halftone such as a photograph or the like, the image quality after printing is greatly deteriorated compared to the original image unless the gradation of each pixel is faithfully reproduced. However, in many ink jet printers, electrophotographic printers, and the like, printing control is performed with a binary expression of whether or not minute dots are printed. Therefore, conventionally, when one pixel constituting an image is expressed in a vertical and horizontal, for example, an 8 × 8 dot matrix, gradation representation in pixel units is performed by increasing or decreasing the number of black dots included in the matrix. ing. This is called the area gradation method or dither method, and is widely used for printer control.

By the way, the conventional techniques as described above have the following problems to be solved.
When an image having gradation is printed using a dot matrix, the size of the dot matrix determines the resolution. Here, when comparing black and white printing and color printing, color printing expresses one pixel by combining at least three dots of different colors. Therefore, when gradation representation using a matrix is performed for each color, the number of dots constituting one pixel increases, and the size of one pixel increases, resulting in a decrease in resolution. That is, there is a problem that the pixel density becomes coarse and the quality of the printed image is deteriorated.

The present invention adopts the following configuration in order to solve the above points.
<Configuration 1>
A printing control apparatus that prints the density of each pixel constituting image data with multiple gradations, and has a different printing area from a first printing section that can form printing dots with different printing areas in a first color. A second printing unit capable of forming printing dots in a second color different from the first color, and the first printing unit and the second printing unit are controlled to form different colors and different printing areas. And a print control unit that prints in multiple gradations by combining the print dots formed in different colors and colors having different print areas. Print control device.

  According to the present invention, a plurality of print dots having a first color with different print areas and a plurality of print dots having a second color with different print areas are combined to perform overprinting. Excellent color printing.

Hereinafter, embodiments of the present invention will be described using specific examples.
<Concrete example>
FIG. 1 is an explanatory diagram of a printing control method according to the present invention.
In the present invention, first, as shown in FIG. 1 (a), one dot is printed using, for example, three types of dots with different areas. In the example of this figure, there are three types of dots, D1 having a minimum area, dot D2 having an intermediate area, and dot D3 having a maximum area. In the example shown here, one pixel can be expressed by, for example, three types of densities of dots D1, D2, and D3. Note that white dots that do not print anything are not included in the number of gradations. A region 1 corresponding to the pixel shown in FIG. 1A indicates a minimum unit of a print image, that is, a pixel of the print image.

  Here, in order to enable more gradation expression, the conventional dither method is combined. (B) shows an example of a dot matrix that constitutes such a dither pattern. Here, a region 1 * corresponding to a pixel that accommodates four dots is set. Here, a maximum of four pixels D1, a minimum area pixel D1, an intermediate area pixel D2, and a maximum area pixel D3 are arranged. Here, for each gradation of K11, K12, K13, and K14, the minimum area dot D1 is increased to 1, 2, 3, and 4 and arranged.

  Next, for the gradations K21, K22, K23, and K24, the number of gradations is increased by replacing the dot D1 having the smallest area with the dot D2 having an intermediate area one by one. When all the dots are replaced with the dot D2 having an intermediate area, the gradation K24 is expressed. Further, when expressing the gradations K31, K32, K33, and K34 on the upper side, the dot D2 having an intermediate area is replaced with the dot D3 having the maximum area one by one.

As a result, by selecting a combination in which a maximum of four dots of three kinds of areas are arranged in a matrix, it is possible to express the density of 12 gradations.
The above is the outline of the print control according to the present invention.

Next, an apparatus for realizing the above gradation expression will be described.
FIG. 2 shows a schematic block diagram of the printer.
The schematic configuration of this printer is not different from the conventional one. That is, the print control unit 3 that receives the received data 2 drives the print unit 4 to print on a sheet (not shown). The print control unit 3 performs print control using a program stored in a ROM (Read Only Memory) 5. A RAM (Random Access Memory) 6 is a memory for storing print data for performing such print control and various parameters.

  The printing unit 4 includes a head driving circuit 7, a head 9, a motor driving circuit 8, a spacing motor (SPM) 11, and a line feed motor (LFM) 12. The head 9 is composed of, for example, an ink jet head, and the head drive circuit 7 is a part that controls each part of the head in accordance with print data and performs ink ejection control. The spacing motor 11 is a motor that drives the print head in the main scanning direction, and the line feed motor 12 is a motor that conveys the paper in the sub scanning direction. The motor drive circuit 8 controls these motors in synchronization with the printing operation.

FIG. 3 is a perspective view of the main part of the ink jet printer.
The printing unit 4 of the printer includes a mechanism as shown in FIG. The line feed motor 12 rotationally drives the roller 17 via the pulley 16. As a result, the paper 15 is conveyed in the direction of the arrow 19. This arrow 19 direction is the sub-scanning direction. Further, the spacing motor 11 reciprocates the head 9 in the direction of the arrow 20 by the pulley 13 and the belt 18. The direction of the arrow 20 is the main scanning direction. An ink tank 21 is mounted on the head 9. In the case of a color inkjet printer, ink tanks for printing black BK, yellow Y, magenta M, and cyan C are installed.

FIG. 4 shows a cross-sectional view of the main part of the head.
In the ink jet printer, the portion for printing by ejecting ink from each ink tank onto the paper has a cross-sectional configuration as shown in this figure. That is, the ink 25 is supplied in the direction of the arrow 24 and fed into the chamber 26. A piezoelectric element 27 made of, for example, PZT or the like is attached to the wall surface of the chamber 26. The wall surface to which the piezoelectric element 27 of the chamber 26 is attached is a vibration plate, and the wall surface of the chamber 26 is vibrated by changing the voltage applied to the piezoelectric element 27 to change the volume of the chamber 26.

  When the chamber 26 expands due to the deformation of the piezoelectric element 27, the ink 25 is sucked into the chamber 26 from a common ink chamber called a manifold. When the chamber 26 expands due to the deformation of the piezoelectric element 27 at the next moment, the ink 25 is sucked into the inside of the common ink chamber 26. When the chamber 26 is compressed by the vibration of the piezoelectric element 27 at the next moment, an ink droplet 29 is ejected from the nozzle 28 and adheres to the paper or the like. By increasing or decreasing the amount of the ink droplet 29, dots D1, D2, and D3 having different areas as shown in FIG. 1A are printed.

FIG. 5 shows a head drive operation time chart for this purpose.
(A) of a figure is a head drive voltage waveform, Comprising: It is a voltage waveform applied to the piezoelectric element 27 shown in FIG. FIG. 5B shows the change over time of the chamber internal volume.
As shown in the figure, the head drive voltage is held at + V volts for the time ta, and then the head drive voltage is lowered to -V volts for the time tb. As a result, the piezoelectric element 27 shown in FIG. 4 extends for the first time ta, and the volume of the chamber 26 is expanded from M to M + Δm.

  Thereafter, the piezoelectric element 27 is compressed for the time tb, and the volume of the chamber 26 is reduced to M−Δm. Therefore, an ink droplet having a volume corresponding to 2 × Δm is ejected from the chamber. That is, if the amount of ink droplets, that is, 2 × Δm, is appropriately adjusted by changing the time ta and the voltage V, the size of the printed dots changes. However, since the accuracy of this control is not high, in the case of an ink jet printer, the limit is several to 16 stages. This is often not sufficient compared to the actually required number of gradations. Therefore, as shown in FIG. 1B, dots are arranged in a matrix and combined with the principle of a dither pattern.

  In the case where only four dots can be arranged in the region 1 * corresponding to the pixel shown in FIG. 1 (b), if gradation expression is to be performed using only one kind of fixed size dots, white is excluded. Only the stage can be expressed. However, by selecting the dot size in three stages, it is possible to express gradations in 12 stages in the example of the figure.

  In the example shown in FIG. 1B, the minimum area dot D1 is increased from the minimum number, that is, one to the maximum number, that is, four, and then the maximum area gradation level K14 is used as a reference. Controls to replace each dot one by one with the size one higher, ie, the intermediate area D2. Even when the dot D3 having the maximum area is used, each dot is replaced with the dot D3 having the maximum area on the basis of a matrix in which the maximum number, that is, four dots D2 having an intermediate area are arranged. By such a method, it is possible to clearly match the set gradation order with the order of change in print density as a result of actual printing output.

  In the above example, the dot area is composed of three types, and the dot matrix is composed of 2 × 2 dots. On the other hand, for example, when the dot matrix is composed of 4 × 4 dots, 16 gradations are expressed by using dots of one kind of area, and by combining different dots with each other, 16 times that is, 256 gradations can be expressed. In the conventional method, if 256 gradations are to be expressed, an 8 × 8 dot matrix must be one pixel. Therefore, from the viewpoint of the number of pixels, it is possible to achieve a high image quality with a resolution of 4 times.

  In the above example, it is also possible to express a finer gradation level by mixing dots of three or more sizes in the area corresponding to the pixel.

<Electrophotographic printer>
FIG. 6 is an explanatory diagram of an electrophotographic printer control method.
(A) of the figure is a perspective view of the photosensitive drum, and (b) of the figure is a graph showing a dot diameter control method.
In the above example, the dot diameter is controlled by the ink jet printer. This can also be realized by an electrophotographic printer. When controlling the electrophotographic printer, as shown in FIG. 6A, the drive current of the head 31 that forms an electrostatic latent image on the photosensitive drum 30 is controlled. A number of LEDs (laser diodes) 32 are arranged in a line on the head 31.

  Each LED 32 is supplied with a driving current from a head driving circuit (not shown) and emits light. This light exposes the photosensitive drum 30. If the energy of this light is large, the exposed dots 34 have a large area, and if the energy is small, the exposed dots 34 have a small area. Large exposure dots are developed into large dot toner images. Small exposure dots are developed into small dot toner images. Here, three types of dots DL1, DL2 and DL3 are shown. If this exposure dot is developed and transferred to a sheet, the dot diameter can be controlled as in the case of an ink jet printer.

  In FIG. 5B, the horizontal axis represents the head drive current, and the vertical axis represents the exposure dot diameter. If the drive current is controlled step by step such as A1, A2, and A3, the exposure dot diameter increases as B1, B2, and B3. In this way, also in the electrophotographic printer, the dot diameter is controlled in the same manner as in the ink jet printer, so that multiple gradations can be expressed by pixels having a small area.

<Selecting the gradation expression method>
FIG. 7 shows a flowchart of the gradation expression method selection operation.
Even if the printer has the above functions, if the above method is uniformly adopted when the image data to be printed does not require multi-level gradation expression, the dither pattern generation process There is a lot of waste in the control for. Here, one dot switches the area of the pixel to three types and enables three-level gradation expression. Therefore, for an image that requires only three-level gradation expression per pixel, area gradation Do not adopt control. In this way, one pixel can be expressed by one dot, and the resolution can be increased. On the other hand, when more gradation expression is required, control can be switched. The flowchart shown in FIG. 7 shows the selection control logic.

  First, in step S1, the required number of gradations is compared with the number of dot types having a printable area. For example, if the required number of gradations is less than the number “0”, “1”, “2”, “3”, the process proceeds from step S2 to step S3 to select a gradation expression method based on the dot area. To do. That is, the gradation is expressed only by the three types of dots shown in FIG.

  On the other hand, if it is determined that the number of gradations is larger in step S2 by the comparison process in step S1, that is, if there is a request such as 8 gradations, 16 gradations, or 256 gradations, only the dot area is used. Since the expression is impossible, the gradation expression using a dot matrix in which a plurality of dots having different dot areas as shown in FIG. As a result, the effects as described above can be obtained.

By providing the printer with the selection function as described above, high-quality printing can be performed without appropriateness depending on the type of image to be printed.
In particular, in the case of full-color printing or the like, there are many images that do not necessarily require multi-tone expression for each color. Therefore, it is possible to optimize the printing operation by selecting such control.

<Combination of light and shade and dot diameter>
In the above example, control is performed to switch the area of dots to be printed in several stages. However, only a few types of switching is the limit only by controlling the ink amount. However, in this example, a combination of a dark ink and a light ink makes it possible to express gradations in more stages with one dot.

FIG. 8 shows an explanatory diagram of a combination example of light and shade and dot diameter.
As shown in the figure, in this example, the three dots on the left side show light-colored dots DB1, DB2, and DB3 whose areas are changed to minimum, middle, and maximum, respectively. In addition, the three dots on the right side indicate dark dots D1, D2, and D3 that are similarly changed in area in three stages. In this way, in this example, it is possible to express in six levels by changing the density of the ink. In the case of black and white ink, a combination of gray ink and black ink is combined. In a color printer, light yellow (LY), light magenta (LM), and light cyan (LC) are used. In practice, an ink tank containing such ink is added to the conventional head. In this way, even in a monochrome printer or a color printer, it is possible to express six levels of gradation with a single dot.

FIG. 9 is an explanatory diagram of a combination control method of shading and dot diameter.
FIG. 4A is a graph in which the horizontal axis represents the dot diameter and the vertical axis represents the density. In other words, the ratio of density change when the dot diameter is gradually increased is shown by a curve. The dashed curve indicates the density change of the dots DB1, DB2, and DB3 using light color ink. A solid line indicates a change in density using dark colored dots DA1, DA2, and DA3.

  (B) of a figure shows the number of gradations corresponding to a control level. The horizontal axis represents the control level, and the vertical axis represents the number of gradations. Control levels CT1, CT2, CT3,... CT6 correspond to pixel values of image data. The larger the pixel value, the higher the number of gradations. That is, it is assumed that printing of dots with high density is requested. Here, if the results shown in (a) are arranged as they are, dots having the number of gradations corresponding to each control level can be printed as shown in the figure. In this example, the conditions are set so that the density is higher when dots with darker density are printed with the minimum area than when the ink with lighter density is printed with the maximum area. This simplifies dot selection control. If such a combination of shading and dot diameter is performed, the application ratio of gradation expression by the dot area proceeding from step S2 to step S3 shown in FIG. 7 increases. Therefore, it is possible to print a high-quality halftone image with a higher resolution.

Furthermore, if the expression using the dot matrix as shown in FIG. 1B is performed, a multi-stage gradation expression can be realized with a smaller matrix configuration. Therefore, it is possible to express multi-tones with a small area pixel, and further increase in image quality can be expected.
In addition, when giving a density difference to ink, you may make it distinguish light and dark by the color of the same type | system | group, for example, dark cyan and light cyan.

<Combination of shading and dot diameter by thinning control>
The following specific example employs a technique in which magenta dots are printed and then thin white dots are overprinted to obtain thin color dots. FIG. 10 shows an example of a combination of light and shade and dot diameter by such thinning control.
In this figure, for example, the dot size can be controlled in four stages. Here, dots of lighter density are realized by overlaying white ink on dots of three types of areas. The dots of four types of areas of the dots DA1, DA2, DA3, and DA4 are printed by, for example, black, cyan, magenta, yellow, and the like. The dots DB1, DB2, and DB3 are obtained by printing the three types of dots DA1, DA2, and DA3, and then printing the white dots that are slightly larger in area than the dots. This white ink is translucent, and the dot printed just before is made a slightly light color dot.

Thus, in this example, the density increases in the order of DB1, DB2, DB3, DA1, DA2, DA3, and DA4, enabling 7 gradation expression.
FIG. 11A is a graph in which the horizontal axis represents the dot diameter and the vertical axis represents the density. (B) is a graph in which the horizontal axis represents the control level and the vertical axis represents the number of gradations. As shown in FIG. 4A, when the dot diameter is increased stepwise, the density changes like dots DA1, DA2, DA3, DA4. If white ink is overprinted on this, the respective densities are reduced to densities such as DB1, DB2, and DB3.

  If the control level is set to 7 levels as shown in FIG. 7B, 7 gradations can be expressed by arranging the dots shown in FIG. As a result, halftone expression is possible by making one dot correspond to one pixel of the image to be printed. In general, when colored inks are superimposed, a darker dark color is obtained. However, in this example, a lighter color is expressed by superimposing a semi-transparent white ink on a colored ink.

  In the above example, the dots printed below with white ink are expressed completely. However, for example, it may be possible to make the dots lightly apparent by covering a part of dots already printed with white ink. In the specific example shown in FIG. 10, the maximum diameter dot DB3 that has been printed thinner than the minimum area dot DA1 is set so as to represent a lower gradation, so that the control is not complicated and easy. .

  In the above example, the light color expression is realized by overprinting the white ink, but a color close to white may be used. In addition, when white ink is overprinted with colored ink, a thinning effect may be produced by mixing the two. In this case, the same effect can be obtained regardless of which ink is printed first, and the order corresponding to the properties of the ink may be selected.

  Further, not only an ink jet printer but also an electrophotographic printer can perform the same processing using a dark color toner, a light color toner, or a thin white toner. That is, dots of the same area with different densities can be printed using a printing material (ink or toner) having the same color and a high density and a printing material having a low density. Furthermore, when performing the thinning process, if an ink jet printer is used, instead of using white ink, dilution with a simple thinning liquid (transparent ink) enables light color expression. In this case, this liquid allows the colored ink to permeate from the low surface to the back, and at the same time, is scattered over a wide area, which is suitable for the effect of reducing the granular feeling (the degree to which the dot is crushed).

FIG. 12 is an explanatory diagram of a configuration example of a head in the case where the above-described printing is performed using an ink jet printer.
(A) of the figure shows the configuration of the head used when only several types of dot areas are changed. This configuration is exactly the same as that of a conventional printer, and includes, for example, black BK, yellow Y, magenta M, and cyan C ink tanks. In the case where the dot area and the density control are performed on the head 9A, a head 9B as shown in FIG. In this head, in addition to the configuration of the head 9A, an ink tank containing light yellow L-Y, light magenta LM, and light cyan L-C is added.

Further, a head 9C shown in FIG. 9C is a thinning control head. In this case, a white W ink tank is added in addition to the head 9A shown in FIG. By using such a head, it is possible to perform the above print control.
It is not always necessary to incorporate all the functional blocks that execute the above operations on the printer side. The method of the present invention can be implemented by combining a personal computer that is an upper device of the printer, various drivers and interfaces for printer control, and the printer main body.

If two or more types of dot areas to be printed are selected, a dot matrix is formed in the area corresponding to the pixels, and gradation expression is performed by combining these areas, the number of dots can be increased using a smaller number of dots. Tones can be expressed. In this way, high-quality halftone expression can be achieved without degrading the image quality of the original image.
For an image that can be expressed by providing several types of dot areas, one pixel and one dot are printed. In other cases, an image to be printed is expressed by using a dot matrix. An appropriate higher-quality printing method can be selected in accordance with the contents of.

  Further, if a combination of pixel shading and dot area is used, a larger number of gradations can be expressed with one dot, and high-quality halftone expression can be achieved. Similarly, even when the dot area and the dot thin print are combined, more multi-level control is possible. Therefore, by incorporating such a method into color printing or the like, a high-quality halftone image can be expressed without reducing the resolution of the color print image.

It is explanatory drawing of the printing control method by this invention. It is a schematic block diagram of a printer. It is a principal part perspective view of an inkjet printer. It is principal part sectional drawing of a head. It is a head drive operation | movement time chart. It is explanatory drawing of the control method of an electrophotographic printer. It is a gradation expression method selection operation flowchart. It is explanatory drawing of the example of a combination of lightness and a dot diameter. It is explanatory drawing of the combination control method of light and shade and a dot diameter. It is a combination explanatory diagram of light and shade by the thinning control and the dot diameter. It is explanatory drawing of the combination control method of the light and shade and dot diameter by thin control. It is explanatory drawing of the structural example of a head.

Explanation of symbols

Area equivalent to 1,1 * pixels D1, D2, D3 dots

Claims (7)

A printing control apparatus that prints the density of each pixel constituting image data in multiple gradations,
A first printing section capable of forming print dots having different print areas in a first color;
A second printing section capable of forming printing dots having different printing areas in a second color different from the first color;
The first printing unit and the second printing unit are controlled so that a part of the printing dots formed with different colors and different printing areas are overlapped and printed, and the colors are different colors and different printing areas. And a print control unit that prints with multiple gradations by combining the formed print dots. The print control apparatus according to claim 1,
At least one of the first printing unit and the second printing unit forms the printing dots with a translucent white developer. The print control apparatus according to claim 2,
A print control device characterized in that the density of a print dot in which the white developer is not superimposed and the smallest print area is higher than the density of the print dot in which the white developer is superimposed on the largest print area . The print control apparatus according to claim 2,
The print control apparatus according to claim 1, wherein the white developer is superposed on another color developer. The print control apparatus according to claim 2,
A print control apparatus, wherein another color developer is superimposed on the white developer. The print control apparatus according to claim 1,
The print control apparatus according to claim 1, wherein the type of print dots that can be formed with different print areas in the first print unit and the type of print dots that can be formed with different print areas in the second print unit are different. The print control apparatus according to claim 1,
The printing control apparatus, wherein the first printing unit and the second printing unit form printing dots with toner used in an electrophotographic printer.

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